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Influence of coincident cracks in concrete on reinforcement corrosion
Cracks can accelerate the penetration of aggressive substances such as chloride and carbon dioxide into concrete leading to premature corrosion of embedded reinforcing bars. Cracks may be coincident i.e. lie above and follow the line of the reinforcing bars, or intersecting i.e. cross reinforcing bars. The former type is widely acknowledged to present a more serious threat to reinforcement corrosion and would appear to be unavoidable in concrete construction. Yet, the research on coincident cracks is almost non-existent. The aim of this project is to investigate the influence of coincident crack width, depth and cement composition on chloride-induced corrosion. Three designs of specimens were employed. Type A consists of concrete slabs with a maximum surface crack width of 0.4mm. Type B contains parallel-sided cracks which were achieved by inserting steel shims into green concrete of equal depth, 0.1mm, 0.2mm, 0.3mm or 0.4mm wide which terminate approximately 9mm above reinforcing bars. Type C contains artificial cracks with identical widths to those of type B specimens but unlike these, the cracks extend to the surface of reinforcing bars. The binder types investigated were 100% Portland cement, 35%Portland cement /65% Ground granulated blast-furnace slag and 70%Portland cement /30% Fly ash. There were 6 type A, 30 of type B and 15 of type C specimens made of all three binder compositions tested. Corrosion was monitored using half-cell potentials, linear polarisation resistance, and zero resistance ammeter. The data was analysed by ANOVA and post-hoc tests. Also, the chloride content of the specimens as well as gravimetric mass losses of the reinforcement were evaluated. The results show that there is no threshold crack width below which there is a low risk of corrosion. The results also show that concrete made of blended cement may offer better protection to embedded reinforcing bars than pure PC mixes.
Influence of coincident cracks in concrete on reinforcement corrosion
Cracks can accelerate the penetration of aggressive substances such as chloride and carbon dioxide into concrete leading to premature corrosion of embedded reinforcing bars. Cracks may be coincident i.e. lie above and follow the line of the reinforcing bars, or intersecting i.e. cross reinforcing bars. The former type is widely acknowledged to present a more serious threat to reinforcement corrosion and would appear to be unavoidable in concrete construction. Yet, the research on coincident cracks is almost non-existent. The aim of this project is to investigate the influence of coincident crack width, depth and cement composition on chloride-induced corrosion. Three designs of specimens were employed. Type A consists of concrete slabs with a maximum surface crack width of 0.4mm. Type B contains parallel-sided cracks which were achieved by inserting steel shims into green concrete of equal depth, 0.1mm, 0.2mm, 0.3mm or 0.4mm wide which terminate approximately 9mm above reinforcing bars. Type C contains artificial cracks with identical widths to those of type B specimens but unlike these, the cracks extend to the surface of reinforcing bars. The binder types investigated were 100% Portland cement, 35%Portland cement /65% Ground granulated blast-furnace slag and 70%Portland cement /30% Fly ash. There were 6 type A, 30 of type B and 15 of type C specimens made of all three binder compositions tested. Corrosion was monitored using half-cell potentials, linear polarisation resistance, and zero resistance ammeter. The data was analysed by ANOVA and post-hoc tests. Also, the chloride content of the specimens as well as gravimetric mass losses of the reinforcement were evaluated. The results show that there is no threshold crack width below which there is a low risk of corrosion. The results also show that concrete made of blended cement may offer better protection to embedded reinforcing bars than pure PC mixes.
Influence of coincident cracks in concrete on reinforcement corrosion
Myrzakulova, Takhmina (author)
2023-10-28
Doctoral thesis, UCL (University College London).
Theses
Electronic Resource
English
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