Comprehensive environmental evaluation of photocatalytic eco-blocks produced with recycled materials

Abstract

The use of photocatalysts, especially titanium dioxide (TiO2) in the construction field, has received increasing attention in recent years because such photocatalytic functional products can display antifogging, self-cleaning, and air-purifying properties. By using recycled materials (locally generated construction and demolition waste and waste glass) and with the incorporation of a small quantity of nano-TiO2, the authors’ research team has successfully developed concrete paving eco-blocks with good air-purifying functions, in particular nitrogen oxide (NOx) removal. In this chapter, comprehensive evaluations of NOx emission, associated health impacts, and greenhouse gases (GHGs) emission are described for producing concrete paving blocks through the life cycle assessment technique by considering a “cradle-to-site” system boundary. The extension to include the NOx removal function during their service life is also made. The eco-blocks were prepared by two TiO2 adding methods, namely an intermixed (IM) method and a spray-coating (SP) method, to obtain different NOx removal abilities. The results demonstrated that eco-blocks prepared by the IM and SP methods had about 17% and 21% lower life cycle emissions of NOx, respectively, when compared with that of the conventional blocks produced with natural materials and without TiO2. By considering the TiO2-induced NOx degradation rate during the service life of the blocks, it is estimated that about 6 years and 11 years would be required for the eco-blocks prepared with IM and SP methods, respectively, to offset the total NOx emissions for producing the eco-blocks. Incorporation of TiO2 in the eco-blocks induced 6%–17% higher GHGs emission during the manufacturing and transportation stage. However, the net GHGs emission of the TiO2-containing eco-blocks was significantly lower than that of the conventional paving blocks due to the use of recycled materials.