Impact of supplementary cementitious materials (SCMs) on physical-mechanical properties and microstructure of styrene polyacrylic (SPA) polymer modified mortars

Polymer-modified mortars (PMMs) have attracted increasing attention for their promising properties, multiple applications, and relatively affordable cost compared to other polymer mortars. This study investigates the impact of substituting 30% of ordinary Portland cement (OPC) with SCMs on the physical-mechanical and microstructural properties of PMM based on a new type of latex polymer, styrene polyacrylic (SPA). This is to contribute to the development of more effective and sustainable PMM, while reducing the carbon footprint associated with cement use. For this purpose, an OPC mortar and a total of 7 mortar mixtures were designed, all with a polymer-to-binder (P/B) ratio (in powder) of 7.5%. The control PMM mixture contains only OPC and SPA latex as binders while the remaining mixtures include binary and ternary cement mixtures, composed of OPC, silica fume (SF), natural pozzolan (NP) and limestone fillers (LF). Tests of workability of fresh mortars and dry weight were carried out and flexural tensile and compressive strengths of hardened mortars were measured over a curing period ranging from 3 to 365 days. The microstructure of PMMs was also studied using XRD analysis and SEM images. The results demonstrated the efficacy of LF integration in improving the workability of PMM while NP or SF addition has a detrimental effect on the rheological properties of PMM, as the flow time increased by 24% and 37%, respectively, so it is necessary to increase the superplasticizer content. The incorporation of SCMs also resulted in the production of lightweight PMMs as evidenced by the reduced density of SCMs. For PMMs with binary binders, the replacement of OPC with 30% SF leads to a significant increase in compressive strength after 28 days ranging from 7 to 15%, along with an improvement in the PMM microstructure. Finally, it should be noted that the combination of NP and SF represents the optimal formulation for the PMM ternary mixture. After 28 days, this combination noticeably increases compressive strength by 8–10% without any decrease in tensile strength.