Effect of crack opening on carbon dioxide penetration in cracked mortar samples

The paper addresses the effect of crack opening on the ability of carbon dioxide to diffuse along a crack. The experimental tests were carried out on mortar samples. A mechanical expansive core was used to generate cracks of constant width across the thickness of the sample. Cracked specimens with crack openings ranging from 9 to 400 μm were exposed to accelerated carbonation for 65 days. Then they were removed to determine the depth of carbonation perpendicular to the crack path. Theses depths were compared to the measured ones on the reference samples. The results show that crack opening significantly influences the ability of carbon dioxide to diffuse along the crack. Indeed, the carbonation depth perpendicular to the crack wall indicates a lower capacity to diffuse in cracks less than 41 μm in width. For crack openings ranging from 9 to 41 μm, there was still diffusion along the crack path. Moreover, carbonation of the interface between steel and mortar was observed inducing a depassivation of the reinforcement. For the duration of the experiments, there was no diffusion in crack openings of less than 9 μm. The effect of interlocking phenomena between the fracture surfaces on the ability of carbon dioxide to diffuse along the crack, was also studied. The results showed that interlocking phenomena in cracks is the main factor limiting the diffusion of carbon dioxide in fine cracks.