The investigation of engineering properties of hybrid lightweigth geopolymer concrete

Traditional cement-based building materials are subject to significant criticism in terms of environmental sustainability due to high energy consumption and carbon emissions. In this context, the development of alternative binder systems has gained importance in order to reduce the carbon footprint of the construction sector. In this study, the compositional differences of hybrid lightweight concrete mixtures produced with fully or partially geopolymer-based binder systems were evaluated. Seven different mixtures were designed in the experimental study. In addition to the completely geopolymer-based mixture (GEO), samples prepared with traditional binders such as lime (SKK), gypsum (PSA) and white cement (SBÇ) and hybrid mixtures (SKK/GEO-SBÇ/GEO) where each of these was replaced with 50% geopolymer were created. In all mixtures, expanded vermiculite was kept constant as lightweight aggregate, while in mixtures containing geopolymer, the granulated form of sodium metasilicate was used as an activator. In addition, the ratios of pozzolanic additives such as fly ash (FA) and blast furnace slag (GGBFS) were varied depending on the binder type. In this study, the most successful mechanical properties were obtained in the GEO (100% Geopolymer) and SBÇ (OPC-based) mixtures. GEO stood out with its high flexural strength and its ability to retain strength up to 100 °C, while SBÇ demonstrated the highest compressive strength and moderate sulfate resistance, making it suitable for structural applications. Among the hybrid systems, SBÇ/GEO (OPC/Geopolymer) showed promising flexural and compressive strength, but experienced significant strength losses under sulfate and acid exposure. The PSA-based PSA mixture exhibited the lowest thermal conductivity and the highest resistance to sulfate attack, although it showed low compressive strength and structural weakness at elevated temperatures. SKK (AAC) and PSA were the most resistant to acid exposure. Overall, geopolymer additives enhanced performance under high temperatures and sulfate exposure but were found to be more vulnerable in acidic environments and under long-term chemical effects. Mixtures with low density and porous structures provided better thermal insulation, while the inclusion of geopolymer increased density and thermal conductivity. Based on the findings, geopolymer-based hybrid systems offer significant advantages in terms of environmental sustainability, lightweight design, thermal insulation, and fire resistance, making them a strong alternative for the development of advanced construction materials.