| 1. |
- Rempling, Rasmus, 1976, et al.
(författare)
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The need for research and innovation to facilitate upscaling of low-carbon concrete
- 2023
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Ingår i: IABSE Congress New Delhi 2023 Engineering for Sustainable Development. - : International Association for Bridge and Structural Engineering (IABSE). - 9781713883128 ; , s. 1199-1206
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Konferensbidrag (refereegranskat)abstract
- For decades, research has been carried out with a focus on concrete structures during curing to mitigate the risk of thermal cracking. Computer programs and aids/tools have also been developed to assess stress and cracking risk analysis of concrete structures during curing. However, today with the recent introduction of low-carbon concretes to reduce the environmental impact of constructions, the reliability of the tools and working procedures, i.e. concrete characterization, is questioned, and a roadmap for research and innovation is called for. The project's primary purpose is to investigate the need for research and innovation regarding upscaling the usage of low-carbon concrete. The nature of the study is based on an industry-focused workshop with specialists from Scandinavia. Increased knowledge of hardening concrete's cracking risk-related properties is of the utmost importance for the construction industry as the need for its understanding has recently increased.
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| 2. |
- Bado, Mattia Francesco, et al.
(författare)
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Characterization of concrete shrinkage induced strains in internally-restrained RC structures by distributed optical fiber sensing
- 2021
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Ingår i: Cement and Concrete Composites. - : Elsevier BV. - 0958-9465. ; 120
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Tidskriftsartikel (refereegranskat)abstract
- The present paper reports the result of an inter-university experimental investigation on concrete shrinkage induced strains on embedded rebars instrumented with Distributed Optical Fiber Sensors (DOFS). The monitoring was performed for a standard 28 days drying time and for a shorter 6 days time span (reflecting realistic constructions schedules accelerations to meet set deadlines). The tested specimens were Reinforced Concrete (RC) tensile members differing in their geometry, DOFS employed and fiber/rebar bonding techniques. Regarding the latter, a combination of cyanoacrylate (for gluing) and silicone (protection) was found to be the optimal one for deployments inside RC structures. The DOFS-reported combined effect of concrete shrinkage and creep on the embedded rebars is compared with the Model Code 2010's predictions and employed to extract conclusions on the residual performance of the RC members at the end of their drying phase.
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| 3. |
- Bado, Mattia Francesco, et al.
(författare)
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Distributed optical fiber sensing bonding techniques performance for embedment inside reinforced concrete structures
- 2020
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 20:20, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- Distributed optical fiber sensors (DOFS) are modern-day cutting-edge monitoring tools that are quickly acquiring relevance in structural health monitoring engineering. Their most ambitious use is embedded inside plain or reinforced concrete (RC) structures with the scope of comprehending their inner-workings and the functioning of the concrete-reinforcement interaction. Yet, multiple studies have shown that the bonding technique with which the DOFS are bonded to the reinforcement bars has a significant role on the quality of the extracted strain data. Whilst this influence has been studied for externally bonded DOFS, it has not been done for embedded ones. The present article is set on performing such study by monitoring the strain measurement quality as sampled by DOFS bonded to multiple rebars with different techniques and adhesives. These instrumented rebars are used to produce differently sized RC ties later tested in tension. The discussion of the test outputs highlights the quasi-optimal performance of a DOFS/rebar bonding technique consisting of incising a groove in the rebar, positioning the DOFS inside it, bonding it with cyanoacrylate and later adding a protective layer of silicone. The resulting data is mostly noisefree and anomalies-free, yet still presents a newly diagnosed hitch that needs addressing in future research.
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| 4. |
- Berrocal, Carlos Gil, 1986, et al.
(författare)
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Characterisation of bending cracks in R/FRC using image analysis
- 2016
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 90, s. 104-116
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Tidskriftsartikel (refereegranskat)abstract
- In this study, experiments were conducted to induce bending cracks of specific surface crack width to reinforced concrete beams made of plain concrete (RC) and reinforced concrete beams made of fibre reinforced concrete (R/FRC). After injecting and impregnating the cracks with dyed epoxy resin, image processing and analysis were employed to investigate the internal crack morphology. Several crack features including crack width (accumulated, effective and maximum), branching and tortuosity were defined and quantified. The results showed that in addition to arrested crack development, the presence of fibres yielded a distinctive change in the internal crack pattern, including increased branching and tortuosity, both of which have positive implications regarding concrete permeation. Likewise, specimens with fibres exhibited reduced maximum individual crack widths near the rebar, potentially increasing the ability of autogenous crack healing and reducing the risk of corrosion initiation.
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| 5. |
- Berrocal, Carlos Gil, 1986
(författare)
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Chloride Induced Corrosion of Steel Bars in Fibre Reinforced Concrete
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chloride-induced corrosion of reinforcement is the most widespread degradation mechanism affecting the durability of reinforced concrete structures. Macro-cracks provide a preferential path for moisture, oxygen and Cl ions to reach the embedded reinforcement, playing a major role in their total transport. Therefore, to effectively control macro-cracking is essential with respect to the service life. Fibre reinforcement, even at low dosages, leads to arrested crack development, also in conventionally reinforced concrete. Thus, it could be advantageous to use fibres in civil engineering structures where their crack limiting effect is of interest. However, despite the increased corrosion resistance of steel fibres, the use of both types of reinforcement in chloride environments raises questions.The present study aimed at investigating the viability of employing fibre reinforcement to improve the durability performance of conventionally reinforced concrete structures with respect to delayed and/or reduced corrosion by controlling the development of cracks. The work includes long-term experiments of naturally corroded concrete elements with and without fibres, in sound and cracked state, subjected to different loading conditions and various crack widths. Complementary material tests to study the influence of fibres on different properties governing the corrosion of steel reinforcement in concrete were also carried out. Additionally, experiments were started to determine the possible formation of galvanic cells between metallic fibres and steel bars.The results showed that while the electrical resistivity of concrete was unavoidably reduced by the presence of steel fibres, the ingress of chloride, assessed through migration and bulk diffusion tests, was not signicantly affected. The analysis of the corrosion initiation period in cracked specimens revealed that, when loaded to reach the same surface crack width, fibre reinforced specimens performed similar or better than their plain concrete counterparts. However, the improvement achieved by adding fibres was, in general, minor compared to the results obtained for uncracked specimens, highlighting the utmost importance of cracks for the initiation of corrosion. Accordingly, corrosion initiated almost immediately in specimens subjected to a sustained load, i.e. with open cracks, regardless of the presence of fibres. This observation indicated the existence of a critical crack width above which the initiation period could be, in practice, disregarded.Questions that remain unclear and that require further research include: (i) the influence of reduced electrical resistivity on the corrosion rate of rebar; (ii) the risk of galvanic corrosion caused by the different steels used for fibres and bars; and (iii) the effectiveness of fibres to control the development of corrosion-induced cracks and spalling of the concrete cover. Forthcoming results from the experiments developed during this project, which are still ongoing, are expected to shed some light on these questions.
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| 6. |
- Berrocal, Carlos Gil, 1986, et al.
(författare)
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Corrosion-induced cracking and bond behaviour of corroded reinforcement bars in SFRC
- 2017
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368. ; 113, s. 123-137
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates, experimentally and numerically, the effect of fibre reinforcement on the initiation of corrosion-induced cracks in concrete and the bond behaviour of corroded reinforcement bars in fibre reinforced concrete. The fibres, due to their confining effect, contributed to delay crack initiation, improve the post-peak bond behaviour and retain the initial splitting strength for corrosion levels of up to 8%. The mechanisms for delayed crack initiation were explained through 3D finite element analyses of the experiments whereas a 1D model, using experimental bond-slip curves as an input, was employed to quantify the beneficial effect of fibres on the reinforcement anchorage length.
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| 7. |
- Berrocal, Carlos Gil, 1986, et al.
(författare)
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Corrosion-induced cracking and bond behaviour of corroding reinforcement bars in SFRC
- 2017
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Ingår i: Nordic Concrete Research. - 0800-6377. - 9788282080569 ; , s. 123-126
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Konferensbidrag (refereegranskat)abstract
- In this study, an experimental programme has been carried out to investigate the influence of fibres on the onset of corrosion-induced splitting cracks. Cylindrical lollipop specimens with a centrally positioned Ø16 mm bar and varying cover depths from 40 to 64 mm were subjected to accelerated corrosion. A constant current of 100 μA/cm2 was impressed through the specimens and the electrical resistance between each rebar and an external copper mesh acting as cathode was monitored. The fibres, due to their confining effect, contributed to delay crack initiation, improve the post-peak bond behaviour and retain the initial splitting strength for corrosion levels of up to 8%.
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| 8. |
- Berrocal, Carlos Gil, 1986, et al.
(författare)
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Corrosion initiation in cracked fibre reinforced concrete: Influence of crack width, fibre type and loading conditions
- 2015
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 98, s. 128-139
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports results from an ongoing project aimed at investigating the influence of fibre reinforcement on corrosion of rebar in chloride environments. Material tests showed that the resistivity of concrete decreased with the addition of fibres, whereas the chloride migration coefficient remained unaffected. Fibres at low dosages (
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| 9. |
- Berrocal, Carlos Gil, 1986, et al.
(författare)
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Corrosion of Steel Bars Embedded in Fibre Reinforced Concrete under Chloride Attack: State-of-the-Art
- 2016
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846. ; 80, s. 69-85
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Forskningsöversikt (refereegranskat)abstract
- This literature review summarises the influence of fibres on the main parameters governing corrosion of conventional reinforcement. The ability of fibres to suppress crack growth has proven to decrease permeation in cracked concrete while chloride diffusion, in uncracked concrete, seems to remain unaffected by the addition of fibres. Steel fibres in concrete are considered to be insulated owing to the high impedance of the passive layer. However, they will become conductive if they are depassivated. Although low carbon steel fibres may suffer severe corrosion when located near the concrete surface or bridging the cracks, embedded fibres will remain free of corrosion despite high chloride contents. Published experimental observations indicate that fibres had little influence on the corrosion rate of rebars. Steel fibres improved corrosion resistance of rebars moderately; this is mainly attributed to a reduced ingress of chlorides due to arrested crack growth.
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| 10. |
- Berrocal, Carlos Gil, 1986
(författare)
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Corrosion of steel bars in fibre reinforced concrete: corrosion mechanisms and structural performance
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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