Abstract:

This paper mainly studied the influence of silica fume （SF） and polyoxymethylene （POM） fiber dosage on the mechanical properties and water resistance of recycled hydraulic concrete. Recycled coarse aggregate （RCA） from the Xinjiang region was selected for the experiment. Twelve mix proportions were designed to explore the influence of SF （0%， 5%， 10%， mass fraction） and POM fiber （0%， 0.3%， 0.6%， 0.9%， volume fraction） dosages on cube compressive strength， splitting tensile strength， flexural strength， softening coefficient， and capillary water absorption of recycled hydraulic concrete. The test results show that compared with the benchmark group without SF and POM fiber， the addition of 10% SF alone increases the 28 d cube compressive strength of the specimens by 16.49%. The addition of 0.6% POM fiber alone increases the 28 d splitting tensile strength of the specimens by 36.46%. The combined addition of 5% SF and 0.6% POM fiber increases the 28 d cube compressive strength， splitting tensile strength， and flexural strength of the specimens by 19.96%， 49.10%， and 43.94%， respectively. The addition of 5% SF and 0.3% POM fiber increases the softening coefficient by 10.88%， and the capillary water absorption at 672 h decreases by 26.38%， indicating that the combined addition leads to a more significant improvement in properties， and the mechanism is attributed to the optimization of the microstructure and reduction of micro-cracks. However， excessive addition （such as 10%SF+0.9%POM fiber） will lead to performance deterioration due to the agglomeration effect and competition for water. This study provides an optimized mix proportion scheme for high-performance recycled concrete used in water conservancy projects in Xinjiang region.

Key words: recycled hydraulic concrete, silica fume, POM fiber, mechanical property, water resistance, microstructure