Production of high-performance cementless foam composites: gypsum-based and hemp fibre reinforced green systems

This study investigated the physical, mechanical, durability and microstructural properties of gypsum-based foam composite reinforced with hemp fiber (HF). A gypsum-based foam composite was produced using foam contents of 20, 50, and 80 kg/m³, and hemp fiber (HF) concentrations of 0%, 1%, and 2%. Additionally, pumice aggregates in the range of 0–4 mm were used in the mixture to support the lightweight foam concrete employed in the study. The demolded specimens were stored at a temperature of 30 °C and a relative humidity of 65%. The flow diameters of the mixtures, which indicate the workability of the mixtures from the fresh state properties, vary between 212 and 288 mm. Fresh unit weights vary between 862 and 1269 kg/m3, while dry unit weights vary between 723 and 1203 kg/m3. The mixtures’ apparent porosity and water absorption values increased as the foam volume increased; the highest apparent porosity was 57.8%, and the highest water absorption value was 96.14% at a foam volume of 80 kg/m³. In terms of mechanical properties, the strength decreased as the foam volume increased. The highest compressive strength of 3.93 MPa was obtained with a foam volume of 20 kg/m³ and 1% HF, while the highest flexural strength of 0.43 MPa was obtained with the same foam volume and 2% HF. The highest compressive strength of 1.34 MPa was achieved even at a foam volume of 80 kg/m³, which exhibited the lowest mechanical properties. In addition, to determine the durability properties of the blends, they were exposed to high temperatures of 250, 500, and 750℃, and weight losses, UPV changes, and mechanical property changes were investigated. After 750℃ high temperature, mixtures with 20 kg/m3 foam content showed the highest mechanical properties, while mixtures with 80 kg/m3 foam content showed a compressive strength of 0.32 MPa. The depths of capillary water treatment of the studied mixtures varied between 14.79 and 19.17 kg/m2. As a result, this study determined that gypsum can be used as a binder in non-bearing foam concrete, with a foam content of 20 kg/m³ and a 1% HF addition.