Experimental study reveals thermal degradation and altered pore fractals in fly ash-blended cementitious composites, indicating reduced durability in nuclear storage environments.
Key Points
To determine how sustained medium-to-high thermal exposure influences the pore-structure evolution, mechanical strength, and carbonation resistance of cementitious composites blended with fly ash.
Prepared cementitious composites containing 0%, 20%, and 40% fly ash replacement, cured them at 23°C for 14 days, and exposed them to temperatures of 80°C, 100°C, and 120°C for 28 days.
Evaluated pore-structure fractal dimensions using mercury intrusion porosimetry for mesopores (<100 nm) and capillary pores (≥100 nm), and analyzed hydration phases using X-ray diffraction and thermogravimetric analysis.
Thermal exposure simplified mesopore structures while increasing capillary pore complexity in 0% and 20% fly ash specimens, accompanied by ettringite and C–S–H decomposition that reduced chemically bound water even at 80°C.
Elevated temperatures initially enhanced compressive strength but led to reductions over prolonged exposure and increased carbonation depth, with degradation most pronounced at higher fly ash replacement rates.
Compressive strength correlated closely with capillary pore fractal dimensions, while carbonation depth depended primarily on mesopore architecture, though both correlations diminished at 40% fly ash replacement due to limited hydrate formation.