Health Monitoring of Berthing Structures

It is increasingly recognized in the recent past that reinforced concrete (RC) berthing structures are not permanently durable and free from maintenance. A large number of cases of damage and failure in RC berthing structures have been reported worldwide, and rehabilitation of such structures involves phenomenal cost, besides challenging technical problems in identifying appropriate rehabilitation techniques and materials. In order to arrive at a suitable rehabilitation strategy, non-destructive tests (NDT) are carried out to assess the condition of concrete in the distressed RC structural elements. Health monitoring of berthing structures through in situ testing is a specialized job requiring reliable test methods and instruments. The paper discusses in detail the rehabilitation of berthing structures at Cochin, Tuticorin and Chennai Port Trusts. In the case of the Cochin Port Trust, distressed RC structural elements of the North Tanker Berth (NTB) jetties and South Tanker Berth (NTB) jetties exhibited half-cell potentials more than −350 mV indicating that there is a greater than 90% probability that reinforcing steel corrosion is occurring in that area at the time of measurement as per the reference guidelines of ASTM C-876. Based on the analysis of the various NDT tests, viz. ultrasonic pulse velocity (UPV) test, core drilling and carbonation tests and the evaluation of chlorides and pH, a detailed rehabilitation methodology including under water micro-concrete jacketing has been suggested for the distressed RC structural elements of the central platform, Breasting dolphin and the approach trestle of both the jetties. coal jetties 1 and 2 and the oil jetties at Tuticorin Port Trust were rehabilitated after conducting detailed NDT investigation in the RC structural elements of the berthing dolphin, main jetties, approach jetties, mooring dolphin and catwalk of the three jetties. The severe distress in the RC structural elements of the three jetties could be attributed to the failure of the earlier repair carried out using shotcreting. Based on the extensive NDT tests conducted, the condition of the concrete was assessed and a rehabilitation methodology consisting of micro-concrete jacketing and installation of self-regulating anodes was suggested for the various distressed RC structural elements of the three jetties. Modification/rehabilitation of finger jetties was carried out at the Chokhani floating dry dock in Chennai Port Trust. NDT tests were conducted to arrive at the rehabilitation methodology. The heavily corroded pile liners were cut and removed from −0.20 m level by using under water cutting gear. The cracked and spalled concrete was fully removed to expose the full circumference of the steel. The rust in steel was completely removed and cleaned by chemical means. Additional steel was provided for modification of pile for fender arrangement. Sacrificial zinc anodes were installed, and leads were provided for connecting to a monitoring box. Under water micro-concrete was used after coating the rebars with a zinc primer. The UPV tests conducted after repair for a period of nearly 6 years at every 6 month interval indicated that the integrity of the concrete were still good. The half-cell potentials measured at every 6 month interval for a period of 6 years showed values more positive than −200 mV indicating that there is a greater than 90% probability that no reinforcing steel corrosion is occurring in that area at the time of measurement. The half-cell potential values more positive than −200 mV even after six years clearly indicate that the self- regulating anodes were effective in preventing further distress to the RC structural elements.