Nele De Belie

Ghent University, Gand, Flanders, Belgium

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Publications (238)326.07 Total impact

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    ABSTRACT: After several years of research in the Magnel Laboratory for Concrete Research (Belgium) to obtain concrete with self-healing properties, two of the most promising mechanisms were tested on a larger scale. One mechanism is based upon the encapsulation of polyurethane which is embedded in the matrix. Self-repair is obtained when crack creation causes capsule breakage, release and subsequent hardening of the polyurethane inside the crack. The second approach relies upon the addition of superabsorbent polymers (SAPs) to the concrete. These SAPs take up water entering via the crack, swell and block the crack. In addition, when they release their water content later on, they induce continued hydration and calcium carbonate precipitation. Real-scale concrete beams (150 mm × 250 mm × 3000 mm), with and without self-healing properties, were made and the self-healing efficiency was evaluated after crack creation by means of four-point bending. Based on the measured crack width reduction over time, it was shown that improved autogenous crack healing was obtained when superabsorbent polymers were added to the mixture. From the acoustic emission analysis, the proof of glass capsule breakage upon crack formation was obtained. X-ray tomography, fluorescent light microscopy and thin section analysis demonstrated that cracks were indeed partially filled with hydration products, calcium carbonate crystals and/or polyurethane which leached from the broken embedded capsules. Although it would be expected from both findings that this would result in a decrease of water ingress into the healed cracks, this could not be proven within this study.
    No preview · Article · Mar 2016 · Construction and Building Materials
  • Ali Behnood · Kim Van Tittelboom · Nele De Belie
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    ABSTRACT: pH is an important parameter to indicate the alkalinity level of concrete. The most severe concrete damages are caused or accompanied by dropping of the alkalinity level and consequently, decrease of the pH value of concrete. Therefore, it is crucial to measure the pH of concrete by an accurate and reliable method. This paper critically reviews the methods that have been developed for measuring the pH of fresh and hardened concrete. These methods are categorized in two broad divisions including destructive and non-destructive methods. The expression, ex-situ and in-situ methods are explained in detail as destructive methods, while the use of embedded potentiometric electrodes (mainly metal/metal oxide electrodes) and fibre optic sensors are evaluated as non-destructive methods. Also, advantages and drawbacks of each method are investigated and they are compared based on different technical and practical aspects. Despite the broad range of used methods for measuring the pH of concrete, there is no standardized test procedure. Because of the important role of pH with regard to durability of concrete structures, it is highly recommended that the required measures are taken to develop a specific standard test method for measuring the pH of concrete with a high level of accuracy, repeatability and reproducibility.
    No preview · Article · Feb 2016 · Construction and Building Materials
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    ABSTRACT: This paper focuses on mechanical regains that can be obtained due to self-healing of cementitious materials. Experimentally, small cracks with a width of around 10 μm were healed by water immersion and corresponding regains were assessed by means of three-point-bending tests. A general discussion about stiffness and strength regains is provided with the help of newly introduced indices. Besides, the first comprehensive finite element model to characterise the micro-mechanical properties of the healing products is introduced, based on the coupling of the microstructural hydration model CEMHYD3D and the finite element code Cast3M. The main objective is to analyse the healing potential and rate, as well as the nature of the healing products. The nature of the simulated healing products is in agreement with observation conducted using SEM/EDX on artificial cracks created at early age.
    Full-text · Article · Feb 2016 · Cement and Concrete Research
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    Didier Snoeck · J Dewanckele · V Cnudde · N De Belie
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    ABSTRACT: Autogenous healing of cracks may offer a solution for brittle cementitious materials. In this study, the healing building blocks are available through the well-designed ultra-ductile microfibre-reinforced mixture with a low water-to-binder ratio and water is available through the inclusion of superabsorbent polymers. As visual inspection demonstrates that the crack is completely closed at the surface, one may ask whether this healing also is present in the interior of the crack. X-ray computed microtomography was therefore used to study the extent of autogenous healing in cracked cylindrical specimens. It was found that the extent of autogenous healing in a cementitious material depends on the crack depth. Only near the crack mouth (0 till 800-1000 μm) the crack is closed by calcium carbonate formation in case of wet/dry cycles. In combination with superabsorbent polymers, the extent of healing was more substantial. For mixtures containing superabsorbent polymers there was even partial healing in the interior of the crack when stored at a relative humidity of 60% or more than 90%. Energy-dispersive spectroscopy combined with microscopic analysis showed that the healing products were mainly calcium carbonate. The smart cementitious material with superabsorbent polymers is thus an excellent material to use in future building applications as the healing capacity is improved.
    Full-text · Article · Jan 2016 · Cement and Concrete Composites
  • J. Feiteira · E. Gruyaert · N. De Belie
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    ABSTRACT: Self-healing concrete aims at the autonomous healing of small cracks with widths in the order of a few hundreds of micrometers. Up to now, the existing research on this topic has relied mainly on CaCO3 and rigid polymers to fill the cracks, which are best suited for healing of static cracks due to their high stiffness and brittle behaviour. This study aims at assessing the strain capacity of flexible polymers bridging healed cracks, thus assessing their fitness for healing of moving cracks. The polymers tested result from the release and curing of encapsulated polymer precursors, which cover a wide range of properties in terms of viscosity, foaming and mechanical properties after hardening. The series of tests performed allowed identifying the precursors with good crack-filling potential, leading to successful sealing of cracks. Despite the sealing achieved, regain of mechanical stiffness is limited to a maximum of 30% and only for crack mouth displacements up to 20 μm. The widening of healed cracks that resulted in no significant deterioration of the sealing performance was, at best, between 50% and 100% of their initial width, due to failure in the polymer matrix or at the interface with the crack walls. The strain capacity achieved shows potential for significantly improving the durability of cracked concrete elements under cyclic loading, although the sealing effect may be disrupted for the long term widening of real cracks due to fatigue.
    No preview · Article · Jan 2016 · Construction and Building Materials

  • No preview · Article · Jan 2016 · Aci Materials Journal
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    Didier Snoeck · Bavo Priem · Peter Dubruel · Nele De Belie
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    ABSTRACT: Energy efficiency in buildings has been a hot topic in recent years and the demand for alternatives regarding heat storage and thermal insulation is high. Materials with a large thermal mass like concrete can be optimized in terms of heat capacity. Useful for this purpose are Phase-Change Materials (PCMs), which show a high heat of fusion with a melting point within the ambient temperature range. In this paper, the effect of encapsulated PCMs on the thermal behavior and setting process of mortar at early age, and on the strength and thermal behavior of hardened mortar were studied. Such hardened PCM-mortar warms up more gradually and expands the thermal comfort in buildings. PCMs delay the setting process and cause a shift of the corresponding heat of hydration peak and reduce the strength. However, the strength remains high enough for many applications. A possible application was studied, related to thermal cracking of insulated concrete sandwich panels, where the encapsulated PCMs show an influence on the thermal properties in a positive way as they reduce strains. PCMs are innovative and promising materials to use in future applications of concrete structures to promote thermal comfort and to reduce thermal cracking.
    Full-text · Article · Jan 2016 · Materials and Structures
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    Full-text · Article · Dec 2015 · Materials
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    ABSTRACT: Attentive monitoring and regular repair of concrete cracks are necessary to avoid further durability problems. As an alternative to current maintenance methods, intrinsic repair systems which enable self-healing of cracks have been investigated. Exploiting microbial induced CaCO3 precipitation (MICP) using (protected) axenic cultures is one of the proposed methods. Yet, only a few of the suggested healing agents were economically feasible for in situ application. This study presents a NO3− reducing self-protected enrichment culture as a self-healing additive for concrete. Concrete admixtures Ca(NO3)2 and Ca(HCOO)2 were used as nutrients. The enrichment culture, grown as granules (0.5–2 mm) consisting of 70% biomass and 30% inorganic salts were added into mortar without any additional protection. Upon 28 days curing, mortar specimens were subjected to direct tensile load and multiple cracks (0.1–0.6 mm) were achieved. Cracked specimens were immersed in water for 28 days and effective crack closure up to 0.5 mm crack width was achieved through calcite precipitation. Microbial activity during crack healing was monitored through weekly NOx analysis which revealed that 92 ± 2% of the available NO3− was consumed. Another set of specimens were cracked after 6 months curing, thus the effect of curing time on healing efficiency was investigated, and mineral formation at the inner crack surfaces was observed, resulting in 70% less capillary water absorption compared to healed control specimens. In conclusion, enriched mixed denitrifying cultures structured in self-protecting granules are very promising strategies to enhance microbial self-healing.
    Full-text · Article · Nov 2015 · Frontiers in Microbiology
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    ABSTRACT: Superabsorbent polymers (SAPs) are a promising additive to be used in the building industry but may induce microstructural changes. Water vapour sorption may be used to characterize the change in pore structure of cementitious materials, but the technique is difficult to interpret. In the present paper, static and dynamic vapour sorption (DVS) measurements were performed and compared to nitrogen adsorption experiments. The models of Dubinin-Radushkevich and Barrett-Joyner-Halenda were hereby applied to study pores in the micro- and mesopore range. The results show that cement pastes with SAPs and without additional water show a slight decrease in porosity in the micro- and mesopore range. Cement pastes with SAPs and with additional water show no significant change of porosity in the micropore range and a slight increase in the larger mesopore range. These new findings give insight into the effects of SAPs on the microstructure and strength of cementitious materials.
    Full-text · Article · Nov 2015 · Cement and Concrete Research
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    ABSTRACT: Natural fibres such as flax and hemp fibres are mainly used in the textile industry, but some have outstanding mechanical properties and have a great potential as reinforcement in cementitious composites, as an alternative to synthetic microfibres. However, due to their hydrophilicity the amount of multiple cracking that occurs in cementitious composites reinforced with natural fibres is reduced. Also, natural fibres may degrade in alkaline environments. Therefore, proper mixtures and multiple chemical treatments are required to improve natural fibre characteristics. The application of flax and hemp fibres in cementitious composites was examined, with a focus on inducing multiple cracking under tensile stresses. The mechanical properties were studied for the natural fibres and the cementitious composites. The degradation of the natural fibres in alkaline environments was also studied. Multiple cracking was achieved and further improvements were made by chemically treating the fibres. Mercerisation with a 2% (m/m) [NaOH] resulted in optimal multiple cracking. This multiple cracking resulted in small cracks widths, which allowed optimal autogenous healing when exposed to wet/dry-cycles. Natural fibres were thus found to be a suitable eco-friendly alternative to synthetic microfibres.
    Full-text · Article · Nov 2015 · Biosystems Engineering

  • No preview · Conference Paper · Oct 2015
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    ABSTRACT: Self-healing concrete holds promising benefits to reduce the cost for concrete maintenance and repair as cracks are autonomously repaired without any human intervention. In this study, the application of a carbonate precipitating bacterium Bacillus sphaericus was explored. Regarding the harsh condition in concrete, B. sphaericus spores were first encapsulated into a modified-alginate based hydrogel (AM-H) which was proven to have a good compatibility with the bacteria and concrete regarding the influence on bacterial viability and concrete strength. Experimental results show that the spores were still viable after encapsulation. Encapsulated spores can precipitate a large amount of CaCO3 in/on the hydrogel matrix (around 70% by weight). Encapsulated B. sphaericus spores were added into mortar specimens and bacterial in situ activity was demonstrated by the oxygen consumption on the mimicked crack surface. While specimens with free spores added showed no oxygen consumption. This indicates the efficient protection of the hydrogel for spores in concrete. To conclude, the AM-H encapsulated carbonate precipitating bacteria have great potential to be used for crack self-healing in concrete applications.
    Full-text · Article · Oct 2015 · Frontiers in Microbiology
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    Didier Snoeck · Nele De Belie
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    ABSTRACT: Cracks in concrete are inevitable and for durability reasons, the cracks should be repaired. Concrete has the intrinsic property to heal itself. But, the passive form of autogenous healing plays only an inferior role for a complete repair of a cementitious material. The main cause is that only cracks of limited width may heal completely. For that reason, microfibers are added to the mixture, as they cause the formation of multiple small cracks. In this way, a ductile material is designed with the property to heal itself efficiently. This paper will overview the different fiber reinforced cementitious composites of the last decade, the link with autogenous healing, results from the literature and future prospects.
    Full-text · Article · Oct 2015 · Construction and Building Materials
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    ABSTRACT: Fiber cement panels were treated with urea and various calcium solutions with and without live or dead cells of Bacillus sphaericus LMG 222 57, to produce a surface layer of biocalcite; they were then exposed to the environment in São Paulo, Brazil, for 22 months. The calcifying treatment that produced the most colonisation-resistant surface was living bacteria + medium B4 + urea. The resistance of these biocalcified panels was related to their low water absorption, porosity and surface hydrophilicity, linked to the smaller size of the crystals compared to other treatments. Carbonation of the fiber cement before calcification visually increased biofilm formation, but the same calcifying treatment produced highest fouling resistance in this pre-carbonated group. Control samples, without calcification, allowed the development of considerable fouling, sometimes including the filamentous cyanobacterial genus, Scytonema, indicative of mature sub-aerial biofilms. There was no significant visual degradation of the calcite crystals associated with the colonising fungi and phototrophs after 22 months’ exposure. Biocalcification may safely be used to reduce the fouling-associated darkening of fiber cement and for protection and repair of cementitious building materials.
    No preview · Article · Sep 2015 · International Biodeterioration & Biodegradation
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    Didier Snoeck · Nele De Belie
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    ABSTRACT: To obtain sustainable highly-durable structures with a long service life, one should tackle the problem of cracking in concrete. Not only is it aesthetically unwanted, cracking may also impair the service life of the construction. Therefore, the ingress of water and harmful substances should ideally be avoided and should be independent of manual repair to be reliable. Autogenous healing in strain-hardening cementitious materials in combination with superabsorbent polymers can be a solution. Here, the superabsorbent polymers will swell to several hundred times their own size when making contact with fluids, thus sealing the crack from intruding fluids. Afterwards, the water is provided to the cementitious matrix for autogenous healing. Further hydration and the precipitation of calcium carbonate crystals may hereby close the crack completely. One of the most important criterions is the crack width control, as only very narrow cracks may close due to autogenous healing. This is achieved by means of incorporated microfibres, leading to bridging action and multiple cracking. In this research, several types of fibres were tested. These include different types of commercially-available polyvinyl alcohol and polypropylene. It was found that some types of synthetic fibres may accelerate the autogenous healing capacity, due to their chemical nature. The type of fibre can hereby promote the nucleation of calcium carbonate crystals on the surface of the fibre, stitching the crack. This is especially the case with fibres consisting of polar hydroxyl groups. In combination with superabsorbent polymers, this feature was improved substantially as the water was gradually released towards the cementitious matrix, leading to a more abundant amount of crystals at the crack faces. The natural fibres are alternatives for synthetic fibres due to their good mechanical properties, but should be chemically treated to receive multiple cracking and to act as nucleation sites for calcium carbonate. In general, the most ideal material is a strain-hardening cementitious material with polyvinyl alcohol fibres and superabsorbent polymers. This material can close cracks efficiently and may thus lead to more durable constructions.
    Full-text · Conference Paper · Sep 2015
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    ABSTRACT: Superabsorbent polymers (SAPs) are a new and promising additive used in the building industry. They are mostly used to mitigate autogenous shrinkage. SAPs, however, have various effects on concrete properties and the most important influence is the possible change in microstructure due to internal curing. The microstructure is closely linked to the strength of the material and the microstructure is thus a key property. Dynamic water vapour sorption (DVS) may be used to characterize the change in pore structure of cementitious materials, but the technique is difficult to interpret. In the present paper, DVS measurements were performed to characterize the changes induced by SAPs in the textural and sorption properties of the material. Different models were hereby applied to study pores in the micro- (Dubinin-Radushkevich) and mesopore (Barrett-Joyner-Halenda) range and to better interpret the sorption measurements. The results show that cement pastes with SAPs and without additional water show a slight decrease in the micro- and mesopore range. The results are closely linked to a cement paste with the same effective water-to-cement ratio. Cement pastes with SAPs and with additional water show no significant difference in the micropore range and a slight increase in larger mesopore range. These new findings give insight into the effects of SAPs on the microstructure and strength of cementitious materials.
    Full-text · Conference Paper · Aug 2015
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    Didier Snoeck · Ole Mejlhede Jensen · Nele De Belie
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    ABSTRACT: Fly ash and blast-furnace slag containing binders are frequently used in the construction industry and it is important to know the extent of autogenous shrinkage and its (ideal) mitigation by superabsorbent polymers in these systems as a function of their age. In this paper, the autogenous shrinkage was determined by manual and automated shrinkage measurements. Autogenous shrinkage was reduced in cement pastes with the supplementary cementitious materials versus Portland cement pastes. At later ages, the rate of autogenous shrinkage is higher due to the pozzolanic activity. Internal curing by means of superabsorbent polymers is successful, independent of this long term higher rate of shrinkage in mixtures with supplementary cementitious materials.
    Full-text · Article · Aug 2015 · Cement and Concrete Research
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    ABSTRACT: Bacteria that can induce calcium carbonate precipitation have been studied for self-healing concrete applications. Due to the harsh environment of concrete, i.e. very high pH, small pore size and dry conditions, protection methods/materials have been used to preserve the bacterial agents. A wide screening of commercially available materials is thus required to evaluate them as alternatives. This study describes the influence of six commercially available possible protection approaches (diatomaceous earth, metakaolin, expanded clay, granular activated carbon, zeolite and air entrainment) on mortar setting and compressive strength when combined with either Bacillus sphaericus spores or Diaphorobacter nitroreducens and their respective nutrients. The influence of two novel, self-protected, bacterial agents was also investigated within the same scope. The most severe effect on setting time was observed as an undesirable delay of 340 min in all samples containing nutrients for ureolytic bacteria. Samples containing B. sphaericus spores showed the most significant decreases in compressive strength up to 68%. Yet, the addition of either D. nitroreducens or its respective nutrients did not cause major impact on both the setting times and the compressive strengths of the mortar specimens. The latter thus appears to be a suitable bacterial agent for further research on self-healing concrete. Likewise, the use of the novel self-protected bacterial agents did not affect the setting and the compressive strength of mortar. These results pave the way to replace protection materials with self-protection techniques. The latter should be further investigated for development of microbial self-healing concrete.
    Full-text · Article · Jul 2015 · Construction and Building Materials
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    Full-text · Conference Paper · Jul 2015

Publication Stats

3k Citations
326.07 Total Impact Points

Institutions

  • 1996-2016
    • Ghent University
      • • Department of Structural Engineering
      • • Department of Biochemical and Microbial Technology
      Gand, Flanders, Belgium
  • 1998-2001
    • University of Leuven
      • Department of Civil Engineering
      Louvain, Flanders, Belgium