Mechanical, Chloride Permeation, and Freeze–Thaw Resistance of Recycled Micronized Powder Polypropylene-Fiber-Engineered Cementitious Composites

Research on engineered cementitious composites was carried out using recycled micronized powder from waste construction waste as a substitute for cement. Consequently, this paper focuses on the investigation of recycled micronized powder (RMP) as the subject of study. Using RMP-PP-ECCA0 as the control group, we explored the impact of polypropylene fiber content (0.5%, 1%, 1.5%, 2%) and the substitution rate of RMP (10%, 20%, 30%, 40%) on the mechanical properties, resistance to chloride ion penetration, and freeze–thaw durability of recycled micronized powder polypropylene-fiber-engineered cementitious composites (RMP-PP-ECCs). It was found that, with the increase in RMP substitution rate and fiber content, the mechanical, chloride ion permeation, and freeze–thaw resistance of recycled micronized powder polypropylene-fiber-engineered cementitious composites showed a trend of increasing and then decreasing when the RMP substitution rate was 10%, and the fiber content was 1.5%; the compressive, tensile, chloride ion permeation, and freeze–thaw resistance of recycled micronized powder polypropylene-fiber-engineered cementitious composites were most obviously improved. Compressive strength performance increased by 18.8%, tensile strength performance increased by 80.8%, maximum tensile strain increased by 314%, and electrical flux decreased by 56.3%. Meanwhile, when the recycled micronized powder substitution rate was 10%, the fiber content was 1%, with the most obvious improvement in flexural and freeze–thaw cycle resistance, compared with the control group 28 d flexural strength increased by 22%, after 150 freeze–thaw cycles, the mass-loss rate was reduced by 26%, and the relative dynamic elastic modulus was improved by 4%. In addition, the chemical composition of the regenerated microfractions and the defects in the matrix of the fracture surface of the tensile specimens, the distribution of polypropylene fibers, the surface morphology, and the failure mode were analyzed by X-ray diffraction and scanning electron microscopy.

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