Bond strength behaviour of fly ash and ground granulated blast furnace slag of geopolymer concrete

Abstract

As of recently, research on geopolymer concrete (GPC) is gaining popularity among construction practitioners and researchers due to its green materials in construction applications. Geopolymer is the result of a chemical reaction between source materials such as fly ash and ground granulated blast furnace slag (GGBFS), and alkaline liquid. It could fully replace Ordinary Portland cement (OPC) in the manufacturing of concrete products and thus reduce the negative impact of the carbon footprint (CO2) on the environment. At present, most of the researches on GPC are mainly focused on the concrete design mix, mechanical properties and other related structural applications such as the cracking mode, flexural and shear behaviour and deflection of GPC. This study focuses on the bond strength behaviour of GPC, which is vital in predicting the cracking mode and behaviour. The main objective of this study is to evaluate parameters controlling the bond strength behaviour of GPC such as compressive strength, concrete cover-to-diameter (c/d) ratio and embedment length. Prior to the experiment, the design mix for the specimens was achieved on trial-and-error method by applying 0 %, 10 % and 20 % GGBFS on the fly ash-based GPC basis to obtain concrete grade of 20, 30 and 40 respectively with OPC as control specimens. All specimens were casted on 100 mm and 150 mm dimensional cube moulds and activated using sodium-based alkaline solution. Fly ash-based GPC specimens were heat cured (60 °C) for 24 hours whereas specimens partially replaced with GGBFS were ambient cured. For bond specimens, the c/d ratio was varied from 4.19 to 7.0 whereas 3.5d and 5.0d for embedment using bond breaker. Overall pull-out tests show that the normalised bond strength for GPC decreased as the concrete grade increased with GPC over OPC concrete. For c/d ratio, there was no significant effect on bond strength for both concrete as the ratio was increased more than 5.75. Specimens with higher embedment length also show reduction in bond strength. In order to further promote the use of environmentally friendly GPC in the construction industry, further structural assessment on the optimum bond strength of GPC needs to be carried out.