Resistance of fly ash geopolymer binders to organic acids

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.

Effect of Scallop Powder Addition on MICP Treatment of Amorphous Peat

“…The biggest challenge in the former techniques was unaffordability, as they required high performance equipment and substantial energy. In the meantime, chemical binders (e.g., Portland cement (PC), fly ash, blast furnace slag, bentonite, and gypsum) were also used to improve the usability of the peat (Aiken et al, 2020;Hebib and Farrell, 2003;Paul and Hussain, 2020;Zulkifley et al, 2014). The PC was the most recommended binder among them, involving hydration processes to harden the peat (Kalantari, 2010;Paul and Hussain, 2020).…”

Simple Model for Alkali Leaching from Geopolymers: Effects of Raw Materials and Acetic Acid Concentration on Apparent Diffusion Coefficient

“…In future work, more advanced (numerical) modeling approaches are to be employed on the leaching results, in order to better separate the physical nature of the effective diffusion coefficient from the chemical binding isotherms, such as in [ 17 ]. Research so far has covered only empirical geopolymer tests on acid resistance [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ], thus neglecting the fundamental chemical aspects behind it. Analogue mechanisms involved in dissolution of zeolites [ 35 ] demonstrate that decomposition of a network aluminosilicate in acid gradually shifts from initially congruent Si and Al dissolution to progressively preferential dissolution of Al, resulting in amorphous silica-rich gels, with gradually increasing Si/Al ratios.…”

“…Therefore, in high-calcium binders such as cement-based and high-calcium alkali-activated materials, acetic acid attack results in a high-porosity surface layer due to dissolution of the highly soluble acetate salts, complexation-enhanced solubility of Ca-rich (and Al-rich) phases and pH buffering characteristics. Aiken et al [ 6 ] also confirmed that fly ash-based geopolymers had a greater resistance to acetic and lactic acids than Portland cement, supported by smaller mass losses. This was ascribed to the higher stability of the geopolymer gel in organic acids compared to dissolvable Ca-rich cement systems, supported by a higher porosity in geopolymers that enables easier inward diffusion of the acid.…”

“…The (V l /S) ratio of the acid solution volume (V l ) to specimen surface area (S) is not specified as they should include accelerated exposure conditions that are realistic for various practical field applications. Therefore, different adaptations of the testing procedures can be found in the literature, e.g., the organic acid solution can be titrated to maintain its pH [4,23] or cyclically replenished [5][6][7], where the time intervals may also vary. The total number of specimens (and even types) per container is also variable, although a single specimen would be preferential to avoid any interactions among them (and especially the different mix types).…”

“…Geopolymers are upcoming inorganic binders with great potential for niche applications in concrete structures [ 1 , 2 , 3 ], particularly where strong resistance against organic acids [ 4 , 5 , 6 , 7 ] as well as mineral acids [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ] is required. A low calcium content in geopolymers represents a vital feature [ 4 ] and separates them from a broader class of alkali-activated binders.…”