International Concrete Abstracts Portal

This paper presents the results of a numerical study carried out by the authors to better understand the structural behavior of prestressed beams with web openings and to identify numerical modelling techniques that allow to adequately predict such behavior. Ultra-High Performance Fibre Reinforced Concrete (UHPC) beams are considered, with a focus on shear-controlled failure modes. For all the beams considered in this study, prestressing is used to resist the main bending moment. However, no other reinforcement is added to the beams, in order to emphasize the structural contribution of the fibers and to focus on solutions that could be economically competitive for the precast industry. The results of non-linear simulations performed with existing finite elements codes are compared and validated against experimental results of tests carried out at the University of Applied Sciences of Western Switzerland. The main assumptions of the numerical simulations are discussed, as well as the results and the limits of the analysis.

X-ray computed tomography (XCT) is noninvasive and nondestructive. It produces three-dimensional digital reconstructions of samples, allowing for a comprehensive view of microstructure. The article discusses the use of XCT to examine cementitious materials. Three case studies are provided: characterization of cellular concrete microstructure, quantitative analysis of cement phases, and real-time investigation of an alkali-silica reaction.

The roadside safety barrier is a protective barrier that is erected around a racetrack or in the middle of a dual-lane highway in order to reduce the severity of accidents. Recently, interest in portable roadside safety barriers has heightened the interest in the development of a low-cost and high-performance alternative to the conventional safety barrier system. A study has been undertaken to characterize fresh and hardened properties of flue gas desulfurization (FGD) cellular concrete (CC) using foaming admixture towards the development of a lightweight roadside safety barrier. Test results indicate that FGD CC using a foaming admixture can be effectively used in manufacturing lightweight roadside safety barriers.

This paper summarizes the final phases of the technical justification for proposed design provisions for AAC structures in the US. It is divided into two parts. The first part describes the design and testing of a two-story, full-scale AAC shear wall specimen that was designed and tested at The University of Texas at Austin, under reversed quasi-static loads representative of those experienced in a strong earthquake. The specimen withstood repeated reversed cycles to story drifts of about 0.3%, and displacement ductility ratios of about 3. The specimen conformed with the two main objectives. Those objectives were: 1) to show that the behavioral models developed for the shear walls also govern in a building; and 2) to demonstrate that a squat wall can exhibit failure governed by flexure. The second part describes the development of R and Cd factors for seismic design of AAC structures. The seismic force-reduction factor (R) specified in seismic design codes is intended to account for energy dissipation through inelastic deformation (ductility) and structural over-strength. The factor (R) is based on observation of the performance of different structural systems in previous strong earthquakes, on technical justification, and on tradition. For structures of autoclaved aerated concrete (AAC), the force-reduction factor (R) and the corresponding displacement-amplification factor (Cd) must be based on laboratory test results and numerical simulation of the response of AAC structures subjected to earthquake ground motions. The proposed factors must then be verified against the observed response of AAC structures in strong earthquakes. The objectives of this paper are: (1) to present a general procedure for selecting values of the factors (R) and (Cd) for use in the seismic design of structures; and (2) using that procedure, to propose preliminary values of the factors (R) and (Cd) for the seismic design of AAC shear-wall structures. The general procedure is based on comparing the predicted ductility and drift demands in AAC structures, as functions of the factors (R) and (Cd), with the ductility and drift capacities of AAC shear walls, as observed in quasi-static testing under reversed cyclic loads. Nonlinear numerical simulations are carried out using hysteretic load-displacement behavior based on test results, and using suites of natural and synthetic ground motions from different seismically active regions of the United States.

Autoclaved aerated concrete (AAC) is a lightweight uniform cellular material, first developed in Sweden in 1929. Since that time, plain and reinforced AAC building components have been widely used in Europe and other parts of the world. Until recently, however, AAC was relatively unknown to the United States precast construction market. Today, AAC prefabricated elements are gaining rapid acceptance in the United States due primarily to increasing energy cost, environmental concerns, and the ease of construction using AAC elements. Although AAC is a well-recognized building material in Europe, very little research work has been done on U.S.-produced AAC products. The primary objective of this work was to study the structural behavior of U.S.-made reinforced AAC elements. The laboratory test program included most commonly used reinforced AAC elements: floor panels, lintels, and wall panels. Two U.S. manufacturers supplied the AAC elements. Floor panels and lintels were tested in bending, whereas the wall panels were tested under axial or eccentric loading. The ultimate load capacity, cracking, deflection, and failure mode were observed and recorded for each test. The results provide a database that will be used to refine the analytical methods for the structural design of reinforced AAC elements. This information is needed to enhance AAC design methodologies and lay the foundation for establishing AAC as a reliable engineered construction material in the U.S.