A Method to Estimate Carbon Dioxide Sequestration in Concrete Pavement Interiors

Ordinary Portland cement (OPC) is used in many pavements which reabsorb some of the CO2 emissions from the initial cement production over time in a process commonly referred to as carbonation. Estimating the extent of CO2 sequestration throughout pavements is crucial in understanding their true carbon footprints. Surface carbonation has been classically modeled with a front of extensive carbonation that slowly moves inward with rates on the order of millimeters per year, but provides little sequestration information beyond the front, which was usually assumed to be negligible. This work proposes an isopleth (chart with lines of similar characteristics) method for estimating average CO2 sequestration deeper within pavement samples based on quasi-steady-state equilibrium partitioning at various ages using material and chemical characteristics. Together with the surface carbonation model, the isopleths might provide more comprehensive carbon dioxide sequestration estimates. One inch (25.4 mm) deep hydrated cement samples were prepared, aged for several years with only their top surfaces exposed, and then analyzed for CO2 sequestration along their depths with thermal gravimetric analyses. The results indicate average interior CO2 sequestration levels exceeding 25 % based on moles of calcium in periods under three years, and even higher levels when samples are made with 25 % low calcium supplementary cementitious material. Similar tests on aged concrete samples would be needed to extrapolate the method to pavements.