Abstract. The awareness of the environmental impact of the building sector is increasing. Steel reinforced concrete is the most commonly used construction material, though with a high-embodied energy and carbon footprint. Large environmental gains may arise if an alternative to steel reinforced concrete is developed. In this context, ultra-high performance concrete (UHPC) materials are shown to be promising alternatives with advantages such as lower embodied energy and reduced environmental impact. Predictions suggest that UHPC composite elements for building envelopes could have other benefits such as an increased service life, optimised use of building area due to thinner elements and minimised maintenance due to the absence of reinforcement or use of non-corrosive reinforcing materials such as carbon fibres. In the framework of the H-HOUSE project funded by the European Commission, composite elements are developed. The aim is to create facade panels combining an autoclaved aerated concrete or cellular lightweight concrete insulation layer with an external UHPC supporting layer. To enhance occupant comfort and health, hygroscopic materials that are capable to buffer indoor air humidity shall be applied to the inside of such elements. Indoor air humidity levels are expected to be more stable, which shall subsequently improve the indoor climate and minimise potential decay to the construction.

The corrosion by severe sulfuric acid attack at pH 2 of two self-compacting concrete (SCC) types that are based on ordinary Portland cement (OPC) and granulometrically optimized blast-furnace slag cement was evaluated by three complementary tests that were performed in different research institutes. The use of SCC is a smart and promising solution to improve the performance of concrete in an aggressive environment, especially regarding ready-mixed concrete applications, since good compaction is less dependent on workmanship. The relevance and practical advantages of the different test protocols and the influence of the experimental parameters are discussed. It appears that the frequency of renewing the acid solution during the exposure period is the main parameter that influences the mass loss and the rate of degradation, while the sample geometry and the ratio between the volume of solution and concrete surface area had no clear influence. Nevertheless, there was reasonable agreement between the methods regarding the magnitude of the concrete degradation (resulting in a mass loss of about 2.5 kg/m² in six months time). The use of granulometrically optimized slag cement provided a moderate increase of the concrete resistance against acid attack, and this practice might be recommended in order to increase the durability of structures exposed to sulfuric acid media. The fact that the difference in comparison with SCC-OPC was rather limited shows that the influence of the cement type becomes less relevant in the case of concrete with low w/c ratio and optimized concrete technology.

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The aim of this study was to develop a lightweight composite facade element for new buildings and for the refurbishment of existing facades. These composite elements have been developed combining an insulation layer of autoclaved aerated concrete (AAC) with an external ultrahighperformance concrete (UHPC) supporting layer. This solution allows avoiding the use of connectors and facilitates the production procedure. The structural behavior of the facade elements is mainly influenced by the presence of the upturning edges that are able to increase the stiffness of the element and reduce the thickness of the external layer. The insulation material has no influence on the structural behavior of the UHPC boxes. Flexural tests were carried out to investigate a potential detachment of the external layer from the upturning edge. The photogrammetric analysis used during the flexural tests essentially confirmed that the bond between the two UHPC layers cast in two steps is reliable. The quality of the bond between the external layer and the upturning edge is a key parameter to define the bearing capacity of the element. K E Y W O R D S autoclaved aerated concrete, flexural testing, photogrammetric analysis, production technology, ultrahigh-performance concrete How to cite this article: Miccoli L, Fontana P, Qvaeschning D, Kreft O, Hoppe J, Meng B. UHPC-AAC facade elements: Structural design, production technology, and mechanical behavior.