The effect of meta-halloysite on alkali\u2013aggregate reaction in concrete

Abstract

Damage to concrete structures may occur as a result of internal effects. Alkali silica reaction (ASR) is a long term reaction between alkalis and reactive aggregate present in the concrete. The reaction product is sodium–potasium–calcium silica gel, able to absorb water, resulting in the expansion and cracking of concrete. The key problem is to find the right method for mitigating the internal damage. This paper presents the results of an investigation into the effectiveness of calcined halloysite (meta-halloysite) in improving the resistance to alkali-silica reaction (ASR). The pozzolanic reactivity of meta-halloysite was also evaluated using Thermo-Gravimetric Analysis. Microstructures of mortar bars were observed by Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (EDS) to investigate the location and chemical composition of ASR gel. The results from this study showed satisfactory level of pozzolanic reactivity when cement was partially replaced by meta-halloysite. It was demonstrated that a 20% addition of meta-halloysite are able to mitigate ASR and lower expansion of mortar bars with reactive aggregate to a safe level of not more than 0.1% at 14 days. Microstructural observations of the specimens containing meta-halloysite indicated the presence of a calcium–alkali–silicate–hydrate gel. But fewer reaction products and with different composition than those forming in the pastes without mineral additives are present.