Jinqiu Yan

Recycled rubber (RR) and recycled spiral steel fiber (RSSF) were added to plain concrete (PC) to prepare recycled spiral steel fiber rubber concrete (SSFRC) with matrix strengths of C30, C40, and C50. Strength tests on the PC, rubber concrete (RC), and SSFRC were carried out, including the cube compressive strength, splitting tensile strength, and flexural strength. The effects of RSSF and RR on the mechanical properties of concrete were analyzed. Simultaneously, the stress–strain curve of the SSFRC was obtained through axial compressive testing, and the toughness of SSFRC was evaluated by three indexes: the tensile compression ratio, bending compression ratio, and toughness index. The results show that adding RR to PC results in a decrease in the mechanical properties of concrete with different matrix strengths, and the addition of RSSF can make up for the strength loss of the rubber. The mechanical strength of SSFRC with different matrix strengths increased first and then decreased with the increase in RSSF content. The cubic compressive strength reached its peak value when the content of RSSF was 1%, and the splitting tensile strength and flexural strength reach their peak values when the content of RSSF was 1.5%. RSSF works best with rubber particles at the right dosage to further increase the toughness of the concrete. When the rubber content is 10%, and the RSSF content is 1.5%, the mechanical strength enhancement effect of SSFRC is at its best, and the toughness is also at its best.

We sorted the waste from mechanical processing to form recycled steel fibers. In order to study the flexural mechanical properties of reinforced concrete beams after the addition of recycled steel fibers, four recycled steel fiber concrete beams (RSFCBs) and one normal concrete beam (NCB) were designed and poured using the volume fraction of steel fibers (0%, 0.5%, 1%, 1.5%, 2%) as the variables. Normal section bending tests were conducted on them under a concentrated load. We obtained experimental data such as the cracking load, ultimate load, mid-span deflection, and steel and concrete strain of the beam by gradually loading the test beam, and we observed and recorded the development of cracks. The results indicate that the NCB exhibits crushing failure, while the RSFCBs exhibit equilibrium failure. The addition of recycled steel fibers effectively controls the extension of cracks, resulting in a better bending toughness of the beam. The bending performance of RSFCBs with different volume additions shows a trend of first increasing and then decreasing with the increase in steel fiber content. The peak value was reached when the steel fiber content was 1.5%, which increased the bending bearing capacity by 54.72% compared with the NCB. With the increase in steel fiber content, the required load value for tensile steel bars to yield also increases, reaching a peak at a content of 1.5%, which increases the bending bearing capacity by 44.64% compared with the NCB. The addition of recycled steel fibers enables the beam to improve its bearing capacity while limiting the development of longitudinal reinforcement strain, allowing the longitudinal reinforcement to yield under higher loads and improving the overall bending performance of the beam.