In the cement mixer truck,the mixer drum will always keep rotating during transport to ensure that the concrete carried does not freeze. At the same time, the rotating can make the sand, stone, and cement in the concrete more uniform.

If the concrete mixer truck does not rotate, during the transportation process, the stones in the concrete will sink into the bottom layer. The middle layer is sand, the upper layer is cement slurry, and the phenomenon of agglomeration occurs after transportation to the construction site. Therefore, the concrete mixer truck rotating during transport can both prevent concrete agglomeration and prevent stratification of the concrete, allowing the concrete to mix more evenly.
1. Such mixer is known as the Transit mixer .{ It is used to shift the ready mix concrete from the batching plant to the exact location where concrete is to be poured }.
2.  The rotation of the drum is for two reasons :

2.1 To avoid segregation of concrete [ Segregation : Separation of sand and aggregate from the cement ,water film ]
3. During transit , the concrete should not spill out from the drum . The drum rotates clockwise during transit . The internal spiral blades push the concrete towards the inner zone of the drum . When reaching the location of pouring , the drum rotation is reversed , thus forcing the concrete to slowly get poured outside [either in the hopper of the concrete pump or in a platform ].

The setting of cement is usually decelerated using appropriate quantity of admixtures