Please use this identifier to cite or link to this item: https://scholarbank.nus.edu.sg/handle/10635/167027
Title: CORROSION INDUCED CRACKING IN CONCRETE
Authors: CHIENG KING WU
Keywords: Corrosion
impressed current
cracking
photoelastic technique
cover
cover/diameter ratios
Faraday's Law
half-cell potential
longitudinal crack
Issue Date: 1990
Citation: CHIENG KING WU (1990). CORROSION INDUCED CRACKING IN CONCRETE. ScholarBank@NUS Repository.
Abstract: This project investigates the corrosion of steel embedded in mortar/concrete by impressed current. An attempt was made through this accelerated corrosion test to determine the inter-relationship between mortar quality, cover thickness and bar size on the intensity of corrosion to cause cracking. Other parameters such as the volumetric fraction of the cement paste, size of aggregates and intensity of impressed current were also studied. Half-cell potential values of embedded bar when the cover cracks and the study of the distribution of stresses on the surface of the specimen using the photoelastic technique were also Investigated. In addition, analytical solutions were obtained to predict the degree of corrosion of the steel bar that would result in cracking of the cover. From the experiments, it was found that the rusting of bare steel and steel bars embedded in mortar by impressed current follows Faraday's Law. For steel embedded in mortar, a linear relationship exists between the initial current density and the cover thickness when a constant voltage is applied. Experimental results show that a more corrosion resistant structure can be produced when both the cover thickness and size of the bar are taken into consideration. Having a constant cover, an increase in corrosion protection can be offered by replacing larger diameter bars with smaller bars having the same cross-sectional area as before. Regardless of the bar size, the same cover to diameter ratios result in similar percentage of weight loss of the bar to crack the cover. The degree of corrosion of the rebar to cause cracking of the cover mortar is not significantly affected by the type of steel bar, concentration of the electrolyte, doubling the applied potential and with the addition of superplasticizer. However, concrete specimens having the same compressive strength as that of mortar specimens has about 25 % to 38 % lower degree of corrosion of the rebar to cause cracking of the cover. Specimens air-cured under laboratory conditions crack when the half-cell potential value versus copper-copper sulphate half-cell electrode is about - 500 mV. This measured potential is not significantly affected by cover thickness. From the photoelastic coating technique, it was found that for a single corroding bar, the maximum tensile stress is always along the longitudinal direction of the bar as expected, which is why corrosion usually results in crack along the length of the bar. The analytical solution obtained can be used to predict the degree of corrosion to cause cracking of the cover. It was found that the predicted values agreed well with that obtained from experiments.
URI: https://scholarbank.nus.edu.sg/handle/10635/167027
Appears in Collections:Master's Theses (Restricted)

Show full item record
Files in This Item:
File Description SizeFormatAccess SettingsVersion 
b17139363.pdf12.83 MBAdobe PDF

RESTRICTED

NoneLog In

Page view(s)

5
checked on Jul 9, 2020

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.