Case Study of Concrete Repairs on Jetty in Port Nolloth, Northern Cape

Abstract

This paper describes the rehabilitation of the jetty in Port Nolloth, Northern Cape. The history of the jetty is not 100% certain, but it is believed that the previous wooden jetty was replaced by the current concrete structure towards the late 1940’s. There were no as-built drawings of the jetty structure available. The jetty was in a deteriorated state and required a very thorough forensic investigation to determine the state of deterioration and to develop a design for the rehabilitation thereof. The forensic study, conducted by a specialist sub-contractor, included ferro-scanning (steel reinforcement number and spacing), core samples, non-destructive testing on the structure and visual inspections. From the investigation it was found that the concrete used for the jetty is generally of good quality (high strength, good compaction, and good aggregate distribution) and cover depths are in most locations in excess of 40 mm. However, after 60 years of marine exposure the structure suffers from very high chloride contamination and severe rebar corrosion damage. Previous repairs were found to generally have failed to offer any noteworthy protection to the structure. Large cracks, spalled concrete and exposed corroded steel reinforcement were evidence of the chloride contamination. A structural analysis to verify the jetty capacity was also completed and it was found that it is imperative that the original cross-sectional area of the piles is restored. The methods proposed and employed to rehabilitate the jetty were patch repair (trowel applied concrete and sprayed concrete), sectional casting of concrete (with formwork), and replacement of reinforcement. The work commenced mid-2016 and was substantially completed end of 2017.