Relationship between fractal characteristics of pore-structure and thermal properties of FA-based AAM under different curing conditions

Abstract

The microstructure of hardened alkali-activated materials (AAM) plays an essential role in determining the mechanical properties at elevated temperatures, particularly the pore structure. Mercury Intrusion Porosimeter (MIP) was employed to study the fractal characteristics of the pore structure of samples under standard and sealed curing conditions, which includes pore size distribution, shape, surface area, and tortuosity of AAM pastes after exposure to high temperatures. Additionally, the compressive strength of AAMs at elevated temperatures was determined. Comparing the samples under standard curing conditions, sealed curing conditions significantly improved the 28-day compressive strength (43.6 MPa) and residual compressive strength (achieving 60.2% of the 28-day strength) when exposed to 1000 °C. Based on research, the fractal characteristics of pore structures have a significant effect on the thermal properties of samples at high temperatures. Differences in thermal properties may be attributable to resistance caused by pore structures with heterogeneity and complexity, as well as the shape of the pores, which have small pore throats and large pore capacities. Under standard curing conditions, the samples exhibited a pore structure characterized by a reduced neck diameter, larger cavity size, a coarser pore surface, and decreased connectivity. As a result, the 28-day samples under standard curing conditions experienced significantly elevated pore pressure.