Investigation into the roles of camellia seed residue powder as a natural foaming agent and a green retarder for α-hemihydrate gypsum

Abstract

The feasibility of natural plant waste, camellia seed residue powder (CSRP), as an admixture for gypsum is investigate in this study. CSRP can function as a foaming agent when incorporated into α-hemihydrate gypsum (α-HH), and exhibits remarkable retarding effects during the hydration of α-HH. Experimental results indicate that CSRP-generated foam possesses high abundance and stability, particularly at a concentration of 24 % CSRP, with foam volume and half-life reaching up to 1560 mL and 1050 min, respectively. This superior performance is attributed primarily to the presence of the surfactant tea saponin in CSRP. Tea saponin molecules densely accumulate at the gas-liquid interface, significantly increasing surface density and forming cohesive interfacial films, and CSRP particles enhance bubble wall rigidity through physical reinforcement while their hydrophilicity maintains hydration shells around bubbles, synergistically prolonging foam lifetime. For CSRP-containing gypsum slurry, the fluidity and retarding time were tested and their results show that CSRP can reduce the fluidity and significantly prolong the setting time. At 2.5 % CSRP content, the final setting time of gypsum slurry is significantly extended to 197 min, meaning 183 min longer than that of blank gypsum. The role of CSRP in α-HH hydration was investigated through adsorption, conductivity, hydration heat, and XRD tests. The active organic components in CSRP, such as polyphenols, polysaccharides, and tea saponin, significantly delay the hydration process by complexing with calcium ions and forming an adsorption layer on the gypsum surface. Additionally, the foams generated by CSRP play a similar role by hindering the accumulation and growth of dihydrate nuclei. SEM images reveal that the incorporation of CSRP resulted in shorter and smaller dihydrate crystals in hardened gypsum, thereby corroborating the proposed mechanism. Furthermore, when the amount of CSRP is more than 1.2 %, gypsum products exhibit the porous characteristics as a lightweight material. The dry density of gypsum containing 1.6 % CSRP can be as low as 636 kg/m³, and the thermal conductivity is 0.2721 W/m·K, which is 60.27 % and 78.59 % lower than blank gypsum, respectively. In this work, CSRP, as an environmentally friendly admixture, can serve directly as both a foaming agent and retarder in gypsum without the need for additional treatment. The result also suggests an innovative recycling approach for solid plant waste CSRP.