Structural Glazing

STRUCTURAL GLAZING IN BUILDING–MODERN GLASS
Modern glass is not only a transparent beauty, but also has unmatched utility. Today, glass is an important building element, which not only offers aesthetics but also proves economical in the long term on account of very low maintenance expense.
Amongst the types of glass made in India,
(a) Float glass
(b) Sheet glass
(c) Plate glass
Float glass is a 100% distortion free glass, manufactured indigenously by three companies in India. Float glass is a recent development that produces a fire polished, nearly optically flat surface that does not have to be ground or mechanically polished.
Sheet glass, including the machine drawn cylinder process simulating hand-blown glass, was known for its wavy irregularities.
Plate glass, first introduced into the U.K. in the mid seventeenth century, was cast and then polished flat.





Undergraduate student, Department of Civil Engineering, NSS College of Engineering, Palakkad-08,Kerala
2.0 PROPERTIES OF GLASS

2.1 Transmission Properties
Transmission through glass can be modified by improving or modifying the
Chemical make-up of the glass to increase the absorption factor. Heat absorbing glasses are designed to absorb as much of the solar infrared radiation as possible while maintaining high transmission in the visible region. Some are also designed to absorb
visible radiation to reduce glare, which further reduces heat transmission. However, due to unavoidable impurities in the soda-lime-silica mix, typical window glass does absorb some radiation that might otherwise pass through.

2.2 Material Composition
The main components of clear glass are silica sand (73%), Calcium oxide (9%), Soda (13%) and Magnesium (4%). The amount and type of additional impurities within the glass affect the wavelength of the absorbed light and the amount of impurities determines how much it will be affected. Manufacturers often purposely add their own impurities such as ion oxides to manipulate absorption effects.

2.3 Thermal Conductivity
The thermal conductivity (K) of a soda lime glass between 5 and 7 Btu/hr Sq.ft F/in. is higher than that of insulating materials, but much lower than that of most metals. Glass of normal thickness offers negligible resistance to heat transfer between the inside and outside of a building and the thermal resistance is predominantly due to the surface films.

2.4 Strength of Glass
Glass is a brittle material and does not deform plastically before failure. It fails in tension regardless of the nature of loading. The potential tensile strength of glass is about 690107N/mm2, but failure occurs at average stresses far below this value because of the stress-raising effect of surface imperfections both inherent in the glass and mechanically created. Glass is most vulnerable at its edges, with surface imperfections from cutting and handling adding to the risk of failure. Because the effect of stress raisers is indeterminate, the allowable tensile strength of glass is determined statically and a sizable safety factor included. By using the value thus established breakage can be reduced to an insignificant level but not eliminated. Glass can be greatly strengthened by development of a “stressed skin” sandwich, where both surfaces are in compression & the middle is in tension. This can be accomplished by heating the glass to near its melting point and rapidly cooling both surfaces. The contraction of the middle (of the thickness) of the sheet develops the desired stress on final cooling.

2.5 Thermal Expansion
The co-efficient of expansion for glass is 4.5x10-6. Thermal expansion and contraction of glass is of importance in the design of glazing details, but it is even more important with respect to the development of stresses within the glass from temperature differential in a pane.

3.0 TYPES OF GLASSES

3.1 Safety glass
Safety Glass is defined as glass, which has passed specific impact tests, and must either not break or break in a manner that will not cause injury. There are 3 main types.
i. Toughened Glass
Toughened glass is obtained when a glass is heated to approximately 7000C in a furnace then chilled rapidly by cold air blown onto both its surfaces. This glass is 4 to 5 times stronger than float glass and, if broken disintegrates into small fragments with dulled edges, which are unlikely to cause serious injury, and therefore it is not termed as security glass. This is a safety glass, as it has the highest impact resistance when hit on the surface, although it is vulnerable to immediate cracking when hit on the edge. It also has a very high thermal resistivity, almost 5 times that of a normal annealed glass.
ii. Laminated glass
Laminated glass is obtained when two or more thin sheets of glass separated by layers of a plastic or resin material. The principal benefit of laminated glasses is their performance under impact, the glass may fracture, but any broken fragments will remain firmly bonded to the interlayer.
There are 2 main types.

a) PVB laminated
Two or more sheets of glass are bonded together with one or more layers of polyvinyl butyral, a plastic interlayer in sheet form. The interlayer in laminated glass provides two additional benefits: sound transmittance is reduced, particularly at the higher frequencies and UV radiation is reduced by atleast 97%.
b) Resin laminated
Such glasses are manufactured by pouring liquid resin into a cavity between two sheets of glass, which are held together until the resin cures. They are principally used for decorative and acoustic purposes, where safety performance is normally of secondary importance.
iii. Wired glass
A steel wire mesh is embedded within the glass and is intended to hold it in place if cracked. The glass breaks in almost the same way as ordinary glass, into sharp dagger-like pieces, but mostly stays in place. The visual quality of the glass is impaired by the wire mesh but this has traditionally been accepted in low-cost fire resistant and roof glazing.
3.2 Security glass
There are similar to safety glass, which has passed specific impact tests and must either not break or break in a manner that will cause injury. Laminated glass is the only glass that qualifies as a security glass.
There are 3 main types
i. Anti-bandit glass
Designed to resist manual attack, such as might be made by a man armed with a hammer, crow bar or pickaxe, and to delay access to the protected space for a short period of time.
ii. Bullet resistant glass
A multi-layered variable thickness laminated glass can function as a bullet resistant glass. A laminated glass upto 80mm thickness can resist an AK-47 bullet. A glass laminated under variable thickness specification can function as a bulletproof glass.
iii. Explosion pressure resistant glass
Basically defined as glazing that affords a defined resistance against a specified explosive blast.

3.3 Solar control glass
This type of glass reduces the amount of heat and light from the sun transmitted through the glass. This is usually done by increasing the amount energy either absorbed within the glass reflected from its surface. There are 2 different ways of producing a solar control glass.
i. Body Tinted glass
This is a mild coloured glass, available in blue, bronze and grey colour tints. They are produced by the addition of metal oxides to the raw materials during float glass manufacture. It not only restricts transparency in glass but also most importantly restricts the sunlight glare, and thereby partially insulating heat transmitted via the sunlight.
ii. Coated Glass
Solar control is achieved by applying a very thin transparent reflective metallic coating to the surface of clear or body tinted glasses. There are two different coating techniques:
 Pyrolitic coating: This coating reduces the proportion of solar energy transmitted through the glass mainly by increasing the amount reflected.
 Sputtered coating: The coating enables the glass to reduce the proportion of solar energy transmitted by increasing the amount absorbed and reflected.
3.4 Low-E coatings
Low-emissivity coatings, called Low-E for short, act to reduce surface emissivity of glass. These glasses provide excellent energy conservation by reflecting majority of the heat and allowing more of visible light thus reducing the heat gain without having to sacrifice much light transmission resulting in dual benefit of less energy requirement to cool the interior of the building as well as less energy for lighting requirement which in turn will help to reduce air-conditioning and lighting cost.


3.5 Spectrally selective glazing
The aim of this glass is to screen out as much ultraviolet and short wave infrared radiation as possible whilst allowing through the maximum amount of visible light. Because this type of glazing can have a virtually clear appearance, they admit more day light and permit much brighter views to outside, whilst still providing order similar to that of dark, reflective tinted glasses
.
4.0 GLASS APPLICATIONS

All the above varieties of processed glasses have ensured safe and functional use of glass in many areas of human life. Amongst them, a few special examples are
4.1Glass skylite/Glass dome
From small to very large spans of ceilings can be covered with glass allowing transmission of natural light permanently. Here, although glass is above our head, there is no fear as these are designed safely. A laminated glass is an ideal concept for glass skylites. While a glass roof does transmit heat faster during the day it also has the benefit of losing heat faster during the night.
4.2 Glass flooring
Today it is possible to walk on glass and be absolutely safe and secure. Proper structural support and adequate cushioning between glasses as well as glass and structure are inevitable. Glasses can be surface treated to prevent skidding. If used carefully, a glass floor does not involve major maintenance.
4.3 Front façade
For every architect or designer, the front facade of any building is very critical. Glass has opened wide avenues, daring opportunities for providing a grand awesome look to the building. Clear view with minimum obstructions, while the inside is cut from outside with regard to noise and pollution, yet due to transparency two worlds are merged.
Toughened or ideally toughened laminated glasses are used here.
4.4 Glass wash basin units
A clean, vibrant, novel, beautiful appearance is derived from a glass washbasin unit.


4.5 Glass furniture
With the advent of skilled workmanship and unique designing techniques, glass can speak different language in versatile styles as an element of furniture. Fusing, blasting, blowing, etching, staining, glue chipping, sticking, colouring, sculpting, chipping are some of the known techniques for beautifying transparent glass into a piece of art. Coffee tables, dining tables, T.V.Stands, corner tables, glass chairs, partitions, lampshades etc. are few of the endless forms of glass interiors.


5.0 GLASS INSTALLATION

There are five main techniques for single glazing.

1. Into rebates without beads
The glass sits in a rebate, held in place by a suitable glazing material, such as putty or a plastic-based compound, which then provides weather proof seal.


2. Into rebates with beads
As before the glass sits in a rebate, but is held in place by the beading. The glazing compound provides the weather seal.

3. Into grooves or channels.
It is usually used for glazing into concrete, store or timber frames with a rebate and bead at the sill, but it can also be modified to suit frames that have beads at the head and sill and grooves at the jambs.



4. Using structural gaskets.
Gaskets are used to hold the glass in a groove or rebate and to provide a weather seal. They can include H-shaped, Y-shaped or single-sided gaskets.

5. Using non-structural gaskets
The glass is held in place by a combination of pressure beads and gaskets.


Check that the clearance is appropriate for the thickness and type of glass. If the glass is in direct contact with the framing materials, it could lead to breakage.

Frameless glass glazing
The use of glass without using wooden or aluminum frames has become a necessity in the present and future concept with the change in the methods of use of thicken float glass in spacious buildings like airports, seaports, multistory buildings, banks, showrooms and spacious offices etc. It is therefore important that the development of such a glass glazing should be accurate and well designed, in accordance with the requirement of the situation and the architectural layout. It is also an important factor that such glass glazing should be fully supported by the hardware used in it with a capacity to sustain wind pressure and structural strength safety based on the necessary material and technique.

6.0 MAINTENANCE OF GLASS

Site Clean up
It is essential that all external glass be thoroughly washed with clean water to eliminate all abrasive and chemical laden dust. Excess glazing compounds and sealants should be carefully removed from the glass and frame surrounds, taking care not to scratch the finished surfaces with tools or abrasives. A solvent such as white spirit or professional glass cleaner may be used to remove any glazing compound, finger marks or grease. Frequent washing is required whilst construction continues on site, since chemicals in dust and particularly in cement may be activated by rain and cause permanent corrosion of the glass surface.
Normal Cleaning
Use a mild liquid detergent solution, then rinse the glass well with clean water and dry off. Under no circumstances may abrasive cleaning products or contaminated cloths be used. If rainwater coming from cement mortar contaminates the surface of the glass, frequent cleaning is necessary to prevent permanent staining.


Regular maintenance
It is essential that all installations are inspected and maintained during the lifetime of the building at regular intervals as recommended by the sealant and framing manufacturers.

7.0 PROTECTION OF GLASS

Glass can be a dangerous material .When standard annealed glass breaks, it forms potentially lethal shards and splinters. Glass manufactures have developed a range of safety glasses adding strength and integrity to this beautiful building material and allowing glass to be used in areas where safety is critical in unprecedented situation. Safety glass is defined as glass, which must have passed an impact test (as per BS 6206: 1981). There are 3 levels of impact: C, B and A, ‘A’ being the highest. Each involves the glass being impacted by a leather bag containing 45kg of lead shot.

Class A - 1219 mm
Class B - 457 mm
Class C - 305 mm
All security glasses automatically qualify a class A safety glasses.
Glass in doors and side panels to doors must be at least:
# a class B safety glazing material if the smaller dimension of the glass is more
than 900 mm.
# a class C safety glazing material if the smaller dimension of the glass in less than 900 mm.
Non safety glass in small panes may be permitted under certain controlled circumstances.



7.1 Permanent screen protection
The use of annealed glass is permitted in a critical location if protected by a permanent, robust screen. The screen must prevent the passage of a 75mm diameter sphere and must not be climbable.
7.2 Bathing areas and areas of special risk
BS 6262 requires that any glazing, forming part of a bath or shower screen or adjacent to or surrounding a bathing area, swimming pool or other wet areas must be at least a class C material. Consideration should also be given to the breakage characteristics. The fragmentation of toughened glass into small dice-like particles would result in, should it enter the pool, being invisible practically impossible to remove, practically causing damage to pumps filters. This can be avoided by using a laminated safety glass an account of the glass fragments remaining adhered to the plastic interlayer. This requirement also applies to all glazing in areas of special risk such as gymnasia and other places of energetic activity. In such areas, the designer must consider whether a higher class is required, or if additional safeguards such as protective rails or screens, or manifestation are necessary.
7.3 Commercial frontage
Robust glass (non-safety thick annealed glass) when fully framed is considered suitable for use in large areas in non-domestic applications, for eg: forming fronts to shops, showrooms, offices, factories, and public buildings.
Glass thickness / size limits for annealed glass that may be used in these locations are shown in the Table 1. Wind loads & other load must be considered when selecting the glass thickness.
Table1 Glass thickness and pane size


Normal Glass Maximum pane size
thickness (mm) (four edge supported )(mm)
8 1100 x 1100
10 2250 x 2250
12 4500 x 4500
15 or thicker No limits


7.4 Glass in furniture
Standard advises minimum BS 6206 classification, glass thickness and support details to insure the reasonable safety of flat glass having a total area of at least 0.02m2.
1. Glass in tables or trolleys
Glass that is not supported over its entire area:
The minimum horizontal area of each support shall be 36mm2. Annealed glass shall be supported for not less than 50% of its total perimeter and the support should be in at least two non-adjacent regions and shall be not more than 100mm from the edge of glass. Minimum BS 6206 classification and nominal thickness for glass that is not supported over its entire area as shown in table 2.

Table 2 Minimum BS 6206 classification and nominal thickness

Area of Nominal Thickness Minimum Nominal thickness
glass (m2) (mm) BS 6206 (mm)
annealed glass classification
Toughened glass Laminated glass


<= 0.25 >=10 Class C >=4.0 >=6.4

< 0.25 to >=10 Class C >=5.0 >=6.4
<=0.5

> 0.5 to >=12 Class C >=6.0 >=6.4
<=0.75

> 0.75 to >= 15 Class B >=8.0 >=8.4
< =1.5
>1.5 >=19 Class A >=10.0 >=10.8


Glass that is supported over its entire area.:
Glass which has an area not greater than 1.5m2 shall comply with the relevant nominal thickness given in table3 below.

Table 3 Nominal thickness of glass

Area of glass (m2) Nominal thickness (m)
Annealed
Toughened glass
Laminated glass
<=0.5 >=4.0 >=4.0 >=4.4
>=0.5 to <=1.0 >=5.0 >=4.0 >=4.4
>=1.0 to <=1.5 >=6.0 >=4.0 >=4.4
>1.5 N/A >=4.0 >=4.4

Contact of glass with other materials:
Hard materials such as other glass, metal or stone should not be allowed to come into direct contact with the edges or surface of the glass. Separation should be ensured by the use of suitable bushes and gaskets. Glass in furniture other than tables or trolleys. Horizontal glass supported over its entire area should comply with Table 3. Glass used to form the external surfaces (excluding horizontal glass supported over its entire area) and which is unbaked should comply with the requirements of table 4.
Table 4 Requirements of glass for external surfaces and unbaked conditions
Smaller dimension (width or height)
Less than 900mm

BS 6206 Class C

Minimum Thickness More than 900mm


BS 6206 Class B


Minimum Thickness
3 mm Fully framed 4 mm
4 mm Partially framed or unframed 6 mm
For sliding door and fixed glass retained in a rebate or groove, the edge cover provided by the rebate or groove shall be at least 4 mm.

7.5 Glass shelves
Glass shelves that are not fully enclosed in a cabinet shall be a class C safety glass to BS 6206 as a minimum. This requirement is most easily met by using toughened glass. Annealed glass is acceptable for use as shelves only when fully enclosed within a cabinet. The maximum evenly distributed safe load that a shelf can support is dependent on glass type, thickness, width and span of the glass between supports.

8.0 DEVELOPMENTS IN SAFETY GLAZING

8.1 Fire resistant glass products
Acceptable glazing products for fire – rated, hazardous locations include transparent glass ceramic and in tumescent glass. Glass ceramic are single glazed products that meet both impact resistance requirements and provide up to a 3-hour fire resistance rating.
In tumescent glass are double – glazed products with an inner layer of transparent sodium silicate that when exposed to high temperature, turns opaque and forms an insulating layer that can provide up to a two hour fire resistance rating. Unlike glass – ceramic, in tumescent glass becomes insulating when exposed to fire. It is also more expensive than glass ceramic.
8.2 Blast resistant glazing
When a building is subjected to bombing it is noted that 60% of the non-lethal injuries sustained in that event were due to shattered glass, shattered glass was found as far as 1 mile from the blast site.
The GSA standard defines performance condition based on the response of glazing to a specified blast event, and the level of protection provided by glazing system as shown in the table below.










Table 5 The level of protection provided by glazing system
Performance Criteria Protection Level Hazard Level Description of Window Glazing Response
1
Safe
None Glazing does not break.No visible damage to glazing or frame.
2 Very high None Glazing cracks but is retained by the frame. Dusting or verysmall fragments near sill or on floor acceptable.
3a High Very low Glazing cracks. Fragments enter space and land on the floor no further than 0.99m from the window.
3b High Low Glazing cracks. Fragments enter space and land on floor no further than 3m from the window.
4 Medium Medium Glazing cracks. Fragments enter space and land on the floor and impact a vertical witness panel at a distance of no more than 3m from the window at a height no greater than 0.6m above the floor.
5 Low High Glazing cracks and window system fails catastrophically. Fragments enter space impacting a vertical witness panel at a distance of no more than 3m from window at a height greater than 0.6m above floor.


9.0 CONCLUSION

1. Structural glass tends to influence modern architecture more and more. It defines not only modernity, but also value, richness and future technology.
2. There have been thousands of other developments in glass manufacture that make it one of the most useful and versatile materials available.

Nature and Behaviour of Soft Clays and their improvement

The growth of Indian port city’s over the last few decades has been phenomenal
and Cochin is no exception with the increase of population, housing and construction of
various facilities have been a problem with urbanization. Having exhausted all the trouble
free hand, man is now on the look out for techniques to improve areas which were
originally considered uninhabitable. Thus studies on the nature and engineering behavior
of
soft clay’s covering long stretches of coastal line and methods to improve there geotechnical properties have been of great relevance, and is explained in the following pages.















2. REVIEW OF COCHIN MARINE CLAY

According to King (1884), 2500 years back, the sea washed up to the high ranges
of Western Ghats. The land between the Western Ghats and the present coastal line was
once well above the sea and was subsequently submerged. It was uplifted again by volcanic
action and again partially covered by sea water. The uplifted area includes the coastal belt
(10 to 30Km wide and 150 Km long) starting from Crangannore at the north to Quilon
at the south. Most of the Cochin city is situated in this belt.















3. PHYSICAL PROPERTIES OF COCHIN MARINE CLAY

Marine clay is formed by the sedimentation of clay soils in marine environments
exhibit unusual physical properties. They posses very high liquid limit and their natural
water content is close to the liquid limit values. The most striking feature of the physical
properties is the phenomenal changes that are caused by drying of sample. Some physical
properties of the Cochin marine clay is shown in the following table.

PHYSICAL PROPERTIES OF COCHIN MARINE CLAY
Sl No Physical properties (%) Moist soil Air dried soil Oven dried soil
1 Liquid limit 131.5 94.5 62.0
2 Plastic limit 53.9 45.2 40.5
3 Plasticity index 77.6 49.3 21.5
4 Shrinkage limit 18.1 18.8 19.2
5 Grain size distribution
(a) Clay
(b) Silt
(c) sand
48
34
18
33
47
20
13
55
32






4. SHEAR STRENGTH

In greater Cochin area the layers of shallow depth have their natural moisture
content quite close to their liquid limit. The clay deposits below vary widely in consisting up
to 40 to 50m where good load bearing stratum can be met with.
The shear strength of clayey soils is dependent on its water content. Any
increase in water content is necessarily accompanied by the reduction in cohesion or shear
strength. But at the same water content, different soils have different shear strength. From
the test results that were conducted at different places in Cochin, it was found that, the shear strength is very low and it is around 0.01Kg/cm² and 0.02Kg/cm².













5. CONSOLIDATION CHARACTERISTICS OF COCHIN
MARINE CLAY

Several series of consolidation tests were carried out on samples of Cochin arine clay varying different parameters like duration of loading, effect of pore fluid, effect
of washing. In the consolidation test which served as the reference test. It was found that
about 2 days were required for a complete dissipation of pore pressure and for reaching
an equilibrium void ratio for a particular loading stage. The clay deposits are highly
compressive with Cc value around 1.5 and natural moisture content
very close to liquid limit. It has been observed that almost all the structures, founded on
spread footings or raft footings invariably show actual settlement far below the computed
values.










6. PROBLEMS DUE TO THICK MARINE CLAY

Cochin City and the surroundings are covered with thick marine clay deposit
extending to a large depth (30 to 40m) below the ground level. Due to the presence of this
soft clay layer, following problems are observed.

 Low bearing capacity
 Higher settlement
 High seepage losses
 Liquefaction during earthquake
 Instability of foundation excavations
 Higher earth pressure on retaining structures

IS: 1904(1966) permits a maximum settlement of 40mm for isolated foundations on
sand and 65mmfor those for clay. The allowable settlement is higher for clay because
progressive settlement on clayey soils permits better strain adjustments in the structural
members. The maximum settlement for raft foundations on sand is 40mm to 65mm and that
on clay is 65mm to 100mm.

For typical industry following issues are to be addressed:

 Large area is covered with thick vegetation. If the area is reclaimed without removal of the vegetation. It will result in a fill with high organic content and high compressibility. On the other hand, if the vegetation is to be removed, it requires dewatering of the area so that powered vehicle can operate on the surface and clear slush and vegetation before selected soil is placed for reclamation.

 While reclaiming the area, particularly for industry requiring very large area, for example refinery, oil terminal, gas bottling plant, etc. the drainage pattern of the area needs to be planned carefully. The flow surface water which was taking place through the area prior to reclamation has to be diversified through special drains/culverts such a way that it does not create any inundation.

 The area avail is low-laying and often inundated with water. Unless the area is raised by soil fill (3 to 4m thick) it is difficult to carryout any construction.

 In many projects, the height of the fill required is 2 to 3m. This will require boundary wall which has a high retaining wall plus a compound wall. In the absence of retaining wall the fill material can encroach in the neighboring areas beyond the property line which may not be acceptable in many cases. Alternately, fill is placed with toe of the slop within the property line .in this case, large area with a width of 6 to 7m all along the periphery of the area remain unutilized.


 The placement of fill can lead to the following foundation problems.
 Negative drag force on pile foundation.
 Lateral flow under surface loading leading to settlement and lateral force on the adjacent foundations.
 Deep-seated slop failure for construction of embankment and heavy surface loading.
 Difficulty in executing foundations requiring deep excavation.







7. GROUND IMPROVEMENT

The clay deposit also needs to be improved to meet the foundation requirements. In early days, areas having clay deposit was avoided for construction. But with scarcity of land in urban areas, we do not have choice and structures have to be built on weak deposits. Pile foundation is of course a possible approach as it by pass the weak deposit and transfer the load on next component layer. Where thickness is very large, pile foundation is uneconomical and time consuming.
The methods of ground improvement that can be adopted depend basically on nature of strata and purpose of improvement. The methods available are as follows.



















8 METHODS OF GROUND IMPROVEMENT

8.1 VERTICAL DRAINS

This method is suitable for deep deposit of soft clay. The natural moisture content in this strata can brought down substantially by installing vertical drains with preloading. The pressures of vertical drains reduce the drainage path of water in the pores of the soil and thereby reduce the time required for consolidation. The spacing of drains depends upon the speed at which required improvement is to be achieved.
In earlier days, such vertical drains were installed by driving a close ended steep pipe o 100 to 200mm diameter up to the full thickness of such clay deposit. The pipe is then filled with sand and withdrawn in stage to form a vertical drain. The pipe is generally refused for installing other drains.
In the recent past, there has been number of different materials developed to replace the sand drains. These are basically plastic sections having thickness varying from 5 to 10mm and width from 100 to 150mm. The sections have channels to permit flow of water. The perimeter of the section is covered with a layer of geo-textile to prevent the entry of soil particles in to the channel. The advantages of such drain are that it results in minimum remoulding of surrounding soil during installation. The process of installation is very fast. The machine is mounted on a crane and typical drain up to 10m depth can be installed in the period of varying 1 to2 minutes including the time for shifting the machine to a new location.
The percentage of consolidation, which can be achieved by such vertical drains, can be theoretically predicted from the design charts developed based on the theory of three-dimensional consolidation. Typically, a deposit, which requires a period of over ten years for 95% consolidation, can complete the same consolidation within a short period of 3 to 6 months when vertical drains are installed.
After the drains are installed, the magnitude of preload to be placed on the required shear strength of the layer after improvement. Depending on the time available for improvement, the degree of consolidation is worked out and the effective over burden pressure (p) is computed. From the plasticity index I\of the soil, the ratio Su/p is determined. The ratios normally remain constant and therefore with increase in value of p the shear strength after treatment increases.

8.2 IN-SITU DEEP MIXING

In- site deep mixing using hydraulically operated helical augers penetrate the ground to the required depth. The hollow stem of the auger is used to inject cement / lime / any other stabilizing compound into the ground. A pair of 2 or 3 augers is operated simultaneously. After injecting the stabilizer in to the ground, the augers are rotated such that the soil along with the stabilizer is churned in-situ and mixed the stabilizer thoroughly with the soil without necessity of taking out the soil. The auger configuration can be chosen such that either a stabilized wall can be formed (to act as a barrier) or the entire area can be stabilized.

8.3 STONE COLUMN

Stone columns are cylindrical columns made below ground level which comprises of granular material of size varying from 25 to 100mm. The hole is made in the soft clay deposit by different techniques and then filled with stones in layer and compacted to form the complete column. When the structure is placed over the area treated by stone column, majority of the load (80 to 90%) is transmitted to the stone columns because of their higher stiffness. Balance 10 to 20%of the load is taken by the clay deposit. With the help of this 10%of surcharge load, the soft clay able to provide adequate confinement to the cylindrical column.

The area treated stone columns can be used to support only flexible structures such as embankment, oil storage tank, etc. because the settlement even after treatment with stone column can be large (50 to200mm). Without stone column the settlement could have been 3 to 4times higher and also the bearing capacity would have been much less.

8.4 VACUUM DEWATERING

In this technique also the layer is provided with vertical drains as mentioned above. The surface is then covered with a layer of a sand blanket 150 to 300mm thick and covered with a thin plastic sheet which is suitably anchored along the perimeter. Vacuum is then applied with a sand blanket which creates a suction pressure up to 50 to60mm height of mercury and forced the pore water out from the deposit through vertical drains. The area is also subjected to atmospheric pressure which then acts as preload. The vacuum pressure is maintained till the required improvement is achieved.

8.5 VIBROFLOTATION

Vibroflotation involves the use of a vibrating probe that can penetrate granular soil to depths of over 100feet. The vibrations of the probe cause the grain structure to collapse thereby densifying the soil surrounding the probe. To treat an area of potentially liquefiable soil, the vibroflot is raised and lowered in a grid pattern. Vibro replacement is a combination of vibroflotation with a gravel backfill resulting in stone columns, which not only increase the amount of densification, but provides a degree of reinforcement and potentially effective means of drainage.



























Figure:1
VIBROFLOTATION.
SCHEMATIC DIAGRAM:1

8.6 DYNAMIC COMPACTION

In dynamic compaction, a heavy weight of 15 to 20ton is raised to a height about 20m above the ground level and freely dropped on the ground surface. The impact on the ground surface transmits compression waves, which spreads radially from the point of impact. The compression waves travels fast and creates Liquefaction of the strata, which is saturated. It is followed by shear waves reorients the soil particle which are liquefied state to denser state and compacts the configuration. The spacing between the treating point, number of impact at each point, etc. can be varied depending on the required improvement.









































Figure : 2
DYNAMIC COMPACTION.



8.7 COMPACTION BY DEEP BLASTING

In this technique, a borehole is made to a depth approximately 3/4 or 2/3 of the total depth. Suitable explosive is lowered to the bottom of the borehole and the space above is back filled with compacted soil (known as stemming). The explosive is attached with cordex, which is taken up to the surface and connected to electric detonator. When the explosive is detonated, it creates a cavity, which expands instantaneously. The cavity expansion generates shock waves. Propagation of these waves densifies the soil to certain extent. After blast, a large conical depression is observed at the place of blast. The water within the pores of the deposit gets expelled out and comes up to the ground and form a large pool in the cone of depression.

The quantity of charge and spacing between the explosive can be suitably selected to achieve the required densification. As a thumb rule, about 15 to 45 grams of explosive is required for densification of every 3m of the deposit. Initial loose deposit which has relative density of about 50% and susceptible to liquefaction can be densified to a relative density of over 60% which is adequate to prevent liquefaction. The vibrations created during the blast are within permissible limits for construction purpose.











8.8 COMPACTION GROUTING

Compaction grouting is a technique where by a slow-flowing water /sand /cement mix is injected under pressure into a granular soil. The grout forms a bulb that and densifies the surrounding soil. Compaction grouting is a good option if the foundation of an existing building requires improvement, since it is possible to inject the grout from the side or at an inclined angle to reach beneath the building.




































Figure:3
COMPACTION GROUTING.
SCHEMATIC DIAGRAM:2



9. CASE STUDY

PILE FOUNDATION FOR VYPEEN ISLAND BRIDGE

The new bridge connecting Ernakulam town with Bolgatti Island and Vypeen Island is supported on 1m diameter bored cast in-situ pile. The design load for each pile is 450tones. The strata comprise of soft marine clay of 20 to 30m. This is followed by alternative layers of dense sand and stiffing clay which contains decayed wood within the deposit. The SPTN value of clay with decayed wood is generally >100 and the pile length were estimated as 45 to 50m.

During excavation of the work, it was noticed that even pile length 45m was not adequate to meet the loading requirement. Due to the large depth of pile, stabilization of the borehole and cleaning of the bore before concreting was found to be difficult. The load test results revealed that the end boring resistance offered by the strata was not significant and particularly all the load was resisted by side friction. To meet the requirement of loading, the pile length had to be increased from 45 to as high as 65 to 70m depending on the strata condition. For the certain piers, before the load test results were available, the piles were terminated with depth of 45m. Additional piles were provided at these locations to meet the loading requirements. It is very rare that large diameter piles have been installed to meet large depth.

The variations in the strata conditions and uncertainty about the behavior of stiff clay with the decayed wood made the designers to adopt a conservative approach which has resulted in large depth of pile. Apart from construction of piles, the strata condition posed followed technical problems.




 Reclamation of large area by dredged material on Vypeen Island.
 Construction of 6 to 8m high approach embankments on soft clay deposit created problems of settlement and negative drag of the pile. To reduce this 2 structural span have been added at the Ernakulam end so that the height of the embankment get reduced and approach embankment can be supported on the available weak strata.

































Figure:4
PILE FOUNDATION FOR VYPEEN ISLAND BRIDGE


10. CONCLUSIONS

Due to the increase in construction activities and urbanization the availability of suitable soils are decreasing. Cochin City and its surroundings are covered with marine clay to large depth. Which posses very low shear strength, low physical and engineering properties. Whenever the soft clay deposits are very loose sand or soft clay and are unsuitable for resting the foundation, the following options can be considered.

 Adopt deep foundation such as pile foundation so that the top soil can be bypassed.
 Treat the existing soil to improve the bearing capacity and reduce the settlement and place the foundation directly over the top soil.

Marina Bay Sands

Following four years of construction in Singapore opened Hotel Marina Bay Sands. The three tower 200 meters is a huge terrace in the form of a gondola with pools and green gardens with total area of 120 thousand square meters. The main pool is located outdoors, is not visible to the rim, because of what the impression that the water's edge terminates at a height. Swimming pool stretches for 150 meters and is the largest swimming pool, built on this level. The hotel has 2,560 rooms, shopping center, conference hall, 2 theaters, a museum and several restaurants. Marina Bay Sands is one of two winning proposals for Singapore's first Integrated Resorts, the other being the Resorts World Sentosa,
Bidders were assessed based on four criteria:
• Tourism appeal and contribution
• Architectural concept and design
• Development investment
• Strength of the consortium and partners
Las Vegas Sands initially committed to invest S$3.85 billion in the project, not including the fixed S$1.2 billion cost of the 6,000,000 square feet (560,000 m2) site itself. With the escalating costs of materials, such as sand and steel, and labour shortages owing to other major infrastructure and property development in the country, Sheldon Adelson placed the total cost of the development at $8.0 billion as of July 2009.




2. DESIGN

Fig(2.1) Architectural model showing the layout of the Marina Bay Sands Integrated Resort:

The hotel and Sky Park are in and on the towers in the background, respectively; the shopping mall, theatre and casino are in the long lower building; and the ArtScience Museum is in flower-shaped building in the foreground.
The resort is designed by Moshe Safdie, who says it was initially inspired by card decks. In addition to the casino, other key components of the plan are three hotel towers with 2,560 rooms and suites, a 200,000-square-foot (19,000 m2) Art Science Museum and a convention centre with 1,200,000 square feet (111,000 m2) of space, capable of accommodating up to 45,000 people.
Conceptually, each tower is composed of two slabs of east and west-facing rooms. The double-loaded towers spread at the base forming a giant atrium at the lower levels, and converge as they rise . the tower slabs also give further character to the massing and relate to the site context: the glazed west side faces the city center while the east side is planted with lush bougainvilleas facing the botanical gardens and ocean beyond in plan, as the parcel varies in width, the cross section is decrease from one tower to the next. The three void spaces are connected by one continuous and conditioned glazed, filling the space between the towers with restaurants, retail spaces, and a public thoroughfare. Each tower slab from is also twisted slightly in relation to its pair, creating a dance-like relationship between the two parts and accentuation the slenderness of the buildings, resulting in the appearance of six towers, rather than three.
In addition to the million square meters of built space the project program also called for the development of extensive exterior gardens with swimming pools, jogging paths, and public spaces. As one of the aims of the project had been to minimize the geight of the podium buildings, seeking to reference Singapore’s pastoral hills more than its urban core, the problem emerged that the complex program left no vacant land suitable for these amenities. Creating gardens on top of the roof of the casino and the convention center was studied, however these vast spaces lacked views, overshadowed and overpowered by the adjacent hotel towers. The idea emerged to bridge between the three towers in order to reclaim exterior garden space and create a 2.5-acre park in the sky.

2.1 THE BELLY
The façade of the project which required careful consideration was thus the “belly” of the sky park. Made of more than 9000 silver-painted metal –composite panels, this skin encloses the mega trusses which bridge the buildings at level 55,as well as a multitude of back of house spaces(i.e., large mechanical rooms with water tanks supporting the pools and a network of corridors and offices for hotel operations staff). The geometry of the sky park began with a platonic torpid form, which was then further shaped to streamline the cross sections of the building. The resulting surface was then regularized and panelized using a computer script, triangulation the façade into simple shapes, the shapes were water-jet cut from flat sheet panels and shipped to the building site in containers pre-designed to be lifted to the top levels of the building.
Once on top of the building, the panels were installed via temporary aluminum frame under slung mobile gantries which traveled on a permanent track of steel rails. The gantry system track serves double day as a building maintenance unit, therefore the track was designed to be hidden within the reveal pattern of the facade panels.






3. CONSTRUCTION

Fig(3.1) When construction started in 2007.

Fig(3.2) Marina bay sands

In May of 2006, after a highly-competitive bidding process, the Singapore government selected Las Vegas sands corp. to build the country's first integrated resort property. It will be one of only two resort-casino properties in the South East Asian city-state and will operate as such for a period of 30 years. the gigantic complex complete with three 60-story hotel towers with 3 stories underground will house 2,600 hotel rooms / suites and a 4,000 car garage; topped by a two acre sky park bridging across the towers consisting of a garden, swimming pool, jogging paths, spas; ‘floating’ crystal pavilions; on the promontory a lotus-shaped museum; a grand, a multi-leveled retail arcade for international luxury brands. Celebrity chef restaurants; an outdoor event plaza; entertainment theaters and night clubs plus a Las Vegas-style casino; highly flexible exhibition halls and a convention centre that can host over 45,000 delegates.


Fig(3.3) Marina bay sands

Fig(3.4) Marina Bay Sands

Skypark is beginning to look like a park with more than 20 trees now planted 200 meters in the air.Closer to the opening, the roof top gardens will be home to 250 trees and 650 plants.


Fig(3.5) The grand arcade trave rse of the MBS hotel
The 340m-long skypark, which will house a 1,2 hectares swimming pools -
equivalent to the size of 10 olympic size swimming pools -, observation decks, gardens, restaurants, spas, and walking trails.it will be cantilevered out some 70m without any support underneath.once completed, the skypark is expected to be a leading tourist spot where one can enjoy a panoramic view of the beaches and downtown singapore.drawing by lim vong marina bay is a bay near central area in the southern part of singapore, and lies to the east of the downtown core. it is an artificial bay and was formed when land reclamation created the marina centre and marina south areas, which form a body of sheltered waters of what was once open sea. This land was reclaimed as part of the long-term strategy for singapore’s growth about 30 years ago, with a view to the downtown core eventually out-growing itself.The reclamation is about more than just increasing land area. The large area of sea which has been embraced by the reclamation has now been isolated from the larger ocean by the building of a dam across the narrow inlet so that, gradually as the singapore river discharges its fresh water load into this area over the next decade or so, it will dilute the sea-water and eventually create a fresh-water reservoir, making singapore politically less dependant on malaysia for its fresh water needs, and creating a great recreational resource in the heart of the city to boot.


Fig(3.6) Marina resort
Fengshui master says the integrated resort has many auspicious elements going for it. The sky park is curved, planes that come around will see a smile from their bird's eyes view. The towers represent three mountains or three warriors guarding the gateway to singapore. Despite fengshui being open to many interpretations, there are rules and principles to the practice, which are guided by the so-called balance of the five elements. its silvery white facade represents metal, while other elements represent fire. wood is in the landscaping and greenery, while water surrounds it.

Fig(3.7) The marina bay sands art and science museum

The lotus shaped art science museum sits at the front of the development. The building's shaped steel frame was among the most difficult parts of all the structural design. However, using software scripting it was possible to analyze this one petal at a time, altering the parameters for each subsequent part. An international team of PERI specialists from singapore and germany created a comprehensive formwork and scaffolding solution for the korean building company, ssang yong engineering & construction. in particular, the skytable large slab tables as well as PERI ACS self-climbing technology have optimised construction progress with reduced crane times. These rised steadily upwards with each floor being completed in only four days.

During construction, three iron structures were propped temporarily at places with the severest inclination beside the post-tension method. Through this, the quantity of temporary work for the main work was reduced by a great deal so that the work could be executed without interference from structures. as a result, constructors succeeded in early march 2009 in connecting at 23F above ground and a height of 70m for the east-side building and the west-side building that were inclined at 52 degrees maximum for towers I, II and III that were rising in the form.
In each case, two asymmetrically curved legs have been positioned against each other which grow together like bridge pylons to form units. although the three hotel towers are still identical with regard to the height and number of floors, the forms of the respective building elements nevertheless have considerable differences in terms of the base width, curvature radius and lateral offset dimension. Furthermore, the individual floors are also offset from one another in a longitudinal direction. Only two cranes per tower were available to the Construction crews, therefore crane independent and crane-saving formwork solutions were used to construct the core walls and floor slabs respectively.
With the help of ACS self-climbing technology and the large-area sky table slab tables, crews were able to finish a complete floor with a standard height of 3 m in only four days. Twelve elevator shafts climbed three cycles in advance and a total of 110 sky table slab tables were required for constructing two complete floors in each case.



Fig(3.8) Construction of deck

Fig(3.9) Construction of deck


Fig(3.10) Construction of deck

Fig(3.11) The marina bay sands construction site
Up to 20 m long and 5 m wide, the 100 m² sky table units could be easily moved with only one crane lift. the innovative moving method ensured that the table was always pulled out of the building in a horizontal position and the operating personnel were always standing in a safe and secure place on the slab edge. Due to the large lowering height of the multiprop props, 20 cm slab offsets and, at the same time, 50 cm parapet wall heights presented no problems. Connected to MRK frames, the tables could be additionally used for the 9 m high intermediate floors.

Fig(3.12) The marina bay sands towers

With the help of ACS, the different-sized shafts with dimensions ranging between 2.30 and 10.10 m, could be shuttered, struck and climbed without the need of a crane. Altogether, five working levels rose at the same time to the next section:
Two platforms for forming, reinforcement work and concreting the shaft walls as well as three finishing platforms for pretensioning the subsequent storey slabs. in combination with CB climbing scaffold and the vario GT 24 girder wall formwork, operational sequences on the construction site were optimized.
The technical team of ssang yong E&C applied the post-tension method that is used mainly in constructing bridges to construct a building inclined at 52 degrees at its highest, which is 10 times more inclined than the leaning tower of pisa. The team adopted a tension method whereby post-tension is installed on a 600 mm thick bearing wall and wire is stretched from inside.



Fig(3.13) Close-up to the marina bay sand middle tower


Fig(3.14) With only one crane lift, 100 square meters of slab formwork could quickly and safely moved.
The project's foundations have had to be massive because of building on marine clay. the team has had to get through the clay to make room for the underground car-parks and railway tunnels which sit beneath the facility. bored piles which go down to over 50m with large bored piles up to 2.8m in diameter have been necessary, typical of many singapore construction projects.





4. OPENING

Fig(4.1) During the 2010 Summer Youth Olympics opening ceremony

Marina Bay Sands was originally planned to be completed in a single phase in 2009, but rising construction costs and the financial crisis forced the company to open it in phases. The first phase's preview opening was further delayed until 27 April 2010, and the official opening was pushed back to 23 June 2010. The rest of the complex remained under construction and was opened after a grand opening on 17 February 2011.On 27 April 2010, Marina Bay Sands had the first of a planned 3 to 4 phase openings. The casino, parts of the conference hall, a segment of the Shoppes, 963 hotel rooms and the event plaza were opened.
The Inter-Pacific Bar Association (IPBA) held the first conference at Marina Bay Sands Convention Centre on 2–5 May 2010, but the event was marred by uncompleted facilities and power failure during a speech. IPBA withheld payment of S$300,000 and was consequently sued by Marina Bay Sands. In June IPBA counter-sued, describing the venue as a complete disaster and that its earlier payments had been imposed by duress, fear and force. An amicable settlement with undisclosed terms was announced in August. On 23 June 2010, the resort had its official opening with a 2-day celebration, this includes the Sands Sky Park, the Event Plaza along Marina Bay, more shops, additional dining options and nightlife offerings, and the rest of the hotel room


5. SPECIALITIES


5.1 CASINO

Marina Bay Sands casino is housed in its own building and offers four levels of gaming in a luxurious, spacious setting. Patrons can enjoy a wide variety of popular table games including roulette, blackjack, baccarat and sic bo, and slot machines featuring the latest games such as video poker, and electronic sic bo and roulette. Premium players and Paiza members have access to exclusive gaming and dining privileges at the casino’s upper two levels, which feature over 30 private gaming rooms.

5.2 SKY PARK

The Sands Sky Park is an architectural masterpiece sitting on top of the three hotel towers at Marina Bay Sands. This 1.2 hectare tropical oasis is longer than the Eiffel Tower is tall and large enough to park four-anda-half A380 jumbo jets. It extends to form the one of the world’s largest public cantilevers. It is 200 meters in the sky. Landscaped gardens are home to 250 trees and 650 plants and 12,400 square meters of space big enough to fit three football fields.


5.3 INFINITY POOL

The Infinity Pool is part of the 380 metre long Sands Sky Park, which spans across the three towers of the Marina Bay Sands complex and covers a total area of 12,000 sq mts. The length of this roof-top deck can be equated to the height of the Eiffel Tower.
The Infinity Pool is one of the world’s largest outdoor pools at three times the length of an Olympic pool and 55 storeys high. The pool creates an illusion of the water extending to the horizon while in reality, the water spills over the edge into a catchment below and is then pumped back into the pool. It has two circulation systems, with the first filtering and heating the water in the main pool and the other, filtering the water in the catch basin and returning it to the upper pool.



Fig(5.1) Infinity Pool








6. CONCLUSION
 Marina bay sand is a magnificent destination for entertainment, business, and shopping.
 The success of project lies in the fact that the inventiveness of the design was matched by an equally inventive and novel approach developed by engineering and constructon teams.
 Delivers once in lifetime experiences.
 This landmark building is situated in the heart of Singapore’s central business district.
 With a luxury hotel, state of art convention, exhibition facilities, and some of the best shopping &dining in the region.
 This is the place to go for world class entertainment.

Enzyme Soil Stabiliser

Enzymes as soil stabilizers have been used to improve the strength of subgrades due to low cost and relatively wide applicability compared to standard stabilizers. The use of enzymes as stabilizer has not been subjected to any technical development and is presently carried out using empirical guidelines based on previous experience. Therefore, it becomes an important priority to study and determine the effects of the enzymes on the strength of different soils.

1.0 INTRODUCTION
In recent years, more attention has been given to the use of enzymes as soil stabilizers due to expansion in manufacturing capacity, low cost, and relatively wide applicability compared to standard stabilizers (hydrated lime, Portland cement, and bitumen) which require large amounts of stabilizers to stabilize soils (high costs). Although enzyme-based soil stabilizers appear to have many advantages compared to conventional chemical stabilizers, it is unclear how these products work and under what conditions. The process has not been subjected to a rigorous technical investigation and is presently carried out using empirical guidelines based on experience. It becomes therefore important to perform a research study that can give objective scientific support to the use of enzymes as a soil stabilizer.
The main objective is to investigate the stabilization mechanism of some of the commercially available enzyme-based products to better understand their potential value for road construction. Limited laboratory experiments are performed to determine if these products improve the material properties of subgrade soils and if they offer superior mechanical properties compared to other types of stabilization for which comprehensive laboratory and field performance already exists.

2.0 SOIL STABILIZATION
Solidification or Stabilization (S/S) is a treatment technology for contaminated soils, either for clean up or remediation alone or as part of a brown field redevelopment. Portland cement, often augmented with other materials, such as fly ash, lime kiln dust, cement kiln dust, and lime, is used as a binding reagent in stabilization because of its ability to solidify, change the physical properties and stabilize the changes in the chemical properties of a wide range of hazardous materials. These types of stabilization materials are termed as soil stabilizers. Solidification increases the compressive strength, decreases the permeability, and encapsulates toxic elements. Stabilization converts hazardous elements into less soluble, mobile or toxic forms. Mixing the right combination of binding reagents into contaminated soils allows them to be either excavated and disposed of in a landfill, or re-used on site to support redevelopment. The solidification treatment has the further benefit of improving the structural properties of the site as whole.

2.1 USES
Stabilization is used to remediate or reclaim a contaminated site. Specific treatment effects include:
 Chemically binding free liquids in waste mater
 Reducing the permeability of waste matter
 Encapsulating waste particles
 Chemically fixing hazardous elements
 Helping reduce the toxicity of contaminants.

2.2 TYPES OF SOIL STABILIZERS
There are mainly two types of soil stabilizers, standard stabilizers and non-standard stabilizers. The non-standard stabilizers, when applied to the appropriate soil and aggregates using the right construction techniques, can produce dramatic improvement on these materials. These non-standard stabilizers are by-products of unrelated processes, modified specifically for use as stabilizers. Unlike the standard stabilizers such as Portland cement, lime and bitumen, these stabilizers have no laboratory tests that can be used to predict their field performance.

2.3 TERMS IN SOIL STABILIZATION WITH NON-STANDARD STABILIZERS
Soils are not an inert material; in fact they are chemical substances and will react with other chemicals if certain conditions are present. These reactions result from the attraction of positive and negative charges in the components of the soil and the chemical substances. If something happens to alter these charges, the reactions are changed and furthermore the properties of the materials are changed. To better understand the stabilizing mechanism of the non-standard stabilizers, the concepts of soil electrolyte systems, osmotic gradient pressure and colloid activity must know, a small summary about these mechanisms are given below;



2.3.1 Soil Electrolyte Systems
Many subgrades, aggregates and mixtures of crushed rock and soils are known to behave as electrolyte systems where ion exchanges occur within the material. Knowledge of the layered lattice structure of clay materials, and of colloid transport and osmotic pressure gradients is critical in understanding the behavior of these electrolytes soils. Most clay has a molecular structure with a net negative charge. To maintain the electrical neutrality, cations (positively charged) are attracted to and held on the edges and surfaces of clay particles. These cations are called “exchangeable cations” because in most cases cations of one type may be exchanged with cations of another type. When the cation charge in the clay structure is weak, the remaining negative charge attracts polarized water molecules, filling the spaces of the clays structure with ionized water.
2.3.2 Osmotic Pressure Gradients
Individual cations are unable to disperse freely in the soil structure because of the attractions of the negatively charged surface of the clay particles. This inability to disperse evenly throughout the solution creates an osmotic pressure gradient, which tries to equalize the cation concentration. As a consequence, a movement of moisture from areas of low cation concentration to areas of high cation concentration is produced to achieve the equilibrium of the cation concentration.
2.3.3 Colloid Activity
Colloids are amorphous molecules without crystalline structure with a size of less than a micron. Particles of this size are strongly influenced by Brownian motion caused by random thermal motion. Colloids are present in high concentrations when clay soils are present. Colloids have a net negative charge that enables them to attract and transport free cations in the soil electrolyte solution, subsequently losing the cation when passing close to the more strongly charged clay particle, leaving as a consequence the colloid free to seek more free cations. Both electrochemical and physical effects influence this mechanism.
The physical phenomena are related to Brownian motion, laminar shear velocity and pore-size distribution. Brownian motion overcomes the effects of gravitational force and prevents deposition; the laminar shear velocity affects the rate of cation exchange with the clay structure; and the pore-size distribution determines the shear velocity and how close the clay lattice is to the passing colloids and cations. The electrochemical effects are related to the forces between positive and negative particles (Van der Waals forces), and to the repulsion forces between ions of the same charge. If a solution with cations is introduced into the clay structure, a micro environment is created in which the cations are prevented from dispersing by their adjacent clay lattice. If the soil is not completely saturated, the liquid phase will move in laminar flow through the soil pores by capillary forces, leaving the higher concentration of cations close to the surface.
This creates an osmotic gradient pressure, which draws colloidal particles from zones of lower cation concentration. These colloidal particles take some of the free cations, reducing the ion concentration and the osmotic gradient pressure. This results in a hydraulic gradient pressure in the opposite directions which takes the cation transporting colloids outward from the original zone of cation concentration to another zone where another clay lattice is present, resulting in a new zone of osmotic pressure and cation concentration.

2.4 MECHANISM OF NON-STANDARD STABILIZERS
The flow of cations through the clay deposits gives the shrinking and swelling properties of the soils; when a stabilizer solution is added to the soil, the magnitude of the effect depends on the characteristics of the particular cation. In general there are two main characteristics, the valence of the cation, i.e. the number of positive charges, and the size of the cation
The size determines the mobility of the cation: smaller ones will travel a greater distance throughout the soil structure (the hydrogen ion is the smallest one). With respect to the valence, the hydrogen ion is doubly effective affecting the clay structure because even though it has only a single charge, the hydrogen ion produces an effect of valence of two due to its high ionization energy. These hydrogen cations exert a stronger pull on the clay layers pulling the structure of the soil together and removing the trapped moisture permitted by the single sodium and potassium cations
This loss of moisture results in a strengthening of the molecular structure of the clay and also in a reduction of the particle size and plasticity. Thus changes in the environment of the clay from a basic to acidic type of environment can result in the change of the molecular structure of the soil for a long period of time.
Organic cations created by the growth of vegetation also have the capacity to exchange charges with other ions in the clay lattice. Some of the organic cations are huge in size equaling the size of the smaller clay particles. These larger organic cations can blanket an entire clay molecule, neutralizing its negative charges, and thus reducing its sensitivity to moisture. Soil bacteria make use of this process to stabilize their environment, producing enzymes that catalyze the reactions between clays and organic cations to produce stable soil.
The Non-Standard stabilizers can be classified in two groups: Chemical stabilizers and Pozzolan stabilizers. The chemical stabilizers are also subdivided into five groups: Sulfonated Oils, Ammonium Chloride, Enzymes, Mineral Pitches and Acrylic Polymers.

2.5 CHEMICAL STABILIZERS
These are chemical substances that can enter into the natural reactions of the soil and control the moisture getting to the clay particles, therefore converting the clay fraction to permanent cement that holds the mass of aggregate together. The chemical stabilizer in order to perform well must provide strong and soluble cations that can exchange with the weaker clay cations to remove the water from the clay lattice, resulting in a soil mass with higher density and permanent structural change.
The sulfonated naphthalene and D-limonene produce powerful hydrogen ions, which penetrate into the clay lattice, producing the breakdown of the structure and the further release of moisture resulting in a dense soil structure. The ammonium chloride produces NH4+ ions that adhere strongly to the edge of the clay, releasing the surface water and altering the surface structure to reduce capillarity.
The mineral pitches are hard resinous pitch that comes from the distillation of pulp waste. This type of stabilizer performs similarly to emulsify asphalt but is capable of developing five times the strength of asphalt cement; it can be used for dust control and surface treatments.
The acrylic polymers are prepared in emulsions formed with forty-to-sixty percent solids; they are non-toxic and non-flammable. On drying they form a glass like thermoplastic coating, which will form a weather resistant web between the soil grains.

2.6 POZZOLAN STABILIZERS
The pozzolans come from coal-burning power plants. These non-standard stabilizers differ from other chemical stabilizers because they are a waste or byproduct from other industrial processes and lack the quality control of chemical commercially produced stabilizers. One of the main products is lime. When lime is introduced into a soil with trapped moisture, it ionizes and produces calcium cations that can exchange with the clay lattice. The calcium cation exchanges with the sodium and potassium in the clay structure in the same way that the chemical stabilizers exchange ions. Because the calcium cation is large it cannot move far into the clay structure; adequate mixing is therefore required to obtain the benefits of this type of stabilization. The stronger ionization energy of calcium pulls together the structure of the clay, releasing the water in excess and breaking down the clay lattice.
The presence of lime increases the pH of the soil. The high pH releases alumina and silica from the pozzolans and from the clay structure. These free alumina and silica react irreversible with the calcium ions to form calcium aluminum silicates that are similar to the components of portland cement. These calcium silicates have net negative charges, which attract ionized water (molecules that act as dipoles) to create a network of hydration bonds that cement the particles of the soil together.
3.0 ENZYMES AS A SOIL STABILIZER
The enzymes are adsorbed by the clay lattice, and then released upon exchange with metals cations. They have an important effect on the clay lattice, initially causing them to expand and then to tighten. The enzymes can be absorbed also by colloids enabling them to be transported through the soil electrolyte media. The enzymes also help the soil bacteria to release hydrogen ions, resulting in pH gradients at the surfaces of the clay particles, which assist in breaking up the structure of the clay.
An enzyme is by definition an organic catalyst that speeds up a chemical reaction, that otherwise would happen at a slower rate, without becoming a part of the end product. The enzyme combines with the large organic molecules to form a reactant intermediary, which exchanges ions with the clay structure, breaking down the lattice and causing the cover-up effect, which prevents further absorption of water and the loss of density. The enzyme is regenerated by the reaction and goes to react again. Because the ions are large, little osmotic migration takes place and a good mixing process is required. Compaction of aggregates near the optimum moisture content by construction equipment produces the desired high densities characteristic of shale. The resulting surface has the properties of durable “shale” produced in a fraction of the time (millions of years) required by nature.
The idea of using enzyme stabilization for roads was developed from the application of enzyme products used to treat soil in order to improve horticultural applications. A modification to the process produced a material, which was suitable for stabilization of poor ground for road traffic. When added to a soil, the enzymes increase the wetting and bonding capacity of the soil particles. The enzyme allows soil materials to become more easily wet and more densely compacted. Also, it improves the chemical bonding that helps to fuse the soil particles together, creating a more permanent structure that is more resistant to weathering, wear and water penetration.

3.1 THE CONCEPT OF ENZYME STABILIZATION
Enzyme stabilization is commonly demonstrated by termites and ants in Latin America, Africa and Asia. Ant saliva, full of enzymes, is used to build soil structures, which are rock hard and meters high. These structures are known to stand firm despite heavy tropical rain seasons.
For many years, road engineers have used additives such as lime, cement and cement kiln dust to improve the qualities of readily available local soils. Laboratory and field performance tests have confirmed that the addition of 6% to 10% of such additives can 'increase the strength and stability of such soils. However, the cost of introducing these additives has also increased in recent years. This has opened the door widely for the development and introduction of other kinds of soil additives including highly cost-effective liquid enzyme formulations.
Liquid enzyme soil stabilizers can significantly enhance the properties of the soil used in the construction of road infrastructure. Results include a better and longer lasting road with increased loading capacity (CBR) and reduced soil permeability. Stabilization with the right brand of liquid enzymes can lower a road's construction and maintenance costs while increasing the overall quality of its structure and surface.
The promise that soil stabilization technology can actually improve the mechanical qualities of local road soil so that stronger, more durable roads can be built has prompted multi-lateral banks and national road ministries around the world to conduct extensive testing to verify that this new technology is truly cost-effective. For example, a comprehensive two year World Bank study in Paraguay confirmed the benefits of soil stabilizers.
The result is that this new advance in “soil stabilization” technology is increasingly being used in both constructing and improving/rehabilitating subsurface and paved roads worldwide. It has been used with excellent and consistent results in more than 30 countries including the US and Canada, and countries in Latin America, Africa, and Asia. Scores of successful projects have been completed, including rehabilitation of nearly 300 kilometers in Honduras and almost 1,000 kilometers in Malaysia.

3.2 REVIEW OF PREVIOUS STUDIES ON ENYME BASED SOIL STABILIZER
Wright-Fox (1993) carried out a study to assess the stabilization potential of enzymes. Standard soil tests were used for the study as no specific standards are available for enzyme-stabilized materials. Results from strength and index tests (e.g. liquid and plastic limit) conducted by Wright-Fox showed an increase in the unconfined compressive strength of the stabilized material as compared to control specimens. There was a 15% increase in the undrained shear strength of the stabilized material. The soil used was silty clay with a liquid limit of 66% and plasticity index of 42%. The index tests performed did not show any variation from the control specimen. Thus the enzymes might not offer waterproofing qualities using the recommended rate of application. Wright-Fox (1993) concluded that enzymes may provide some additional shear strength for some soils and that the soil stabilization with enzymes should be considered for various applications but only on a case-by-case basis.
Brown and Zoorob (2003) carried out research on the stabilization of aggregate clay mixes with enzymes. Standard tests such as liquid limit and compressive strength were used for this study. A summary of the findings of that investigation is shown in Table 1. It can be seen that there is a possibility of achieving stabilization with soils containing Keuper Marl type of clays.
The tests performed during this research have shown inconclusive improvements on the control properties. The authors recommended that further investigation should consider the importance of running tests to determine the soil’s organic content, or, even better, run to perform a full chemical analysis on the compounds contained in the soil prior to stabilization. This investigation did not take into account several important factors such as curing temperatures and times, durability tests and enzyme concentration.

Table 1
Brown and Zoorob Study of Enzyme Stabilization on Soils.

Type of Soil
Liquid Limit Moisture
Evaporation
Rate Compressive
Strength


China Clay Increases Lower than
control
specimen Decreases


Gault Clay Increases Lower than
control
specimen Inconclusive


Keuper Marl
Decreases Similar to
control
specimen Inconclusive


3.3 DESCRIPTION OF INVESTIGATION
Based on the investigations done before, here it is a small description about the experiment methods, their results and improving properties of the soil using enzymes. For that consider, two commercially available enzyme-based products were evaluated in this study, product A and B. The manufacturer’s information available for these two products is presented below. Product A and B are organic non-biological enzyme formulations supplied as a liquids. Enzymes are natural organic compounds which act as catalysts. Their large molecular structures have active sites, which assist bonding and interactions. Product A is also blended with a biodegradable surfactant to reduce the surface tension and promote enzymatic reactions, which has a wetting action that improves compactibility, allowing higher dry densities to be achieved. It is claimed that the treatment with this product is permanent and that the treated layer becomes impermeable.
The enzyme is made from fermenting sugar beets a process similar to beer brewing, but the process continues until everything is fermented. The enzymes increase the wetting action, allowing higher compaction. The enzyme cements the soil by forming weak ionic bonds between negative and positive ions present in the soil structure.
Enzymes can be used to stabilize a wide variety of soils. The manufacturer reports the following advantages of using their products for soil stabilization: low cost, easy application, wide applicability, and environmentally friendly. In addition, it results in a soil with a high resistance to frost heaving.
The Civil Engineering Research Foundation (CERF) funded by the Federal Highway Administration made an evaluation of the environmental impact of the use of enzymes as soil stabilizer. The study found that there are seven chemicals in the enzyme soil solution.
The chemical concentrations in soil were compared with Risk-Based Concentrations (RBC) in residential soil, which was developed by the Environmental Protection Agency (EPA) as a screen level for contaminants on a concerned site. It was found that the enzymes did not increase risk-based concentrations (RBC) levels of soils and it was practically nontoxic in all the toxicological analyses.
The enzyme is a natural organic compound derived from crop-plant biomass. It is similar to proteins and acts as a catalyst. The large molecular structures contain active sites that assist molecular bonding and interactions. Enzymes accelerate the cohesive bonding of soil particles and create a tight permanent layer. Unlike inorganic or petroleum-based products that have a temporary action, enzymes create a dense and permanent base and subgrade that resists water penetration, weathering and wear.
In normal road construction methods, compaction levels in the range of 90-95 percent are usually obtained, while with enzyme compaction densities of up to 100-105 percent may be reached. The enzyme stabilization can be applied to most soils, which contain a minimum of eight to eleven percent of cohesive fines. The basic effects of the action of the enzyme into the structure of the soil can be summarized as follows. Initially, the film of absorbed water is greatly reduced and in fact entirely broken, as shown schematically in Figures 1 and 2.



Fig.1 Absorbed Water in the Structure of the Soil

Fig.2 Elimination of the Absorbed Water in the Soil

The most difficult problem is raised by the presence of absorbed water in the soil that adheres to the entire surface of each soil particle. This film of water enveloping the particles, which ultimately governs the expansion and shrinkage of colloidal soil constituents, cannot be completely eliminated by purely mechanical methods. However, by means of temperature effects, addition or removal of water with mechanical pressure, it is possible to vary the amount of water held in this manner. Such variations are attended by swelling or shrinkage. This provides an ideal point of operation for the enzyme.
The electrostatic characteristics of soil particles will also have to be considered to understand the mechanism of soil-enzyme interaction. As a result of lowering the dipole moment of the water molecule by the enzyme, dissociation occurs in a hydroxyl (-) and a hydrogen (+) ion. The hydroxyl ion in turn dissociates into oxygen and hydrogen, while the hydrogen atom of the hydroxyl is transformed into a hydronium ion. The latter can accept or reject positive or negative charges, according to circumstances. Normally the finest colloidal particles of soil are negatively charged. The enveloping film of absorbed water contains a sufficient number of positive charged metal ions – such as sodium, potassium, aluminum and magnesium – which ensure charge equalization with respect to the electrically negative soil ion.
In bringing about this phenomenon, the positive charges of the hydronium ion or of the negatively charged hydroxyl ion will normally combine with the positively charged metal ions in the water adhering to the surface of the particles. Because of the effect of the enzyme formulation in reducing the electric charge of the water molecule, there is sufficient negative charge to exert adequate pressure on the positively charged metal ions in the absorbed water film. As a result of this, the existing electrostatic potential barrier is broken. When this reaction occurs, the metal ions migrate into the free water, which can be washed out or removed by evaporation. Thus the film of absorbed water enveloping the particles is reduced. The particles thereby lose their swelling capacity and the soil as a whole acquires a friable structure.
The hydrogen ions, which are liberated in the dissociation of the water molecules, can once again react with free hydroxyl ions and form water along the gaseous hydrogen. It is important to note that the moisture content of the soil affects the surface tension and is thus a factor affecting compaction. The enzyme reduces surface tension making the soil compaction easier to perform.
After the absorbed water is reduced, the soil particles tend to agglomerate and as a result of the relative movement between particles, the surface area is reduced and less absorbed water can be held, which in turn reduces the swelling capacity.

Some of the properties modified by the stabilization process according to the manufacturers are listed below:
 Increased compressive strength: the enzyme acts as a catalyst to accelerate and strengthen road material bonding. The enzyme creates a denser, more cohesive and stable soil.
 Reduced compaction effort and improved soil workability: lubricates the soil particles. This makes the soil easier to grade and allows the compactor to achieve targeted soil density with fewer passes.
 Increased soil density: helps reduce voids between soil particles by altering electrochemical attraction in soil particles and releasing bound water. The result is a tighter, dryer, denser road foundation.
 Lowered water permeability: a tighter soil configuration reduces the migration of water that normally occurs in the voids between particles. It produces a greater resistance to water penetration deterioration.
Some of the advantages of using enzyme-based stabilizers instead of the traditional stabilizers are listed below:
 Environmentally safe: enzymes are natural, safe (organic) materials. These materials are nontoxic and will cause no harm or danger to humans, animals, fish or vegetation.
 Cost effective: all-weather, low-maintenance soils for road construction can be achieved for a small fraction of bituminous paving or other resurfacing costs.
 Simple to use: the enzyme is added to water, applied with a sprayer truck and mixed into the material. Normally the enzyme comes in liquid concentrate. This benefit eases handling and preparation procedures and adds to the cost effectiveness.

3.4 CASE STUDY
The enzyme products have been used in more than 40 countries in the construction of structures from rural roads to highways for the past 30 years. According to the manufacturers in the overwhelming majority of the cases enzyme stabilization provided a tool that enhanced the life-cycle and quality of the resulting product. A short review of some of the projects where enzymes were used as a road stabilizer is presented below.
A World Bank study on soil stabilization using enzymes in Paraguay reported consistent road improvements and better performance from soil stabilizer treated roads compared to untreated roads. The conclusions were drawn based on data gathered on a large-scale study from multiple sites using commercial enzymes and documentation of road performance for up to 33 months.
Stabilization with enzymes has been used in India. Good performance of these roads despite the heavy traffic and the high rainfall has been found. Besides an increase in the strength and durability of the roads, a reduction in project cost has also been achieved.
Enzymes have been used successfully to stabilize roads in Malaysia, China and the Western USA at low cost. In Mendocino County, California Department of Transportation has conducted several tests of a compaction additive based on enzymes. This natural product helped the road base to set very tightly, reducing dust and improving chip-seal applications. With air quality and water quality agencies requiring dust reduction, this is a potentially effective new product, cheaper than asphalt.
Emery County in Utah has more than 40 miles of surface-dressed roads treated with the products that have been in use for several years. The climate is extremely arid and the 15 to 20% clay content in the aggregates has a very low Plasticity Index (PI) (<3%). A practical procedure for application of the treatment has been evolved. Jerome County in Idaho is nearby and reported a similar experience.
Two city streets in Stillwater, Oklahoma were also treated with enzyme products. The clay had a plastic index of 20% and good performance was reported.
A number of projects have been completed in Panaji (India) with the use of enzymes. A rural road and a city road in Maharasthra have lasted for more than two years without any damage.
Road sections placed in western Pennsylvania in the fall of 1992 passed subfreezing winters and over forty freeze-thaw cycles and required no maintenance for ruts, potholes or wash boarding during three years. The road sections then received chip-seal coats and asphalt surfaces with no requirement for repairs to the stabilized base .Enzymes have been used to stabilize more than 160 miles of subgrades and road surfacing in sites located across the National Forest land of the United States Department of Agriculture, where intense rainfall, highly erosive aggregate surfacing and expansive clay are found. The performance of the test sections shows improvement over non stabilized control sections and historical performances of these sections before stabilization. Failures in the test sections have been related with the misuse of the enzymes, such as application over the wrong type of soil and gradation.

4.0 EXPERIMENTAL APPROACH
The seminar is not detailing to the experimental approach of enzyme soil stabilizers, only discussing about some examples from previous experiments. The use of enzymes as stabilizer has not been subjected to any technical development and is presently carried out using empirical guidelines based on previous experience. It is not clear how and under what conditions these products work.
4.1 CHEMICAL ANALYSIS
4.1.1 Introduction
A chemical analysis of the stabilizing solutions is performed to obtain information relevant to understanding the stabilization process. The analysis includes determining the solution pH, the protein content (enzyme content), metals concentration, total organic carbon concentration and inorganic anion concentration.
The composition and activity of two commercial soil stabilizers were evaluated using both standard and innovative analytical techniques. The goal of these analyses was to determine how the soil stabilizers work (what is the mechanism of stabilization). In addition, surface tension testing was done to study if the two enzyme base products analyzed in study showed surfactant-like behavior as claimed by the manufacturers. A typical example is given below;

4.1.2 Experimental Methods
Full-strength sub-samples or diluted solutions of the soil stabilizers were used in the analyses. Dilutions were prepared using high-purity deionized (DI) water or tap water (for surface tension tests only) and the resulting solutions were analyzed for pH, metals concentrations (e.g., Ca, Fe, and Al), total organic carbon concentration, and inorganic anion concentrations (e.g., Cl-, NO3-, SO42-) as described in table 2

4.1.3 Protein Content and Enzymatic Activity
The protein content (a measure of enzyme content) and enzymatic activity of the product A were evaluated. Probe compounds were used to analyze for the presence of active aminopeptidase (protein degrading), lipase (lipid degrading), or glucosidase (sugar degrading) enzymes. The objectives of these analyses were to:
1. Determine if active enzymes are present in the product A and
2. Attempt to determine how product A stabilizes the soil






Table.2
Standard methods used in chemical analysis
Analysis Method
Ph pH meter
Dissolved metals ICP-MS1
Protein content Lowry method2
Inorganic anions
Ion chromatography3
1 ICP-MS = inductively coupled plasma – mass spectrometry
2 Lowry et al. (1951)
3 761 Compact IC with 766 IC Autosampler, Metrohm-Peak, Houston, TX

Three fluorogenic model substrates containing either 4 methylumbelliferone (MUF) or
7-amino-4-methyl coumarin (AMC) were used as probe compounds: leucine-AMC (tests for aminopeptidase activity), MUF-heptanoate (tests for lipase activity), an MUF-α-glucoside (tests for glucosidase activity). Product was added to buffered (Tris-HCl, pH 7.5) solutions containing one of the probe compounds. In these experiments, the degradation of the probe compound results in an increase in fluorescence as measured by a fluorometer. The response of the test solution is compared with the response of a simple buffered water solution (negative control). If the reaction proceeds faster (i.e. greater slope of fluorescence reading versus time) in the presence of the enzyme solution than in the control, then the test solution has catalyzed the degradation of the probe compound.
4.1.4 Surface Tension
The surfactant-like behavior of product was assessed by measuring the surface tension of product solutions over a range of concentrations. Proteins are large macromolecules that resemble surfactants in chemical structure and behavior (e.g., protein solutions exhibit foaming when shaken). The experiment was repeated for other product once this product was made available. The surface tensions of the test solutions were measured with a tensiometer (Fisher Surface Tensiomat, Model 21, Fisher Scientific, and Pittsburgh, PA) as shown in Figure 3. The results from the analyses of the products solutions were compared with those obtained from the analysis of solutions of a common surfactant (sodium dodecyl sulfate or SDS).









Fig.3
Photograph of Tensiometer

4.1.5 Result
For example, an experimental observation of two products, A and B were given in table.3 and table.4 .The pH of product A was 4.77 while the pH of Base-1 was 11.34. Thus, product A is acidic and the Base 1 is basic. The concentrations of metals and common inorganic anions (Cl- and SO4 2-) in the two soil stabilizers are provided in Table 3.and Table 4, respectively. The main conclusions from these data are that the product A has a very high concentration of potassium (K), and moderate-to-high concentrations of calcium (Ca), magnesium (Mg), and sodium (Na). These results seem to indicate that these metals do not play a significant role in the soil-stabilizing activity. On the other hand, the extremely high concentrations of Na and silicon (Si) in the Base-1 solution suggest that this product primarily contains sodium silicates. In the presence of sufficient calcium (Ca) and water, the silicates should form a calcium silicate hydrate or cement-like material similar to that formed in concrete.







Table 3
Comparison of Metal Concentrations in Products A and Base-1
METAL
CONCENTRATION ,mg/L


Al A Base-1

2.74
60.4
Ca 719 420
Fe 24.1 3.19
K 7800 1.55
Mg 337 2.13
Mn 2.11 <1.0
Na 169 31000
P <1.0 2.94
Rb 11 <1.0
Si 318 63000
Zn 3.05 <1.0

Table 4
Comparison of Common Inorganic Anions in products A and Base 1
METAL CONCENTRATION, mg/L
A BASE-1
Cl- 1150 14.5
NO3- ND* ND*
SO4 2- 664 27.8
• ND* = not detected.

Protein Concentration and Enzyme Activity
The protein concentration in the undiluted product A was 9230 mg/L. Proteins are biomolecules comprising of amino acids that may or may not exhibit enzymatic activity. Enzymatic activity would be indicated by the ability to catalyze a reaction, such as the breakdown of glucose. Thus, the presence of protein alone does not indicate that the solution will exhibit enzymatic activity.
In the enzyme activity tests, the fluorescence readings of the product A test solutions were typically less than those in the negative controls, which suggests quenching of the fluorescence by substances in product A (data not shown). In any event, the presence of product A did not result in an increase in the slope of the fluorescence versus time curve for any of the substrates. Thus, it was concluded that the product A exhibited no detectable enzymatic activity for the aforementioned substrates.
The three substrates used in these experiments test for the activity of three major classes of enzymes. The inability of product A to catalyze the degradation of these compounds does not definitively preclude the presence of active enzymes in the samples as there are thousands of enzymes that catalyze the breakdown of virtually all organic compounds.
Nevertheless, the absence of enzymatic activity in these experiments is curious, and suggests that either:
1. Product A is a highly purified enzyme solution that contains only a single enzyme or group of enzymes that catalyze reactions not tested for in our experiments or
2. Product A may not stabilize soil via enzymatic activity but rather via some other mechanism, possibly due to their surfactant-like characteristics.
Surface Tension
Product A is more effective at reducing the surface tension of water than a common surfactant (SDS).Thus; it appears that the proteins in product A cause this product to behave like a surfactant. In addition, qualitative observations of foam production during agitation of diluted product A solutions also confirm its surfactant-like behavior.
It is therefore hypothesized that the surfactant-like character of the product A may be responsible for its soil stabilizing performance, by enhancing the ability to compact the soil and remove water. More work is needed, including soil testing, to confirm this hypothesis. On the other hand, product B did not reduce the surface tension of water and no foam production during mixing was observed, therefore, product B does not behave like a surfactant.


4.1.6 Summary
Two soil stabilization products, product A and Base-1, were first tested to determine their chemical composition and mode of action. The product A contains a high concentration of protein, but did not appear to contain active enzymes based on standard enzymatic activity assays. The results from quantitative surface tension testing and qualitative observations on product A and on an additional product B made available later in the study suggest that product A behaves like a surfactant and product B does not behaves like a surfactant; this behavior may play a role in its soil stabilization performance. Base-1, on the other hand, contains high concentrations of sodium and silicon, which suggests that it acts like cement by forming hydrated calcium silicate when added to soil.

4.2 MECHANICAL TESTING
4.2.1 Specimen Preparation
Laboratory compaction methods that reproduce the same effects as those produced by compaction equipment in the field are required for specimen preparation. Static compaction for clayey soils seems to poorly represent field compaction. Kneading compaction procedure instead represents a better way to reproduce the effects of field compaction (tamping feet).
The “three kneading feet tool” was used as a laboratory compaction device for the specimen preparation. Dry densities of the samples are close to the in situ densities if the kneading compaction technique is used with five layers and a pressure of 1.25 MPa .
The three kneading feet tool was made of a wood disk (100 mm diameter) under which three wood kneading tampers of 30 mm diameter are fixed. The dimensions of the tampers were set to have the same percentage of the surface covered in the field by a typical caterpillar tamping roller. The position of the three kneading feet is such that they have to be applied eight times to compact the whole surface of the specimen (45 degrees rotation between two successive loadings). This also corresponds to a normal field practice of eight passes.
The target density was 95% of the maximum dry density obtained in laboratory procedure, and the target moisture was the optimum water content. The addition of the enzyme was done according to the manufacturer instructions. The enzyme was considered part of the water needed to obtain the optimum moisture content.
According to the manufacturers, the rate of application is 1 cc of enzyme per 5 liters of water used to obtain the optimum moisture content. The following steps were performed to prepare the samples:
• First the soil was dried for 24 hrs at a temperature of 140°F.
• Then the soil was chopped into small pieces and pushed through the sieve No 4.
• The soil and the additive were mixed using the target density and optimum moisture content (enzyme is part of the water added to obtain 95% of the maximum dry.
• The mixture (or blend) was placed in five layers in the 4" mold for compaction using a static load frame.
• Each layer was compacted using the kneading compactor platen eight times to cover the surface of the sample. After compaction, the dry density of the specimens was calculated.










a b c

Fig.4
a) 4" Mold and Platens, b) Sample of Soil II after Compaction, c) 4" Mold and Kneading Compaction Platen







5.0 CONCLUSIONS AND RECOMENDATIONS
Based on many researches and experiments, some conclusions and recommendations were made by investigators. They are listed below;
1. The specimen preparation process showed that product reduced the compaction effort and improved soil workability. Thus, less pressure was used to obtain the target density of the treated specimens compare to the untreated specimens.
2. By the addition of enzymes in soils, it will increase the stiffness of soil to a average value of 69-77%.
3. The type of soil affected significantly the effectiveness of the treatments. The percent of fines and the chemical composition are properties that affect the stabilization mechanism. Therefore, special attention should be paid to select the proper treatment to be used for different soils.
4. Limited number of tests showed that at least four months of curing time are needed to observe an improvement on the shear strength of both soils.
5. Addition of enzyme in soil increases the shear strength of soil by a average value of 9% - 39%.
6. A better and longer lasting road with increased loading capacity (CBR) and reduced soil permeability.

The conclusions presented above refer to a limited number of soil and enzyme stabilizers combinations tested in laboratory conditions and should not be extrapolated to other combinations of materials. These results should be validated with field experiments that involve the same combination of materials used in this study.











REFERENCES

1. Kouassi, P., Breysse, D. Girard, H., and Poulain, D. (2000), “A New Technique of Kneading Compaction in the Laboratory”. Geotechnical Testing Journal, Vol. 23, No1, pp. 072-082.

2. Wright Fox, R. Macfarlane, J. G. Bibbens, R. F. (1993), “Alternate Chemical Soil Stabilizers. Minor Research Report”. CalTrans.

3. http://www.internationalenzymes.net/

4. http://www.permazymeusa.com.

5. http://www.terrazyme-europe.net

Cold Weather Masonry

Introduction
Planning and preparation are the keys to successful construction of masonry in cold weather. While some changes in procedures, equipment, and supplies are required, extension of the construction season into cold weather avoids seasonal construction delays and permits better utilization of a mason contractor's resources, particularly manpower. With careful planning and implementation of an effective cold weather construction program, successful masonry construction can proceed despite cold weather. The Specification for Masonry Structures (ACI-530. 1-95/ ASCE 6-95/TMS 602-95)considers cold weather construction to exist when ambient temperature falls below 40' F (4.5' C). As the temperature of mortar materials falls below normal:




• Water requirement to reach a given consistency is reduced.
• A given amount of air-entraining agent yields more entrained air.
• Initial and final set of the mortar is significantly delayed.
• Heat-liberating reaction rates between portland cement and water are substantially reduced and become minimal as mortar temperatures drop below 40' F (4.5' C).
• Strength gain rates are reduced.




Cold masonry units lower the temperature of mortar placed in contact with those units. As noted above, this will slow reaction rates between cement and water, reduce strength gain rates, and delay tooling and setting times. If the units are cold enough, the temperature of the mortar may rapidly drop below freezing and result in disruptive expansion of the mortar as water in the mortar freezes. Wet or ice covered unit surfaces prevent development of good bond between mortar and unit.In addition to affecting the performance of masonry materials, cold weather may also affect the productivity and workmanship of masons.During cold weather, in addition to attending to normal construction tasks, masons are concerned with personal comfort and safety, additional materials preparation, handling, and protection of masonry. These extra activities consume more time as temperatures continue to drop.
The goal of a cold weather construction plan is to eliminate or minimize the undesirable effects of cold weather on materials and people in a cost-effective manner. Strategies for accomplishing that goal can include optimizing the selection of masonry materials for cold weather performance, protecting materials, heating materials, protecting or enclosing work areas, or heating work areas and in place work. Combinations of these strategies may be required depending on the severity of weather. Selection of techniques to implement these strategies is usually the responsibility of the mason contractor, who must evaluate the effectiveness and practicality of techniques in the context of the specific project and weather conditions encountered .

Masonry Materials
Selection: Masonry units are typically selected on the basis of aesthetic or structural properties rather than consideration of performance in cold weather construction. Mortar type is also often determined by structural or other performance criteria. However, knowledge of how mortar and unit properties interact in cold weather masonry construction enables the mason contractor to modify construction procedures to accommodate the specified materials. The initial water content of mortar required for workability is in the range of 11 to 16 percent. Mortar used to lay units stiffens as mixing water contained in the mortar is absorbed by units, evaporates, or reacts with the portland cement in the mortar. Water content of mortar needs to be below 6 percent to avoid disruptive expansion upon freezing. Units having high initial rates of absorption (suction) will accelerate stiffening by absorbing water from the mortar. Low absorption or wet units remove very little water from the mortar. The water retentive properties of a mortar also affect the rate of moisture loss and stiffening. Mortars having high lime content or fine sands tend to have higher water demands and higher water retentivity than higher strength mortars or mortars made using well-graded sands. Air entrainment increases water retentivity, but reduces initial water demand required to achieve a workable consistency and has been shown to reduce susceptibility of mortar to damage by early freezing. The rate at which portland cement reacts with water is primarily influenced by the temperature of the mortar. The use of higher fineness cements, such as Type lll cement, or accelerators increases reaction rates. These materials can be used in mortar to augment, but not substitute for, other cold weather construction practices. Accelerators are sometimes mistakenly called"antifreeze" admixtures. Their function is not to reduce the freezing point of mortar, but to increase the rates of early-age strength development. Thus, they don't eliminate the need to protect mortar from freezing, but they may limit the amount of time that protection is required. Calcium chloride (at a limit of 2% by weight of cement) is commonly used in concrete as an accelerator, but its use in mortar is prohibited by the Specification for Masonry Structures (ACI 530.1-95/ASCE 6-95/TMS 602-95) because it con tributes to corrosion of embedded metal such as wall ties, anchors, and joint reinforcement. ASTM C270 indicates that admixtures are not to be used unless specified. Therefore, unless the project specifications call for the use of an accelerator, the mason must request permission from the specifier in order to use an accelerator. Only non-chloride based accelerators, as verified by the admixture manufacturer, should be allowed. Protection, Storage, and Heating. All masonry materials should be protected from rain, snow, and ice. Masonry units and packaged mortar materials should be securely wrapped with canvas or polyethylene tarpaulins and stored above the reach of moisture migrating from the ground. Sand piles should also be covered and care taken to avoid contamination of the sand with mud and clay.




Masonry materials may need to be heated prior to use to assure cement hydration in mortar. When placed, the mortar temperature should be in the range of 40' F (4.5' C) to 120' F (49' C). At temperatures of less than 40? F (4.5' C), cement hydration necessary for strength development is minimal. At temperatures of 120' F (49' C) or higher, flash set is imminent. If ambient temperatures are falling below freezing, a minimum mortar temperature of 70' F (21' C) is recommended. Water is often the first material to be heated for two reasons: it is the easiest material to heat and it can store much more heat, pound for pound, than the other materials used in mortar. Although recommendations vary as to the highest temperature to which water should be heated, Some specifiers put a maximum of 180' F (82' C) because higher temperatures pose a personnel safety hazard and could result in flash set. To avoid flash set, heated water should be combined with cold sand in the mixer before adding the cement. Sand is typically delivered to the project and used in a damp loose condition. Therefore, even though sand piles are covered, it may be necessary to heat sand to thaw frozen lumps when temperatures fall below freezing. Generally, sand is heated to about 50' F (10' C), although higher temperatures are permissible as long as the sand is not scorched and as long as resultant mortar temperatures do not exceed 120' F (49' C). Masonry units should not have any visible ice on bedding surfaces when used, nor should the temperature of masonry units be less than 20' F (- 6.5' C) to avoid rapid lowering of mortar temperatures. Better productivity is often attained using units having a minimum temperature of 40' F (4.5'C) . Masonry units should be kept dry, except that very high-absorption fired-clay brick may need to be wet ted, but not saturated, prior to use. Various techniques can be used to heat mortar materials. Water is often heated in barrels or tubs. Sand piles can be heated using electric heating pads, by placing sand over a heated pipe, or by using steam heating systems. Masonry units are usually heated on pallets in an enclosure or stored in a heated area.
Protecting Work Areas and Construction
Wind breaks, heated wall coverings, enclosures, or heated enclosures are used to maintain adequate mortar temperatures and to improve the comfort and efficiency of masons and laborers. The level of protection required will depend on the severity of weather encountered. The Specification for Masonry Structures (ACI 530. 1 -95/ASCE 6-95/-95TMS 602-95) defines certain cold weather construction requirements as summarized in Table 1. It includes provisions needed during the work day while masonry is being laid, as well as protection requirements for newly constructed masonry. Several means of implementing these provisions are available to the mason contractor, recognizing that regional climatic differences and project-specific factors must be taken into account when selecting the most effective methods of protection for a given project. Basic principles required for satisfactory cold weather masonry construction are well established as indicated in this publication and the referenced documents. The use of innovative construction and protection techniques based on these established principles can often improve the effectiveness and efficiency of a cold weather construction program.

Table 1 - Cold Weather Construction Requirements
Provisions for work in progress
Condition
Ambient temperature above 40° F (4.5° C)
Ambient temperature below 40° F (4.5° C) or temperature of units below 40° F (4.5° C).



Ambient temperature is between 25° F (-4° C) and 20° F (-7°C)


Ambient temperature is below 20° F (-7° C). Requirement
Normal construction practice. Cover stored materials.

Heat mortar materials to produce mortar temperatures between 40°F (4.5° C) and 120° F (49° C) at time of mixing. Maintain mortar above freezing until used in masonry. If units have a temperature below 20° F (-7° C), heat to above 20° F (-7° C). Remove visible ice from units.

Heat masonry under construction from both sides. Install wind breaks when wind velocities reach 15 mph (24 km/h).

Provide heated enclosure for masonry under construction and maintain temperature above 32° F (0° C) within that enclosure.
Protection of newly completed work
Condition

Mean daily temperature above 40° F (4.5° C)

Mean daily temperature between 40° F (4.5° C) and 25° F (-4° C)

Mean daily temperature between 25° F (4° C) and 20° F (-7° C)

Mean daily temperature below 20° F (-7° C) Requirement

Normal construction practice. Cover top of unfinished masonry work to protect it from weather.

Cover completed masonry with weather resistive membrane to protect from rain or snow for 24 hrs. after construction.

Cover masonry with insulating blankets or equivalent protection for 24 hrs. after construction.

Maintain temperature of masonry above 32° F (O° C) for 24 hrs. after construction.