Abstract
To alleviate the heavy burden on landfilling, construction and demolition wastes (C&DWs) are recycled and reused as aggregates in cementitious materials. However, the inherent characteristics of recycled fine aggregates (RFA), such as the high crushing index and high-water absorption, magnify the reusing difficulty. Nevertheless, attributing to the high porosity and high level of calcium hydroxides existing in the old mortar, RFA is featured with a high specific surface area and a high alkalinity. These features are useful to augment the total photo-degradation of SO2 by nano-TiO2 (NT) intermixed mortar, leading RFA to be an excellent potential carrier to load nano-TiO2 and prepare the composite photocatalyst. Hence, this study proposed to load NT onto the surface of RFAs and river sands (RSs) (the control) by the soaking method, preparing composite photocatalysts denoted as NT@RFA and NT@RS, respectively. The prepared composite photocatalysts were then utilized as sands in photocatalytic mortar to evaluate for SO2 degradation. Experiments identified a 50% higher amount of NT was loaded onto the surface of FRA relative to the control. This higher loading amount plus higher alkalinity ultimately translated into a higher photocatalytic activity. In addition, the mortar containing NT@RFA exhibited 46.3% higher physiochemical absorption and 23.9% higher photocatalytic activity than that containing NT@RS. In addition, the durability, embodied by the reuse and anti-abrasive properties, of NT@RFA exceeded that of NT@RS. The overall findings reveal that the NT@RFA not only garners beneficial effect from the high porosity but also generates positive effect from the high alkalinity. Though a number of studies deal with building materials with NT, this study is the first to load NT onto RFA and prepare composite photocatalysts which were then used as fine aggregates in building materials. Consequently, this study proves the potential high-added-value reusability of RFA in green construction materials and provides a low-cost, high-efficiency approach to degrade atmospheric SO2.
Highlights
Construction and demolition wastes (C&DWs) are considered globally important because billions of tons are generated annually [1,2]
A hybrid composite based on T-zinc oxide (ZnO) and carbon nano-onion (CNO) is prepared based on a facile one-step process that has an easy accessibility of the characteristic features of both tetrapod-shaped ZnO (T-ZnO) and CNO
The durability is mainly embodied by the abrasion resistance of the mortar, as determined by the retained photocatalytic activity after mechanical abrasion
Summary
Construction and demolition wastes (C&DWs) are considered globally important because billions of tons are generated annually [1,2]. Previous studies revealed that high alkalinity benefits the photocatalytic degradation of acid pollutant gases such as NOx [15,16] and SO2 [17] because acidic gases are attracted and adsorbed by the alkaline constituents, namely portlandites, of hydrated cement paste. In our previous research [20], CPs prepared using recycled clay brick sands and NT showed excellent NOx and methyl orange removal with the NT concentration of 1 g NT per 100 mL water Their improved performance relative to river sand-based CPs indicated the benefits of the high porosity. The research combined RFA and NT into a composite photocatalyst (NT@RFA) and described a theoretical functionalization of a common construction materials (mortar) incorporating with NT@RFA as a photocatalytic mortar for atmospheric pollution degradation. The study contributes the characterization of NT-functionalized RFA-based mortar as a photocatalytic material for atmospheric SO2 degradation
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