The Study On Utilization Of Portland Cement For Preparation Of Aerated Concrete

The economic development of China is undergoing the transformation from extensive mode to intensive one. The purpose of this stage is to boot GDP with decreasing energy consumption of unit output, namely to improve the efficiency of energy. There is almost 33% of energy consumption to be used in building operation process. Thus, to decrease the energy demand and improve energy efficiency, it is necessary to optimize energy consumption of buildings, which consequently promotes the development of building efficiency and innovation of wall materials. As for the latter, the usage of aerated concrete can effectively increase the green degree of buildings. However, the existing problems in production and utilization impeded its promotion and application. To solve the problem of long-cycle production and high energy consumption of autoclaved aerated concrete, portland cement was used to prepare non-autoclaved aerated concrete in this study. The effect of raw materials on foaming process, compressive strength, as well as hygric and thermal properties of some optimized proportion were specifically investigated. The main conclusions in this paper were summarized as the following:Increasing dosage of Al and NaOH would contribute to rising expansion rate of paste in early stage. The total volume of foaming was increased with dosage and fineness of Al, but the specimens prepared with finer Al had more water content and worse water absorption. Mixing with excessive NaOH not only decreased the expansion increment of cement paste, but also deteriorated compressive strength development in the late stage.The time length of foaming process can be prolonged by increasing w/c ratio or blending proper amount of gypsum. The addition of gypsum significantly improved the effect of high alkalinity on cement hydration by retarding its hydration rate in early age, therefore it also increased the mechanical properties of high-alkali cement paste. Nonetheless, the excessive dosage of gypsum would dramatically retard the foaming process, which in turn altered the pore size distribution of surface layer of hardened paste, resulting in worse water absorption.Blending with fly ash could contribute to foaming process but deteriorate the volume stability and strength development of cement paste. However, the early curing with high temperature could improve the dilute effect. Mixing with silica fume or limestone powder, the expansion rate of cement paste was decreased, but the compressive strength of hardened paste increased with silica fume content.With the given concentration of sodium dodecyl sulfonate(SDS), the foaming rate of cement paste was increased, but it resulted in remarkable shrinkage in the late stage. Although the foaming rate of paste mixed with calcium stearate(CS) was lower than the one with SDS, the total foaming volume was greater. The use of retarder such as sucrose or citric acid caused no retard effect, but acceleration of setting instead. Cement paste with sucrose even set abnormally.The addition of proper amount of PVA fiber not only accelerated the foaming rate, but also increased compressive strength and decreased drying shrinkage of aerated concrete. With content of 0.2% fiber, the drying shrinkage of the specimen decreased by 40%. Nevertheless, the addition of fiber in aerated concrete would increase the sensitivity of drying shrinkage in the early period during water loss process.