Effect of polyether-type SRA on the drying shrinkage, pore structure and properties of blended mortar incorporating limestone powder

摘要

Currently, the incorporation of industrial solid wastes such as limestone powder (LSP) has been proofed to be an effective solution to reduce cement consumption and further carbon dioxide emissions. However, the volume changes caused by shrinkage may induce high tensile stresses, which result in warping especially when the material is partly or wholly restrained. It has been reported that the addition of shrinkage reducing agent (SRA) in cementitious materials could largely reduce the magnitude of drying shrinkage, but causes negative side effects at the same time. To examine the influence of SRA on the performance of blended mortar with LSP, flowability, mechanical properties and porosity of mortars were studied. Mixtures without SRA, with 1.0%, 1.5%, 2.0%, 2.5% and 3.0% of a polyether-type SRA (by mass of cement) were prepared. The specimens were characterized by measuring their air content, packing density, flexural/compressive strength, drying shrinkage and corresponding mass loss. Pore characteristics were also investigated by mercury intrusion porosimetry (MIP) for mortars with and without SRA. The experimental results show, that polyether-type SRA improves the flowability of fresh mortar but reduces the packing density, flexural and compressive strength. Mixtures with SRA show a comparative reduction in long-time drying shrinkage and mass loss, which can be defined by two stages: (i) high mass loss during the first days, (ii) drying shrinkage increasing linearly with the mass loss. Pore size distribution results indicate that the addition of SRA increases the pore size coarseness and average pore radius of mortar. The shrinkage reduction mechanism of polyether-type SRA could be the double effect of decreasing surface tension and increasing average pore radius accordingly. (C) 2020 Elsevier Ltd. All rights reserved.