Environmental effects on cover cracking due to corrosion

This paper examines the environmental conditions under which the time to cracking of concrete, due to pressure caused by rust production on the surface of steel bars, is short. To determine this time, volume compatibility is assumed, which allows for compaction of all materials affected by the pressure, including the rust itself. A fracture mechanics concept is also used to signal cover failure. The model reveals that time-to-cover-cracking is a function of the rust production and the strength of the system to resist the resulting pressure. It is found that the highest corrosion rates are towards the end of autumn and the beginning of spring, when humidity reaches relatively high values with moderate temperatures. On the other hand the highest resistance of the system to corrosion production is during summer, since the humidity is low. In addition, rust pressure drops during summer due to creep; water moves out of the concrete which also deforms, giving more space into which the rust can expand. Structures exposed to humid summers would suffer from high rust production and rapid cover spalling. The model can assist in the decision-making process to identify when a bridge is more likely to corrode, which could indicate that new materials, like fibre reinforced polymers might be the most suitable design solution despite their higher initial cost.