Polyurethane-modified foamed geopolymers: mechanical properties, pore structure, and thermal conductivity
摘要
Ultra-light foamed geopolymers face problems of low strength and pore wall cracking. Polyurethane dispersion was used to reinforce foamed geopolymer, and its effects on strength, pore structure, apparent density as well as thermal conductivity were investigated. GGBFS, FA, water glass, sodium hydroxide, hydrogen peroxide and calcium stearate were used to prepare foamed geopolymer. Polyurethane generated by polyether polyol and isocyanate was added to fresh geopolymer paste in order to produce a polyurethane-modified foamed geopolymer. The mechanical reinforcement imparted by polyurethane on geopolymer strength and its influence on hydration kinetics were evaluated using Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and so on. The effects of polyurethane on strength, apparent density, thermal conductivity, and pore structure of foamed geopolymer were investigated by servo press, Nano Measurer, Image Pro Plus, Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM&EDS) along with other characterization technique. Despite the absence of significant enhancements in compressive strength or detectable crystalline phase alterations, the incorporation of polyurethane yielded substantial improvements in flexural performance. Specifically, flexural strength increased by 19.6% at 3 days and 21.7% at 28 days. Concurrently, microstructural refinement was evidenced by a reduction in pore concentration distribution peak from 2798 to 765 nm, indicating pore size distribution refinement. Furthermore, FT-IR analysis revealed a non-monotonic trend in the Si–O–T(Al/Si) asymmetric stretching vibration band intensity near 971.4 cm−1 (associated with N/C–A–S–H gels), exhibiting an initial increase followed by a reduction with escalating polyurethane content. When polyurethane was applied to foamed geopolymer with different dosage of hydrogen peroxide, the flexural strength and compressive strength were significantly improved by 35.3–60.0% and 27.9–128.6%, respectively; the pore structure was refined and average pore diameter was decreased from 2.4 to 1.2 mm; holes and cracks on the pore walls were reduced obviously; those structural improvements lead to a 6.9% reduction in thermal conductivity. This research contributes a method to strengthen pore walls of foamed geopolymer and makes foamed geopolymers lighter, stronger, and relatively lower thermally conductivity, thereby enhancing their potential for building engineering applications.