Effects of Calcium Silicate-Containing Civil Construction Waste on Soil N2O Emissions

Abstract

Currently, there is a trend to utilize calcium silicate (CaSiO₃) containing civil construction waste as a soil amendment or conditioner in Japan as well as in European countries. Autoclaved lightweight Aerated Concrete (AAC) is a CaSiO₃ containing porous material made from industrial waste of civil construction. AAC is utilized as a soil amendment that can influence terrestrial carbon dioxide (CO₂) emissions. Still, no evidence exists regarding its impact on the emission of nitrous oxide (N₂O), which has a higher global warming potential than CO₂. This study investigated the impact of AAC (Inenica, Clion Co., Ltd, Japan) on N₂O emissions from paddy soil under both compacted and non-compacted conditions, at 60% and 100% Water-Holding Capacity (WHC). Samples (24) were incubated in glass vials (25°C) for 21 days. During the incubation, the vials were covered with a polyethylene film (0.02 mm thickness) to ensure minimal evaporation while maintaining air exchange. Emissions of N₂O were measured at 0 (incubation starting day), 1,3,7,14 and, 21 days using gas chromatography during the incubation period. All measurements were performed in triplicate. In addition, a separate set of samples was incubated under the same conditions for NH₄⁺-N, and NO₃^–-N measurements. Results revealed that AAC significantly (p<0.05) lowered N₂O emission during the whole period of incubation. The cumulative N₂O emissions of samples with AAC were approximately 43% and 51% lower, respectively, in compacted and non-compacted soils, compared with samples without AAC at 60% WHC. At 100% WHC, the cumulative N₂O emissions of samples with AAC in compacted and non-compacted soils respectively, showed 52% and 67% decline (significant at p<0.05), compared with samples without AAC. When compacted, the N₂O was significantly high, showing the influence of soil physical conditions, and N₂O emissions were significantly lower at higher WHC (100%).  AAC suppressed N₂O emissions from soil under both compaction and WHC levels. Results confirm that AAC supports suppressing terrestrial N₂O emission, indicating its potential as a sustainable soil amendment that enhances climate change resilience.

Keywords: Autoclaved lightweight aerated concrete, Calcium silicate, Greenhouse gases, Nitrous oxide