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This paper presents the experimental results on the effect of nano-CaCO 3 on compressive strength development of mortars and concretes containing high volume fly ash (HVFA). The effect of various nano-CaCO 3 contents such as 1, 2, 3 and 4% (wt.%) as partial replacement of cement on the compressive strength of mortars are evaluated in the first part. The nano-CaCO 3 content which exhibited the highest compressive strength above is used in high volume fly ash mortars and concretes containing 40% and 60% class F fly ash. The results show that among four different nano-CaCO 3 contents, the addition of 1% nano-CaCO 3 increased the compressive strength of mortars and concretes. The addition of 1% nano-CaCO 3 also increases the early age and 28 days compressive strengths of HVFA mortars and concretes. The X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis results also support the above findings.

This paper presents the effects of nano-SiO2 and nano-CaCO3 on the microstructure of High Volume Fly Ash (HVFA) cement paste. The microstructure of HVFA cement paste containing 40% and 60% class F fly ash were evaluated at 28 days using nanoindentation, Xray diffraction (XRD), thermogravimetric (DTA/TGA) and mercury intrusion porosimetry (MIP) analysis. There was a reduction of calcium hydroxide (CH) in XRD analysis of HVFA pastes containing nanoparticles. This observation was also confirmed in the DTA/TGA analysis. The nanoindentation results also showed the evidence of pozzolanic reaction in the HVFA pastes where the addition of 2% nano-SiO2 and 1% nano-CaCO3 increased the volume fractions of high-density and low-density calcium-silicate-hydrate (CSH) gels and confirmed the ability of nanoparticles in reducing the porosity of HVFA pastes, which was in consistent with the MIP analysis. The improved nano and microstructure of HVFA pastes due to the addition of nano-SiO2 and nano-CaCO3 obtained in this study show that high strength and highly durable sustainable concrete can be produced with less repair and maintenance requirements of the concrete structures.