In 1935, engineers constructed the first experimental soil-cement pavement. The 1.5-mile (2.4 km) stretch of road outside of Johnsonville, South Carolina, represented a significant development because it proved to be a long-sought means to stabilize local soils and provide good economic road base. More than 70 years later, soil-cement pavements are still giving good service at low maintenance costs and more than 100,000 miles (160,900 km) of highway have been built using soil-cement.

Soil-cement, also referred to as cement-modified soil and cement-treated aggregate base, is a dense, highly compacted mixture of soil or roadway material, portland cement, and water. Soil material can be almost any combination of sand, silt, clay, gravel, or crushed stone. Granular soils are preferred, however, because they pulverize more easily and require less cement to achieve the required strength and durability.

Laboratory tests are performed to determine the proper cement content, compaction, and water requirements of the soil material to be used. The soil-cement can be mixed in a central plant or mixed-in-place. Central plant mixed soil-cement requires a non-cohesive, usually granular material. For mixed-in-place operations, clay or granular soils can be mixed.

For mixed-in-place construction, contractors follow four basic steps of soil-cement paving—spreading, mixing, compacting, and curing. When the roadway has been shaped to grade and the soil loosened, the proper quantity of cement is spread on the in-place soil. Mixing machines then thoroughly mix the cement and the required amount of water with the soil.

The mixture is next tightly compacted with rollers, shaped to the proper contour and rolled again to achieve a smooth finish. Finally, the soil-cement is cured by spraying water and sealing with a bituminous mixture to supply and maintain the moisture needed for hydration.

Soil-cement's advantages of high strength and durability combine with low first cost to make it an economical material. About 90 percent of all the material needed for soil-cement is already in place, keeping handling and hauling costs to a minimum. Like concrete, soil-cement continues to gain strength with age. Because soil-cement is compacted into a tight matrix during construction, the pavement does not deform under traffic or develop potholes as unbound aggregate bases. Soil-cement is capable of bridging over weak subgrade areas and is highly resistant to deterioration caused by seasonal moisture changes and freeze/thaw cycles.

The use of soil-cement has expanded since its initial development in 1935. Soil-cement has been used primarily as a base course for roads, streets, highways, airports, and parking areas. More on soil-cement for paving.

Soil-cement is also used as slope protection, ditch lining, and foundation stabilization. Soil-cement is used in every state in the United States as well as in all the Canadian provinces. More on soil-cement for water resources.

 
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