When should the drum of a truck mixer NOT be turned after adding materials?

The drum of a truck mixer should not be turned after adding materials when the mix is too thick. This is because turning the drum in such conditions can lead to inadequate mixing, which may result in an incomplete distribution of the materials, adversely affecting the overall homogeneity and workability of the concrete.

When the mix is already thick, further agitation can cause the materials to clump rather than blend seamlessly. This clumping can lead to weak spots in the concrete and negatively impact its strength and durability. It is crucial for the main components—such as cement, aggregates, and water—to be mixed thoroughly to achieve the desired properties of the concrete.

In contrast, when water or admixtures are added, turning the drum is essential to ensure these components are evenly distributed throughout the mix. Adequate mixing after adding these materials promotes a uniform consistency, which is vital for the performance of the concrete.

Understanding the significance of mixing in different scenarios helps ensure that the resulting concrete meets the necessary standards for strength and quality.