A good road or pavement requires a good foundation. The pavement base provides the thickness and stiffness necessary to support traffic and provide long-term performance.
Stabilized pavement bases, such as soil-cement and cement-treated base, have provided economical, long-lasting pavement foundations for more than 70 years. Soil cement's improved strength and durability, combined with its low first cost and ease of construction, make it an outstanding value for use as a base and subbase material.
Soil-cement is a simple, highly compacted mixture of soil, portland cement, and water. As the cement reacts, or hydrates, the mixture gains strength and improves the engineering properties of the raw soil. The major variables that control the properties and characteristics of soil-cement mixtures are the type of soil or aggregate material, the proportion of cement in the mix, the moisture conditions, and the degree of compaction. It is possible, simply by varying the cement content, to produce soil-cement that ranges from a basic modification of the compacted soil (or cement-modified soil) to fully hardened soil-cement that is strong, durable, and frost-resistant.
Although soil-cement is known by various local and regional names, the three most commonly used terms are described below.
Cement-modified soil (CMS)—This describes a soil that has been treated with a relatively small amount of cement in order to improve its engineering properties so that it is suitable for construction. For example, CMS may be used to decrease a clay or silty clay soil's cohesiveness (plasticity), decrease its volume change characteristics, increase its bearing strength, or transform a wet, soft subgrade into a surface that will support construction equipment.
Cement-treated base (CTB)—This refers to all hardened soil-cement that meets the project specified minimum durability and strength requirements for a base. CTB uses more cement than CMS, resulting in a strong, durable, frost-resistant layer for the pavement structure.
Full-depth reclamation (FDR)—This describes a special case of CTB in which aggregate for the cement-treated base is obtained by pulverizing and recycling the old asphalt surface and base material into a new fully hardened, durable, frost resistant base.
WHY USE SOIL-CEMENT?
The use of soil-cement can be of great benefit to agencies responsible for building and maintaining roads. Its cost compares favorably with that of granular-base pavement. When built for equal load-carrying capacity, soil-cement is almost always less expensive than other low-cost site treatment or pavement methods.
The use or reuse of in-place or nearby borrow materials eliminates the need for hauling of expensive, granular-base materials; thus both energy and materials are conserved.
This low cost has made soil-cement an attractive alternative to designers of roads and pavements. In addition, soil-cement has considerably more load-carrying capacity than flexible pavements, requiring less thickness to carry a given load. Pavement engineers praise soil-cement's performance, its low first cost, long life, and high strength. Soil-cement is constructed quickly and easily—a fact appreciated by local government agencies and the traveling public.