[Show abstract][Hide abstract] ABSTRACT: Up to now, glass capsules, which cannot resist the mixing process of concrete, have been mostly used in lab-scale proof-of-concept to encapsulate polymeric agents in self-healing concrete. This study presents the design of polymeric capsules which are able to resist
the concrete mixing process and which can break when cracks appear. Three different polymers with a low glass transition temperature Tg have been extruded: Poly(lactic acid) (PLA) (Tg = 59 °C), Polystyrene (PS) (Tg = 102 °C) and Poly(methyl methacrylate/n-butyl methacrylate) (P(MMA/n-BMA)) (Tg = 59 °C). After heating the capsules prior to mixing with other components of the mix, to shift from a brittle state to a rubbery state, their survival ratio considerably increased. Moreover, a part of the capsules, which previously survived the concrete mixing process, broke with crack appearance. Although some optimization is still necessary concerning functional life of encapsulated adhesives, this seems to be a promising route.
Cement and Concrete Composites 01/2015; · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Self-healing concrete has been scrutinized by several researchers and some industrial concrete producers in relation to the remediation of the occurrence of micro-cracks. Such cracks are a quite well known problem that can lead to corrosion of the steel reinforcement and thus to the possible failure of the entire concrete structure. The need to repair these cracks as soon as possible leads to maintenance costs which can be of the order of €130 (direct costs) per m3 of concrete. Recent scientific studies indicate that a Microbial Induced Carbonate Precipitation (MICP), using microbial spores as active agent, can be an alternative for the actual repair methods. However, the production of bacterial spores is yet imposing considerable costs. According to some concrete producers they would be willing to pay about €15 to €20 per m3 of concrete for a bio-based self-healing product. However, the actual cost of spores production and encapsulation represent a total cost which is orders of magnitude higher. This article analyzes the costs for the biological self-healing in concrete and evaluates the industrial challenges it faces. There is an urgent need to develop the production of a bio-additive at much lower costs to make the biological self-healing industrial applicable. Axenic production and a possible non-axenic process to obtain ureolytic spores were analyzed and the costs calculations are presented in this paper.
Journal of Commercial Biotechnology 01/2015; 21(1):31-38.
[Show abstract][Hide abstract] 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.
Materials and Structures 01/2015; · 1.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Superabsorbent polymers (SAPs) are particles which can take up a significant amount of fluid. In this paper workability, microstructure and strength properties were compared for mixtures with(out) SAPs and with(out) additional water. SAP particles reduce the flow, cause a densification of the matrix due to internal curing and also reduce the strength due to macro-pore formation. These characteristics need to be taken into account when using high amounts of SAPs in a mixture. The microstructure of mixtures with SAPs and additional water tends towards the one of the reference mixture without SAPs. The strength upon water addition, however, decreases slightly.
Construction and Building Materials 12/2014; 72:148–157. · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Natural fibres such as flax and hemp fibres are mainly used in the textile industry, but have
outstanding mechanical properties. These natural fibres have a great potential as
reinforcement in cementitious composites, as an alternative to synthetic microfibres. The
multiple cracking capacity of cementitious composites reinforced with natural fibres,
however, is inferior due to the hydrophilicity, and the fibres may degrade in alkaline
environments. Consequently, a proper mixture design and chemical treatments were
investigated to improve 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 of the natural fibres, as well as of the cementitious
composites and the degradation of the natural fibres in alkaline environments were studied.
Multiple cracking was achieved and further improvements were made by chemically treating
the fibres. Mercerization with 2 m% concentration sodium hydroxide (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 valid eco-friendly alternative to synthetic microfibres.
3rd International RILEM Conference on Strain Hardening Cementitious Composites, Dordrecht; 11/2014
[Show abstract][Hide abstract] ABSTRACT: While the use of insulated concrete sandwich panels results in more energy efficient buildings, the presence of this insulation layer can induce thermal crack formation. As cracks form a preferential path for aggressive agents to enter and degrade the concrete matrix and as they are not wanted in this application from an aesthetical point of view, they need to be treated. In this study it was aimed to invisibly seal the cracks in concrete sandwich panels in an autonomous way. Therefore, the efficiency of various encapsulated healing agents was compared by inducing thermal cracks in concrete sandwich panels causing capsule breakage and thus release of the agents into the cracks. It was shown that encapsulation of both polyurethane and a water repellent agent can result in a reduction of the water uptake by cracks, however, only in the case a water repellent agent was released, cracks were healed in an almost invisible way. From this study, it was shown that the self-healing approach consisting of encapsulated polymer based healing agents can also be applied in concrete sandwich panels although more research will be needed to meet the specific healing requirements for this application.
[Show abstract][Hide abstract] ABSTRACT: Superabsorbent polymers (SAPs) have already found their way in many applications. These ‘smart’ polymers undergo major characteristic changes by small environmental variations. In the present work, copolymer networks composed of acrylic acid, acrylamide and N,N′-methylenebisacrylamide have been synthesized using free radical precipitation polymerization. The polymers obtained have been characterized for their chemical structure, moisture (de)sorption and swelling behaviour using, respectively, attenuated total reflectance-infrared spectroscopy, high-resolution magic-angle spinning NMR spectroscopy, dynamic vapour sorption and swelling studies. The results indicated a remarkable moisture uptake capacity at high relative humidities of more than 90 % the original polymer weight with a negligible hysteresis. The latter implies that the SAPs developed are very promising water reservoir candidates, which become useful in concrete-related applications. Furthermore, the swelling data revealed that polymers with a low cross-linking density result in materials with superabsorbent properties. In addition, these SAPs show a pH-dependent swelling behaviour up to 450 times their original weight at pH 12.
Journal of Materials Science 10/2014; · 2.31 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dynamic water vapor sorption (DVS) may be used to characterize the pore structure of cementitious materials, but the technique is difficult to interpret as the microstructure is very sensitive to drying and rehydration due to humidity exposure. The removal of interlayer water or chemically bound water can cause microstructural shrinkage. As all drying techniques more or less dehydrate C–S–H and ettringite, they cause a restructuration of the C-S-H.
In the present paper, DVS measurements were performed to characterize the changes induced by different drying techniques in the textural and sorption properties of the material, while thermogravimetric analysis was used to elucidate carbonation.
The ideal drying technique, which can preserve the microstructure and can remove only the non-bound water, does unfortunately not exist. All drying techniques separately affect the microstructure to some extent. However, these changes are minimized when using vacuum-drying and the solvent-exchange-method with isopropanol as drying techniques.
Cement and Concrete Research 10/2014; 64:54–62. · 3.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bacterial-based self-healing is a promising solution for sustainable concrete maintenance. In this study, bacterial spores were first encapsulated into hydrogels and then were incorporated into specimens to investigate their healing efficiency. The precipitation of CaCO3 by hydrogel-encapsulated spores was demonstrated by Thermogravimetric analysis (TGA). The mortar specimens with hydrogel-encapsulated spores, showed a distinct self-healing superiority: the maximum healed crack width was about 0.5 mm and the water permeability was decreased by 68% in average. Other specimens in non-bacterial series had maximum healed crack width of 0–0.3 mm and the average water permeability was decreased by 15–55% only.
Construction and Building Materials 10/2014; 68:110–119. · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Self-healing strategies are regarded as a promising solution to reduce the high maintenance and repair cost of concrete infrastructures. In the present work, a bacterial-based self-healing by use of hydrogel encapsulated bacterial spores (bio-hydrogels) was investigated. The crack closure behaviour of the specimens with/without bio-hydrogels was studied quantitatively by light microscopy. To have a view of the self-healing inside the specimens, a high resolution X-ray computed microtomography (X-ray μCT) was used. The total amount and the distribution of the healing products in the whole matrix were investigated. This study indicates that the specimens incorporated with bio-hydrogels had distinct improved healing efficiency compared to the reference ones with pure hydrogel only. The healing ratios in the specimens with bio-hydrogels were in the range from 70 % to 100 % for the cracks smaller than 0.3 mm, which is more than 50 % higher than for the ones with pure hydrogel; and the maximum crack bridging was about 0.5 mm (in 7 d), while pure hydrogels only allowed healing of cracks of about 0.18 mm. The total volume ratio of the healing product in the specimens with bio-hydrogels amounted to 2.2 %, which was about 60 % higher than for the ones with pure hydrogel (1.37 %).
Cement and Concrete Composites 10/2014; · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Marine environments are very aggressive, since sea water consists mainly of chlorides and sulphates. So, to predict concrete’s durability as exactly as possible it is important to know the combined attack mechanisms as realistic as possible.
In this research, the reciprocal influence of Cl- and SO42- was investigated for four mixtures, namely with Ordinary Portland Cement, High Sulphate Resistant cement, and with Blast-Furnace Slag (50% and 70% cement replacement). Chloride penetration depths and diffusion coefficients were measured to investigate the influence of SO42- on Cl- attack. Besides, length and mass change measurements were performed to examine the influence of Cl- on SO42- attack. Since the formation of ettringite, gypsum and Friedel’s salt plays an important role, XRD-analyses were done additionally.
It can be concluded that chloride penetration increases when the sulphate content increases at short immersion periods, except for HSR concrete. Concerning the sulphate attack, the presence of chlorides has a mitigating effect.
Cement and Concrete Composites 10/2014; · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There are two facts that can be taken almost for granted when applying a cementitious material. One, it will gain the wanted compressive strength and two, it will crack. As cracking can often not be prevented and repair sometimes happens too late, cracking and water ingress should ideally be controlled by taking preventative steps. Superabsorbent polymers (SAPs) can assist to first self-seal a crack upon fluid ingress as their swelling capacity may block a crack from intruding fluids. But also, by releasing their absorbed water, they will promote autogenous healing. In this study, the effect of SAPs on the permeability is investigated by performing low-pressure water permeability and gas permeability tests. Also, the ability of (promoted) autogenous healing is investigated by comparing the mechanical properties after performing repeated four-point-bending tests. Specimens with SAP/C = 0.01 (SAPs versus cement weight) show a reduction in water permeability by a factor 104 and an increase in gas permeability up to 50% compared to specimens without SAPs. There was a regain in strength properties when specimens with SAPs were allowed to heal in wet/dry cycles (75% after 28 days of healing). A cementitious material with SAPs is thus superior to promote self-sealing and self-healing.
International Conference on Application of Superabsorbent Polymers and Other New Admixtures in Concrete Construction, Dresden; 09/2014
[Show abstract][Hide abstract] ABSTRACT: Cementitious materials are sensitive to crack formation and it would be beneficial if the material could reach again the original strength. Autogenous healing is an already-present feature in cementitious materials, but it is an inferior mechanism as it can only heal cracks up to 50 µm in the presence of water. Therefore, a cementitious material with synthetic microfibres and superabsorbent polymers (SAPs) is proposed. The microfibres will cause multiple crack formation and will result in a vast amount of small healable cracks. If superabsorbent polymers (SAPs) are also included, the self-healing can be promoted as SAPs are able to extract moisture from the environment and to provide it to the cementitious matrix for autogenous healing. But, if the building blocks are exhausted due to a first healing cycle, healing at second reloading may be less efficient. A crack can thus possibly heal only once. In this study, the ability of (promoted) autogenous healing to repeat itself is investigated by comparing the mechanical properties after performing repeated four-point-bending tests. Specimens are able to heal and to regain some of the mechanical properties after being preloaded and pre-cracked under four-point-bending. Even if those healed samples are reloaded for a second time, there is some regain in mechanical properties. If SAPs are added, there is even healing in an environment without liquid water (relative humidity of more than 90%), also in repeated healing actions. The cementitious composite with microfibres and SAPs thus shows partial repeatability of self-healing.
XIII International Conference on Durability of Building Materials and Components, São Paulo; 09/2014
[Show abstract][Hide abstract] ABSTRACT: Since the construction sector uses 50% of the Earth’s raw materials and produces 50% of its waste, the development of more durable and sustainable building materials is crucial. Today, Construction and Demolition Waste (CDW) is mainly used in low level applications, namely as unbound material for foundations, e.g., in road construction. Mineral demolition waste can be recycled as crushed aggregates for concrete, but these reduce the compressive strength and affect the workability due to higher values of water absorption. To advance the use of concrete rubble, Completely Recyclable Concrete (CRC) is designed for reincarnation within the cement production, following the Cradle-to-Cradle (C2C) principle. By the design, CRC becomes a resource for cement production because the chemical composition of CRC will be similar to that of cement raw materials. If CRC is used on a regular basis, a closed concrete-cement-concrete material cycle will arise, which is completely different from the current life cycle of traditional concrete. Within the research towards this CRC it is important to quantify the benefit for the environment and Life Cycle Assessment (LCA) needs to be performed, of which the results are presented in this paper. It was observed that CRC could significantly reduce the global warming potential of concrete.
[Show abstract][Hide abstract] ABSTRACT: A completely recyclable concrete (CRC) is designed to have a chemical composition equivalent to the one of general raw materials for cement production. By doing so, this CRC can be used at the end of its service life in the cement clinkering process without need for ingredient adjustments, and with improvement of the resource efficiency of cement and concrete production. Copper slag is interesting as an iron source for the production of such a CRC and can be added to concrete, either as alternative binder or as aggregate. By isothermal calorimetry and compressive strength tests it was found that the addition of copper slag as cement replacement is of minor interest. But a study toward the compressive strength and durability of concrete with copper slag as aggregate replacement had promising results. The performance of these concretes was comparable with or even better than the reference concrete, regarding strength and most durability aspects such as porosity and permeability, and resistance against carbonation and chloride ingress. Only the resistance to freeze-thaw attack with deicing agents was inferior.
Journal of Materials in Civil Engineering 08/2014; · 1.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In today’s cement and concrete research, mineralogical quantification of (un)hydrated cement samples by X-ray Diffraction/Rietveld analysis becomes more and more important. As the results from XRD/Rietveld analysis are becoming increasingly more accurate, it became a widely used tool to study the hydration of cementitious materials besides other techniques e.g. isothermal calorimetry or thermogravimetric analysis. To quantify amorphous or non-identified phases, an internal standard might be added to estimate these so-called ‘other’ phases. Compared to unhydrated samples which are almost completely crystalline, it has a higher significance in hydrated samples, as certain cement hydrates, such as C-S-H, hydrogarnet, hydrotalcite, AFm, etc., are often poorly crystalline. Within the development of Completely Recyclable Concrete (CRC – a concrete designed for reincarnation within the cement production following the Cradle-to-Cradle Principle) the hydration of the regenerated cement was assessed by XRD/Rietveld analysis. Within this study it was found that the particle size distributions of the sample and the internal standard should not be underestimated within the quantification of the ‘other’ phases.
Non-traditional Cement and Concrete symposium NTCC, Brno, Czech Republic; 06/2014