Abstract: This study focuses on the multi-scale synergistic enhancement effect of 5·1·3 type magnesium hydroxide
sulfate hydrate whiskers (MHSHW-513) and steel fibers in basic magnesium sulfate cement (BMSC). Comparative experiments
were conducted with single-doped steel fibers and composite-doped MHSHW-513 and steel fibers. The fluidity,flexural
strength,compressive strength,and water resistance of BMSC were systematically tested,and its microstructure was observed using
scanning electron microscopy (SEM). The results show that steel fibers play a dominant role in improving the mechanical
properties of BMSC. With a single doping of 2% steel fibers,the 28-day compressive strength increased significantly by 41. 7%
compared to the reference group. Meanwhile,MHSHW-513 significantly improves the water resistance of the material by filling
pores and optimizing the interface. When the steel fiber content was fixed at 2% with 1% MHSHW-513 added,the softening coefficient
of the specimen remained at a high level of 0. 90 even after 56 days of water immersion. SEM analysis revealed that the
externally added MHSHW-513 and the endogenous whiskers form a multi-level crack-blocking system at the steel fiber-matrix
interface zone,delaying crack propagation at the micro-scale,while steel fibers consume energy through bridging and pulling out
at the macro-scale. Their synergy achieves a stepwise improvement in the mechanical properties and durability of BMSC.

Key words: steel fiber,MHSHW-513 whisker,basic magnesium sulfate cement (BMSC),mechanical properties,water
resistance,microstructure