Design of nano-modified cementitious composites for bridge deck application

Unlike conventional concrete, the material design process for Engineered Cementitious Composites (ECC) involves micromechanics-based design theory, paving the way for the use of high volumes of fly ash (HVFA) as a major component. Using high volumes of fly ash (up to 85% weight fraction of cement) in ECC mixtures enables improved tensile ductility (approximately a 3% increase in long-term tensile strain) with reduced crack widths, although it also leads to significantly reduced early-age compressive and tensile strength and chloride ion resistance. However, nano-mineral additives are known to improve mechanical strength and durability of HVFA systems. In this sense, within the scope of present thesis emphasis was firstly placed on the utilization of different nano-mineral additives in HVFA ECC production to tailor the basic mechanical properties of the mixtures. Secondly, focus was placed on the effects of different Class-F fly ash/cement ratios on hydration properties and microstructural characteristics, transport and mechanical properties of ECC mixtures designed with different mineral additives. Experimental results confirm that nano-additives could significantly improve both flexural strength and ductility of ECC, especially at early ages. Although different optimum levels can be selected to favor various ECC properties; optimum weight fraction of FA (fly ash) is dependent on the mechanism of nano-modification (i.e. type of modifier).