Carbon Sequestration in Old and New Portland Cement Concrete Pavement Interiors

Abstract

Measurements of carbon emissions and sequestration are important in estimating the global warming potential of the built environment. Manufacturing of portland cement contributes to a portion of anthropogenic CO2 emissions through the chemical process of calcination. CO2 can also be sequestered from the air into concrete in the reverse process commonly called carbonation. Most research studies on carbonation typically focus on the exposed surfaces where the levels might be high. There is little information on the CO2 which might be sequestered in the interior of pavements. Together, the near surface measurements and the interior levels will provide better information on carbon sequestration. Pavement samples that were from one to 85 years old were sliced and paste/mortar specimens were chipped from different depths. CO2 sequestration was estimated using a thermo-gravimetric analysis (TGA) for the carbonate levels and X-ray fluorescence analysis (XRF) for elemental analysis. The results indicate that the amount of carbon sequestration in the interior of these pavements is in the early years of life around 10% of that released during calcinations increasing to 25% or more in arid climates. Interior carbon sequestration in humid climates might exceed 35% or more over several decades, but more information is needed to validate this.