Civil Engineering March 2021 | Vol 29 No 2

Civil Engineering March 2021 37 TESTING Concrete testing should be carried out on existing structures as a way of ensuring the concrete is appropriately repaired. The following tests can be utilised to determine the corrosion causing mechanism: Carbonation tests The testing of concrete for carbonation involves the application of phenolphtha- lein indicator onto the freshly exposed surface of the concrete. Phenolphthalein appears purple to light pink when in contact with an alkaline substance and remains colourless should the substance have a low pH (less than 8). Applying phenolphthalein to the surface of a carbonated concrete core will result in a certain depth of the concrete on the exposed face side remaining the same colour, this is measured as the depth of carbonation. Concrete cover tests It is the layer of concrete covering the embedded steel reinforcement which resists the ingress of carbon dioxide and chlorides and provides protection against corrosion. Testing the depth of this concrete cover can be done on in-situ concrete using various electromagnetic scanning equipment. Cover measurements assist in the prediction of a remaining service life of the concrete structure affected by corrosion. The remaining service life is accepted as the time from the current age of the structure to the time at which it is no longer serviceable. Chloride profiling Chloride profiling involves measuring chloride content at different depths into the concrete. A significant chloride con- tent at the exposed surface of the concrete and a decreasing content with depth moving into the concrete would indicate that chloride ingress is occurring. Durability tests Concrete durability tests (oxygen permeability test and water sorptivity test) provide an indication of the perme- ability of the concrete, thereby providing information on the likelihood of moisture and carbon dioxide ingress. The chloride conductivity durability test provides information on how freely chlorides can move in the concrete. CASE STUDY Naidu Consulting was appointed to provide ad-hoc structural and drainage services to SANRAL’s Eastern region. This included the condition assessment and repair of four bridges and one culvert that were identified as requiring im- mediate investigation and repair through SANRAL’s Bridge Management System (BMS) – an inventory of information collected on all bridge structures owned by SANRAL. The defects observed in the structures included spalling and cracking of the concrete, that varied in degrees of urgency across the structures as well as in each element of individual structures. The aim of the concrete testing was to determine the cause of defects, to confirm the ap- propriate repair methodology which will form part of the project specifications, and to provide a reference against which the deterioration rate could be established for future maintenance. No as-built drawings were available for most of the structures and the results of the testing investigation would therefore also form part of the as-built records. Figure 3 is an image of a drawing prepared by Naidu Consulting of one of the bridges, specifying where cores were to be drilled on the structure for the concrete testing. Images of the bridge elements were also shown on the drawing, allowing the con- tractors to better understand and price the access requirements. Figure 1 Severe spalling occurring on a bridge structure Figure 2 Spalling occurring on a bridge structure