Carbonation of cementitious building materials with CO2 at elevated pressure or in the supercritical state

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This research proposal is based on the results of first part of the DFG project entitled carbonation of cementitious materials with CO2 at elevated pressures or in the supercritical state. New issues have emerged in the research work which are to be clarified by further investigations aimed at the utilisation of the positive effects of carbonation for the production of innovative cementitious materials with defined properties which are immediately available after treatment. In the first period of funding, parameters such as alkali content, initial porosity (w/c ratio) and moisture content of the hardened cement paste specimens were varied as well as the pressure of the CO2 treatment and its duration. Moreover, the effect of additions such as ground granulated blast-furnace slag, limestone and dolomite flour on the carbonation process and the properties of the carbonated material was investigated. The proposed research deals with open questions on the evolution of phases, strength and volume during and after treatment with supercritical or gaseous CO2. and gaseous CO2 at elevated pressures. The investigations focus on the effect of the fineness and mineralogical composition of Portland cement (C3A, and C4AF content, Na2O eq.). Thermodynamic calculations for the system [CO2 (supercritical or gaseous) - pore solution -hardened cement paste phases] will further the understanding of the mechanisms of carbonation under different conditions.One possible practical application in the future is the treatment of porous cement-based prefabricated elements such as cementitious fire protection panels or wall boards. In particular, the contact zone between a fibreglass reinforcement and the hardened cement paste matrix is to be investigated in order to determine the effect of carbonation on bonding behaviour and the effectiveness of fibreglass reinforcement.