Analysis on rheological and workability properties of steel-polypropylene fibers reinforced self-compacting concrete with recycled coarse and fine aggregates

Rheological and workability properties are important for the design of steel-polypropylene fibers reinforced recycled aggregates self-compacting concrete (SPFRA-SCC). In this work, the rheological and workability behavior of SPFRA-SCC was investigated to provide guideline for structural application. The SPFRA-SCC mixtures were prepared with various combined replacement contents of recycled coarse aggregate (RCA) and recycled fine aggregate (RFA). Meanwhile, the influences of steel-polypropylene fibers (milling steel fiber and polypropylene fiber) with different combined volume fractions, silica fume and fly ash on the rheological and workability properties of SPFRA-SCC were also studied. Modified-Bingham and Herschel-Bulkley models were employed to describe the rheological behavior of SPFRA-SCC. Based on the experimental results, the multi-output least-squares support vector regressor (MLS-SVR) method was adapted to predict the rheological parameters of SPFRA-SCC. Test results showed that RCA, RFA, and hybrid steel-polypropylene fibers had a negative effect on the workability and rheological properties of SPFRA-SCC, while appropriate content of silica fume and fly ash could ameliorate the rheological and workability parameters. Both Modified-Bingham and Herschel-Bulkley models could characterize the shear thickening behavior of SPFRA-SCC, and MLS-SVR method could be well applicable to predicate a close estimation of rheological parameters based on the experimental results.