Corrosion inhibition in self-compacting concrete

Blankson, Marva Angela (2013) Corrosion inhibition in self-compacting concrete. PhD thesis, University of Nottingham.

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This research was undertaken to investigate the effectiveness of carboxylic corrosion inhibitor in fly ash and silica fume (respectively FM and SM) samples and nitrite-based corrosion inhibitors in fly ash (FGC) sample. The findings from this research show that the addition of the carboxylic inhibitor altered the hydration of fly ash and silica fume self-compaction concretes (SCCs) by delaying the formation of ettrngite and the production of portlandite in the FM and SM samples and ultimately causing the calcium aluminate hydrates to surround the fly ash and cement particles. It was shown that this resulted in slight setting retardation in the silica fume particles but significant delay in the hydration of the fly ash SCC. Further, this development brought about by the use of the carboxylic inhibitor contributed bleeding of different levels in the fly ash and silica fume samples and this condition was shown to increase the heterogeneity of the FM and SM SCCs. Although addition of the nitrite-based inhibitor retarded the setting of paste of the fly ash SCC, no noticeable delay in the hardening of the concrete was manifested. When the nitrite-based inhibitor was included in the fly ash SCC, the physical structure of the interfacial transition zone and the bulk of the mortar were found to be less porous and hence the concrete displayed a higher level of homogeneity.

The incorporation of the carboxylic inhibitor increased the corrosion resistance of the silica fume concrete to chloride -induced corrosion but the corrosion resistance of the fly ash SCC was only improved when exposed to low concentration of chloride ions. The reduction in the inhibiting capacity of the FM SCC to high chloride load was the result of the elevated degree of porosity and higher propensity to chloride migration resulting from the use of the carboxylic compound. On the other hand, when the nitrite compound was used in the fly ash SCC, the current density was reduced which is ascribed to the effectiveness of the inhibitor and the reduction in the porosity and chloride migration that resulted from the incorporation of the inorganic compound. However, as the concentration of the corrosion inhibitors increased, the corrosion resistance of the inhibited SSCs reduced. The study also shows that the nitrite fly ash see showed the ability to undergo self-healing of corroded reinforced concrete but the carboxylic inhibited types of SCCs (FM and SM) could only prevent further corrosion after the corrosive environment is removed. Comparative testing showed that, in all three types of inhibited SCCs, there is a high probability that the inhibiting capacity will become depleted under certain conditions of chloride exposure.

Using the nitrite inhibitor in the fly ash SCC also imparted moderate to significant improvement to the 7 - 60-day compressive strengths but the long term strength of the concrete was slightly lower than that of the traditional fly ash SCC. When the carboxylic compound was used in the fly ash SCC, the 7 - 28-day compressive strengths were marginally lowered and the 60 - 90-day compressive strengths were profoundly reduced. The addition of the carboxylic inhibitor to the silica fume SCC also significantly reduced the 28 - 90-day compressive strengths of the concrete.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Dawson, A.R.
Thom, N.H.
Keywords: Carboxylic corrosion inhibitor, Fly ash self compaction concrete, Silica fume self compation concrete, Chloride exposure
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 27792
Depositing User: Blore, Mrs Kathryn
Date Deposited: 17 Nov 2014 10:28
Last Modified: 26 Dec 2017 10:22

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