Workability, mechanical properties, pore characteristics and microstructure of magnesium phosphate cement-based concrete: Influence of curing age, fiber type and dosage
Tao Li, Jing Zhang, Zheliang Yao, Yuanyuan Yao, Xiamin Hu, Hongfa Yu, Jianming Yang, Huizhen Jin, Mingwei Zhou, Jiaming Wu
Abstract
Magnesium phosphate cement (MPC) as a new type of inorganic cementitious material has received wide attention in recent years. However, MPC has the disadvantages of expensive price and brittleness , and the existing research mainly focuses on the preparation and material properties of MPC and mortar, with fewer studies on its concrete material properties and fiber modification. In this study, a total of 22 groups of MPC-based concrete (MPCC) mixtures were prepared by incorporating mineral admixtures , aggregates and fibers to investigate the effects of different fiber types , volumetric fiber dosage and curing age. The setting time, fluidity, cubic compressive strength (CCS), splitting tensile strength (STS), pore structure , chemical composition and microstructure were evaluated, and the working mechanism and failure modes of the fibers in the matrix were explored by mercury intrusion porosimeter, X-ray diffraction and scanning electron microscopy. Finally, a mathematical model was developed to describe the relationship between the strength and porosity. The results indicated that the effect of fiber types on the workability of MPCC was in the order of end hooked steel fibers (EHSF) > long straight steel fibers (LSSF) > short straight steel fibers (SSSF) > basalt fibers (BF). The addition of fibers doped with 0.5 % SSSF and 1 % LSSF increased the 1-day and 3-day CCS by 6.3 %-7.0 % and 14.3 %-33.7 %, respectively, and had no significant effect on the 28-day CCS. The STS of MPCC specimens increased with the increase of steel fibers, and EHSF with 1 % fiber doping showed the greatest enhancement effect, with STS of 7.6 MPa, 8.2 MPa, and 8.6 MPa at 1, 3, and 28 days, respectively. However, the addition of EHSF and BF negatively affected the CCS and STS. The microscopic results suggested that the fibers were effective in optimizing the pore size distribution and effectively reducing the matrix pore size.