Pore structure of geopolymer materials and its correlations to engineering properties: A review

• Multiscale pore structures in geopolymers and their differences compared with ordinary Portland cement are revealed. • The major influence factors on geopolymer pore structures and the basic rules to control the pore structure are summarized. • The relationship between the pore structure and engineering properties of geopolymer are established. The pore structure plays an important role in determining the performance of solid materials. This paper reviews the studies about the pore structure of geopolymers, a rising kind of eco-friendly low-calcium-content cementitious material. Geopolymers usually show a four-leveled multiscale pore structure. The abundance in nano pores is the key feature of the pore structure of geopolymers comparing with that of ordinary Portland cement. Factors, such as raw materials, alkali activators, additional materials and etc. could alter the pore structure of geopolymers and thus have effects on the performance of these materials. A variety of macro properties, such as compressive strength, thermal conductivity, permeability and etc., have close relationship with the pore structure of geopolymers. General rules to optimize the pore structure and performance of geopolymers are figured out in this review, which would help the rational design and application of geopolymers. Further research trend is also discussed.