Effect of alkali content in cement on its hydration kinetics and mechanical properties

The work aims to investigate the effect of alkali content in Portland cement on its hydration kinetics and mechanical properties. Four kinds of cement clinkers with different alkali content were chosen, and K2SO4 was added to adjust the alkali content of cement. The heat release of hydration, non-evaporable water content, electrical resistivity of the pastes and compressive strength of cements were tested. The hydration products, ion concentrations and pH value of the pore solution were analyzed. The results show that the alkali in cement accelerates the hydration at early ages but suppresses its hydration at later ages. Alkali addition increases the main heat evolution of cement with low alkali content and shortens the induction period of cement with high alkali content. The dissolution of C3S and the formation of Ca(OH)(2) are promoted by alkali addition, but the formation of AFt is suppressed. Alkali addition is detrimental to the enhancement of the compressive strength of cement at later ages, the effect on the compressive strength at early ages is related to the total alkali content in cement. A positive effect is present in cement with low alkali content, the effect is negative in cement with high alkali content. (C) 2019 Elsevier Ltd. All rights reserved.