Calorimetric Studies of Alkali-Activated Blast-Furnace Slag Cements at Early Hydration Processes in the Temperature Range of 20-80 °C.

Aleksandr Usherov-Marshak,Girts Bumanis,Danutė Vaičiukynienė,Pavel Krivenko

doi:10.3390/ma14195872

Abstract

In the hydration process of inorganic cements, the analysis of calorimetric measurements is one of the possible ways to better understand hydration processes and to keep these processes under control. This study contains data from the study of thermokinetic processes in alkali-activated blast-furnace slag cements compared to ordinary Portland cement (OPC). The obtained results show that, in contrast to OPC, the heat release values cannot be considered as a characteristic of the activity of alkali-activated blast-furnace slag cements. In addition, it is concluded that in the case of OPC cements, cumulative heat release is a criterion for the selection of effective curing parameters, while in the case of alkali-activated blast-furnace slag cements, a higher heat rate (which increases sharply with increasing temperature from 20 to 40 °C) is a criterion. From the point of views of thermokinetics, the rate of heat release at temperatures up to 40 °C can be a qualitative criterion that allows to choose the parameters of heat curing of alkali-activated cement concretes. By introducing a crystallo-chemical hardening accelerator, such as Portland cement clinker, into the composition of alkali-activated blast-furnace slag cements, it is possible to accelerate the processes not only in the condensation-crystallization structure formation stage, but also in the dispersion-coagulation structure formation stage. Portland cement clinker increased the efficiency of thermal curing at relatively non-high temperatures.

Highlights

In recent years, alkali-activated cements have become a viable ecological alternative to traditional cementitious materials
Compared with ordinary Portland cement (OPC), alkali-activated cements are more environmentally friendly, and the raw materials are usually industrial waste, which can contribute to the waste disposal
The aim of the study was to perform calorimetric studies of hydration processes at the early stages of alkali-activated blast-furnace slag cements in the temperature range of 20–80 ◦ C compared to OPCs, and to substantiate the appropriate criteria for selecting optimal thermal curing parameters when using alkali-activated blast-furnace slag cement concrete

Summary

Introduction

Alkali-activated cements have become a viable ecological alternative to traditional cementitious materials. They have good durability, mechanical strength, thermal properties and reduced carbon footprint. The common raw materials of these binders could be a wide range of the industrial aluminosilicate byproducts or wastes, such as slag, fly ash, bottom ash, zeolitic waste, glass powder [1,2]. The initial interaction stages of the aluminosilicate component with the highly alkaline (pH > 11.5) liquid phase at normal and elevated temperatures are important. At these stages, the interrelationships between flowing processes and many factors related to cement composition and temperature could be most revealed. To better understand the nature of hydration processes, it is necessary to analyze the results of calorimetric measurements: the amount of heat released and the rate of heat evolution

Objectives

Results

Conclusion