Corrosion of steel bars in fibre reinforced concrete: corrosion mechanisms and structural performance
Doktorsavhandling, 2017

The viability of employing fibre reinforcement to improve the durability performance of RC structures by delaying and/or reducing rebar corrosion and by mitigating the structural impact of corrosion-induced damage have been investigated. Given the enhanced crack control of FRC, it could be advantageous to use fibres in civil engineering structures to decrease the ingress of corrosion-initiation substances. However, the combined use of both types of reinforcement in chloride environments raises questions regarding the potential influence that fibres may have on the corrosion process of conventional rebar. Long-term experiments were carried out featuring naturally corroded RC elements subjected to different loading conditions and varying crack widths. Complementary short-term experiments were carried out to isolate the influence of fibres on individual parameters governing the process of reinforcement corrosion, such as chloride diffusion, internal cracking and electrical resistivity, as well as on corrosion-induced damage, such as cracking and spalling of the cover. From the experiments it was found that the ingress of chloride ions into concrete, assessed through migration and bulk diffusion tests, was not significantly affected by the presence of fibres. The internal crack pattern of conventionally RC beams subjected to bending loads revealed a tendency for crack branching and increased tortuosity when fibres were present, which can potentially decrease the permeation of concrete and promote crack self-healing. The time to corrosion initiation, evaluated through half-cell potential monitoring, for fibre reinforced beams were similar or longer than the plain concrete ones. However, the effect of fibres was minor compared to the difference between cracked and uncracked specimens, thus highlighting the importance of cracks for the initiation of corrosion. The DC resistivity was found to be unaffected by steel fibres, indicating that they do not pose a risk for increased corrosion rates. Gravimetric steel loss measurements showed that the corrosion level of reinforcement bars embedded in FRC beams was similar or even lower than for plain concrete beams. Moreover, the examination of the corrosion patterns and a detailed analysis of individual corrosion pits revealed a tendency for more distributed corrosion with reduced cross-sectional loss in FRC. Corrosion-induced cracking of the cover was somewhat delayed by fibre reinforcement, particularly for small cover thicknesses, which was attributed to the additional source of passive confinement provided by the fibres. Thereafter, corrosion-induced cracks were effectively arrested by fibres, which resulted in an enhanced bond behaviour of SFRC with no apparent loss of bond strength and high residual bond-stresses. Fibres also had a positive effect on the residual flexural capacity of corroded beams, which generally displayed a slightly increased load-carrying capacity and rotation capacity compared to plain concrete beams with corroded reinforcement. The promising results obtained in this study indicate that FRC may be effectively used to extend the service life of civil engineering structures by delaying and reducing reinforcement corrosion as well as by mitigating the structural effects of corrosion-induced damage.

chloride-induced corrosion

cracking

Fibre reinforced concrete

electrical resistivity

residual flexural capacity

durability

reinforcement bond

Lecture hall SB-H1, Sven Hultins gata 6, Chalmers
Opponent: Prof. Henrik Stang, Department of Civil Engineering, Technical University of Denmark, Denmark

Författare

Carlos Gil Berrocal

Chalmers, Bygg- och miljöteknik, Konstruktionsteknik

Characterisation of bending cracks in R/FRC using image analysis

Cement and Concrete Research,; Vol. 90(2016)p. 104-116

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Corrosion-induced cracking and bond behaviour of corroded reinforcement bars in SFRC

Composites Part B: Engineering,; Vol. 113(2017)p. 123-137

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Corrosion initiation in cracked fibre reinforced concrete: Influence of crack width, fibre type and loading conditions

Corrosion Science,; Vol. 98(2015)p. 128-139

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Corrosion of Steel Bars Embedded in Fibre Reinforced Concrete under Chloride Attack: State-of-the-Art

Cement and Concrete Research,; Vol. 80(2016)p. 69-85

Artikel i vetenskaplig tidskrift

C.G. Berrocal, K. Hornbostel, M. Geiker, I. Löfgren, K. Lundgren, D. Bekas - Electrical resistivity measurements in steel fibre reinforced cementitious materials

C.G. Berrocal, I. Löfgren, K. Lundgren - The effect of fibres on steel bar corrosion and flexural behaviour of corroded RC beams

The most widely used construction material in the world is concrete and reinforced concrete (RC) structures are therefore vital for the built environment and the infrastructure. But as due to its versatility, concrete is used for structures exposed to harsh environments. Constructing durable structures is extremely important to owners of infrastructure and for society. Presently, corrosion of reinforcement due to chlorides, present in the sea water and in de-icing salts used to remove ice and snow from the roads, is today regarded as one of the major problems affecting the durability of RC structures. In uncracked concrete, steel reinforcement bars are protected by the alkaline environment provided by the concrete while the concrete cover acts as a physical barrier against the ingress of chlorides and other corrosion-inducing agents. In practice, however, cracks can be found in most of the existing RC structures. These cracks often become preferential paths for the ingress of external agents, which have a negative impact on the durability of the structures. As a result, current structural codes specify restrictive crack width limitations as a way of ensuring the durability of RC structures.

The concept of using discrete fibres to improve the behaviour of building materials is ancient and intuitive. One of the main benefits of using fibre reinforced concrete (FRC) in combination with conventional reinforcement bars is a better control of the cracking process, which results in a reduction of both the crack widths and crack spacing. Despite the great potential of FRC, a generalized use of fibre reinforcement in large civil engineering structures is, today, still limited to a few applications. Through a series of experimental studies, the present work investigates the effect of fibre reinforcement on the mechanisms controlling the corrosion of steel bars in concrete as well as on the structural performance of corroding RC elements.

The main finding from this work, which is of interest to owners of the civil infrastructure, contractors and engineers, is that FRC could be used in civil engineering structures exposed to chloride environments to effectively delay and reduce reinforcement corrosion as well as to mitigate the structural effects of corrosion-induced damage, leading to an extended service life of such structures.

Drivkrafter

Hållbar utveckling

Styrkeområden

Building Futures

Materialvetenskap

Ämneskategorier

Samhällsbyggnadsteknik

Annan materialteknik

Kompositmaterial och -teknik

Korrosionsteknik

ISBN

978-91-7597-608-2

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4289

Utgivare

Chalmers tekniska högskola

Lecture hall SB-H1, Sven Hultins gata 6, Chalmers

Opponent: Prof. Henrik Stang, Department of Civil Engineering, Technical University of Denmark, Denmark