Soil cement is a mixture of Portland cement, water and soil. Types of soil cement, their composition, mix preparation, applications and advantages are discussed.
In the present scenario, most of the building materials price has gone high. A building material available cheap would be a real appreciation. One such material is soil cement. People who are more familiar with this material call them as dirt cement. It consist a little Portland cement and a huge amount of soil.
Soil cement can be defined as a compacted mixture of Portland cement, water and a major amount of pulverized soil. This together would form a hardened mixture like concrete, under the hydration action of cement. It is found to be durable in an extent that it can be employed for low-cost paving materials.
- Material Composition of Soil Cement
- Soil Cement Construction Details
- Types of Soil Cement
- Advantages of Soil Cement
- Applications of Soil Cement
Material Composition of Soil Cement
As discussed soil cement is a combination of Portland cement, water, and soil which must follow certain requirements.
The water employed in soil cement should satisfy the conditions similar to what we follow in the production of cement concrete. It has to be clean and free from harmful alkalis, acids or organic matter or debris. As mentioned in standard codes, a quality of water equivalent to the water we drink is the best.
Fig.1: Soil Cement Composition Compaction by Rollers
The Portland cement used are based on standard codes used in that area. This must meet the requirements that are mentioned in the codes.
The soil used in soil cement production have no restrictions. But some type of soil prefers more cement content while other won’t. When we use silt or clay, they prefer less cement content. When we use beach sand, it demands higher cement content. So, based on the material availability and economy as well the design requirement a decision must be made.
Soil Cement Construction Details
As in any construction procedure, the materials are subjected to a laboratory test to study the activity and characteristics of each material. This is to establish the cement content, the water requirement of the soil, which in turn would help us to know the compaction efficiency.
Even though the material is found to be cheap, no mind work is performed. All the calculations are made based on specific tests. This would ensure attainment of strength as well as long term durability.
The three basic processes involved in construction with soil cement:
The mixing of soil cement mixture is done at a central mixing plant. The final mixture is conveyed to the job site and laid over the already prepared sub-grade level (For a pavement construction).
Fig.2: Cement Laid Over Prepared Soil Subgrade
When the soil cement preparation is done at the site, there are four stages
- Cement spreading
First, a proper quantity of cement is being spread over the soil. They are mixed homogeneously. Then measured water is added and mixed thoroughly. The mixing can be done by several hands mixing equipment or machines.
Next is compaction of the whole mixture by normally used compaction equipment. The compaction must be performed with high precision to bring the maximum advantage of the cement used.
Once done, the whole mixture layer is cemented permanently at a very high density. This won’t let the soil to undergo further consolidation or settlement under huge traffic.
The last step is curing which is performed to prevent evaporation of water to the atmosphere. Only adequate amount of water will enable proper cement hydration. For this, a bituminous coating is laid over the layer and would act as a bituminous surface. The thickness of the layer can be increased if the pavement is constructed in an area with huge traffic.
Types of Soil Cement
There are different types of soil cement based on the materials used. The method of construction remains the same irrespective of the type of soil cement used.
The different types of soil cement are:
- Cement Modified Soil
- Soil Cement Base
- Cement Treated Base
- Acrylic Copolymer
CMS or Cement Modified Soil
This contains a small proportion of cement compared to ordinary soil cement. It improves bearing ratio and shear strength. It decreases plasticity and volume changes.
SCB or Soil Cement Base
This contains a higher amount of cement compared to CMS. A final coat is required to keep moisture out. To avoid wear and tear a final coat of asphalt concrete is placed for pavement construction.
The strength is found to increase with an increase in age resulting in higher durability.
CTB or Cement Treated Base
The mixture is granular soil aggregates plus water and Portland cement. All the performance and behavior is like soil cement base.
It is also called as rhino snot. It is a water-soluble acrylic polymer. This gains a property to penetrates the soil or sand mix and bind together. This is hence used instead of cement.
When the whole mixture dries up, it becomes waterproof, and UV resistant. It also withstands wear and tear. This was developed in desert conditions by the U.S military. It can also be used for roads, parking lots. Etc.
When compared to other Subgrade or pavement construction the thickness that the soil cement possess is very less. This less thick, highly cemented rigid material enable the load to be distributed over a larger area. It shows characteristics like the slab and strength like the beams.
The maintenance reports on already constructed soil cement pavement shows that they are having good service at low maintenance costs. The ease of maintenance unlike other methods of pavement construction is a matter to be appreciated.
Specimens were taken at the installation and after a certain period. The analysis showed that the strength and other performance factors increased with the age. It was found to be four times greater than the initial values. This proved that they possess a high reserve strength capacity.
Advantages of Soil Cement
- Widely available resources
- Cheap and highly economical
- Maintenance cost is less
- Better weather resistant and strength
- Can be employed for small works
- Soil swelling can be reduced
- Quantity of water must be checked
- Formation of cracks
- Not suitable for some soils
- Proper supervision needed
Applications of Soil Cement
Soil cement is mainly employed in pavement construction for:
- City or country roads
- Airports pavements
- Parking lots
- Interstate highways
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