Effect of silica fume with various fineness levels on the strength degradation of concrete after steam curing

Steam curing is widely employed to produce pre-cast concrete components. However, the strength degradation of steam cured concrete after high temperature curing poses significant risks to structural safety and reliability. Adding silica fume (SF) effectively mitigates strength degradation, with finer SF particles demonstrating a more significant improvement in concrete strength. To understand the underlying mechanism, the experimental measurements on deformation, pore structure evolution, and reaction processes were conducted to investigate the microstructural changes associated with strength degradation. The experimental findings reveal that a combination of thermal damage and delayed ettringite formation (DEF) was the primary cause of strength degradation in steam cured concrete. This positive effect of SF was attributed to its pozzolanic reaction, which refined the microstructure, reduced the brittleness, and finally improved the thermal damage resistance. In addition, the pozzolanic reaction reduced the DEF by reducing available Ca2 + and Al3+ ions in the cement systems. Notably, using SF with high fineness prevented thermal damage and DEF and subsequent strength degradation through extensive pozzolanic reaction.