The project, identified as 22115‑N and carried out by the research association Kalk‑Sand e.V., was financed through the Industrial Community Research Programme (IGF) of the German Federal Ministry of Economics and Energy, following a decision of the Bundestag. The study was conducted over a multi‑year period and involved close collaboration between the research association and two lime‑sand brick manufacturing plants. The research team performed laboratory and pilot‑scale experiments, while the plants supplied production data and enabled up‑scaling trials. The overall aim was to reduce the carbon footprint of lime‑sand bricks by lowering the use of calcined lime and replacing it with alternative binders such as cement and pozzolans.

Seven different binder formulations were sourced and characterised. In the laboratory, lime‑sand bricks were produced with systematic variations in binder content, mix ratios, and process parameters. Phase analysis of the resulting suspensions revealed that even when calcined lime was fully substituted by cement, calcium‑silicate‑hydrate (CSH) phases—particularly tobermorite—were still formed. The altered chemical composition caused shifts in phase assemblages, with changes in the calcium‑to‑silicon ratio affecting the prevalence of tobermorite and xonotlite. At high substitution levels, some binder components remained unreacted after autoclaving, indicating they did not participate in the steam‑hardening process.

Pilot‑scale trials demonstrated that bricks could be produced with binder substitutions as low as 2 % by mass. However, the resulting bricks exhibited higher total porosity and lower compressive strength compared with reference mixes that used only calcined lime. A clear inverse relationship was observed: as porosity increased, especially the proportion of air pores, compressive strength decreased. These trends were consistent across different binder types and substitution levels.

The research then moved to full‑scale production at the two partner plants. Optimised binder mixes, derived from laboratory and pilot‑scale data, were implemented under real industrial conditions. The bricks produced at plant scale showed similar trends in porosity and strength, confirming the laboratory findings. Importantly, the study found that increasing steam pressure from 8 bar to 16 bar did not enhance compressive strength, suggesting that lower pressure and shorter steam‑hardening durations could be employed without compromising product quality. This adjustment would reduce energy consumption and associated CO₂ emissions during manufacturing.

A comprehensive modelling component quantified the economic, energetic, and environmental impacts of the binder substitutions. Calculations of production costs indicated potential savings due to lower material and energy inputs. Energy consumption modelling projected reductions in steam‑generation energy, while CO₂ emission modelling estimated a significant drop in greenhouse gas output—primarily from the reduced calcined‑lime requirement and the possibility of shorter steam cycles. The modelling also highlighted the trade‑off between material performance and environmental benefits, guiding the optimisation of binder ratios.

In summary, the project demonstrated that partial replacement of calcined lime with cement and pozzolans is technically feasible, though it leads to modest increases in porosity and reductions in compressive strength. By carefully tuning binder proportions and process parameters, the lime‑sand brick industry can achieve measurable CO₂ reductions while maintaining acceptable product performance. The collaboration between the research association and the manufacturing plants, supported by federal funding, provided a robust framework for translating laboratory insights into industrial practice.