Autoclaved aerated concrete (AAC) block masonry has been widely used for bearing walls of multi-story buildings or non-bearing walls of high-rise buildings because of its unique advantages, such as lightweight, low pollution output, and excellent thermal insulation performance. However, traditional AAC block masonry has the disadvantages of high water absorption, poor adhesion to mortar, and low construction efficiency. In order to improve the performance of traditional AAC masonry, this paper proposed a new kind of mortar-free AAC block masonry with concrete core-columns. Fundamental mechanical properties of compression and shear were studied. We divided a total of 16 compression specimens into four groups according to different hollow ratios and strength grades of the block, and eight shear specimens into two groups based on different hollow ratios. Each specimen consists of three-layer blocks with two core columns at the point of quadri-section. The diameters of columns were, respectively, 100 mm and 80 mm. The specimens were loaded at a constant speed to evaluate their bearing capacity, displacement response, crack development, and damage state. The formula of the average values and design values of the compressive and shear strength of masonry were obtained statistically. The stress–strain constitutive relation of masonry expressed by a three-stage curve was presented. Furthermore, the result of numerical analysis using the ABAQUS finite element program aligned well with the experimental results. The compressive strength and shear strength of the new type of masonry are no less than traditional AAC masonry, and new masonry has higher construction efficiency and more stable strength.

Preface In recent years, autoclaved aerated concrete(AAC) has been widely used in walls because of its excellent performance of lightweight, sound and thermal insulation, energy-saving, and flexibility (Laukaitis and Fiks 2006; Muszynski and Gulas 2001; Jerman et al. 2013; Laurent and Guerrechaley 1995; Tanner et al. 2005; Ghazi Wakili et al. 2015; Fudge 2011). However, AAC blocks have the disadvantages of poor water retention, mortar fluidity, and strong water absorption capacity (Wittmann 1983). The quality defects in masonry construction are challenging to eliminate, including the plumpness of mortar joint depends heavily on the workers' proficiency, the bond force between mortar and blocks are discrete, the mechanical properties of masonry usually fail to meet the design requirements (Bingel and Bown 2009). Besides, traditional masonry construction is becoming outdated due to its low construction efficiency.

In the dry-stack masonry construction, some measures to improve the performance of masonry structure and construction efficiency have been developed and applied around the world (Sokairge et al. 2017; Zahra and Dhanasekar 2018; Fonseca et al. 2019; Bolhassani et al. 2016; Oliveira 2003; Martinez and Atamturktur 2019; Thanoon et al. 2008; Kalliontzis and Schultz 2017; Fay et al. 2014; Zhou et al. 2017; Ngowi 2005). Ngowi (2005) summarized the preliminary development of dry-stack masonry and explored its general failure mode and load capacity. To improve the bearing capacity of dry-stack masonry, Fonseca et al. (2019) used different strength grades of concrete to fill the holes in the blocks and find the disciplinarian of the strength of the grouted masonry. Sokairge, Rashad and Elshafie (Sokairge et al. 2017) conducted a post-tensioning test on the dry-stack masonry to improve crack load and ultimate load. Bolhassani et al. (2016) conducted a partial grouting test on the masonry. In the experiments, the grouted part and the unfilled part formed a frame style structure, and the lateral strength of the masonry was improved. To numerically analyze the mechanical property of grouted masonry, Zhou et al. (2017) proposed the ANN and ANFIS models, which can accurately calculate the shear strength of reinforced masonry. Kalliontzis and Schultz (2017) presented an analysis method to improve the mechanical research of a fully grouted masonry shear wall by accounting for the reverse-cyclic loading and the three mechanisms of rocking, flexure, and shear. Gokmen et al. (2019) investigated the seismic behavior of autoclaved aerated concrete low-rise buildings with reinforced walls according to the relevant ASTM standards (C15.04 2007; C27.60 2009; C15.10 2009).

As stated in reference Fudge (2011), the use of AAC masonry is becoming more and more appealing. To give full play to the mechanical property of masonry structures, the use of reinforced concrete core columns set to confine AAC masonry has been proved effective. When reinforced fiber mesh crammed the vertical gaps between masonry units, higher average compression strength and elasticity modulus could be acquired. Also, when the structural columns have been located in the corners or wall intersections of buildings, both static and shaking table tests showed noticeable improvement of the resistance and ultimate deformation capacity of the walls. Furthermore, the mechanical properties of AAC masonry will be significantly improved by reducing the concrete core-column spacing properly and increasing the number of columns regularly. However, the knowledge regarding their mechanical behavior is still insufficient.

Given the high surface flatness of AAC blocks, a new type of AAC block, with two circular holes at points of the quarter span of the block (Fig. 1), is proposed in this study. The holes of the blocks were made manually by a concrete core drilling machine. Though the blocks were crisp, the drilling process went exceedingly well. Almost all holes of the blocks were successfully drilled without any crack or break. During construction, the holes of the AAC blocks are aligned vertically, and the blocks are staggered to form a dry-stack masonry. Then the high fluidity concrete is poured into the vertical through-holes. Eventually, the cooperation of the core columns and AAC blocks ensures the performance of the masonry. The joints need to be sealed by plastering to guarantee the thermal insulation and waterproof performance of masonry. Since no mortar was used, the masonry structures have many new advantages of reducing pollution on the construction site, accelerating construction, and improving construction quality. The structure of the new masonry, core-column non-mortar aerated concrete block masonry (CNACBM), is shown in Fig. 2.

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