Effects of two retarders on the fluidity of pastes plasticized with aminosulfonic acid-based superplasticizers

The effects of two retarders, sodium gluconate (SG) and citric acid (CN), on the fluidity and flow loss of pastes containing aminosulfonic acid-based superplasticizers (AS) were investigated. The appropriate SG dosages resulted in a better workability of cement pastes than when only AS was used. However, at the same dosages, CN did not improve workability. The mechanism behind this phenomenon was investigated by analyzing the amount of AS adsorbed on the cement particles and on each mineral, ettringite formation in C(3)A-gypsum pastes, and the degree of tricalcium silicate (C3S) hydration using ultraviolet spectrophotometry and thermogravimetric analysis in the presence of AS and different SG or CN dosages. The effects of SG on the competitive adsorption and ettringite formation enhancement were weaker than those of CN. In addition, SG retarded C3S hydration. Thus, the workability of the pastes plasticized with AS was improved. (C) 2011 Elsevier Ltd. All rights reserved.