Compressive Behavior, Microstructural Properties, and Freeze–Thaw Behavior of Tailing Recycled Aggregate Concrete with Waste Polypropylene Fiber Addition

Abstract

To improve the high brittleness of recycled aggregate concrete containing iron ore tailings (TRAC), the feasibility of adding polypropylene fiber (PPF) to TRAC was studied by performing a compression stress–strain curve test, scanning electron microscope characterization, and a freeze–thaw cycle test. The results indicated that PPF had a beneficial impact on reducing the brittleness of TRAC. With the increase in PPF content, the peak strain increased, the elastic modulus decreased, and the peak stress and energy absorption capacity increased at first and then decreased. Furthermore, the microstructure investigation revealed that the interface friction between the PPF, aggregate, and cement matrix was the main source of energy dissipation. When the load acted on the concrete, the stress was dispersed to the fiber monofilaments, thus effectively enhancing the peak stress and peak strain of concrete and suppressing the generation and development of cracks in the concrete. In terms of freeze–thaw resistance, adding a small amount of PPF could reduce the negative effects of the freeze–thaw process on the cement matrix. On the premise of ensuring strength, the waste utilization should be as high as possible. Therefore, it was suggested that the content of PPF in fiber-reinforced tailings recycled aggregate concrete (TRAC-PP) should be 0.6%.

Mechanical Properties of Polypropylene Fiber Recycled Brick Aggregate Concrete and Its Influencing Factors by Gray Correlation Analysis

“…These dispersed PPFs could effectively play a positive role, such as connecting the substrate and transferring the load. Figure 10b shows the crisscrossing and disorderly distribution of PPFs in the matrix, which eventually formed a three-dimensional distribution network within the concrete [34]. This structure could effectively reduce the stress concentration and the generation and development of cracks in the concrete, which had a positive impact on the macromechanical properties [64].…”

“…PPFs do not participate in the hydration reaction of the recycled concrete, which improved the mechanical properties of the concrete through physical connections that inhibited the generation and development of pores and improved the pore structure [32,33]. Xu et al [34] performed a scanning electron microscopy (SEM) analysis of recycled concrete. The results showed that the PPFs transferred the load to the surrounding matrix through bridging cracks, which effectively improved the mechanical properties of the recycled concrete.…”

Research on Flexural and Freeze–Thaw Properties of Polypropylene-Fiber-Reinforced Pavement Concrete Containing Waterborne Epoxy

“…The fracture toughness is determined using the critical stress intensity factor (KIC) by using the following equation [45,46]: ],…”

“…As a consequence, cracks may be induced when these pressures finally exceed the tensile strength of the concrete. With increasing freezing and thawing cycles, this damage will be more severe, and the concrete stripping off will arise [45]. about by PP fibers and the interpenetrating organic-inorganic structure, all of which had the beneficial effect of inhibiting the appearance of cracks.…”

“…As a consequence, cracks may be induced when these pressures finally exceed the tensile strength of the concrete. With increasing freezing and thawing cycles, this damage will be more severe, and the concrete stripping off will arise [45]. Therefore, the freeze-thaw resistance of concrete could be improved by reducing the ingress of water.…”