Soil stabilization plays a crucial role in road construction, enhancing the engineering properties of natural soil and providing a stable foundation for roads. There are two primary soil stabilization methods: mechanical and chemical.
Mechanical Stabilization in Road Construction
Mechanical stabilization involves mixing various grades of soil to achieve a desired grade and improve stability by altering the particle size distribution.
Chemical Stabilization in Road Construction
Chemical stabilization involves the treatment of soil with chemical agents to enhance its properties. Common agents include Portland cement, lime, and asphalt binders.
Cement Stabilization in Road Construction
Cement stabilization is a technique that combines water, soil, and Portland cement, which is then mixed and compacted to create a high-density layer. Generally, 5% to 14% of Portland cement by volume is used. Most soils, except organic soils and soils containing sulfates, can be stabilized using Portland cement.
Steps in Cement Stabilization:
- Pulverize the Soil: Thoroughly pulverize the soil before mixing it with cement. The existing roadway material is scarified to the required depth if it’s to be used.
- Mix Cement with Pulverized Soil: The required amount of Portland cement is mixed with pulverized soil, either on the road or in a central plant. In road mixing, cement is delivered in bulk and spread uniformly, while in plant mixing, the soil is mixed with cement and water in a controlled environment.
- Compact the Mixture: Compaction should occur promptly before the mixture sets. For road mixing, compaction should be completed within one hour, while plant-mixed material allows up to two hours.
- Cure the Layer: To prevent moisture loss, a thin layer of bituminous material, such as RC-250 or MC-250, is applied.
Lime Stabilization in Road Construction
Lime stabilization is one of the oldest methods used in road construction to improve soil properties. It’s effective for both base and sub-base stabilization. Materials commonly used include calcium hydroxide and dolomite.
Steps in Lime Stabilization:
- Cation Exchange: Adding lime to fine-grained soil initiates cation exchange, replacing sodium and potassium with calcium and magnesium, which reduces the soil’s tendency to swell with moisture increase.
- Ensure Desired PI Values: Most suitable clayey materials should have a PI value less than 10.
- Analyze and Mix Correctly: The quantity of lime is determined based on reducing plasticity and increasing soil strength, often between 3% to 10% by dry weight of the soil.
Carbonation Prevention: Ensure the stabilized layer does not dry out during hardening to prevent surface loosening from carbonation.
Asphalt Stabilization in Road Construction
Asphalt stabilization aims to waterproof and bind natural materials, improving soil durability and cohesion.
Steps in Asphalt Stabilization:
- Waterproofing: This helps maintain water content and reduce surface water penetration, protecting the subgrade from moisture increase.
- Soil Mixing: The mixing of soil with asphalt binders can be performed in a plant or roadside. Plant mixing automates the combination of water and bituminous materials, while road mixing uses rotary speed mixers.
- Layer Spreading and Compaction: The mixture is spread evenly in uniform layers and compacted thoroughly using suitable rollers.
Soil stabilization in road construction ensures a durable and reliable road infrastructure, utilizing techniques like cement, lime, and asphalt stabilization to improve soil properties and ultimately enhance road safety and longevity.