Thermal stability, pore structure and moisture adsorption property of phosphate acid-activated metakaolin geopolymer

• Studied the thermostability of phosphate activated metakaolin geopolymer (PMG). • The pore structure distribution of PMG was investigated. • Revealed the water vapour adsorption and desorption properties of PMG. Phosphate acid-activated metakaolin geopolymer (PMG) was successfully prepared using a two-step curing method and the thermal stability, pore structure and moisture adsorption property of the obtained PMG were studied by techniques of thermogravimetry (TG), mercury intrusion porosimetry (MIP) and dynamic vapor sorption meter (DVS). TG result shows that thermal decomposition of the PMG majorly occurs in the range of 220−550 ℃, much higher than that of the common binder of C-S-H, due to the removal of the chemically bonded water and the water content of the PMG is around 16%. MIP measurement indicates that the porosity of the PMG is 13.6% and the most probable pore size is about 100 nm. DVS results shows that the water adsorption amount of PMG powder is about 0.132 ml/g, which is in good agreement with the total porosity measured by MIP test.