Carbonation Shrinkage of Hydrated Cement Paste

Synopsis: Large samples of hcp were prepared with W/C from 0.3 to 0.8 and small prisms of 3/3/90 mm were cut off. After drying the samples at constant rh ranging from 30 to 90 % up to equilibrium lengths, CO2 was introduced and its concentration kept constant at 2%. The length changes were recorded as a function of time. It is shown that carbonation shrinkage of hcp can be well described by the hyperbolic function ∆l/l = at / b+t. (where l is the length, t the time), a and b parameters).The highest carbonation shrinkage reaches 3 to 4 mm/m. The time necessary to reach half of the final shrinkage (the parameter b) is minimum between 50 and 80 % rh for all hcp samples studied. After the shrinkage measurements, all prisms were crushed and the CO2 content, i.e. the CO2 uptake of all specimens, was determined. The relationship between shrinkage and CO2 uptake is discussed with respect to the microstructure and the formation of minerals other than calcite