Influence of Mixing Sequence on Cement-Admixture Interaction. Paper by Chun-Tao Chen and Leslie J. Struble

摘要

The discusser thanks the authors for their interesting study on mixing sequence and cement-admixture interaction. Although the findings are well presented with respect to paste rheology, the following two points merit discussion.rnThe authors mention in the Research Significance section that mixing sequence and procedure in the presence of high-range water-reducing admixture (HRWRA) should be investigated to ensure that the concrete quality at the job site is the same as in the laboratory trial mixtures. The contents of the paper, however, do not convey or demonstrate that one can produce a better quality concrete by the delayed addition of admixture. Conclusions about delayed admixture addition from paste rheology studies may not be applicable to concrete, which contains coarse and fine aggregates as well. Hence, the authors' findings of a 2.5-second delay time may not match the delay time required for similar dispersion in concrete. The paper does not give a way for a practicing engineer to obtain improved concrete mixtures by changing the mixing sequence.