Acid resistance of alkali-activated binders based on clays from phosphate mining by-products

• Published in: Journal of Building Engineering Vol. 95; p. 110106
• Main Authors: Mabroum, S., Garcia-Lodeiro, I., El Machi, A., Chhaiba, S., Taha, Y., Benzaazoua, M., Blanco-Varela, M.T., Hakkou, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.10.2024
• Subjects: Acid resistance; Dealumination; Durability; Geopolymerization; Mine waste precursor; Durability; Dealumination; Mine waste precursor; Geopolymerization; Acid resistance
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2024.110106

This paper outlines the results of studying the resistance of alkali-activated materials (AAM), based on calcined yellow clay from phosphate mine by-products as a precursor, to an acid attack (with sulfuric and phosphoric acids, 5 %, pH ≈ 0,8–2). Calcined yellow clay (YC850) is used as the source of aluminosilicates, containing montmorillonite, dolomite, and quartz. The alkali-activation of such materials allows the determination of an adequate valorization way and evaluating their durability leads to defining the range of application. The residual compressive strengths were measured after 1, 2, and 4 weeks of immersion in those acids. The deterioration suffered by the paste specimens was examined using different techniques. The degree of deterioration differs from one acid to another; in sulfuric acid, the strengths decrease from 47 MPa to 10.6 MPa presenting 77.4 %. While in phosphoric acid, the decrease was about 36.2 % (30 MPa) after 28 days of attack. This detriment in the strengths is associated with changes not only in the microstructure but also with the alteration of the reaction products, mainly the binding gels C-A-S-H and (C,N)-A-S-H, which undergoes dealumination and decalcification. What is more, the chemical attack involves several reactions; calcium coming from the precursor reacts with the sulfates (in the H2SO4 attack) inducing the precipitation of gypsum, which is responsible for the significant strength loss. In addition, the dissolution of crystalline minerals, such as periclase and gehlenite (present in the precursor) generates higher porosity explaining the obtained results. •Calcined clays by-products were used as precursor for the formulation of alkali-activated materials.•The alkali-activation leads to the formation of two binding gels CASH and (N,C)ASH with a compressive strength of 47 MPa.•The acid attack generates a significant decrease in the strength with producing high porosity.•After acid attack, the binding gels C-A-S-H and (C,N)-A-S-H undergoes dealumination and decalcification.