Preparation, Performance Test, and Microstructure of Composite Modified Reinforced Concrete

To investigate whether the compound modification means which mixes modified Polyvinyl chloride (PVC) aggregate and polypropylene fiber in concrete could gain “positive hybrid effect” and cope with more sophisticated engineering circumstances, four groups of test specimens were prepared: concrete doped with unmodified PVC aggregate, concrete doped with modified PVC aggregate, concrete doped with unmodified PVC aggregate and polypropylene fiber, and concrete doped with modified PVC aggregate and polypropylene fiber. The fiber content is 0.9 kg/m³, the modified solution content is 1 mol/L NaOH, and the replacement amount of PVC fine aggregate in replacement sand is 0%, 5%, 10%, 20%, and 30%. Mechanical property and durability tests were carried out to compare and analyze the measured compressive strength, splitting tensile strength, flexural tensile strength, water absorption rate, and impact failure energy. Moreover, scanning electron microscopy and XRD diffraction were used to analyze micromorphology and crystal structure of concrete. The test results demonstrate that as the content of PVC aggregate increases, the compressive strength, splitting tensile strength, and flexural tensile strength of the concrete decrease significantly, while the brittleness is improved. Meanwhile, the water absorption rate increases and the impact resistance shows an approximately linear increase trend. Under the same content of PVC aggregate, the most effective way to improve compressive strength is to use modified PVC aggregate. The rapid decrease of compressive strength caused by PVC aggregate can be effectively delayed by doping polypropylene fiber and modified PVC aggregate. Adding polypropylene fiber or using the modified PVC aggregate can improve the brittleness, tensile strength, flexural tensile strength, and impact resistance, but they have different modification and reinforcement effects. The concrete prepared by doping polypropylene fiber and modified PVC aggregate has better performance in tensile strength, flexural tensile strength, brittleness, and impact resistance, and the water absorption and the compressive strength of the concrete are enhanced compared with the normal group. Therefore, composite modified reinforced concrete doped with modified PVC aggregate-polypropylene fiber has broad application prospects.

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