Influence of cracks on concrete carbonation resistance

Abstract

In reinforced concrete (RC) structures carbonation induced corrosion is one of the biggest durability issue. There are many factors that affect carbonation process (CO2 concentration, relative humidity, temperature, curing conditions and concrete porosity). Probably, the most important factor that affects carbonation process is the appearance of cracks on RC structures. With relatively low concrete tensile strength, cracks are almost inevitable. According to the current state of the art, the cracks have not yet been considered as a parameter in carbonation depth prediction model which is used for defining the service life of concrete structures. The main objective of this research is to analyse the influence of cracks on concrete carbonation resistance using own experimental results and the application of available prediction models regarding carbonation depth. For that purpose, prismatic RC samples without cracks and with different crack width (0.05 mm, 0.10 mm, 0.15 mm, 0.20 mm and 0.30 mm) were made and subjected to accelerated carbonation. The accelerated carbonation tests were performed during 28 days at a CO2 concentration of 2%, relative humidity (RH) of 65±5% and a temperature of 20±2°C. The conducted analysis showed that even with low crack widths (0.05 mm) the maximum carbonation depth was significantly higher compared with the uncracked samples. In all cases, the cracks behaved as an additional exposed surface through which the CO2 molecules were diffused perpendicularly to the crack wall. The crack impact area was approximately the same regardless of the crack width. Further than 10 mm, the carbonation depths remained constant. Also, with decreasing the length at which the average value of the carbonation depth was calculated (averaging length), the mean carbonation depth increased. Finaly, the ratio between the calculated carbonation depths (according to fib-Model Code 2010) of cracked and uncracked samples was up to three times.