Preliminary Investigation Into the Rate of Carbonation of Concrete Blocks Under Normal Production Yard Conditions

The release of CO2 from calcination during the manufacture of cement can be partially or fully offset by the CO2 it naturally absorbs during its lifetime. This paper reports results from a preliminary investigation into the rate of carbonation in concrete blocks stacked in a production yard over a period of 6 months. The blocks were stacked in a normal manner under natural exposure conditions. Carbonation progress was determined by splitting the blocks and spraying the freshly exposed surface with a phenolphthalein solution at intervals over the test period. It was found that the rate of the carbonation front progression differed depending on the exposure face and the type of block. Carbonation fronts on exposed front (FF) or side faces (SF) were seen to advance at rates of well over 1 mm per week for the initial 6 months of exposure. Exposed top faces (TF) of blocks showed a slower rate of carbonation; just over 0.6 mm per week. The speed of the advance of the carbonation front into concrete slowed over time, however, it was noted that slower progression occurred during the second half of testing over the wetter winter period. Rates of carbonation and estimates of carbon sequestration were calculated using the measurements taken in the investigation. The findings suggest that carbonation should be included in the manufacturing stage of life cycle assessments for open textured concrete products such as blocks. This research identifies parameters that should be included in future testing as well as areas where the test methodology would benefit from development.