ABSTRACT
High-strength concrete (HSC) has a high compressive strength, high density, excellent durability, and seepage resistance, but its deformation ability is weak. Adding fibers can improve the physical and mechanical properties of HSC. Additionally, the HSC structure may face the threat of fire. In the process of fire extinguishing, the damage mechanism of high-temperature-resistant concrete is complicated due to the different contact conditions with water at different locations. Hence, it is essential to conduct pertinent research on the behavior of fiber-reinforced HSC with different cooling methods after high-temperature action. In this paper, polyvinyl alcohol fiber (PVA fiber) was selected to be added into the HSC to carry out high-temperature experimental research, so as to explore the apparent changes, failure pattern, and mass loss rate of the fiber-reinforced HSC using different cooling methods and analyze the influence of its residual compressive strength and flexural strength. The test results suggest that, with the increase in heating temperature, the color of the specimen's surface transitions from dark blue-gray to white, and the quantity of surface cracks on the specimen gradually rises. The mechanical strength gradually decreases as the heating temperature increases. At a consistent heating temperature, the mechanical strength initially rises, and then falls with an increase in fiber content. The maximum compressive strength and flexural strength were achieved at PVA fiber contents of 0.2% and 0.3%, respectively. For different temperatures and fiber contents, the mechanical strength after natural cooling is generally higher than that after immersion cooling. In addition, X-ray polycrystalline diffractometry (XRD) and scanning electron microscopy (SEM) tests were conducted to analyze the compositional alterations and microstructure of the fiber-reinforced HSC following high-temperature exposure, accompanied by an explanation of the factors influencing the alterations in the physical and mechanical properties. Therefore, the findings of this study can serve as a valuable reference for the utilization of HSC in engineering structures and contribute to the advancement of HSC technology.
ABSTRACT
Alkali-activation is an effective municipal solid waste incineration fly ash (MSWIFA) solidification/stabilization (S/S) technology. However, the characteristics of calcium-rich silica-poor aluminum phase in MSWIFA easily cause the structural instability and contamination of alkali activated MSWIFA S/S bodies. Therefore, the aluminosilicate solid wastes are used in this work to optimize the immobilization and structural properties. Results showed that incorporation of aluminosilicate solid wastes significantly improved the compressive strength and heavy metals pollution toxicity of MSWIFA S/S bodies. Compared to alkali activated MSWIFA, the compressive strength of S/S bodies with addition of coal fly ash, silica fume and granulated blast furnace slag improved by 31.0%, 47.6% and 50.8% when the curing time was 28 days, respectively. Leachability of Pb, Zn and Cd in these alkali activated MSWIFA S/S bodies was far below the threshold value specified in Standard GB16889. Aluminosilicate solid wastes provided abundant Si/Al structural units, and some new phases such as ettringite(AFt, 3CaOâ Al2O3â 3CaSO4â 32H2O), calcium sulfoaluminate hydrate (3CaOâ Al2O3â CaSO4â 12H2O) and Friedel's salt (CaOâ Al2O3â CaCl2â 10H2O) can be detected in S/S matrix with aluminosilicate solid wastes, along comes increased the amount of the amorphous phases. Lower Ca/Si molar ratio tended to form the network structure gel similar to tobermorite with higher polymerization degree. Meanwhile, the silica tetrahedron of the gels changed from the oligomerization state like island to the hyperomerization state like chain, layer network or three-dimensional structure, and average molecular chain length increased. These findings provide theoretical basis for structural properties optimization and resource utilization of MSWIFA S/S matrices.
