Most domestic operations utilize wet-mix concrete mixer trucks. These vehicles transport either ready-mixed concrete from a batching plant or a mixture of aggregates (sand and gravel), cement, and water. During transit, the drum continuously rotates at a slow speed to agitate the wet materials, thereby preventing premature setting and segregation. However, the time elapsed between production and pouring generally must not exceed 1.5 hours to avoid concrete hardening. Consequently, for longer-distance transport, dry-mix or semi-dry-mix mixer trucks are employed.
Dry-mix mixer trucks allow dry aggregates and cement-proportioned according to the mix design-to be loaded directly into the mixing drum. The dry materials are agitated during transit, and water is added either just before arrival at the construction site or upon arrival to complete the mixing process.
Semi-dry-mix mixer trucks also transport aggregates and cement proportioned according to the mix design and containing some water; however, the water content is insufficient for pouring. Additional water must be added and mixed in either just before the vehicle reaches the construction site or after it arrives.
