Over time, carbon dioxide from the environment reacts with the calcium hydroxide in cement. The reaction produces calcium carbonate and reduces the pH in the concrete. As the pH reduces, the protective oxide layer in steel reinforcing starts to break down, resulting in corrosion of the steel reinforcing. Once this occurs the structure starts to deteriorate more rapidly, and the structural integrity is affected.
ALS recently led the durability and structural assessment of a pre-stressed concrete water tank. In this project, the carbonation test of the shotcrete layer protecting the pre-stressed wires on the external face of the tank showed that although the average depth of carbonation was about 5mm, the carbonation front has deeply progressed in cracks and resulted in depassivation of shotcrete around pre-stressed wires and spot corrosion of wires. Our further metallurgical assessment of wires showed an average 30% cross-sectional loss due to the spot corrosion has impacted the pre-stressed wires and this strength reduction factor is required to be applied in our structural adequacy calculations.
ALS offers a range of concrete inspection testing services for a number of civil and water infrastructure, industrial plants, port facilities ageing assets.
If you have a concrete structure you are concerned about, please contact our structural and durability assessment team.