Physico-mechanical and microstructural properties of waste geopolymer powder and lime-added semi-lightweight geopolymer concrete: Efficient machine learning models

This study investigated the mechanical, physical, and microstructural properties of the compos-ites produced from waste geopolymer powder like semi-lightweight concrete. Hydraulic lime (150 kg/m3) was used as CaO source in geopolymer mixtures. Quartz powder was also used as filler to reduce porosity in the mixtures. While the binder ratio in the mixtures varies between 800 and 1200 kg/m3, the Na2SiO3/NaOH ratio is 2.5. The hardened unit weight of the mixtures varies between 1878 and 2041 kg/m3. After heat curing for 12 h at 60 and 80 degrees C, compressive strength of 9.7-26.6 MPa was obtained. Their compressive strength generally decreased, if the mixtures were left in the air for 28 days after heat curing. However, the compressive strength of the samples subjected to water curing for 28 days varies between 10.7 and 35.5 MPa. When the curing temperature increased, the capillary water absorption of the samples decreased. If hy-draulic lime is used at the rate of 15% of the binder amount, the capillary water absorption value has decreased below 5 kg/m2. A machine learning-based model was created for the mixtures produced within the scope of the experimental study. The results showed that decision tree and neural network models led to the best fits. Furthermore, among the factors, the amount of quartz powder is the most critical factor for improving mechanical properties. Despite the unit weight being less than 2000 kg/m3, the compressive strength of more than 25 MPa could be obtained with lime supplementation (%15) in a short time, like 12 h.