Effect of Metakaolin and Ground Granulated Blast Furnace Slag on the Performance of Hybrid Fibre-Reinforced Magnesium Oxychloride Cement-Based Composites

Abstract This study investigates the effect of ground granulated blast furnace slag (GGBFS) and metakaolin (MK) on the strength and ductility of magnesium oxychloride cement (MOC) based hybrid basalt and polyethylene fibre reinforced cementitious composite (FRMOC). MOC was chosen as the matrix due to its unique properties and environment friendliness as a green cement. MK and GGBFS were selected as primary additives to reinforce the MOC matrix owing to their outstanding performance in cementitious composites, coupled with their widespread availability and sustainable characteristics. The influence of GGBFS and MK on physical and mechanical properties of FRMOC was studied in this paper through extensive physical and mechanical testing and microscopic analysis. It was found that the hardened density of FRMOC was not significantly affected by these additives, and it ranged from 1909.3 to 1976.0 kg/m 3 , retaining its lightweight characteristics. Compressive strength of specimens cured for one day reached approximately 69.1–84.0% of that for specimens cured for 28 days, indicating the high early strength characteristics of the material. All FRMOC specimens exhibited tensile strain hardening properties, with tensile strength and strain capacity ranging from 6.74 to 8.58 MPa and 1.14 to 2.22%, respectively. The mix containing 30% GGBFS, 0.75% basalt fibre, and 1.25% polyethylene fibre was identified as the optimum MOC mix with enhanced compressive strength (73.9 MPa), tensile strength (8.52 MPa), and strain capacity (2.22%). Microscopic analysis further revealed that the addition of GGBFS-MK blends did not alter the primary phase composition of hydration products but essentially promoted the formation of phase 5, demonstrating their effectiveness in enhancing the performance of FRMOC.