Civil Engineering March 2021 | Vol 29 No 2

38 March 2021 Civil Engineering TESTING Concrete testing was recommended to the client and carried out to gather informa- tion on the condition of the concrete, as well as to determine the cause of corro- sion in the concrete structures. Three of the bridge structures are located along the South Coast, and two structures are located inland, one near Volkrust and another near Colesberg. The likelihood of chloride-induced cor- rosion was deemed to be low for both the structures located inland, based on their low exposure to chlorides from airborne salts and seawater, and the absence of any indication of chlorides in the ground- water. Chloride tests were therefore not conducted on these two structures. Figure 4 shows the location of the structures and Table 1 summarises the respective tests performed on each bridge. RESULTS The results of the concrete tests per- formed on one of the structures on the South Coast (Bridge 1) are discussed to illustrate why concrete testing is impera- tive and what conclusions can be drawn from such an investigation. The results are presented in Table 2. COMPRESSIVE STRENGTH TESTS It was concluded that the compressive strength tests conducted on the cores which were drilled from each of the structures all performed well and had shown adequate in-situ concrete strength. Concrete performing well in compressive strength did not however mean that the structure was at a lower risk of defects. There is evidence that carbonation locally increases the cement paste density and as a result, can increase the compressive strength (Neville, 1996). CHLORIDE PROFILE RESULTS In all three structures, the chloride con- centration profile remained constant with depth (presented by an average content). It was concluded that the chlorides recorded were built into the concrete mix during construction and had not migrated into the concrete. The results obtained were compared to chloride content limits across codes and literature. SANS 10100-2:2014 limits the total chlorides, as a per- centage of the cementitious material, to 0.2%. Beyond this threshold, the Figure 3 Bridge drawing prepared by Naidu Consulting Figure 4 Locality plan of the five bridge structures Table 1 Tests carried out for each of the five bridge structures Bridge 1 Bridge 2 Bridge 3 Bridge 4 Bridge 5 In-situ compressive strength test      Concrete cover tests      Carbonation test      Oxygen permeability test      Water sorptivity test      Chloride conductivity test      Chloride profiling     