18. Concrete repair methodology based on crack width and location

Water ingress via cracks in concrete can lead to significant degradation in reinforced concrete structures. It has traditionally been assumed that damage is proportional to crack width. As such, repair work has sought to prevent water ingress via a combination of grouting and surface coating. Repairing undersurface cracks, particularly on the underside of bridge structures, usually requires scaffolding and is more labor-intensive and time-consuming.

We used an internal imaging system to investigate water penetration in concrete. We found there was less water ingress via cracks on the undersurface compared to cracks on the top and side surfaces. Interestingly, when we compared undersurface cracks of width 1 mm and 0.2 mm, we found less evidence of water ingress through the wider crack, as well as limited penetration (see Figure 1). We also found that applying a coating to the undersurface hinders natural evaporation and actually leads to an increase in internal moisture levels, with the associated risk of steel corrosion (see Figure 2).

In light of the above, we conclude that repairs to concrete cracks on the undersurface should give priority to suppressing concrete flaking rather than preventing water ingress as such. Repairs to top surface cracks, on the other hand, should be designed to prioritize preventing water penetration (see Figure 3).