The decarbonisation of concrete remains the biggest opportunity, given the market share among materials in construction. The current situation is that the market share of this technology is equal to 96.6% in new construction. Clinker emits 10.75 Mt CO2 (decarbonisation of CaCO3 and combustion), 13% of all industrial emissions, 58% of the emissions of the building products industry. Industry targets are to decrease -24% by 2030 and -80% by 2050. And the target for 2050 is to emit 131 kg CO2/t of cement. The challenges to be met are technological and investment-intensive. How difficult is it? Very difficult. But in REBUILD we will discuss their solutions. Process optimisation, fossil fuels, new low carbon composition for cement, and the best applications -2D, 3D, composites… – to achieve it.