Experimental and Model Calculation Research on Shrinkage of Hybrid Fiber-Reinforced Recycled Aggregate Concrete

Recycled aggregate concrete (RAC), which is made by replacing all natural coarse and fine aggregates with recycled aggregate, plays a significant role in improving the recycling rate of construction materials, reducing carbon emissions from construction, and alleviating ecological degradation issues. However, due to its low strength and significant shrinkage and deformation problems, RAC has limited application. The effort of fiber type, fiber admixture, and fiber hybridization on autogenous shrinkage were studied to improve the structural safety of building materials and broaden the application of RAC. Test results indicate that the shrinkage of RAC decreases with an increase in fiber admixture, and steel fiber-reinforced RAC is more resistant to shrinkage deformation than polypropylene fiber-reinforced RAC. The shrinkage deformation of the hybrid fiber group is smaller than that of the single fiber group, and the inhibition of shrinkage deformation is most effective when the volume fraction of steel fiber is 0.5% and the polypropylene fiber content is 1.5 kg/m³. At 120 days, the PF15SF05 mixture showed a 65.3% reduction in shrinkage compared with ordinary RAC. By merging the shrinkage deformation characteristics of fiber-reinforced RAC and introducing the fiber influence coefficient, three theoretical calculation models for autogenous shrinkage applicable to single and hybrid fiber-reinforced RAC were established based on the experimental data.