With the premise of investigating mechanical properties, the thermal conductivity of autoclaved aerated concrete (AAC) is a key index of self-insulation block walls for building energy conservation. This study focused on the effect of pore structures on the mechanical performance and thermal conductivity of AAC with the comparison of AAC base materials. Different kinds of AAC and their base materials were prepared and experimentally investigated. While maintaining a consistent mix proportion of the AAC base material, the pore structure of AAC was changed by the dosage of aluminum power/paste, foam stabilizer, and varying the stirring time of aluminum paste. The steam curing systems of AAC and the base material were determined based on SEM (Scanning Electronic Microscopy) and XRD (X-ray Diffraction) tests. With almost the same apparent density, the pore size decreased with the increasing content of foam stabilizer, and the mixing time of aluminum paste and foam stabilizer has a great influence on pore size. The thermal conductivity test and compressive test results indicated that that pore size had an effect on the thermal conductivity, but it had little effect on the compressive strength, and the thermal conductivity of sand aeration AAC was 8.3% higher than that of fly ash aeration AAC; the compressive strength was 10.4% higher, too. With almost the same apparent density, the regression mathematical model indicates that the thermal conductivity of AAC increased gradually with the increase of pore size, but it had little effect on the compressive strength. From the test results of basic mechanical properties, the mechanical model of cubic compressive strength, elastic modulus, axial compressive strength, and splitting tensile strength was obtained. The proposed stress–strain relationship model could well describe the relationship of AAC and the base material at the rising section of the curve.
This paper performed a detailed study on the fundamental properties and thermal conductivity of autoclaved aerated concrete (AAC) self-insulation block, and the mechanical properties and heat transfer resistance of the AAC self-insulation block masonry. Different kinds of joints and the plastering surface were used to build the masonry specimens. The distinctive feature of the blocks and mortars is the lower thermal conductivity with expected strength. Compared to those with larger thickness of insulation mortar joints, the masonry with thin-layer mortar joints had better compressive performance and lower shear strength. The compressive strength of masonry was related with the block and mortar strengths, the shear strength of masonry along mortar joints was related with the mortar strength. The stress–strain relationship of masonry in compression could be predicted by the similar expression of conventional block masonry. The tested heat transfer coefficient of AAC self-insulation block masonry with thickness of 250 mm without plastering surfaces was (0.558 ± 0.003) W/(m2·K). With the plastering surfaces, the heat transfer coefficient reduced by 4.4% to 8.9%. Good agreements in values of heat transfer coefficient existed by using the test, theoretical computation and ANSYS (ANSYS Inc. Canonsburg, PA, USA) analytical methods. Based on the extensibility analyses, the heat transfer coefficients of AAC self-insultation block masonry with different thickness are proposed. The best thickness is proposed for the outer walls of residential buildings in different cold zone to meet the design requirement of energy conservation.
Separating finer particles from raw fly ash is a popular method to produce high-performance admixture of concrete. However, the supply of separated fly ash is obviously behind the demand and the residue fly ash is difficult to be disposed. Ground fly ash is another method to improve the particle size and reactivity, but the change of particle morphology during grinding may affect the rheological properties of cement paste and concrete, which limits the application of ground fly ash in concrete projects. In this study, the raw fly ash, separated fly ash, and ground fly ash of the same particle size range were studied and the particle morphology was analyzed by Image-Pro Plus process and spherical particles proportion calculation. On this basis, the fluidity and rheological properties of cement paste with different fly ash content were tested and the mechanism was discussed by packing density and zeta potential analysis. The results showed that the total amount of spherical particles in fly ash-cement paste system was reduced due to the spherical particles of ground fly ash being destroyed during the grinding process. Thus, compared with the separated fly ash of similar particle size range, the fluidity of ground fly ash was significantly decreased while the yield stress and plastic viscosity increased significantly, which indicated that the rheological properties of fly ash cement paste are closely related to the particle morphology of fly ash. The results provide theoretical basis and technology support to the application of ground fly ash.
Autoclaved aerated concrete (AAC) self-insulation block masonry is often used for the infill walls in steel and concrete frame structures. To work together with the frame under earthquake action, it is essential to understand the seismic behavior of AAC self-insulation block masonry walls. In this paper, six AAC self-insulation block masonry walls were experimentally studied under the pseudo static test. The load-displacement hysteretic curves were drawn with the test data. The failure characteristics, loading capacity, stiffness degeneration, energy dissipation capacity and hysteretic behavior are analyzed. The results indicate that the blocks underwent internal failure due to the lower strength with a larger size, but the walls had good energy dissipation capacity with a rational bearing capacity. Accompanied by the influence of vertical compressive stress on the top surface of the walls, the cracking resistance, ultimate bearing capacity, deformability and energy dissipation capacity of the walls were affected by the masonry mortar joints. Comparatively, the walls with thin-layer mortar joints had better seismic performance than those with insulation mortar joints or with vertical joints filled by mineral wool plates. Finally, the shear capacity of the walls under seismic load is evaluated referring to the formulas of current design codes for masonry walls.
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