Abstract
Low-calcium fly ash-based geopolymer concrete is generally reported to be less vulnerable to alkali-silica reaction (ASR) than conventional ordinary Portland cement concrete. However, the lack of understanding of pore solution composition of the low-calcium fly ash-based geopolymer limits the investigation of the underlying mechanisms for the low ASR-induced expansion in the geopolymer concrete. This study presents a systematic investigation of the pore solution composition of a low-calcium fly ash-based geopolymer over a period of one year. The results show that the pore solution of the fly ash geopolymer is mainly composed of alkali ions, silicates, and aluminosilicates species. The lower expansion of the geopolymer concrete in the current study is most probably due to the insufficient alkalinity in the geopolymer pore solution as the hydroxide ions are largely consumed for the fly ash dissolution.
Highlights
Alkali-silica reaction (ASR) is one of the major durability issues in ordinary Portland cement (OPC) concrete, which was firstly identified as a cause of concrete deterioration since 1940 [1]
This paper evaluated the ASR expansion behavior of the OPC and low-calcium fly ash-based geopolymer concrete containing alkali-silica reactive aggregates by using the concrete prism test
Pore solution analyses in terms of ion concentrations, pH, chemical bonds, and short-range order of the silicon and aluminum were conducted on the fly ash geopolymer paste at different ages up to one year
Summary
Alkali-silica reaction (ASR) is one of the major durability issues in ordinary Portland cement (OPC) concrete, which was firstly identified as a cause of concrete deterioration since 1940 [1]. The reaction occurs when the reactive form of silica in aggregates is attacked and dissolved by the hydroxyl ions in the alkaline pore solution in the OPC matrix. Using sufficient quantities of supplementary cementitious materials (SCM) is one of the most common means of controlling ASR in OPC concrete [4]. While the appropriate SCM dosage in a concrete to mitigate ASR has to be determined by the ASR testing case by case [5], as the SCM content required to control ASR varies widely depending on the nature of the SCM, the aggregates reactivity, the availability of the alkalis within the concrete and the exposure conditions of the concrete [6]. It should be cautious that high substitution levels of OPC with SCM can adversely affect other concrete properties, i.e., strength development, setting, and freeze–thaw resistance [4]
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