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

Date

2021-11-24

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University of Nairobi Research Archive

Abstract

With increased competing demands of sustainable structures to support the United Nationssustainable development goals, new technologies are evolving for efficient design,manufacture and construction of civil and environmental engineering projects. Researchershave upscaled their effort to develop techniques that can monitor the performance of civilengineering structures within their service life for optimum return from investment. Reinforcedconcrete structures constitute a good percentage of components of civil engineering structuresin water conveyancing structures. The service life of these structures affect sustainable systemsincluding hydropower generation, water supply for consumption and for irrigation. Existingservice life models of reinforced concrete structures are structure specific and each of themhave inherent limitations resulting from the specific use.Most codes of practice define the design life of reinforced concrete water conveyancingstructures as 50 years. The performance of a structure at any reference age within the servicelife of a structure should be able to be defined. Deterioration due to reinforcement corrosionaffects 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 isneed to create a service life model to predict their performance. The main objective of thisresearch was to create a corrosion model to predict the service life of water conveyancingstructures.To realize the main objective an accelerated corrosion experiment to monitor evolution andpropagation of crack width to 0.2mm maximum. There was a variation of concretecharacteristic strength and reinforcement cover. In order to extend the service life of reinforcedconcrete, corrosion inhibitors are often used. Corrosion inhibitors prevent corrosion or lowersthe rate of corrosion. Test samples from four selected corrosion inhibitors; a calcium nitrite andvinitrate based, a dimethylathanolamine based organic inhibitor and fly ash in combination witha selected brand of cement X, Y or Z were used. From the results, the rate of corrosion decreaseswith increase in concrete cover and strength. The results were used in derivation of a corrosionmodel for the service life of reinforced concrete water conveyancing structures.A corrosion model for prediction of the service of reinforced concrete water conveyancingstructures was formulated by dividing the service life into the initiation period and propagationperiod. The initiation period was found by dividing the critical penetration depth by the rate ofcorrosion. Models for calculating the critical penetration depth were evaluated from which theXu and Shayan model was selected as applicable for this work. A model for the propagationperiod was derived by calculating the period from corrosion initiation to appearance of 0.05mmcrack and adding up to propagation of the crack width from 0.05mm to 0. 2mm.The results ofthe proposed corrosion propagation period model were compared with the experimental resultsand models of other researchers and found that it has a strong correlation with the laboratoryoutput.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 wasalso noted that all the selected corrosion inhibitors increased the bond strength of reinforcedconcrete. A corrosion current density model was formulated for corrosion propagation period.A corrosion model for prediction of the service life of reinforced concrete water conveyancingstructures was proposed and compared with experimental work and models of otherresearchers. 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.

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