Resistance of fly ash geopolymer binders to organic acids
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ORIGINAL ARTICLE
Resistance of fly ash geopolymer binders to organic acids Timothy A. Aiken . Jacek Kwasny . Wei Sha
Received: 25 April 2020 / Accepted: 12 August 2020 Ó The Author(s) 2020
Abstract Fly ash geopolymers are a relatively new class of binders with the potential to reduce the CO2 emissions associated with Portland cement based construction materials. This paper reports on the organic acid resistance of fly ash geopolymers following exposure to acetic and lactic acid. Organic acids are prevalent in many circumstances including agriculture, production processes and waste management. These findings demonstrate that the surface of fly ash geopolymers had superior resistance to organic acids when compared with traditional Portland cement, evidenced by smaller mass losses. This was attributed to the formation of reaction products which were less susceptible to acid attack than those formed in Portland cement systems due to their lower calcium content. However, despite the surface of fly ash geopolymers appearing less deteriorated due to organic acid attack, they were found to have a higher porosity than their Portland cement counterparts making them more susceptible to acid ingress. Keywords Geopolymer Fly ash Acetic acid Lactic acid Porosity Corrosion
T. A. Aiken (&) J. Kwasny W. Sha School of Natural and Built Environment, Queen’s University Belfast, Stranmillis Road, Belfast BT9 5AG, UK e-mail: [email protected]
1 Introduction Organic acids, such as acetic, lactic propionic and butyric acid, can be particularly aggressive to cementitious materials. It is especially significant, as they can often come into contact with agricultural infrastructure and sewage systems [1, 2]. Despite organic acids often being described as weak acids compared with strong mineral acids (e.g. sulfuric and hydrochloric acids), the attack on cementitious materials is not necessarily less aggressive. This is due to buffer effects (i.e. slower increase in the pH of the acid solution for weak acids allowing increased degradation potential) and the high solubility of the organic salts produced following organic acid attack [3–6]. In agriculture, organic acids occur from a range of sources including animal feed [7–9], animal waste [10–12], anaerobic digestion [13, 14] and crop storage [15–18]. When grass is stored as winter feed for livestock, it undergoes a fermentation process converting sugar to acids thus producing silage effluent which contains acetic and lactic acids [17, 19–21]. Figure 1 shows typical damage observed on concrete walls in a silage effluent storage tank. At the average level of silage effluent in the tank, significant damage is visible (Fig. 1b). Large portions of cement paste and mortar have been removed and coarse aggregates have been exposed (Fig. 1c). These concrete walls have been in place for approximately 10 years and are only exposed to silage effluent for a few months per year. Despite this, significant damage has occurred
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