Abstract: Expanded perlite (EP) synergistically solidifies sludge with cement and other binding agents, simultaneously achieving sludge-water separation and exhibiting pozzolanic activity. To verify the pozzolanic activity effect of EP, the initial approach was to immerse EP in a saturated Ca(OH)₂ solution. The pozzolanic reaction of EP in an alkaline environment was systematically examined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and other test methods. It is found that the main products resulting from the pozzolanic reaction of EP are calcium silicate hydrate (C-S-H) gels, and the porous architecture of EP provides a large specific surface area that promotes the growth of hydration products. The extent of pozzolanic reaction is affected by the duration of immersion. After mixing EP with sludge and using cement for solidification, an investigation would be conducted to study the changes in strength. Combined with Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) test, the microscopic mechanism by which EP enhanced the strength of solidified soil was revealed. The test results show that the pozzolanic reaction process of EP is indirectly reflected in the change of pH in solidified soil. The strength of EP-cement solidified soil derives from both the cementing effects of hydration products and the pozzolanic activity of EP. This reaction enhances frictional interactions between the cement hydration products, sludge, and EP, thus increasing the soil’s resistance to deformation. EP slowly leaches active silica and aluminum under alkaline conditions. These elements subsequently react with Ca2+ to form gel-like substances, such as C-S-H, which enhance the bonding effect among sludge particles, hydration products of cement, and EP.

Key words: expanded perlite, pozzolanic reaction, deformation coefficient, shear strength, pH