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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.

In this study, we investigated the destructive effect of autoclaved aerated concrete (AAC) masonry walls subjected to close-in explosions. First, full-size refined finite-element models of the AAC masonry wall were established, and the accuracy of the models was verified by comparison with the test results. The destruction pattern and damage characteristics of the AAC wall were studied, and the effects of block size, wall thickness, mortar compressive strength, and explosion distance on the destruction degree of the AAC masonry walls were analyzed. The results showed that the destruction pattern of the AAC masonry wall subjected to close-in explosion manifested as punching damage in the middle of the wall. When the scaled distance remained unchanged, the punching damage area of the AAC masonry wall was positively correlated with the block size and negatively correlated with the wall thickness and mortar compressive strength. When the explosive equivalent remained unchanged and the explosion distance increased, the punching damage area first increased and then decreased. According to the damage mechanism of the AAC masonry wall, a calculation method for predicting the punching damage area of the AAC masonry wall was established, and the accuracy of this method was verified by comparing it with the numerical results. In addition, the damage criterion based on the punching damage area was established to determine the destruction levels of AAC masonry walls.

The purpose of this research is to investigate the utilization potential of recycled powder made from spent coffee grounds (SCGs) and aerated concrete blocks (ACBs) in green-growing concrete. The green-growing concrete is prepared using ACB powder and SCG ash as raw materials instead of 5%, 15%, and 25% and 5%, 10%, and 15% cement, respectively. Then, the two raw materials are compounded with the optimal content. The compressive strength and alkalinity of green-growing concrete at 7d and 28d and the frost resistance after 25 freeze–thaw cycles at 28d are studied. The results showed that the optimum content of ACB powder and SCG ash was 5%. Replacing 5% cement with recycled powder could improve the strength of concrete. The alkalinity of concrete containing ACB powder gradually increased, while the alkalinity of concrete containing SCG ash gradually decreased. The alkalinity of ACB-SCG powder was lower than that of ACB powder but slightly higher than that of SCG ash. The frost resistance of concrete containing ACB powder decreased gradually, and the frost resistance of concrete containing SCG ash increased first and then decreased greatly. The frost resistance of ACB-SCG powder could neutralize that of ACB powder and SCG ash.

Autoclaved aerated concrete (AAC) is the lightest masonry material available in today’s building industry. It shows properties, such as high strength per unit weight, lesser density, lower shrinkage, higher thermal insulation, and fire resistance as compared to traditional concrete. Not only engineering properties of AAC make it popular in construction industry, but also its eco-friendly nature also contributes in conservation of energy. AAC produces about 67% lower carbon emission than the clay bricks. Consequently, it becomes a cost-effective product which reduces the cost of construction. This paper provides thorough insight into possible solutions for the waste utilization. It has been inferred that fine aggregates can be replaced by these wastes in the preparation of AAC. This replacement will improve its physio-mechanical properties, such as bulk-density, moisture absorption, compressive strength, along with microstructure. These properties are comprehensively presented to categorize the investigation which has been done in such fields earlier. The ongoing research work at the author’s institute, i.e., the development of lightweight concrete by using different kind of waste materials, such as marble slurry, fly ash, etc., is being presented.HighlightsThe paper presents the feasibility to use different agro-industrial wastes to develop AAC.Studies on the effect of fiber reinforcement on the physio-mechanical properties of AAC have been discussed.Ca/Si ratio affects the tobermorite formation and the mineralogy of AAC.Influence of porosity on the microstructure of AAC has been investigated.Ongoing R&D work at the author’s institute has been described.

Confined walls are popular in areas exposed to seismic action. The advantage of such structures is increased load-bearing capacity, ductility, and energy dissipation. Confined masonry walls are also used to restrain the intensity of cracking and improve load-bearing capacity in areas exposed to seismic action. This paper describes the research on 18 confined walls and presents a comparison with research on unconfined walls (referenced models). The confined models were classified into three series: HOS-C-AAC—without openings and with confining elements around the perimeter; HAS-C1-AAC with a centrally positioned opening and circumferential confinement; and HAS-C2-AAC with a centrally positioned window opening and additional confinement along the vertical edges of the opening. The area of the window opening was 1.5 m2. All walls were made of autoclaved aerated concrete (AAC) masonry units of the nominal density class of 600. The walls were tested under initial compressive stresses σc = 0.1; 0.75; and 1.0 N/mm2. The reference models without confinement (six models of the series HOS-AAC without openings and the series HAS-AAC with openings) were prepared from the same masonry units, had almost the same outer dimensions, and were tested under the same initial compressive stresses σc. The analysis was performed for the morphology of cracks, stress values at the moment of cracking and failure, stiffness, and angles of shear strain. The morphology of cracks was found to depend on initial compressive stresses and the presence of an opening. A significant increase in compressive stress leading to cracks and failure stresses was observed with increasing values of initial compressive stresses. As the wall behavior was clearly non-linear, the bilinear relationship described by energy dissipation E, stiffness at the moment of cracking Kcr, and maximum displacement uu was proposed to be included in the engineering description of the relationship between horizontal load and displacement of confined walls. Confinement along the vertical edges of the opening having an area of 1.5 m2 (acc. to EN 1996-1-1) increased the maximum forces Pmax by ca. 45% and marginally affected the ductility of the wall when compared to the elements with circumferential confinement.

In this paper, the possibility of retreated lithium slag (RTLS) with a high content of alkali, sulfate and fluoride as a partial replacement for fly ash (FA) to produce autoclaved aerated concrete (AAC) was investigated. The influence of the RTLS dosage on the AAC performance were examined. The composition and microstructure of hydrates as well as the microstructure of the RTLS-FA-based AAC compositions were determined by XRD, FTIR, TG-DSC and SEM. The results illustrated that the incorporation of RTLS changed the crystal structure and the microstructure of the tobermorite. With increased RTLS contents, the morphology of tobermorite was changed, and the grass-like tobermorite gradually transformed into network-like tobermorite. The newly formed tobermorite improved the mechanical performance of the AAC. Compared with the RTLS10, the content of tobermorite in the RTLS30 increased by 8.6%.

An experimental study on the shear behavior of autoclaved aerated concrete (AAC) confined masonry walls is presented. A total of eight full-scale confined walls were tested in the laboratory under in-plane reverse cyclic loads. The variables studied were the aspect ratio and the axial compressive stress of walls. The shear behavior was characterized by diagonal cracks or flexure-shear and diagonal cracks. The final cracking pattern of the walls was defined by the traditional \"X\" pattern. Equations for shear strength and flexure-shear strength based on experimental data obtained in this and previous studies are proposed for AAC confined walls. A limit is established for the shear strength of walls as a function of axial compressive stress. The proposed equations predicted well the experimental strength of the AAC confined walls considered in this study.

Minor-destructive (MDT) and non-destructive (NDT) techniques are not commonly used for masonry as they are complex and difficult to perform. This paper describes validation of the following methods: semi-non-destructive, non-destructive, and ultrasonic technique for autoclaved aerated concrete (AAC). The subject of this study covers the compressive strength of AAC test elements with declared various density classes of: 400, 500, 600, and 700 (kg/m3), at various moisture levels. Empirical data including the shape and size of specimens, were established from tests on 494 cylindrical and cuboid specimens, and standard cube specimens 100 mm × 100 mm × 100 mm using the general relationship for ordinary concrete (Neville’s curve). The effect of moisture on AAC was taken into account while determining the strength fBw for 127 standard specimens tested at different levels of water content (w = 100%, 67%, 33%, 23%, and 10%). Defined empirical relations were suitable to correct the compressive strength of dry specimens. For 91 specimens 100 mm × 100 mm × 100 mm, the P-wave velocity cp was tested with the transmission method using the ultrasonic pulse velocity method with exponential transducers. The curve (fBw–cp) for determining the compressive strength of AAC elements with any moisture level (fBw) was established. The developed methods turned out to be statistically significant and can be successfully applied during in-situ tests. Semi-non-destructive testing can be used independently, whereas the non-destructive technique can be only applied when the developed curve fbw–cp is scaled.

The article describes the first exploratory studies on the reinforcement of heat-insulating autoclaved aerated concrete with a basalt microfiber. The aim of the work is to obtain autoclaved aerated concrete of reduced density with improved tensile and bending characteristics. The first results obtained using basalt microfiber for reinforcing cellular concrete with a density of 150 kg/m3 are analyzed.

The production of autoclaved aerated concrete via the autoclaving process incurs substantial energy consumption, posing a challenge to sustainable economic development. Herein, a novel nonautoclaved aerated concrete (NAAC) was prepared using sulfoaluminate cement as the primary raw material and aluminum powder as the aerating agent. The physicomechanical characteristics and pore structures of the sulfoaluminate-cement-based (SAC) NAAC (SAC-NAAC) were examined through X-ray diffraction, thermogravimetry, and scanning electron microscopy. The findings revealed that the optimal mechanical attributes of the SAC-NAAC were achieved at a water–cement ratio of 0.55, with a specific content ratio of polycarboxylate superplasticizer–borax–calcium stearate–sodium hydroxide at 0.24%:0.32%:0.36%:2.90%, along with 0.40% aluminum powder. The SAC-NAAC samples, with a bulk density range of 600–750 g/m3, exhibited a compressive strength of 3.55–4.16 MPa, porosity of 45.9–63.5%, and water absorption rate of 60.2–74.4%. The weight loss in the SAC-NAAC with different aluminum powder contents ranged between 15.23% and 16.83%. The prismatic ettringite (AFt) crystals served as the main source of strength for the SAC-NAAC, and AH3 was attached to the AFt surfaces in a microcrystalline gel phase, thereby further enhancing the strength of the SAC-NAAC. Thus, the lightweight, high-strength SAC-NAAC has great potential as a nonautoclaved aerated concrete.