Characterizing the Chemistry of One-Part Green Geopolymer Foams: The Role of Silica Fume and Fiber Hybridization

This study aims to investigate the mechanical, physical, durability and microstructure of slag-based and environmentally friendly foam geopolymer concrete with glass and polypropylene fiber hybridization using sustainable materials such as waste marble dust, silica fume (SF) and sodium metasilicate. One of the most critical advantages of geopolymer concrete compared to traditional Portland cement is its low carbon emissions. In the study, foam geopolymer concrete was produced using glass fiber (GF) and polypropylene fiber (PPF) additives and three different silica fume ratios (0%, 7.5%, 15%) and the effects of these additives on the workability (flow diameter), transfer performance (sorptivity), compressive strength, flexural strength, thermal conductivity, high-temperature performance and freeze-thaw resistance were investigated. The experimental results showed that the hybridization of GF and PPF significantly increased the compressive strength and flexural strength of samples without silica fume. However, high silica fume content negatively affected the mechanical properties by creating voids in the matrix. The flexural performance of geopolymer foams was significantly improved by fiber reinforcement. Mainly, improvements were observed in both peak load and displacement values of hybrid fiber geopolymer foams. In addition, GF and PPF admixtures increased the strength of concrete, especially after high temperatures of 200 and 400 °C. However, the compressive strength of samples exposed to high temperatures of 600 °C decreased. It was determined that the hybridization of GF and PPF increased the thermal insulation performance of foam geopolymer concrete. SEM analyses revealed that silica fume and fiber additives significantly affected the microstructure and mechanical strength of geopolymer foams. This study highlights that waste marble powder has the potential to be utilized in environmentally friendly geopolymer concrete and that the use of SF, GF and PPF additives at optimum rates is essential for the performance of foam geopolymer concrete.