Performance Assessment of a Calcium Silicate Coproduct of the Phosphate Industry as a Sustainable Supplementary Cementitious Material

Abstract The concrete industry is facing a challenging task in decreasing its carbon footprint as traditional supplementary cementitious materials (SCMs) such as fly ash and slag become less available. This study evaluated the possibility of a calcium silicate–based coproduct of the phosphate production industry (J-Rox), as a sustainable SCM for use in concrete mixtures to improve their strength and durability properties. Three J-Rox formulations (JR-A, JR-B, and JR-C) were tested at 15%, 20%, and 25% replacement rates of the portland cement content in concrete mixtures and compared with control concrete mixtures—one with 100% cement, and one with 20% fly ash. An experimental program of paste-, mortar-, and concrete-level validations was conducted to assess the influence of J-Rox on fresh and hardened properties, including setting behavior, compressive strength, modulus of elasticity, Poisson’s ratio, drying shrinkage, and surface resistivity. The results demonstrated that J-Rox inclusion in the test mixtures generally led to delayed setting, although setting remained within reasonable limits for typical construction applications. At early ages, J-Rox mixtures exhibited strength reductions in both mortars and concretes. By 90 days, JR-B and JR-C mortars outperformed both ordinary portland cement (OPC) and fly ash, whereas concrete mixtures had formulation-dependent trends: JR-A (15%) outperformed OPC by 28 days and remained superior, whereas JR-B concretes recovered more slowly but had strengths comparable to that of OPC at 90 days. Surface resistivity measurements further confirmed the enhanced resistance of systems containing J-Rox (particularly JR-B) to the ingress of deleterious ions, particularly chlorides, indicating superior durability in aggressive chloride-rich environments. The drying shrinkage performance of J-Rox concretes mostly met performance requirements; JR-A exhibited steady dimensional behavior, and JR-B exhibited moderate variability. Regression analyses revealed contradictory findings: higher P 2 O 5 content, inherent to J-Rox, correlated negatively with strength and stiffness but positively with resistivity. Collectively, the findings establish J-Rox as a viable SCM capable of contributing to sustainable concrete infrastructure, particularly when chemical composition and physical properties are optimized, and the material is used in concrete mixtures at 15%–20% replacement levels.