Abstract
Carbonation is a well-known aging process of concrete. Thermodynamic stable CaC03 is
formed when air or water-borne C02 dissolves in the concrete pore water. When the
carbonation layer is formed during service life, the carbonate species need to penetrate
through the carbonated layer and the carbonation rate slows down with the square root of
time (rough approximation). When concrete structures are demolished and refined to
Recycled Concrete Aggregates (RCA) the surface area is largely increased. The C02
binding rate per unit mass of concrete and thus the total amount of bound C02 may
therefore increase in the secondary life (after demolishing stage) provided sufficient access
to C02. By applying the prevailing cement chemistry, it was shown that 72 % of the total
CaO in Portland cement are available for carbonation. The preliminary estimates showed
that the C02 binding capacities per cubic meter of concrete were in the range 83-124 kg
C02/m3 and 64-84 kg C02/m3 for Portland cement (CEM I) and fly ash cement (CEM 11/AV),
respectively. The calculations showed that the COz-binding by concrete carbonation
cannot be neglected when the environmental footprint of concrete is assessed.
formed when air or water-borne C02 dissolves in the concrete pore water. When the
carbonation layer is formed during service life, the carbonate species need to penetrate
through the carbonated layer and the carbonation rate slows down with the square root of
time (rough approximation). When concrete structures are demolished and refined to
Recycled Concrete Aggregates (RCA) the surface area is largely increased. The C02
binding rate per unit mass of concrete and thus the total amount of bound C02 may
therefore increase in the secondary life (after demolishing stage) provided sufficient access
to C02. By applying the prevailing cement chemistry, it was shown that 72 % of the total
CaO in Portland cement are available for carbonation. The preliminary estimates showed
that the C02 binding capacities per cubic meter of concrete were in the range 83-124 kg
C02/m3 and 64-84 kg C02/m3 for Portland cement (CEM I) and fly ash cement (CEM 11/AV),
respectively. The calculations showed that the COz-binding by concrete carbonation
cannot be neglected when the environmental footprint of concrete is assessed.
