Remedial Technology completed the condition assessment and designed the repair and cathodic protection (CP) system for the Houshi Wharf in Xiamen, China. This impressed current CP system is the first such installation to a major existing wharf structure in China and is an innovative application of a cost effective corrosion control solution to a marine structure.
In May 2013, Remedial Technology was commissioned to develop a remediation solution for the Houshi Wharf in Xiamen, China.
The wharf was originally built in 1997. Signs of localised concrete deterioration appeared approximately 10 years after construction and led to the application of patch repair to all defective areas. Our inspection in 2013 revealed that the repair work had actually accelerated the concrete deterioration problems with evidence of new spalling, delamination and cracking around the repaired areas.
The investigation of the wharf included delamination testing of the entire structure to assess the extent and the nature of the problem. In addition, detailed testing including chloride analysis, half-cell potential mapping and resistivity testing was undertaken alongside a pilot CP installation to determine the optimum CP current required to stop the ongoing corrosion.
The results of the investigation suggest that existing deterioration was mainly due to the initial cracking of the concrete in certain locations of the pile caps, which has allowed accelerated ingress of chloride through the cracks, leading to reinforcement corrosion and concrete deterioration. In the good concrete areas of the pile caps, and in most cases, the thick (80-90mm) concrete cover and relatively dense and good quality concrete had until now prevented the ingress of chloride to the level of the steel reinforcement.
Due to budget constraints, a staged approach was adopted for the rehabilitation process. Stage 1 of the process was to control the corrosion of the embedded reinforcement in the spalled concrete and high risk corrosion areas. Stage 2 of the process involved the future incorporation of any newly identified high risk corrosion and spalled areas into the CP system. During Stage 1 of the work, repair was carried out to all identified delaminated and spalled concrete areas. Mixed Metal Oxide (MMO) ribbon anodes were installed within, and at the perimeter of the repaired areas to protect the reinforcement in the repaired areas and eliminate the possibility of incipient anode formation in the adjacent concrete areas. In addition, a CP global system, which has the capacity to protect the entire structure was incorporated into the structure. This global system allows any new concrete areas which could potentially deteriorate in the future to be incorporated within the CP system without the need for the installation of any new conductor bars in the concrete, cabling, junction boxes or new T/R units. The addition of any new CP areas in the future will simply require extending and welding the conductor bars connecting the anodes in the newly repaired areas to an already existing network of conductor bars which are installed at pre-determined locations within the structure.
The CP design allows for verification of the current delivery to each pile cap of the structure using a combination of systematic selection of the locations of reference electrodes and cabling design. The repair work and CP installation was completed in January 2014.
Our extensive experience in the assessment of concrete marine structures and in the design and installation of a large number of CP systems in Australia and globally over the past 25 years was used in this project to deliver a state of the art, heavy duty, reliable and low maintenance CP system for the corrosion protection of Houshi Wharf. This new staged approach of repair and CP application used by Remedial Technology in this project is an example of an innovative and cost effective application of technology engineering in the field of infrastructure rehabilitation.