Effect of recycled fine powder on autoclaved aerated concrete: Gas-foaming, physic-mechanical property and hydration products

Abstract

The production process for cement and quicklime consumes a large amount of energy, and involves chemical reactions that inevitably release CO2. High calcium solid wastes, recycled fine powder (RFP) and carbide slag, are used to replace the cement and quicklime to prepare autoclaved aerated concretes (AAC) for reducing the carbon emissions and energy consumption. The effects of the content and activation by ball milling of recycled fine powder on the rheological, gas foaming, bulk density and compressive strength of AAC were studied in this study. The influence of activated recycled fine powder on the early hydration degree of cement and the reactivity of siliceous materials (fly ash and quartz) under hydrothermal conditions were further investigated by Isothermal Micro-Calorimetry (IMC) and 29Si NMR. The results show that AAC products with good performance can be prepared by using high content of solid waste. With the increase of RFP content, the bulk density of AAC products increases due to the decrease of foaming rate of AAC slurry, but the decrease of tobermorite content has a negative effect on the mechanical property of AAC products. The increasing fineness of recycled fine powder promotes the foaming rate of slurry and produces more amorphous C–S–H gels to form tobermorite under hydrothermal conditions, so finer recycled fine powder can effectively enhance the strength of AAC products.