Based on the moisture content of the concrete transported, concrete mixer trucks are classified into three types: wet-mix, dry-mix, and semi-dry-mix.
Wet-mix concrete mixer trucks are the most common type used domestically. They transport either ready-mixed concrete from a batching plant or a mixture of aggregates (sand and gravel), cement, and water combined according to a specific mix ratio. During transit, the wet mixture is continuously and slowly agitated to prevent 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 used.
Dry-mix mixer trucks are loaded with dry aggregates and cement-proportioned according to the mix design-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 transport aggregates and cement that have been proportioned according to the mix design and contain some water; however, the moisture content is insufficient for pouring. Additional water must be added and mixed into the load either just before the vehicle reaches the construction site or after it arrives.
