Effects of ettringite formation on the compressive strength of mortar during activation of blast-furnace slag without ordinary Portland cement

Abstract

The manufacture of ordinary Portland cement emits large amounts of CO2. To reduce these emissions, alternatives to ordinary Portland cement have been sought for use in the construction industry. The use of geopolymers as substitutes for ordinary Portland cement is increasing as a result of their lower energy consumption and lower CO2 emissions during manufacture, their similar compressive strength to ordinary Portland cement products and their cost-effectiveness. The main geopolymer of interest is blast-furnace slag treated with alkali activators. However, blast-furnace slag is slow to hydrate and therefore has a lower compressive strength than ordinary Portland cement in the early stages of hydration. As a result, its applications have so far been limited. This study investigated the effects of the formation of ettringite during the activation of blast-furnace slag on the early development of compressive strength in pure blast-furnace slag. Calcium sulphoaluminate and gypsum were used as activators to accelerate the hydration of blast-furnace slag.