Effect of nano-CaCO3 slurry on the mechanical properties and micro-structure of concrete with and without fly ash

The effect of nano-CaCO3 slurry on the mechanical properties and microstructure of concrete with and without fly ash was studied in this paper. Experimental results showed that nano-CaCO3 slurry was helpful to increase the mechanical strength of concrete with and without fly ash at early ages due to the acceleration of cement hydration from seeding effect and the more compact microstructure of cement paste from nano-filling. However, the efficacy of nano-CaCO3 slurry on the concrete without fly ash was quite limited at the late ages just like other nano-materials. This may well affect the application of nano-materials in concrete. On the other hand, nano-CaCO3 slurry was still helpful to enhance the mechanical strength of concrete with fly ash at late ages. Furthermore, the enhancement degree of mechanical strength of concrete with fly ash at 56 days increased with the increasing content of fly ash when 2% fly ash was substituted by nano-CaCO3. The results of X-Ray diffraction analysis and SEM observation indicated that the pozzolanic reaction degree of fly ash could be accelerated by nano-CaCO3 slurry at late ages. Therefore, a feasible technique for the usage of composite nano-materials in concrete may well be provided by using nano-CaCO3 with fly ash due to the acceleration hydration of cement at early ages and that of fly ash at late ages.