Mixing cementitious materials into the natural soil is the most widely used method to provide a uniform strengthened layer to support the pavement above it. The reason is that this method is both reliable and cost-effective. Since 1935, soil cement stabilization has a proven track record across the United States and the world of being both durable and economical. Now in the modern era, it is as important to build long-lasting pavements as it was during that era of depression when this reliable and economic stabilization method was developed.
Cement stabilization is a method that provides both strength and flexibility for a bonded layer of soil subgrade by creating soil cement agglomerations that generally have a 7-day unconfined strength target of 150-250 psi. If insufficient cement is used then the soil cement will not have the best performance, similarly if too much cement is added the soil cement will be too rigid and will not have
the desired flexibility. To determine the appropriate amount of cement to use, a cement series is performed on a representative sample of the soil which consists of varying percentages of cement in the soil with optimized moisture content, typically 2, 4, and 6 percent. The samples are then molded into cylinders that are tested for unconfined compressive strength and the values are plotted and the amount of cement needed is determined by identifying which amount will achieve the target strength.
Cement alone, when mixed appropriately with the natural material on a project, can stabilize the widest range of soil types. Modern pulverization equipment can more thoroughly blend cement in a higher range of soil plasticity. Cement stabilization alone provides the strongest, most reliable, and economical method to stabilize pavement subgrades on the planet.
The strength and permanence of cement stabilization along with the ability to cure rapidly and speed up construction has prompted many agencies, cities, and counties to utilize cement stabilization even in the most difficult soils with clay. High-speed modern reclaiming equipment can blend cement alone in dryer
soil in the moderate plasticity index (PI) range (20-35). Soils with high plasticity present a challenge for blending cement with saturated belts of clay with high plasticity indexes. To overcome this natural gumminess of higher PI clay the soil can be treated with limited amounts of lime (or polymers) to reduce
the PI. This reduction of PI is due to the breaking up of the clay bands (flocculation). After PI reduction is accomplished then the soil can be cement stabilized with the standard procedure for immediate strength. This is a two-step method where lime is blended in first and immediately followed up by blending cement. If high sulfates in the soil are suspected, then curing time (3-7 days) could be allowed to allow the ettringite expansion of soil to take place beforehand.
There are proprietary products that utilize cementitious products and lime to be blended with difficult soils in a one-step process, but these products are not readily available in all markets across Texas and are generally more expensive. However, many users in the metropolitan areas where these products are
available are amendable to the one-step process and are happy with their performance.
Soil cement stabilization using high-performance cement is a permanent modification to the soil that will add to the longevity and durability of the overall pavement. Not only does it provide premium support for the pavement, but it also provides a good working platform for the overall project construction and
temporary traffic handling. When time equals money, soil cement stabilization provides immediate strength for expedited construction of subsequent pavement layers. Cement stabilization no matter how you slice it (or mix it) is a best practice for pavement construction.
