Study On The Forming, Characterization And Effection Of Autoclaved Aerated Concrete Pores

The steady advancement of walling material renovation and building energy efficiency has provided a strong stimulus to the growth of autoclaved aerated concrete (AAC). However, common quality problems occurring during the process of application have seriously hampered the popularization of AAC. As AAC is characterized by porosity, the pore structure is the primary factor that affects AAC's performance. The lack of systematic research on ACC's most important characteristic– the pore structure– has hindered the efforts to enhance the control of AAC performance and remedy its common quality problems. Focused on the AAC pore structure, this paper presents an in-depth study of the factors that influence the formation of the AAC pore structure, and examines the patterns of such influence, in terms of raw materials and process parameters. Moreover, modern testing technology and computer image processing technology are used to probe the appearance and formation of AAC pores and structural characteristics. By using interdisciplinary methods on the basis of a full understanding of existing theoretic knowledge, the sources of the related theories are examined, the patterns of AAC's pore structure on its performance is systematically studied, conventional theories are explored and improved, and related models are built.On the basis of analyzing aeration principles of aluminum powder, the formation of air bubbles in AAC, the expansion of slurry, and the stabilization of air bubbles, the raw materials required for production and the objectives of process parameter adjustments are established. This is followed by a study of the influence of the water-slurry ratio, raw materials such as aluminum powder, lime and gypsum, and the mixing ratio on the structure and performance of AAC, as well as a summarization of the patterns of influence and requirements of usage in the production process. Afterwards, the influence of process parameters such as placement temperatures, static stop temperatures and autoclaved curing system on the AAC pore structure and performance is examined, and the static stop environment and the autoclaved curing system are improved.The appearance of pores and the crystalline phase of pore walls inside AAC are described and analyzed using modern testing technologies such as SEM and XRD, thereby obtaining a preliminary understanding of AAC pores. Afterwards, in light of the failure of current pore structure testing methods and approaches to describe the characteristics of AAC, a Matlab-based image analysis method is proposed for describing the characteristics of AAC's pore structure. This method can be used to accurately measure and characterize the porosity, size and distribution of macro and micro pores in AAC. Measurement of pores in Grade 06 AAC using this particular method shows that it has a porosity of 50.4%, and that, pores smaller than 0.5mm account for 23.2% of the total, pores ranging from 0.5mm to 1mm account for 23% of the total, pores ranging from 1mm to 1.5mm account for 18.1% of the total, pores ranging from 1.5mm to 2mm account for 10.1% of the total, and pores larger than 2mm account for 25.6% of the total. Pores in AAC are also classified by appearance and characteristic structure.The relationship between the characteristics of AAC pores and their properties such as water absorption, moisture transfer, heat conduction, and duration is also studied. Specifically, this paper studies the influence of porosity on the water absorption of AAC, explores the influence of porosity on water absorption height and rate by applying the capillary theory, and presents a model for the cumulative amount of water absorption inside AAC and the relative moisture content at any given coordinates. In addition, this paper examines the influence of porosity on the moisture absorption and moisture liberation of AAC, and expounds the moisture transfer rate and isothermal moisture absorption coefficient of AAC under the condition of gas-liquid coexistence. Moreover, this paper investigates the influence of porosity and moisture content on the heat conductivity coefficient of AAC, and presents a model for forecasting the heat conductivity coefficient of AAC on the basis of mixed models. Furthermore, this paper provides an in-depth analysis of the dry shrinkage mechanism of AAC under capillary effects, presents a dry shrinkage stress model and a strain model on the basis of a modified theory of capillary tension, and uses the dry shrinkage mechanism to account for the characteristics of the dry shrinkage of AAC. This paper also studies the influence of porosity on the frost resistance and carbonization performance of AAC.