Compatibility of hydrogarnet, Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub x}(OH){sub 4(3−x)}, with sulfate and carbonate-bearing cement phases: 5–85 °C

• Published in: Cement and concrete research Vol. 83
• Main Authors: Okoronkwo, Monday Uchenna, Department of Pure and Industrial Chemistry, Abia State University, P.M.B 2000 Uturu, Abia State, Glasser, Fredrik Paul
• Format: Journal Article
• Language: English
• Published: United States 15.05.2016
• Subjects: ATOMIC FORCE MICROSCOPY; CARBONATES; COMPATIBILITY; MATERIALS SCIENCE; PORTLAND CEMENT; SILICON OXIDES; SOLID SOLUTIONS; SULFATES
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/J.CEMCONRES.2016.01.013

The stable existence of hydrogarnet in Portland cement compositions cured at temperatures below 55 °C has long been predicted from application of equilibrium thermodynamics. However hydrogarnet is not often reported in hydrated commercial Portland cements. The substitutions (SO{sub 4}–CO{sub 3}–OH) in AFm have previously been shown to stabilise AFm to higher temperatures and raise the temperature at which AFm converts to Si-free hydrogarnet, C{sub 3}AH{sub 6}. But unanswered question remains about the compatibility of AFm and AFm solid solutions with Si-substituted hydrogarnet, Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub x}(OH){sub 4(3} {sub −} {sub x)}. Phase relations of C{sub 3}AH{sub 6} and Ca{sub 3}Al{sub 2}(SiO{sub 4}){sub x}(OH){sub 4(3} {sub −} {sub x)} at sulfate and carbonate activities conditioned respectively by (gypsum and SO{sub 4}-AFt) and (calcite and CO{sub 3}-AFt) have been determined experimentally in the range 5–85 °C. The results confirm the instability of Si-free hydrogarnet with carbonate and sulfate-bearing cement phases, but do indicate that a range of silica-substituted hydrogarnet solid solutions are stable under conditions likely to be encountered in blended cement systems.