Cement-treated base (CTB) is an intimate mixture of aggregate material and/or granular soils combined with measured amounts of portland cement and water that hardens after compaction and curing to form a durable paving material. A bituminous or portland cement concrete wearing course is placed on the CTB to complete the pavement structure. Cement-treated base is widely used as a pavement base for highways, roads, streets, parking areas, airports, and materials handling and storage areas.
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.
Benefits of CTB
- Lower costs thru use of local or marginal aggregates
- Eliminates subgrade infiltration into base
- Fast construction
- Reduced moisture susceptibility
- Reduces work stoppages due to rain (open base sheds water)
- Frost-resistant
- Spans weak subgrades
