Polypropylene fiber reinforced alkali-activated ultra-light foam insulation material: Performance study and mechanism analysis

Reducing building energy consumption has become an important measure to achieve sustainable development in urban construction worldwide, and installing insulation materials on building envelopes has been proven to be an effective means of reducing building energy consumption. This study developed a high toughness ultra-light foam insulation material (FIM) by combining polypropylene (PP) fiber, expanded polystyrene (EPS) lightweight aggregates, and alkali-activated multiple cementitious materials. Its purpose was to reduce building energy consumption while promoting the recycling of solid waste. The effects of PP fiber length and content on the dry density, flexural strength, compressive strength, thermal conductivity, and volumetric water absorption of FIM were studied, and the improvement mechanism of PP fiber was revealed. Scanning electron microscopy was used to observe the microscopic morphology of FIM. It was exciting to note that all developed FIM had a dry density of less than 150 kg/m³, and a minimum thermal conductivity of only 0.0423 W/(m·K). PP fiber with a length of 9 mm played a key role in improving the flexural performance of FIM, which increased by 21.05% compared to the control group. PP fiber with a length of 3 mm showed the most significant improvement in the thermal conductivity of FIM, which was 13.5% lower than the control group. A response surface methodology (RSM) was used to propose a prediction model for five performance indicators of FIM, with PP fiber length and content as variables. The results showed a high correlation between the predicted value and test value, which verifies the validity of the prediction models. The proposed models can provide important reference basis for mix proportion design.