Early Strength-Promoting Mechanism of Inorganic Salts on Limestone-Calcined Clay Cement

Abstract

This study aims to report the early strength effect and hydration mechanisms of limestone-calcined clay cement (LC3) with sodium carbonate, sodium sulfate and sodium chloride. The experimental results show that it is feasible to add three kinds of insoluble inorganic salts to improve the early strength of LC3 through different promotion methods. In comparison to sodium sulfate, the strengthening effects of sodium carbonate and sodium chloride on early strength of LC3 are more significant. The hydration heat evolution, mercury intrusion porosity and a set of tests for microstructural characterization (XRD, FTIR and SEM) were utilized to better understand the enhancement mechanism of inorganic salts in LC3 system. The mechanism by which sodium carbonate promotes the early strength of LC3 is mainly the strengthening of the aluminate reaction and pozzolanic reaction of metakaolin. The mechanism by which sodium sulfate promotes the early strength of LC3 is mainly the additional ettringite. The mechanism by which sodium chloride promotes the early strength of LC3 is mainly the strengthening of the silicate reaction and the generation of Friedel’s salt by alumina from tricalcium aluminate and metakaolin.