8.3 : 预拌混凝土

Concrete that is prepared at a centralized facility and then delivered to the job site in trucks, ready for placement, is known as ready-mixed or pre-mixed concrete. It comes in three types: Central-mixed concrete, Truck or transit-mixed concrete, and Shrink-mixed concrete.

Central-mixed concrete undergoes batching and complete mixing of the ingredients at the plant. It is then carried to the site in an agitator truck that rotates between 2 to 6 rpm.

In truck-mixed or transit-mixed concrete, the ingredients are batched at the plant and mixed in the truck, rotating between 4 to 16 rpm, either during transit or just before discharging concrete on site.

Shrink-mixed concrete is partially mixed at the plant and completely mixed in the truck, rotating between 4 to 16 rpm en route to the site.

Ready-mixed concrete ensures uniform quality through controlled batching, utilizes agitator trucks to avoid segregation, and is adaptable for use in congested sites or when concrete is needed intermittently.

According to ASTM guidelines, the truck's mixer should not exceed 300 revolutions to avoid segregation, and the concrete must be placed within 90 minutes of the start of mixing.