Experimental investigation of photocatalytic effects of concrete in air purification adopting entire concrete waste reuse model

This research investigated the capacities of recycled aggregate concrete adopting entire concrete waste reuse model in degrading NO2. Two major issues within environmental sustainability were addressed: concrete waste reuse rate and mitigation of hazards substances in the polluted air. The study consisted of two stages: identification of proper replacement rates of recycled concrete wastes in new concrete mixture design, and the evaluation of photocatalytic performance of recycled aggregate concrete in degrading NO2. It was found that replacement rates up to 3%, 30%, and 50% for recycled power, recycled fine aggregate, and recycled coarse aggregate respectively could be applied in concrete mixture design without deteriorating concrete strength. Recycled aggregates contained both positive attributes (“internal curing”) and negative effects (e.g., lower hardness) to concrete properties. It was found that 30%-50% of natural coarse aggregate replaced by recycled coarse aggregates coated with TiO2 would significantly improve the photocatalytic performance of concrete measured by degradation rate of NO2. Micro-structures of recycled aggregates observed under microscope indicated that soaking recycled aggregates in TiO2 solution resulted in whiskers that filled the porosity within recycled aggregates which enhanced concrete strength.