Atmospheric Carbon Dioxide and Premature Deterioration of Steel-Reinforced Concrete Structures

Estimates of atmospheric carbon dioxide (CO2) concentration have been increasing from a two thousand year low set in the early 1600s to record highs today. Although current concentrations may still appear small on a human scale (0.04%), they represent about a 40% increase in the chemical concentration of CO2 in the atmosphere. It is now recognized that change to this degree can have significant consequence to materials at the molecular level.

Several decades ago, a pattern of earlier-than-anticipated deterioration of steel-reinforced concrete structures began to emerge. This pattern would later be described as a global phenomenon, a significant financial burden on society, and one of the most demanding challenges facing the construction industry.

While various causes of reinforced concrete deterioration have long been recognized, changes in concrete formulation and construction practices that were implemented in the 1960s, ‘70s, and 80s are now seen as contributing to reduced durability. Recently, a new causal factor was recognized – rising concentrations of atmospheric carbon dioxide that can accelerate a process known as concrete carbonation. Wang et al. (2010) and Stewart et al. (2011) found that increasing CO2 levels will increase the rate of carbonation and the likelihood of carbonation-induced corrosion of reinforcing materials within reinforced concrete worldwide. Anticipated higher temperatures will also likely contribute to increases in concrete deterioration rates.

This report summarizes findings regarding premature deterioration of steel-reinforced concrete structures, causes, implications, and potential solutions. Links to additional information sources are provided.