Experimental and Modeling Investigations on the Water Sorption Behaviors of Autoclaved Aerated Concrete

Study on the Hydrophobic Modification Mechanism of Stearic Acid on the Surface of Coal Gasification Fly Ash

In this study, the hydrophobic modification of coal gasification fly ash (FA) was investigated given the adverse effects of surface hydrophilic structures on the material field. The surface of FA was modified using stearic acid (SA), which successfully altered its hydrophilic structure. When the contact angle of S-FA increased from 23.4° to 127.2°, the activation index increased from 0 to 0.98, the oil absorption decreased from 0.564 g/g to 0.510 g/g, and the BET-specific surface area decreased from 13.973 m2/g to 3.218 m2/g. The failure temperature of SA on the surface of S-FA was 210 °C. The adsorption mechanism of FA was analyzed using density functional theory (DFT) and molecular dynamics (MD). The adsorption of water molecules by FA involved both chemical and physical adsorption, with active adsorption sites for Al, Fe, and Si. The adsorbed water molecules on the surface of FA formed hydrogen bonds with a bond length of 1.5-2.5 Å, leading to agglomeration. In addition, the long alkyl chain in SA mainly relied on the central carbon atom in the (-CH3) structure to obtain electrons in different directions from the H atoms in space, increasing the Coulomb repulsion with the O atoms in the water molecule and thereby achieving the hydrophobic effect. In the temperature range of 298 K to 358 K, the combination of FA and SA became stronger as the temperature increased.

Influence of Recipe Factors on the Structure and Properties of Non-Autoclaved Aerated Concrete of Increased Strength

At present, the load-bearing enclosing structures of buildings and structures are designed and built considering the increasing requirements for energy efficiency and energy saving of such structures. This is due to the need for a thrifty attitude to the energy consumed and the need to strive for the greening of construction and increase the energy efficiency of buildings and structures. In this regard, one of the most effective and proven building materials is cellular concrete. The purpose of this study was to study the influence of some prescription factors on the structure formation and properties of non-autoclaved aerated concrete with improved characteristics. Standard test methods were used, as well as SEM analysis of the structure of aerated concrete. Non-autoclaved aerated concrete with the replacement of part of the cement with microsilica in an amount from 4% to 16% MS showed higher strength characteristics compared to aerated concrete, where part of the cement was replaced by the addition of granulated blast-furnace slag and a complex additive. The maximum value of compressive strength was recorded for aerated concrete with 16% MS addition. The largest increase in the coefficients of constructive quality was observed in compositions of aerated concrete with the addition of silica fume from 11% to 46% compared with the control composition. The addition of microsilica makes it possible to achieve an improvement in the thermal conductivity characteristics of non-autoclaved aerated concrete (up to 10%). Replacing part of the cement with slag and complex additives does not have a significant effect on thermal conductivity. The obtained dependencies were confirmed by the analysis of the structure formation of the studied aerated concrete at the micro level. An improvement in the microstructure of aerated concrete with the addition of microsilica in comparison with samples of the control composition has been proven.

Mathematical Modeling and Experimental Substantiation of the Gas Release Process in the Production of Non-Autoclaved Aerated Concrete

The widespread use of aerated concrete in construction has led to the emergence of many types and compositions. However, additional research should fill theoretical gaps in the phenomenon of gas release during the formation of the structure of aerated concrete. Based on theoretical analysis and experimental studies, the article proposes a mathematical model of the swelling process based on the physicochemical laws of convection and molecular diffusion of hydrogen from a mixture and the conditions of swelling, precipitation, and stabilization of the mixture. An improved method for the manufacture of aerated concrete is proposed, which consists of introducing cement pre-hydrated for 20–30 min into the composition of the aerated concrete mixture and providing improved gas-holding capacity and increased swelling of the mixture, reducing the average density of aerated concrete up to 29% and improving heat-shielding properties up to 31%. At the same time, the small dynamics of a decrease in the strength properties of aerated concrete were observed, which is confirmed by an increased structural quality factor (CSQ) of up to 13%. As a result, aerated concrete has been obtained that meets the requirements of environmental friendliness and has improved mechanical and physical characteristics. Economic efficiency is to reduce the cost of production of aerated concrete and construction in general by about 15%.