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Highlights: [•] The concrete–steel bond of LWC is characterized for different failure mechanisms. [•] In splitting, the bond strength of LWC was 70% that of normal concrete. [•] The bond strength of LWC can be more than twice that of NWC of equal compressive strength. [•] It has been shown that the normative expressions proposed for LWC may be too unrealistic. [•] A new approach for estimating the LWC bond strength has been suggested. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the compressive strength of a wide range of structural lightweight aggregate concrete mixes is evaluated by the non-destructive ultrasonic pulse velocity method. This study involves about 84 different compositions tested between 3 and 180days for compressive strengths ranging from about 30 to 80MPa. The influence of several factors on the relation between the ultrasonic pulse velocity and compressive strength is examined. These factors include the cement type and content, amount of water, type of admixture, initial wetting conditions, type and volume of aggregate and the partial replacement of normal weight coarse and fine aggregates by lightweight aggregates. It is found that lightweight and normal weight concretes are affected differently by mix design parameters. In addition, the prediction of the concrete’s compressive strength by means of the non-destructive ultrasonic pulse velocity test is studied. Based on the dependence of the ultrasonic pulse velocity on the density and elasticity of concrete, a simplified expression is proposed to estimate the compressive strength, regardless the type of concrete and its composition. More than 200 results for different types of aggregates and concrete compositions were analyzed and high correlation coefficients were obtained. [Copyright &y& Elsevier]

• Pre-walls system: two pre-cast concrete panels and a cast-in-situ concrete core. • High performance pre-cast concrete and low-cement lightweight cast-in-situ concrete. • Thermophysical properties of concretes for dry, hygroscopic and capillary ranges. • An application study of the pre-walls system to a swimming pool was carried out. • Low-cement lightweight concrete in the core improve the system thermal performance. An innovative system of pre-cast high performance concrete pre-walls, combined with low-cement cast-in-situ lightweight concrete core, is studied experimentally from the standpoint of the thermophysical properties of the concrete compositions under various hygroscopic conditions. Thermal conductivity, volumetric heat capacity and thermal diffusivity are experimentally determined, by a transient method, for eight concrete compositions in the dry state, hygroscopic and over-hygroscopic ranges. The incorporation of lightweight aggregates in the concrete mixture allowed to reduce the thermal conductivity (up to 53%) and thermal diffusivity (up to 41%), in comparison to normal weight concrete. The moisture content, regardless of the composition of the concrete, impacts negatively the thermal performance, with a rise of both thermal conductivity and diffusivity, which was also captured by analytical expressions. An application study of the pre-walls system to a swimming pool showed reductions of thermal conductance of up to 38% when combining high mechanical performance concrete in the pre-walls with lightweight aggregate concrete with high thermal performance in the core. These results highlight the importance of assessing thermophysical properties in service conditions, with the moisture content effect included, and selecting the types of concrete in composite pre-walls systems to enhance both mechanical and thermal performance. [ABSTRACT FROM AUTHOR]