Monitoring the setting process of alkali-activated slag-fly ash cements with ultrasonic P-wave velocity

One of the shortcomings of alkali-activated materials in concrete applications is quick setting time that has been poorly understood. The objective of this study is to explore the setting process of sodium silicate-activated slag-fly ash cements using ultrasonic P-wave velocity. The effect of incorporating sodium carbonate and sodium sulfate on the setting process of sodium silicate-activated samples is also investigated. The results show that partial substitution of sodium silicate with sodium carbonate and sodium sulfate activators has no noticeable effect on the initial setting time, while the final setting time increases significantly. Comparative assessment of ultrasonic measurements with Vicat setting times and calorimetry heat flow curves shows that condensation reaction between the aluminosilicate units formed near the particle surface is most likely responsible for setting. A specific ultrasonic velocity range can be used to estimate the setting times of the studied AASF cements. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the effect of sodium carbonate and sodium sulfate on the setting process of sodium silicate-activated slag-fly ash cements. The results show that the partial substitution of activators has no noticeable effect on the initial setting time, but significantly increases the final setting time. The condensation reaction between aluminosilicate units near the particle surface is likely responsible for setting, and a specific ultrasonic velocity range can be used to estimate the setting times of the studied cements.