Combined influence of carbonation and leaching on freeze-thaw resistance of limestone ternary cement concrete

Abstract

Performance of OPC and composite cements including limestone ternary blended concretes and pastes exposed to natural carbonation, leaching, and freeze-thaw (FT) cycles and their coupling were investigated. The combined regime is analogous to the Capillary suction, internal damage and Freeze-thaw (CIF) test. The freeze-thaw test results showed that composite cement concretes are more susceptible to surface scaling and internal damage. Microanalysis of complementary cement pastes revealed partial carbonation after equilibration at 65% RH. Decalcification due to leaching accompanied capillary suction, profound in the partially carbonated ternary cement pastes such that portlandite was depleted from the surface before the FT cycles commenced. Successive cycles increased porosity; heterogeneity and coarsening of the pore structures were drastic when carbonation and leaching preceded FT, modifying the C-S-H morphology and composition. Curtailing carbonation and leaching reduced surface scaling and internal damage to comparable levels as OPC of the same strength class. These findings imply that changes in porosity and phase assemblage in composite cements caused by carbonation and leaching contributed to their FT susceptibility.