15421Mixing

The effect of mixing is to blend all the constituent materials into a homogeneous concrete mixture. This is affected greatly by the sequence used to load the materials into the mixer and the efficiency of the mixer to blend the materials. It should be noted, however, that total automation of concrete production and delivery always improves consistency as a measure of workability in placement. Admixtures seem to be most effective if they are introduced after the cement is wetted. In the case of truck mixing, the temperature of the concrete as delivered should not exceed 42° C. If water demand becomes excessive or slump loss rapid, the dosage of chemical retarders or superplasticizer has to be increased. If the problem persists, such as in hot summers and in hot-weather concreting, ice or chilled aggregates have to be used to lower the temperature.

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