Effect of Continuous Agitation on Concrete Rheology

Experiments were designed to compare concrete and paste flow behavior in mixtures containing water reducing admixtures by measuring concrete slump, concrete rheology, mortar rheology, and paste rheology (using low-amplitude oscillatory shear) at times up to about 2 h after mixing. Some concretes were continuously agitated, and others were allowed to rest between tests. Stiffening was observed in most of the concretes during this time. Continuous agitation reduced this stiffening. Concrete slump and paste modulus showed a weak correlation in most mixtures. Both concrete slump and paste modulus were sensitive to agitation, especially in mixtures containing a water reducing admixture. Based on these results, it is recommended that laboratory studies simulate the agitation expected in the field.