Cement-Treated Base (CTB)
What is a Cement-Treated Base?
Cement-Treated Base (CTB) is a type of Soil-Cement describing an intimate mixture of native soils and/or manufactured aggregates with measured amounts of portland cement and water that hardens after compaction and curing to form a strong, durable, frost-resistant paving material. CTB is versatile as it can be either mixed in place and compacted after blending, or mixed in a central plant where it is hauled to the placement area and spread on a prepared subgrade or subbase and compacted. A bituminous or portland cement concrete wearing course is placed on top of the cured CTB to complete the pavement structure. CTB is widely used as a pavement base for highways, roads, streets, parking areas, airports, and materials handling and storage areas. View or download a CTB fact sheet.
In cement-treated base construction the objective is to obtain a thorough mixture of an aggregate/granular material with the correct quantity of portland cement and enough water to permit maximum compaction. The completed CTB must be adequately cured to both let the cement hydrate and to harden the cement-aggregate mixture. The fundamental control factors for quality CTB are:
- Proper cement content
- Adequate moisture content
- Thorough mixing
- Adequate compaction
- Proper curing
The aggregate/granular material, cement, and water are typically mixed in a central mixing plant. Central plants can either be continuous-flow or batch-type pugmill mixers. CTB can also be mixed-in-place using transverse-shaft pulvermixers or traveling mixing machines.
The thickness of Cement-treated Bases is less than that required for granular bases carrying the same traffic because CTB is a cemented, rigid material that distributes the load over a large area. Its slab-like characteristics and beam strength are unmatched by granular bases that can fail when interlock is lost. This happens when wet subgrade soil is forced up into the base by traffic loads. Hard, rigid CTB is practically impervious. It resists cyclic freezing, rain, and spring-weather damage. Cement-treated base continues to gain strength with age even under traffic. This reserve strength accounts in part for CTB's excellent performance.
A stabilized base spread loads and reduces stress on the subgrade.
Unstabilized Granular Base