The Effects of Waste Iron Powder and Steel Fiber on the Physical and Mechanical Properties of Geopolymer Mortars Exposed To High Temperatures

Abstract

Geopolymer (GP) concretes have the potential to be an excellent alternative to cement-based traditional concretes for more sustainable concrete production. GP concretes have advantages such as low production temperature, low energy consumption, low carbon dioxide (CO2) emission, and rapid strength gain. However, GP concretes, similar to conventional concretes, lose a large part of their residual strength and durability capacities when exposed to possible high temperatures such as fire due to the deterioration of their internal structures. One efficient way to minimize the loss of strength and durability properties of GP concretes subjected to high temperatures is to use various waste materials and fibers in GP mixtures. This study aimed to improve GP mortar's physical and mechanical properties by adding steel (ST) fiber and waste iron powder (WIP) to GP mixtures. This study fundamentally investigates the spreading diameters (SD), mass loss (ML), external surface changes, residual compressive strength (RCS) and residual flexural strengths (RFS), and microstructural properties of GP mortars reinforced with ST fiber and WIP before and after high-temperature effects. According to the results, although ST fiber and WIP negatively affected GP mortars' workability and reduced GP mortars' SD values, they significantly increased GP mortars' RCS and RFS capacities. At 800 degrees (C), the RCS and RFS capacity reductions of the S0 control sample were 83.30% and 75.27%, respectively. In contrast, the drops in the RCS and RFS capacity of the S6 sample, in which 20% of WIP and 2% of ST fiber were used in hybrid form, decreased by 70.72% and 65.31%, respectively. However, ST fibers and WIP slightly reduced the ML of the GP mortars after the high-temperature effect due to ST fibers and WIP being ineffective in preventing peeling on the sample surface. At 800C, while the ML of the S0 control specimen was 4.47%, the ML values of S1-S6 specimens where WIP and ST fibers were used in single and hybrid forms varied between 4.16% and 4.38%. © 2023 Institution of Structural Engineers