مهندسی عمران شریف (Sep 2024)
The investigation of the combined effect of nano-silica, steel, and polypropylene microfibers on the mechanical characteristics, permeability, and chloride attack resistance of cement composite
Abstract
The objective of this study was to investigate the combined impact of nano-silica, steel microfibers, and polypropylene microfibers on the mechanical properties, permeability, and resistance to chloride attack of cement composite. To achieve this goal, a 2% weight ratio of nano-silica was used as a cement substitute, while 1.0% steel and 0.2% polypropylene microfibers, respectively, by volume of the binders were separately and simultaneously employed as additives in the cement composite. Experimental analyses, including compressive, flexural, and tensile strength tests, were conducted to evaluate the mechanical properties. Additionally, the ultrasonic pulse velocity (UPV) and sorptivity tests were employed to assess permeability, and the durability against chloride attack was examined using the Rapid Chloride Migration Test (RCMT). The results demonstrate that the simultaneous incorporation of nano-silica, steel microfibers, and polypropylene microfibers in the cement composite mixture resulted in a significant enhancement in compressive strength, flexural strength, flexural toughness, and tensile strength by 59.3%, 32.3%, 67.2%, and 25.9%, respectively, compared to the control sample after a curing period of 90 days. Moreover, significant decreases were observed in terms of the initial and secondary water absorption rates. Furthermore, the penetration depth of chloride ions was notably reduced from 33.6 mm (in the control composite) to 14.2 mm (in the composite containing the combined effects of nano-silica, steel microfibers, and polypropylene microfibers) after 90 days. The enhancement of mechanical properties, permeability, and durability against chloride attack in cement composite can be attributed to the synergistic mechanisms promoted by the utilization of nano-silica, steel microfibers, and polypropylene microfibers. The filling effect, nucleation sites, and pozzolanic activity of silica nanoparticles significantly contribute to the reduction of porosity and refinement of the cementitious matrix's microstructure. Simultaneously, the inclusion of steel microfibers and polypropylene microfibers reinforces the cement matrix and effectively controls existing microcracks, thereby impeding the propagation of macrocracks and brittle failure in the cement composite. Furthermore, the bridging effect of steel and polypropylene fibers aids in the control of cracks caused by plastic shrinkage during the early stages and secondary or thermal cracks, thereby further improving the properties of cement composite.
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