PORE STRUCTURAL AND FRACTAL ANALYSIS OF THE INFLUENCE OF FLY ASH AND SILICA FUME ON THE MECHANICAL PROPERTY AND ABRASION RESISTANCE OF CONCRETE

Dam concrete suffers from serious abrasion damages in southwestern China, the abrasion resistance of concrete is therefore one of the most important factors determining the reliability even the safety of the dams. In the present work, the effects of fly and/or silica fume on the mechanical properties, drying shrinkage, as well the cracking and abrasion resistance of concrete were investigated, then the pore structures of concrete added with fly ash and silica fume and the pore surface fractal dimensions (Ds) were determined by the mercury intrusion porosimetry (MIP) method and a fractal model, respectively. Finally, the relationships between the abrasion resistance of concrete and the porosity as well as the Ds were revealed and discussed. The results indicate that silica fume significantly increases the drying shrinkage especially at early age, while the incorporation of fly ash and silica fume together can decrease the early plastic shrinkage-induced cracking risk and the final shrinkage to some degrees. Besides, the utilization of 5wt.% silica fume and 20wt.% fly ash together increases the abrasion resistance and mechanical property by about 4-9% at various ages. In addition, the compressive strength and the abrasion resistance of concrete are linearly correlated with the concrete porosity and the Ds. Both the fly ash and silica fume could decrease the porosity of concrete and increase the Ds, therefore the concrete containing fly ash and silica fume have desired mechanical property and abrasion resistance. Moreover, Ds has a more profound effect on the abrasion resistance of concrete than the concrete porosity. The addition of 5wt.% silica fume and 20wt.% fly ash together is suitable for the concretes used for wearing surfaces in terms of mechanical property, cracking and abrasion resistance.

Automated summary

The addition of silica fume and fly ash can improve the mechanical properties and abrasion resistance of concrete, while reducing the risks of drying shrinkage and cracking. Concrete mixtures with 5wt.% silica fume and 20wt.% fly ash show increased abrasion resistance and mechanical properties at various ages. Both fly ash and silica fume can decrease concrete porosity and increase the pore surface fractal dimensions (Ds), resulting in desired mechanical properties and abrasion resistance.