International Concrete Abstracts Portal

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.

The apparent density of lightweight aggregate (LWA)-modified ultra-high-performance concrete composite is 2080 kg/m3, and the compressive strength is not less than 110 MPa at 28 days. Lightweight ultra-high-performance concrete (LUHPC) not only has light weight and high strength, but also reduces the consumption of raw materials and the section size of the structure, thus reducing the cost. The macroscopic properties are closely related to the pore structure characteristics, but the structural nature of LUHPC under different curing regimes and the LWA on their pore structure remain unclear. To comprehensively understand the pore structure of LUHPC and then control its properties, capillary absorption method, low-field nuclear magnetic resonance (LF-NMR), computed tomography (CT), and nitrogen adsorption (BET) technologies were used to characterize the pore structure characteristics of LUHPC. The experimental results show that there are many nanoscale pores (mainly harmful and more-harmful pores) in LUHPC. With the increase of water absorption of the added LWA, the porosity of LUHPC and the proportion of less-harmful pores increase, thus changing the pore structure of LUHPC. With the increase of temperature and pressure, the internal curing effect of LWA is accelerated. Heat treatment promotes the formation of dense additional hydrates such as tobermorite and xonotlite, and the average chain length of the hydrates and the pozzolanic reaction between supplementary cementitious material and Ca(OH)2. Steam curing increases the total porosity and coarsens the pore size while accelerating the hydration of cementitious paste. Autoclaved curing can stimulate the pozzolanic activity of inert SiO2, promote the formation of secondary hydration products, and fill the pores in the matrix. The evolution of the pore structure of LUHPC plays a key role in improving its performance due to the curing regimes and presence of LWA.

The use of lightweight autoclaved aerated concrete (AAC) block masonry is gaining popularity in earthquake-resistant infilled reinforced concrete (RC) frame buildings due to its various benefits. Therefore, appropriate knowledge of the strength properties of AAC block masonry is necessary for a reasonable evaluation of the seismic behavior of such buildings. In the present study, the uncertainties related to the two most critical parameters that control the resistance capacity of infilled masonry are investigated through laboratory experiments, and the best-fitted probability density functions are recommended. Furthermore, the in-plane seismic performances of typical RC frame buildings infilled with AAC block masonry are evaluated in a probabilistic framework considering the recommended probability density functions showing the ineffectiveness of an assumed normal distribution for this purpose. Although lightweight AAC block masonry slightly increases the seismic risk of the building compared to traditional brick masonry due to its lower strength properties, it can be safely used as an infill material in areas with high seismicity, as it achieves the code-prescribed reliability index.

Based on the unified strength theory as the yield criterion, an elastic-plastic constitutive model of autoclaved aerated concrete block (AACB) considering the intermediate principal stress was proposed. Meanwhile, the mechanical properties and failure mechanism of AACB were investigated by the uniaxial compressive, tensile, shear, and static triaxial compressive tests. The yield function based on the unified strength theory of AACB was derived. Moreover, the proposed model was integrated into the general finite element package ABAQUS by UMAT to simulate the deformation process of AACB under triaxial compressive. The numerical simulation results of AACB were in good accordance with but slightly larger than the static triaxial test results, which implied that the proposed constitutive model could be used to characterize the mechanical characteristics of AACB under complex stress states with high computational efficiency.

Autoclaved aerated concrete (AAC) is a cellular concrete with consistent material properties. AAC structures have many advantages including ease of construction, low density, and high fire and thermal resistance. In this study, a suite of 14 scaled floor diaphragms were tested to determine physical behavior of the system subjected to either monotonic and cyclic loads. Next, a simple strut-and-tie model (STM) was used as a mechanism to predict the strength of floor diaphragms subject to in-plane lateral loads. Testing validated that although the model violates the minimum angle of 25 degrees, individual panel movement and nodal confinement permit sufficient rotation. Test results indicate that the STM provides conservative predictions for the strength of floor diaphragms.