Fly ash influence on the properties of high performance concrete

Bulk density, matrix density, open porosity, pore size distribution, bending and compressive strength, effective fracture toughness, fracture energy, effective toughness, freeze-thaw resistance, resistance against de-icing salts, corrosion resistance in various environments, carbonation, water vapor diffusion coefficient, water absorption coefficient, apparent moisture diffusivity, hygric strain, thermal conductivity, specific heat capacity and chloride adsorption isotherms of high-performance fly ash concrete (FC) are measured and compared with reference Portland cement concrete (PC). Experimental results show that 10% of fly ash as Portland cement replacement can be considered as a suitable amount from the point of view of preserving the high-performance properties of this concrete. At this fly ash replacement level, basic physical properties, water transport properties and heat transport are virtually unaltered. Compressive and bending strength after 28 days is only slightly lower. Fracture mechanical parameters of FC are after 28 days worse but after 90 days effective fracture toughness is 10% higher and effective toughness even 60% higher as compared with PC. The carbonation extent is for FC much lower, chlorid binding capacity is up to 10% higher. Durability of concrete FC is even for the low fly ash addition of 10% quite satisfactory. It frost resistance and resistance against de-icing salts are worse than in the case of PC but still safety meet the required criteria Corrosion resistance of FC is for most studied environments better than for PC; in particular the resistance against HCl is found to be quite superior.