The strength of alkali-activated slag/fly ash mortar blends at ambient temperature

The implementation of sustainable development in civil engineering society has led to the use of new materials with low environmental impact. Ordinary Portland cement (OPC) is the primary material in the production of traditional concrete. However, the manufacturing of OPC has led to environmental concerns over the production of CO2. The use of fly ash and slag, the most commonly used industrial by-products, as replacements for PC, has helped to reduce these CO2 emission. Recent research has also shown that it is possible to use fly ash or slag as a sole binder in concrete by activating them with alkali components through a polymerization process. However, the main issue of the use of fly ash as a replacement material for cement is the need of heat curing regime to achieve structural integrity. While, the standard curing regime used for OPC concrete can be applied to the alkali-activated slag (AAS) due to the similar characteristic of the hydration product. This paper reports the detail of the experimental work that has been undertaken to investigate the strength of AAS/fly ash (AASF) mortar blends. The AASF specimens were prepared using a mix of ground granulated blast-furnace slag (GGBS) and low calcium class F fly ash activated by high alkaline solution. The mix compositions of slag to fly ash were 1:0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.6:0.4 and 0.5:0.5, respectively. The standard curing regime at ambient temperature was applied. The results showed that the mix proportion of 0.5 slag : 0.5 fly ash produced the best strength results. The standard deviation values also reduced along with the increase of fly ash content indicating an improved stability of the specimens. It also suggested that 0.5 slag : 0.5 fly ash blend could provide a solution for the need of heat curing for fly ash-based geopolymer. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).