This study focuses on the development of sustainable construction materials via geopolymers synthesized from metakaolin and slag, aiming to identify environmentally friendly alternatives for construction material systems. A metakaolin–slag geopolymer mortar (MK–slag) was prepared using metakaolin and slag as fully solid waste raw materials, with sodium silicate solution and sodium hydroxide acting as composite activators. Initially, single-factor experiments were conducted to determine the optimal ranges for metakaolin–slag content, water/binder ratio, and water glass modulus. Subsequently, response surface methodology was employed to develop regression equations that analyze the main and interaction effects of these variables on the 7-day and 28-day compressive strength and water absorption of the mortar. The optimal mix ratio was then identified. The microstructure and formation mechanisms of MK–slag mortar were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and mercury intrusion porosimetry (MIP). The results indicate that all factors follow quadratic polynomial relationships with the response variables, showing a regression coefficient (R2) greater than 0.98, indicating an excellent model fit and prediction accuracy. According to model predictions, the optimal mix parameters under multi-objective optimization were found to be a metakaolin-to-slag ratio of 45%: 55%, a water/binder ratio of 0.45, and a water glass modulus of 1.3. After 28 days of curing, the primary hydration products were gel-like substances such as N-A-S-H and C-A-S-H. These gels interweave and overlap to form a high-density, structurally robust binary solid waste geopolymer mortar. This approach expands the application of solid waste materials, such as metakaolin and slag, while enhancing the recycling and utilization efficiency of these waste products.
Yin et al. (Sun,) studied this question.
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