Influencing factors of mechanical and thermal conductivity of foamed phosphogypsum-based composite cementitious materials

In this study, the phosphogypsum-based cementitious materials were modified by adding raw lime, fly ash and cement into hemihydrate phosphogypsum. Then the modified phosphogypsum-based cementitious materials were foamed by different foaming methods. Finally, the synergistic strengthening effect of mechanical and thermal insulation properties of foamed phosphogypsum-based cementitious materials was studied. The results show that when the content of phosphogypsum is 60 %, the water-binder ratio is 0.300, the content of fly ash is 30 %, and the content of quicklime is 8 %, the mechanical and thermal insulation properties of phosphogypsum-based cementitious materials are the best. Although the porosity of physical foaming specimens is lower than that of chemical foaming specimens, the mechanical and thermal insulation properties of physical foaming specimens are better than those of chemical foaming specimens. The larger the pore diameter and the more connected the pore, the more serious the stress concentration of the specimen under compression, resulting in the decrease of the compressive strength. In addition, the porosity increases with the increase of foaming agent content, but the thermal conductivity does not decrease significantly with the increase of porosity. The reason is that with the increase of foaming agent content, the pore diameter also increases, which reduces the thermal resistance of the specimen and affects the further reduction of the thermal conductivity. This study can provide a theoretical basis for the practical engineering application of phosphogypsum as thermal insulation building materials.