Simulation Model for Prediction of the Service Life of Water Conveyancing Reinforced Concrete Structures

Abstract

With increased competing demands of sustainable structures to support the United Nations sustainable development goals, new technologies are evolving for efficient design, manufacture and construction of civil and environmental engineering projects. Researchers have upscaled their effort to develop techniques that can monitor the performance of civil engineering structures within their service life for optimum return from investment. Reinforced concrete structures constitute a good percentage of components of civil engineering structures in water conveyancing structures. The service life of these structures affect sustainable systems including hydropower generation, water supply for consumption and for irrigation. Existing service life models of reinforced concrete structures are structure specific and each of them have inherent limitations resulting from the specific use. Most codes of practice define the design life of reinforced concrete water conveyancing structures as 50 years. The performance of a structure at any reference age within the service life of a structure should be able to be defined. Deterioration due to reinforcement corrosion affects the performance of reinforced concrete water structures and hence their service life. Because of the high investments involved and risk associated with water structures, there is need to create a service life model to predict their performance. The main objective of this research was to create a corrosion model to predict the service life of water conveyancing structures. To realize the main objective an accelerated corrosion experiment to monitor evolution and propagation of crack width to 0.2mm maximum. There was a variation of concrete characteristic strength and reinforcement cover. In order to extend the service life of reinforced concrete, corrosion inhibitors are often used. Corrosion inhibitors prevent corrosion or lowers the rate of corrosion. Test samples from four selected corrosion inhibitors; a calcium nitrite and vi nitrate based, a dimethylathanolamine based organic inhibitor and fly ash in combination with a selected brand of cement X, Y or Z were used. From the results, the rate of corrosion decreases with increase in concrete cover and strength. The results were used in derivation of a corrosion model for the service life of reinforced concrete water conveyancing structures. A corrosion model for prediction of the service of reinforced concrete water conveyancing structures was formulated by dividing the service life into the initiation period and propagation period. The initiation period was found by dividing the critical penetration depth by the rate of corrosion. Models for calculating the critical penetration depth were evaluated from which the Xu and Shayan model was selected as applicable for this work. A model for the propagation period was derived by calculating the period from corrosion initiation to appearance of 0.05mm crack and adding up to propagation of the crack width from 0.05mm to 0. 2mm.The results of the proposed corrosion propagation period model were compared with the experimental results and models of other researchers and found that it has a strong correlation with the laboratory output. From the experiments, it was noted that due to variation in chemical composition of cement, the choice of cement brand affects the rate of corrosion of steel embedded in concrete. It was also noted that all the selected corrosion inhibitors increased the bond strength of reinforced concrete. A corrosion current density model was formulated for corrosion propagation period. A corrosion model for prediction of the service life of reinforced concrete water conveyancing structures was proposed and compared with experimental work and models of other researchers. The proposed service life model compares well with the experimental work. Further research has been recommended to improve the model. Keywords: Corrosion, Hydropower, Service life model, Water conveyancing structures.