In a current research project together with the research partner Bimolab gGmbH and with the friendly support of the sand-lime brick industry, the Department of Civil Engineering at the Institute of Materials Testing of the Free Hanseatic City of Bremen (MPA) is dedicated to the goal of producing low-CO₂ ecomasonry bricks by hydrothermal hardening of recycled crushed sands from construction waste processing. Behind the project is an innovative approach to climate protection and the Green Deal.

In Germany, approx. 55 to 60 million tons of recycled aggregates from construction waste are processed annually in various material qualities and have so far been largely reused in earthwork and road construction. About half of this is concrete rubble. Other mixes originate from mixed masonry, such as sand-lime bricks, bricks or aerated concrete with adhesions of lime, cement or gypsum plasters. While coarse recycled aggregates can usually be used without any problems, e.g. increasingly as a substitute for natural aggregates in "R-concrete", fine RC aggregates can so far only be marketed at low proceeds or not at all ("recycling sand problem").

In this context, the Civil Engineering department is focusing on the development of low-CO₂ masonry blocks ("eco-masonry blocks"), especially from crushed concrete sands. Due to their usual composition, which usually always contains cement paste and thus Ca(OH)₂ as well as quartz-containing sands from fine aggregate fractions, concrete crushed sands have an independent hydrothermal curing potential. Pressed pellets made solely from crushed concrete sands harden in autoclaves to form molded bricks that can be used in construction, analogously to sand-lime brick technology. The otherwise necessary use of the primary binder quicklime, the production of which is associated with high CO₂ emissions, is minimized or eliminated completely.

The project aims to transfer the process, which has so far been investigated in the laboratory, to the production technology of the sand-lime brick industry. A model approach is currently being developed for this purpose, in which the required crushed sand properties, manufacturing parameters and targeted properties are incorporated, and which is intended to contribute to the transfer of this climatically valuable further development into an economically demanding standard way of production practice for wall-building materials - without having to make major investments. The sand-lime brick industry would thus make a valuable contribution to reducing climate-damaging CO₂ emissions.