Influence of industrial effluent treatment ettringite on the compressive and tensile strength and microstructure of soil-cement mixtures

• Published in: Soils & rocks Vol. 47; no. 1; p. e2024001023
• Main Authors: Rios, Angélica, Sguarezi, Fernando, Benatti, Cláudia, Lukiantchuki, Juliana
• Format: Journal Article
• Language: English
• Published: Associação Brasileira de Mecânica dos Solos 01-01-2024
• Subjects: ENGINEERING, CIVIL; Ettringite; Microstructure; Indirect tensile strength; Portland cement; Unconfined compressive strength
• ISSN: 1980-9743; 2675-5475; 2675-5475
• DOI: 10.28927/SR.2024.001023

It is increasingly important to find solutions for the problem of the aluminium anodising industry which generates a large amount of acid and alkaline wastewater, composed of high amounts of phosphates, sulphates, nitrates and aluminium. The sulphate removal trough ettringite precipitation is a simple process and involves a low-cost operating. The ettringite can be also formed during the cement hydration in soil-cement mixtures which causes several damages such as expansion. However, the effect of ettringite on the compressive strength, tensile strength and microstructure have few studies. This paper presents a novel experimental study on the influence of the industrial effluent treatment ettringite in resistance and microstructure of soil-cement mixtures. Experimental tests were performed using natural soil, soil mixed with 5% and 6% of cement and soil mixed with 5% and 6% of cement and ettringite for each material. The resistance of the materials was evaluated by unconfined compressive strength and indirect tensile strength, after 3, 7 and 14 days of cure. Additionally, several characterization tests and microstructure analysis were performed. Regarding the experimental results, the compressive strength and tensile strength decreases about 75% and 85%, respectively, when ettringite was added in soil-cement mixtures. The microstructure of natural soil, soil-cement and soil-cement-ettringite mixtures shows that the addition of cement and ettringite, simultaneously, increases the ettringite crystal formation mainly because the cement functions as a source of sulfate ions contributing with the formation of more crystals. Experimental results indicate that the incorporation of ettringite in soil-cement mixtures is not suitable for geotechnical applications.