The effect of pore behavior and gel structure on the mechanical property at different initial water content

Abstract

This study synthesized geopolymers with different content of water from 34.35% (10 mol) to 43.97% (15 mol), and the effect of initial water content in pore behavior and gel structure of geopolymer was investigated. The microstructure of geopolymer was characterized through MIP analysis, SEM, TGA-MS, XRD, FTIR and NMR measurement. As the water content in synthesis increasing, the compressive strength of geopolymer significantly decreased from 40.3 MPa to 10.2 MPa. The high initial water content results in a large increase in the diameter of pore in geopolymer, which lead to the transformation of harmless pores to harmful pores. In addition, excess water will also introduce more water to participate in the geopolymer network, so that the content of Q3 structures increased 2.94% from 19.24%, which leads to a decrease in the degree of polymerization. Both of pore behavior and gel structure changes reduce the mechanical property of geopolymers. When the initial water content is low (10–11 mol), the change of geopolymer gel structure has a greater impact on the strength of the geopolymer, while when it is high (12–15 mol), the compressive strength is dominated by the pore structure.