Experimental Investigation and Modeling of the Sulfur Dioxide Abatement of Photocatalytic Mortar Containing Construction Wastes Pre-Treated by Nano TiO2

Abstract

A photocatalytic mortar containing recycled clay brick powder (RCBP), recycled fine aggregate (RFA), recycled glass (RG), and nanoscale titanium dioxide (NT) was fabricated to degrade low-concentration sulfur dioxide. Instead of intermixing or dip-coating, NT was firstly loaded onto the surface of carriers (RFA and RG) using a soaking method to prepare composite photocatalysts (CPs) denoted as NT@RFA and NT@RG. The prepared CPs can both take full advantage of the intrinsic characteristics of construction wastes, namely, the high porosity and alkalinity of RFA and the light-transmitting property of RG, and can significantly reduce the cost of using NT. RG in high dosage potentially triggers alkali–silica reaction (ASR) in cement-based materials, which affects the durability of the prepared mortar. RCBP, another typical construction waste sourced from crushed clay bricks, was proven to be a pozzolan similar to grade II fly ash. The combined use of RCBP and RG in photocatalytic mortar is expected to simultaneously improve durable performance and further raise the upper content limit of construction wastes. Results exhibit that 70% cement plus 30% RCBP as cementitious material can sufficiently control ASR to an acceptable level. The filling effect and the pozzolanic reaction caused by RCBP result in a decline in porosity and lessened alkalinity, which decreases sulfur dioxide removal. The paper uses both response surface methodology (RSM) and an artificial neural network (ANN) to model photocatalytic efficiency with various initial concentrations and flow rates and finds the ANN to have a better fitting and prediction performance.