HPZ-Mauerwerk - High-performance exterior brick walls without additional thermal insulation

A quarter of all heat flows between the interior and exterior of a building pass through the exterior wall. This illustrates the importance of the exterior wall on the energy demand of a building. Driven by legal regulations on "energy saving and thermal insulation", external thermal insulation composite systems have become established. Although these fulfil the required thermal insulation properties, they cause air temperatures in neighbourhoods to rise in summer, prevent the extraction of solar thermal energy during the heating season and have to be disposed of as hazardous materials at the end of their relatively short service life. The monolithic, minerally plastered brick wall, on the other hand, can meet both the sustainability requirements and the high thermal requirements of urban residential and office buildings as long as the architecture, the masonry and the brick are optimised for this purpose. The thermally optimised, highly porous bricks currently on the market are weak. They cannot be used to realise the architecture of choice, namely multi-storey housing. The project presented here does not work on improving the fired clay properties (microstructure), but pursues a macrostructural approach. The load-bearing capacity of the brick is to be increased by reducing the proportion of holes without worsening the thermal insulation properties. This seemingly paradoxical goal has already been theoretically achieved and was patented under the name TRALAM. A case study of an 8-storey residential building showed that the load-bearing capacity requirements of a 50 cm TRALAM masonry wall are met for a building height of 22 m, the heating requirement according to the U-value method corresponds to that of an ETIC system and an additional solar energy gain of 10% is achieved via the non-insulated opaque outer surface. It is obvious that an increase of the load-bearing capacity without changing the fired clay strength, more clay has to be fired and consumed. Thus, all the associated characteristic values of the ecological footprint become worse but only those of the production’s footprint. In return, the high-performance masonry requires only one third of the building ground and one third of the roof area to create the same living space, no insulation material is used in 8-storey buildings, the service life is significantly extended and it brings solar energy gains in winter and a reduction in summer overheating. In order to be able to transfer these promising results to reality, comprehensive experimental verification is necessary. The TU-Graz plans to carry out such a project in cooperation with the Austrian brick industry. One of the goals of this R&D project is to carry out a 1-year field test in one of the test houses at the TU-Graz. This test is for determining the actual total energy balance by measurement. However, the production of the necessary bricks has not yet been tested and is thus a high project risk. This should be minimised by starting the “Sondierungsprojekt” presented here as a preliminary step, focusing only on the feasibility of the production and the final optimisation of the brick design and the masonry bond. It is expected that a reduction of the air gap thickness from 8 to 4mm can be realised in terms of production technology. Laboratory tests and numerical physical simulations shall be carried out for determining the mechanical and building physics characteristics to make sure that the follow-up project can be developed in detail. Therefore, approximately 200 prototype quarter bricks shall be produced.