Mesoscale modelling of carbonation in concrete made with RCA

Concrete is the most widely used construction material worldwide, relying
heavily on natural aggregates and sand. Their growing scarcity, together with
the need to reduce CO2 emissions and construction and demolition waste, has
increased interest in recycled concrete aggregates (RCA) produced by crushing
concrete waste. However, RCA exhibit strong variability, which may compro-
mise longevity. Among durability concerns, carbonation is critical because it
depassivates steel reinforcement, which initiate corrosion. Carbonation kinetics
are strongly controlled by transport properties (CO2 diffusion and moisture
transport) and by the amount of carbonatable material. Therefore, quantifying
how RCA characteristics affect these effective properties is essential to assess
long-term performance and to support mix design.
This work investigates the influence of key concrete parameters on effective
transport properties and carbonatable material content. Using a mesoscale ap-
proach, a numerical workflow is developed to build representative volume ele-
ments (RVEs) including aggregates, and solve mesoscale transport problems to
obtain homogenized properties such as effective diffusion coefficients and car-
bonatable material content. A sensitivity/parametric analysis is then performed
to rank the most influential RCA-related parameters and quantify the variability
induced by the heterogeneity of recycled aggregates.
The outcomes provide key insights into how RCA properties govern transport-
driven durability processes and offer guidance for designing recycled aggregate
concretes with improved carbonation resistance.