A new cement‐based mortar with high early strength and toughness was developed by adding micro steel fibers (MSF) in magnesium phosphate cement (MPC) mortar. The compressive and flexural tests were carried out to investigate the effect of curing time, MSF volume fraction, sand‐cement mass ratio, and water‐cement mass ratio on the strength and flexural toughness of MSF‐reinforced MPC mortar (MSFRMM). Also, the flexural toughness and ductility of MSFRMM were evaluated according to ASTM C1609. The results of this study showed that the addition of MSF from 0% to 1.6% by volume significantly improved the compressive strength of MSFRMM. The MSFRMM showed high early strength, especially during the first 3 days. The addition of MSFs changed the flexural failure mode of MPC‐based mortar from brittleness to ductility, and the flexural toughness of MSFRMM remarkably increased with the increase of MSF volume fraction from 0% to 1.6%. The toughness and ductility of MSFRMM slightly increased with the increase of the dosage of cement. The toughness and ductility of MSFRMM increased with the decrease of the water‐cement mass ratio due to the improved density of the mortar caused by the reduction of water.

Waste concrete was recycled and crushed into fine aggregate to prepare a high ductility cementitious composite (HDCC) in this study, for helping dispose the massive amount of construction waste and for reserving natural resources. Firstly, the features of recycled fine aggregate (RFA) were analyzed in detail and compared with natural fine aggregate (NFA). After that, the mechanical properties, including compression, flexure, bending and tension, and the microstructure of high ductility cementitious composite (HDCC) prepared with RFA were systematically investigated and compared with that of HDCC prepared with NFA. The results show that, since RFA has a higher water absorption rate and contains 4.86 times as much crush dust as NFA, HDCC with RFA forms a denser matrix and a higher bond between fiber and matrix than HDCC with NFA. Thus, HDCC with RFA has higher compressive, flexural, bending and tensile strength. Meanwhile, the higher bond between the fiber and matrix of HDCC with RFA and the finer particle sizes of RFA can greatly promote the development of multiple cracking. As a result, HDCC with RFA exhibits more remarkable stain hardening, and presents 182.73% higher peak deflection in bending and 183.33% higher peak strain in tension than HDCC with NFA. Finally, with the consideration of fiber volume fraction, the prediction models for the peak strengths of HDCC with RFA were proposed. The prediction results show a good agreement with the test results.

Novel multiple hooked-end steel fibers possessing high anchorage with the concrete matrix have been invented and are desired to achieve significant improvement in the performance of steel fiber–reinforced concrete (SFRC). In this study, C50/C70/C80 notched concrete beams containing 4D steel fibers with 1.5 hooked ends at a dosage of ${0–110\mathrm{kg}/\mathrm{m}}^3$ , 5D fibers with double hook-ends at a dosage of ${0–110\mathrm{kg}/\mathrm{m}}^3$ , and 3D steel fibers with a single hooked end at a dosage of ${0–70\mathrm{kg}/\mathrm{m}}^3$ were tested under three-point bending. The experimental results indicated that increasing fiber dosage and the number of hooked ends were generally effective in improving the flexural tensile behavior of concrete beams, especially high-strength concrete beams. The two linear relationships of the equivalent flexural tensile strength $f_{\mathrm{eq},2}$ and $f_{\mathrm{eq},3}$ , evaluated by RILEM TC 162-TDF, as well as the residual flexural tensile strength $f_{r,1}$ and $f_{r,4}$ , evaluated by BS EN 14651, were confirmed to be appropriate for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Based on the experimental results from this study and more in the literature, the analytical equation, proposed by Naaman et al. and simplified by Pajak et al., was verified to be reliable for predicting the maximum flexural tensile strength for concrete beams reinforced by 3D, 4D, and 5D steel fibers. Furthermore, the analytical equation, proposed by Venkateshwaran et al., that can explicitly take into account the effects of concrete compressive strength, fiber volume fraction, fiber aspect ratio, fiber length, and number of fiber hook ends, was modified for predicting the residual flexural tensile strength ($f_{r,i}$ ) of novel multiple hooked-end SFRC. It was found that the modified Venkateshwaran et al. equation was approved as valid for high-strength SFRCs in this study, whereas the original one only applies for low-strength and normal-strength SFRCs. All these represent a step forward in advancement on the knowledge and understanding of SFRC with novel multiple hooked-end steel fibers.