Continuous monitoring of the moisture, shrinkage, and carbonation effects on foam concrete performance

The carbonation of conventional concrete is a slow process that generally affects exposed surfaces, however, this reaction is significantly facilitated in foam concrete because of its highly cellularized cementitious matrix. Coupled with the rapid moisture loss, foam concrete tends to exhibit drastic compositional, dimensional, and mechanical changes over a short period of time, highly contingent on environmental conditions. In this study, we investigated the change in the shrinkage, resonant frequency, compressive strength, and carbonation degree of foam concrete at various density levels (2.0, 1.0, and 0.6 g/cm³), under 50% and 100% relative humidity conditions, over 84 days. Under each condition, a physical and a chemical approach (sand and shrinkage-reducing admixture, respectively) were compared to determine the most suitable shrinkage mitigation. The results show that foam concrete undergoes intensive shrinkage within a couple of days when exposed to ambient conditions, with higher values present for the lower density levels. While both mitigation approaches effectively restrain shrinkage of the 1.0 g/cm³ samples, the physical-based shrinkage mitigation can cause marked foam degradation to the 0.6 g/cm³ samples. Additionally, results indicate that, due to rapid carbonation of both Ca(OH)₂ and C–S–H, substantial CO₂ uptake can take place in foam concrete within 84 days.