Multi-objective optimization, performance characterization and polymerization mechanism for eco-friendly polymer mortar with steel slag powder

Cement, as a non-renewable resource, is associated with significant carbon dioxide emissions during its manufacturing process. To curtail cement consumption and promote the recycling of industrial by-products, this study describes the mix design and polymerization mechanism of an eco-friendly polymer mortar incorporating steel slag powder (SSPM). Firstly, based on the Dense Packing Theory, the modified Andreessen & Andersen model was employed to determine the mix proportions of steel slag powder (SS), granulated blast furnace slag (GS), silica fume (SF), and river sand (RS). Subsequently, the Response Surface Method was applied to construct functional models correlating the design parameters and key performance indicators of SSPM, thereafter optimizing the water–cementitious materials ratio (W/C), sodium silicate solution–cementitious material ratio (L/C) and SiO 2 –Na 2 O ratio (Si/Na). Afterwards, the pore structure, phase composition, and microstructure of SSPM were characterized, together with the schematic models of its mixing, hydration and polymerization stages to clarify the polymerization mechanism. The results show that the volume fractions of SF, GS, SS and RS are determined as 0.126, 0.218, 0.184 and 0.472, respectively. Elevating the L/C ratio induces a first rise, then a decline in mechanical strengths and shrinkage of SSPM. However, increasing the Si/Na ratio exerts a similar effect on mechanical strength to L/C, yet elevates its shrinkage. Subsequently, the optimal W/C, L/C, and Si/Na ratios are identified as 0.37, 0.22, and 1.89, respectively, and the SSPM prepared with this ratio exhibits a fluidity of 205 mm, a 28d compressive strength of 45.50 MPa, and a shrinkage of 660 με, is well-suited for precast concrete components. Notably, the hydration polymerization products of SSPM are dominated by cross-linked N-A-S-H and C-A-S-H gels, whose secondary filling effect on the voids between solid materials, as well as the dense stacking design concepts, are the strength formation mechanism. This study proposes an integrated computational design method for geopolymers, with key implications for solid waste utilization and sustainable development of engineering materials.