Action mechanism of superplasticizer in consideration of early hydration of cement

Abstract

Superplasticizers (SPs) are widely used in various concrete made in Japan to decrease the amount of water required for cement mixing. The use of hot-weather concrete is increasing. The number of interstitial cement phases, such as the aluminate and ferrite phases, will be increased to treat waste and byproducts in the cement industry. In such cases, early hydration will affect cement phase fluidity. Therefore, chemical admixtures, especially SPs, are gaining importance. It has been reported that changes in concrete fluidity with time are affected by SP molecular structure. However, the mechanisms of fluidity change is still not completely clarified. It is therefore necessary to study the interaction between cement and SPs. This study focuses on the mechanism of SP action, especially during early hydration. Polycarboxylate- based SP showed better fluidity retention than naphthalene sulfonate-based SP. This difference in fluidity-retaining performance is related to the amount of SP adsorbed per unit area. The fluidity reduction of cement paste with naphthalene sulfonate-based SP is attributed to a decrease in residual SP concentration in the liquid phase.