Composition optimization of cement-gypsum based silica aerogel with low thermal conductivity insulation mortar

Abstract

Although the thermal conductivity of mortar can be effectively reduced by adding appropriate amount of SiO₂ aerogel to the inorganic cementitious material matrix, the thermal conductivity of thermal insulation mortar is still different from that of organic thermal insulation materials. Therefore, in order to further reduce the thermal conductivity, this paper optimized the composition and formula of cement gypsum silica aerogel thermal insulation mortar. To explore the influence of the amount of polystyrene particles (EPS) (3.9 kg/m³, 5.2 kg/m³, 6.5 kg/m³), the amount of aerogel instead of gypsum (30 wt%, 40 wt%, 50 wt%) and the silica fume ratio of mineral powder (4:1, 1:1, 1:4) on the thermal conductivity, density and compressive strength of mortar. By using X-ray diffraction, scanning electron microscopy, and nuclear magnetic resonance analysis, the mineral composition, microstructure, and pore size distribution of mortar were studied to clarify the correlation between the microstructure of insulation mortar and its insulation performance. The results show that: The influence degree of the above three factors on thermal conductivity and compressive strength of thermal insulation mortar specimens is ranked as follows: silica fume ratio of mineral powder $>$ EPS particle content $>$ aerogel content. The order of influence degree on density is: EPS particle content $>$ silica fume ratio of mineral powder $>$ aerogel content. When the EPS particle content is 5.2 kg/m³, the aerogel content is 30 wt%, and the ratio of mineral powder to silica fume is 4:1, the thermal conductivity of the thermal insulation mortar specimen is 0.032 W/(m∙k), the density is 0.18 g/cm³, and the compressive strength is 0.09 MPa. Changing the composition parameters of the mortar do not alter the mineral composition of the insulation mortar specimens, only the degree of hydration. As the thermal conductivity of mortar decreases, the volume of macropores inside the mortar gradually decreases (decreasing by 13.9 % and 33.2 % respectively), while the volume of transition pores and capillary pores gradually increases (increasing by 6.7 %、29.4 % and 2.6 %、4.6 % respectively).