This study investigates the effect of elevated temperatures on slag-based geopolymer composites (SGC) with the inclusion of firebrick powder (FBP). There is a limited understanding of the properties of SGC with the inclusion of FBP when exposed to elevated temperatures and the effects of cooling processes in air and water. In this regard, in the preliminary trials performed, optimum molarity, curing temperature, and curing time conditions were determined as 16 molarity, 100 °C, and 24 h, respectively, for SGCs. Then, FBP from construction and demolition waste (CDW) was substituted in different replacement ratios (10%, 20%, 30%, and 40% by slag weight) into the SGC, with optimum molarity, curing temperature, and curing time. The produced SGC samples were exposed to elevated temperature effects at 300, 600, and 800 °C and then subjected to air- and water-cooling regimes. The ultrasonic pulse velocity, flexural strength, compressive strength, and mass loss of the SGCs with the inclusion of FBP were determined. In addition, scanning electron microscopy (SEM) analyses were carried out for control (without FBP) and 20% FBP-based SGC cooled in air and water after elevated temperatures of 300 °C and 600 °C. The results show that the compressive and flexural strength of the SGC samples are higher than the control samples when the FBP replacement ratio is used of up to 30% for the samples after the elevated temperatures of 300 °C and 600 °C. The lowest compressive and flexural strength results were obtained for the control samples after a temperature of 800 °C. As a result, the elevated temperature resistance can be significantly improved if FBP is used in SGC by up to 30%.

Firebricks are generally used in furnace basins where glass, ceramics, and cement are produced. Firebricks have an important place in construction and demolition waste (CDW). However, there is a limited understanding of the effects on fresh and hardened state properties of cementitious composites. This study investigates the mechanical, physical, and microstructural properties of cementitious composites incorporating firebrick powder (FBP) from CDW. In this regard, the FBP was used at 5, 10, 15, 20, and 25% replacement ratio by weight of cement to produce cementitious composites. The consistency, setting characteristics, and 3, 7, and 28 days compressive and flexural strength tests of produced cementitious composites were performed. In addition, ultrasonic pulse velocity, water absorption, porosity, unit weight, and microstructure analysis of cementitious composites were conducted. As a result, the 28-day compressive strength of the cementitious composite mortars containing up to 10% firebrick powder remained above 42.5 MPa. The flow diameters increased significantly with the increase of the FBP. Therefore, it has been determined that the FBP can be used up to 10% in cementitious composites that require load-bearing properties. However, FBP might be used up to 25% in some cases. Using waste FBP instead of cement would reduce the amount of cement used and lower the cost of producing cementitious composites.

The physicochemical structure of the mixing water used in concrete has a significant effect on the physical and mechanical properties of cementitious composites. The studies on the effect of magnetized water (MW) on the properties of FA/BFS-based cementitious composites are still in their infancy. This study explores the effect of MW on the fresh and hardened properties of fly ash (FA)/blast furnace slag (BFS)-based cementitious composites. A total of 22 different mixture groups having FA/BFS (0, 5, 10, 15, 20, and 25%) by weight of cement were produced using tap water (TW) and MW. The fresh-state properties (the initial and final setting times and the consistency) and hardened-state properties (the compressive strength, water absorption properties, and rapid chloride ion permeability test) of produced cementitious composites were investigated. The development of hydration products was analyzed using scanning electron microscopy (SEM) and the mercury intrusion porosimetry (MIP) test. The results reveal that the fresh- and hardened-state properties of cementitious composite samples produced with MW are significantly improved. The properties of the samples utilizing MW showed that FA and BFS could be used at a higher rate for the same target properties in cementitious composites by using MW as mixing water. Using up to 25% FA/BFS in cementitious composites prepared with MW is recommended.