Study on Damage Model of Polypropylene Fiber Recycled Concrete with Different Mix Proportions

In order to study the effect of different mix proportions on the compressive strength of polypropylene fiber reinforced recycled concrete, 30 sets of specimens with coarse aggregate particle sizes of 5~10 mm and 10~20 mm at 4∶6, 5∶5, and 6∶4 were designed and conducted. Through uniaxial compression tests, the stress-strain curves, elastic modulus, peak strength, and other parameters of each set of specimens were obtained. The test results show that: As the coarse aggregate particle size decreases, the peak stress shows an overall downward trend; Polypropylene coarse fibers have the best strengthening effect on the elastic modulus, and the mixing of coarse and fine polypropylene fibers has the best strengthening effect on the peak stress of recycled concrete. A statistical damage constitutive model for polypropylene fiber reinforced recycled concrete was established, and it was found that the specimen with a ratio of 5∶5 for coarse aggregates of 5~10 mm and 10~20 mm exhibits the most severe damage, and the mixture of coarse and fine fibers had the best inhibitory effect on damage. Finally, support vector machine regression was used to predict the post peak strain of recycled concrete. The study show that using a linear kernel function and using the post peak compressive machine strain as the input variable had the best prediction effect.