Study on hydration process of alkali-activated slag cement activated by weakly alkaline components

Abstract

Alkali-Activated Slag Cement (AASC) activated by weak alkaline components has good workability and safety. Sodium carbonate (Na2CO3, SC), sodium sulfate (Na2SO4, SS), reactive magnesium oxide (R-MgO), and calcium hydroxide (Ca(OH)2, CH) were used to prepare the AASC. The hydration process, phase composition and hydration kinetics of AASC were studied. The results showed that the pH value of AASC slurry activated by weak alkaline components ranging from 10.8 to 13.2. CH could significantly affect the pH of AASC slurry. When the dosage reached more than 5%, the pH value of AASC slurry reached more than 12.0. The hydration heat release of AASC activated by weak alkaline components was mainly concentrated in 1 day. Two hydration heat release peaks appeared. The initial hydration peak appeared within 0.5 h-1 h, and the acceleration hydration peak appeared within 1 h-8 h. When the content of CH was 5%, and the content of SS and SC was 7% and 4%, the acceleration peak of AASC was much higher than that of others. At the same time, the Krstulovic-Dabic model was used to study the hydration kinetics of AASC. The increase of SS content prolonged the NG-I and I-D processes. CH accelerated the hydration rate of AASC and shortened the hydration process of AASC. The main hydration products of AASC activated by weakly alkaline components were C-(A)-S-H gel, calcite, ettringite, hydrotalcite and gaylussite. R-MgO was favorable for the formation of hydrotalcite, while SS was favorable for the formation of ettringite.