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ABSTRACT: Bacterially induced carbonate precipitation has been explored for the protection and consolidation of ornamental stone. Attempts to improve the efficiency of this biodeposition process were primarily focused on the microbial aspects, i.e. type of microorganism and metabolic pathway. In this study, the influence of the chemical parameters, i.e. concentration of calcium salts and urea, on the effectiveness of the biodeposition treatment has been examined. The amount of calcium carbonate that can be precipitated in the stone is conditioned both by the amount of cells retained in the stone and the concentration of urea and calcium used. From sonication experiments, a good consolidation was observed for limestone prisms treated with a calcium dosage of 17 g Ca2+ m−2 with no improvement at higher concentrations. For limestone prisms of 4 cm × 2 cm × 1 cm, the biodeposition treatment resulted in a 63% lower weight loss upon sonication compared to untreated specimens. The waterproofing effect was observed to increase with increasing calcium dosages. While for a calcium dosage of 17 g Ca2+ m−2 the water absorption was similar to that of untreated specimens, concentrations of 67 g Ca2+ m−2 resulted in a 50% decrease of the rate of water absorption. For calcium dosages higher than 34 g Ca2+ m−2 a significant change in the visual aspect (ΔE > 6) of the treated stones could be observed. Overall, the urea/calcium chloride-based biodeposition treatment attained a protective performance comparable with that of the commonly used ethylsilicates
Ecological Engineering 03/2013; 36(2):99-111. · 3.11 Impact Factor
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ABSTRACT: The hydration of ordinary Portland cement (OPC) blended with blast-furnace slag (BFS) is a complex process since both materials
have their own reactions which are, however, influenced by each other. Moreover, the effect of the slag on the hydration process
is still not entirely known and little research concerning the separation of both reactions can be found in the literature.
Therefore, this article presents an investigation of the hydration process of mixes in which 0–85% of the OPC is replaced
by BFS. At early ages, isothermal, semi-adiabatic and adiabatic calorimetric measurements were performed to determine the
heat of hydration. At later ages, thermogravimetric (TG) analyses are more suitable to follow up the hydration by assessment
of the bound water content w
b. In addition, the microstructure development was visualized by backscattered electron (BSE) microscopy. Isothermal calorimetric
test results show an enhancement of the cement hydration and an additional hydration peak in the presence of BFS, whilst (semi-)adiabatic
calorimetric measurements clearly indicate a decreasing temperature rise with increasing BFS content. Based on the cumulative
heat production curves, the OPC and BFS reactions were separated to determine the reaction degree Q(t)/Q
∞
(Q=cumulative heat production) of the cement, slag and total binder. Moreover, thermogravimetry also allowed to calculate
the reaction degree by w
b(t)/w
b∞. The reaction degrees w
b(t)/w
b∞, Q(t)/Q
∞ and the hydration degrees determined by BSE-image analysis showed quite good correspondence.
KeywordsBlast-furnace slag-Hydration-Calorimetry-Bound water
Journal of Thermal Analysis and Calorimetry 04/2012; 102(3):941-951. · 1.60 Impact Factor
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ABSTRACT: The resistance of seven different concrete mixtures against a 0.5% sulfuric acid solution was examined. The difference between
high sulfate resistant Portland cement and blast furnace cement, as well as the influence of polymer modifications of the
concrete and the addition of silica fume were issues of the investigation. All concrete mixtures were submitted to an alternating
immersion and drying during 18 weeks in a 0.5% sulfuric acid solution using a testing apparatus for accelerated degradation
tests. The corrosion of the concrete was quantified by measuring the change in dimensions of the test specimens with laser
sensors. The mixture with addition of silica fume was most vulnerable to corrosion. Depending on the polymer type used, polymer
modification of the concrete resulted in an increase and a decrease in the resistance of the concrete respectively. The concrete
made with blast furnace cement had the highest resistance of all tested concrete types.
La résistance de sept bétons différents à l’action corrosive d’une solution contenant 0,5% d’acide sulfurique a constitué
le sujet de cette recherche. La différence entre un ciment Portland à haute résistance aux sulfates et un ciment de haut fourneau,
ainsi que l’influence de la modification de polymères et de l’ajovt de fumée de silice ont été examinées. Tous les bétons
ont été soumis, en alternance pendant 18 semaines, à une immersion dans la solution sulfurique et à un séchage, au moyen de
l’appareil d’essais de corrosion accélérée. L’action de la corrosion a été mesurée avec des lasers mettant en évidence les
changements de dimension des éprouvettes. Le béton contenant de la fumée de silice a présenté la moins bonne résistance par
rapport aux autres bétons. La résistance du béton augmente ou diminue suivant le type de polymère utilisé. Parmi tous les
bétons, c’est le béton fait de ciment de haut fourneau qui a offert la meilleure résistance.
Materials and Structures 04/2012; 36(4):242-249. · 1.28 Impact Factor
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ABSTRACT: Different types of healing agents have already been tested on their efficiency for use in self-healing cementitious materials. Generally, commercial healing agents are used while their properties are adjusted for manual crack repair and not for autonomous crack healing. Consequently, the amount of regain in properties due to self-healing of cracks is limited. In this research, a methyl methacrylate (MMA)-based healing agent was developed specifically for use in self-healing cementitious materials. Various parameters were optimized including the viscosity, curing time, strength, etc. After the desired properties were obtained, the healing agent was encapsulated and screened for its self-healing efficiency. The decrease in water permeability due to autonomous crack healing using MMA as a healing agent was similar to the results obtained for manually healed cracks. First results seem promising: however, further research needs to be undertaken in order to obtain an optimal healing agent ready for use in practice.
Smart Materials and Structures 11/2011; 20(12):125016. · 2.09 Impact Factor
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ABSTRACT: Crack repair is crucial since cracks are the main cause for the decreased service life of concrete structures. An original and promising way to repair cracks is to pre-incorporate healing agents inside the concrete matrix to heal cracks the moment they appear. Thus, the concrete obtains self-healing properties. The goal of our research is to apply bacterially precipitated CaCO₃ to heal cracks in concrete since the microbial calcium carbonate is more compatible with the concrete matrix and more environmentally friendly relative to the normally used polymeric materials. Diatomaceous earth (DE) was used in this study to protect bacteria from the high-pH environment of concrete. The experimental results showed that DE had a very good protective effect for bacteria. DE immobilized bacteria had much higher ureolytic activity (12-17 g/l urea was decomposed within 3 days) than that of un-immobilized bacteria (less than 1 g/l urea was decomposed within the same time span) in cement slurry. The optimal concentration of DE for immobilization was 60% (w/v, weight of DE/volume of bacterial suspension). Self-healing in cracked specimens was visualized under light microscopy. The images showed that cracks with a width ranging from 0.15 to 0.17 mm in the specimens containing DE immobilized bacteria were completely filled by the precipitation. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were used to characterize the precipitation around the crack wall, which was confirmed to be calcium carbonate. The result from a capillary water absorption test showed that the specimens with DE immobilized bacteria had the lowest water absorption (30% of the reference ones), which indicated that the precipitation inside the cracks increased the water penetration resistance of the cracked specimens.
Journal of Industrial Microbiology 09/2011; 39(4):567-77. · 1.80 Impact Factor
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ABSTRACT: Due to the physico-chemical characteristics of cementitious materials the aesthetic quality of these materials tend to decrease easily. On the other hand, the photocatalytic activity produced by TiO2 loaded cementitious materials have recently allowed them to include self-cleaning and air-purifying properties. However, because a better understanding of these properties is still needed, only a limited number of these materials is present in the construction market. As a strategy to improve this situation, non standards tests based on photodegradation of organic dyes have become widely used to evaluate the photocatalytic action of the different materials. Today, a wide spectrum of non easily comparable results have been produced. In order to improve this situation, this paper focuses on the description of the developed laboratory tests as well as on the evaluation of the self-cleaning potential of the first buildings containing TiO2. Finally, future research challenges in this field are identified.Debido a las características físico-químicas de los materiales a base de cemento, la calidad estética de estos materiales tiende a disminuir con facilidad. Por otra parte, la actividad fotocatalítica producida por los materiales a base de cemento que contienen TiO2, ha permitido incorporar recientemente en estos materiales propiedades de auto-limpieza y purificación del aire. Sin embargo, actualmente sólo existe en el mercado un número limitado de dichos materiales, dado que aún se necesita conocer mejor las mencionadas propiedades. Para mejorar esta situación, se vienen desarrollando ensayos no estandarizados donde se evalúa la foto-degradación de colorantes orgánicos producida por los diferentes materiales. Por tanto, se han producido una gran cantidad de resultados no fácilmente comparables entre sí. Este artículo presenta una descripción de los diferentes ensayos de laboratorio desarrollados, así como una evaluación del potencial de auto-limpieza de los primeros edificios que contienen TiO2. Finalmente, se identifican los futuros desafíos de investigación en este campo.
Materiales de Construccion. 01/2010;
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ABSTRACT: To evaluate the effectiveness of various antimicrobial mortar formulations in inhibiting the growth of a selection of pathogens of environmental and hygienic concern.
Mortar prisms containing triclosan-incorporated fibres or different concentrations of silver copper zeolites were incubated with Escherichia coli, Listeria monocytogenes, Salmonella enterica or Staphylococcus aureus at 4 or 20 degrees C for 24 h. From plate counting, a substantial bactericidal effect (>4 log units) could only be observed for the mortar specimens containing more than 3% zeolites on cement weight base, the effect being more pronounced at 20 degrees C compared to 4 degrees C. No inhibitory effect could be observed for mortar specimens containing antimicrobial fibres. Adenosinetriphosphate (ATP) measurements allowed for a rapid indication of the occurrence of antimicrobial activity.
In order to obtain a bactericidal effect on mortar surfaces, concentrations of silver copper zeolites of more then 3% are required.
To our knowledge, this is the first study in which the effectiveness of various antimicrobial mortar mixtures towards the inhibition of pathogens has been evaluated in a quantitative way. Antimicrobial concrete mixtures can be used for the improvement of the hygienic conditions in a variety of environments.
Journal of Applied Microbiology 06/2009; 108(1):62-72. · 2.34 Impact Factor
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ABSTRACT: The interaction between bovine claws and a concrete floor with defined roughness and friction coefficients is described using a finite element model. The model was built by using x-ray tomography scanner images of an unloaded fore and hind bovine claw. These images were used to reproduce the geometry of the claw horn capsule, which was used to create a finite element model. Young's moduli of 382, 261, and 13.6 MPa were attributed to the dorsal wall horn, abaxial and axial wall horn, and bulb horn, respectively. Poisson's ratio was set at 0.38. The horn was considered an isotropic elastic material. The model was completed by introducing a rigid support that simulated a concrete floor. The floor was moved to establish contact with the claw and was loaded with a force of 2 or 6 kN. The top border area of the horn capsule was fixed, but angular rotations were allowed. With this model, the effect of varying floor roughness and claw-floor friction on contact pressures and von Mises stresses in the claw horn could be evaluated. This was demonstrated by simulating the contact between the claw models and a smooth and rough floor with a center-line roughness value R(a) of 0 or 0.175 mm, respectively, either without friction or with a static coefficient of friction of 0.75 and a dynamic coefficient of friction of 0.65. Contact pressures ranged from 2.14 to 27.55 MPa. The roughness of the floor was the main determinant in subsequent contact pressures. Maximum von Mises stresses were registered in the claw sole and were mostly between 5.04 and 16.44 MPa, but could be higher in specific situations. The variables claw (fore or hind) and floor (smooth or rough) had significant effects on the contact pressures; in addition, the floor resulted in significantly different von Mises stresses in the claw horn. The variable friction (frictionless or with friction) had a significant effect on the von Mises stresses. The load did not result in significantly different contact pressures and von Mises stresses because of the large increase in contact area with the exerted load.
Journal of Dairy Science 02/2008; 91(1):182-92. · 2.56 Impact Factor
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ABSTRACT: The development of the autogenous shrinkage of a high performance concrete HPC has been
investigated in detail as there is a cracking risk at early age due to restrained shrinkage existing in a steel-
HPC bridge deck with U-shaped precast in Belgium. The autogenous shrinkage determination was carried out
on a test rig designed to start the measurements just after casting. The test rig is immersed inside a temperature
controlled bath. The displacements of the upper head of the specimen are measured by an external transducer.
The concrete is placed in a corrugated PVC mold to avoid any friction during the test. The initialization
time, t0, of the deformations is fixed after the observation of two different methods of ultrasonic
monitoring of setting (BTPULS, LCPC’s prototype and FreshCon, University of Stuttgart).
the 8th International Conference on Creep, Shrinkage and Durability of Concrete and Concrete Structures (CONCREEP 8); 01/2008
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ABSTRACT: The intention of this research was to study the impact of concrete floor surface roughness on a bovine claw model and to assess the deformation of the bovine claw model under load. The pressure distribution between the floor and the claw is the key method in this research. Monitoring foot-to-ground pressure distributions may provide insight into the relation between high local pressures and foot lesions. Concrete floor samples were made with 5 different finishing methods. Their roughness was determined by measuring the heights of the "peaks and the valleys" of the surface with a high-precision laser beam. The smoothest surface was the sample finished with a metal float (surface roughness R(a) = 0.062 mm) and the roughest surface occurred with the heavily sandblasted sample (surface roughness R(a) = 0.488 mm). The roughness of the concrete floor samples was related to the mean and peak contact pressures that can occur in a laboratory test bench between floor and bovine claw. It was found that the claw itself has approximately 2 times more effect on these contact pressures than the surface roughness. Peak pressures found were high enough (up to 111 MPa) to cause damage to the bovine claw sole horn. The strains occurring in the horn wall were measured and related to the floor-finishing method and the load. Strain gauge measurements indicated that it is difficult to predict what kind of deformation of the claw wall will occur at a certain location. Different strains will occur for different floor-finishing methods. The corresponding stresses in the horn wall did not exceed the yield stress (14 and 11 MPa for dorsal and abaxial wall horn, respectively).
Journal of Dairy Science 09/2006; 89(8):2952-64. · 2.56 Impact Factor
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ABSTRACT: Concrete specimens weathered for over a decade in the moderate Belgian climate, showing a black organic outer layer that mainly
consisted of lichens, were cleaned with a new biological technique. A mixture of sulphur oxidising bacteria of the genusThiobacillus supplemented with an appropriate nutrient was applied to a fouled concrete surface, either by sprinkling or by submersion.
The aim was to remove the fouled layer in such a way that the surface is uniformly cleaned. The general effect of the technique
was evaluated by colorimetry and microscopy. Two sets of weathered concrete specimens, containing blast furnace slag cement
or ordinary portland cement, were investigated. The effectiveness of the technique depended on the cement type of the concrete
specimens. The effect on the ordinary portland cement concrete specimens was in some cases up to a factor 2 stronger than
the result on the blast furnace slag cement specimens. The sprinkling treatment was about 50% as effective as the submersion
treatment but was very promising in the case of in situ acidification. A side effect was the formation of a gypsum layer on
some of the specimens, resulting in a whiter colour.
Des échantillons de béton, exposés pendant plus d'une décennie au climat modéré de la Belgique et couverts d'une couche noire
de lichens, ont été nettoyés avec une nouvelle technique biologique. Des bactéries de type Thiobacillus ont été appliquées
en combinaison avec des substances nutritives appropriées, en utilisant une technique de submersion ou d'arrosage. L'objectif
était d'enlever la couche sale et d'obtenir une surface uniformément nettoyée. L'effet du traitement était mesuré par colorimétrie
et microscopie. Deux types d'échantillons ont été examinés: du béton à base de ciment de Portland et à base de ciment de laitier
de haut fourneau. Des différences d'efficacité ont été enregistrées selon le type de ciment: le nettoyage des échantillons
à base de ciment de Portland était dans certains cas 100% plus efficace que celui des échantillons à base de ciment de laitier
de haut fourneau. La technique d'arrosage était environ 50% moins efficace que la technique de submersion. Un effet secondaire
était la formation des cristaux de gypse sur quelques échantillons, menant à une couleur plus blanche.
Materials and Structures 11/2005; 38(10):875-882. · 1.28 Impact Factor
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ABSTRACT: Geologists and engineers recently have adopted computerised X-ray microtomography (microCT), a radiological imaging technique, for geological and petrophysical applications such as the assessment of sediment characteristics, CT-measurement of compressibility and compaction, multiphase flow studies, measurement of bulk density and moisture content, and of porosity and permeability. This study focuses on another application: the monitoring of biological weathering of natural building stones and concrete. Microbial activity as a determining factor in the deterioration process of building materials has a major economic impact. Because of its non-destructive character, microCT could be the ideal monitoring technique. With this technique, three-dimensional (3D) images of the entire inner structure of the material can be obtained, together with quantitative data. In depth changes of porosity of concrete and stone specimens due to bacterial weathering were assessed in this work. Also, porosity was visualised based on 3D data with homemade software. Scanning electron microscopy (SEM) images provided additional information and supported conclusions drawn from the X-ray microCT data. Resolution improvement will make the study of petrophysical aspects of physical weathering and/or biological deterioration processes of natural building stones and concrete a promising subject for further microCT-application.
Science of The Total Environment 05/2005; 341(1-3):173-83. · 3.29 Impact Factor
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ABSTRACT: To simulate chemical degradation of concrete in an automated and standardized way, an apparatus for accelerated degradation
tests was developed. Because alternated wetting and drying often accelerate concrete degradation, cylindrical test specimens
are subjected to a cyclic procedure of turning through an aggressive solution and drying by air. After every attack cycle
the test specimens are brushed with rotary brushes to simulate mechanical abrasion. The degradation of the concrete, in terms
of change of the dimensions of the test specimens, is determined by means of a non-contact distance measurement with laser
sensors. Out of the measured data the change of the cylinder radius and the surface roughness are calculated. To illustrate
the test procedure, experimental results concerning sulfuric and lactic/acetic acid degradation are provided.
Un appareil a été développé pour simuler de manière automatisée et standardisée l'attaque chimique du béton. Vu que l'alternance
de submersions et de séchages accélèrent souvent le processus de dégradation, des échantillons cylindriques sont exposés à
une procédure cyclique qui les fait tourner dans une solution agressive suivie d'un séchage à l'air. Suite à chaque cycle
d'attaque les échantillons sont brossés avec des brosses rotatives pour simuler l'abrasion mécanique. La dégradation des échantillons
de béton est mesurée à l'aide de lasers, qui déterminent sans aucun contact, la distance entre le béton et le laser. Sur la
base de ces données, le changement du rayon du cylindre et la rugosité de la surface sont calculés.
Materials and Structures 07/2002; 35(7):427-433. · 1.28 Impact Factor
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ABSTRACT: New equipment and procedures for chemical and microbiological tests, simulating biogenic sulfuric acid corrosion in sewerage systems, are presented. Subsequent steps of immersion and drying, combined with mechanical abrasion, were applied to simulate events occurring in sewer systems. Both chemical and microbiological tests showed that the aggregate type had the largest effect on degradation. Concrete with limestone aggregates showed a smaller degradation depth than did the concrete with inert aggregates. The limestone aggregates locally created a buffering environment, protecting the cement paste. This was confirmed by microscopic analysis of the eroded surfaces. The production method of concrete pipes influenced durability through its effect on W/C ratio and water absorption values. In the microbiological tests, HSR Portland cement concrete performed slightly better than did the slag cement concrete. A possible explanation can be a more rapid colonisation by microorganisms of the surface of slag cement samples. A new method for degradation prediction was suggested based on the parameters alkalinity and water absorption (as a measure for concrete porosity).
Cement and Concrete Research.
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ABSTRACT: The use of polymer-modified mortar and concrete (PMM and PMC) is investigated to improve the durability of concrete sewer pipes. The aim of the research is to ameliorate the resistance of concrete to biogenic sulphuric acid attack through polymer modification. Prior to the durability tests, experimental research is carried out to reveal the influence of polymer modification on the physical and mechanical properties of mortar and concrete. The results of this research are presented in this paper. Due to the interaction of the cement hydrates and the polymer particles or film, an interpenetrating network originates in which the aggregates are embedded. The density, porosity and location of the polymer film depend on the type of polymer emulsion and on its minimum film-forming temperature (MFT). If air entrainment is restricted, an increased flexural strength is measured. Scanning electron microscope (SEM) analyses reveal the presence of polymer film and cement hydrates in the mortar. The polymer film causes a retardation of the cement hydration as well as a restriction of crystal growth.
Cement and Concrete Composites.
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ABSTRACT: Inadequate properties of concrete floors in cattle houses are a major cause of claw problems, resulting in economic losses and impaired animal welfare. Many claw diseases are sequels of an extreme local overload due to high floor roughness or are caused by the indirect effects of the slipperiness of the floor. In this paper, the roughness of the concrete floor, the frictional interactions between bovine claw and floor and the relation between roughness and frictional properties, are studied.Concrete floor samples were made with five different finishing methods. Their roughness was determined by measuring the heights of the ‘peaks and valleys’ of the surface with a high-precision laser beam. The smoothest surface was the sample finished with a metal float (average surface roughness Ra=0·080 mm) and the roughest surface occurred with the heavily sandblasted sample (average surface roughness Ra=0·296 mm). Their roughness was also approximated with the ‘sand-patch’ method: the texture depth was calculated by dividing a fixed volume of fine dry sand by the surface area of the circle-shaped sand patch. Again the smoothest surface appeared to be the sample finished with a metal float (texture depth=0·19 mm) and the roughest surface was the heavily sandblasted sample (texture depth=0·59 mm). The sand-patch method appeared to be a reliable way of assessing the roughness of the floor.The static coefficient of friction μstat and the dynamic coefficient of friction μdyn between bovine claw models and dry and wet floors were determined by using the ‘drag method’ (a loaded bovine claw was dragged using a hand-operated winch over a flat floor sample while the tensional force was recorded). The five concrete floor panels with different roughnesses were used, but also two types of synthetic floor coverings (mat and mattress) were added to the test. The static coefficient of friction on dry floors varied between 0·60 (mattress) and 0·79 (mildly sandblasted concrete); the dynamic coefficient of friction ranged between 0·47 (mattress) and 0·69 (heavily sandblasted concrete). In wet circumstances only three floor types were tested. The static coefficient of friction varied between 0·65 (metal-floated concrete) and 0·80 (heavily sandblasted concrete) while the dynamic coefficient of friction yielded values between 0·56 (metal-floated concrete) and 0·69 (heavily sandblasted concrete). Significant differences were found between the floor types, but these were mainly due to the values measured on the metal-floated concrete, the mattress and the mat. Only in dry circumstances did the fore claws produce significantly higher coefficients of friction than the hind claws. The effect of the floor type on the coefficients of friction was in all cases many times higher than the effect of the claw itself. The static and the dynamic coefficients of friction in wet conditions were found to be larger than the same coefficients in dry conditions.The skid or slip resistance was measured separately, on wetted surfaces, with the skid-resistance tester (SRT) pendulum. The values found ranged between 20·2 (metal-floated concrete) and 49·6 (mattress). Significant differences between the floor types were found.Significant correlations were found between the static and the dynamic coefficients of friction, in dry and wet conditions, and the roughness values Rx and the texture depth. Significant correlations were also found between the SRT values and the roughness values Rx. Significant correlations were found only between the dynamic coefficients of friction and SRT values.The measured coefficients of friction were all higher than the required coefficients of friction, hence the tested floor samples provided enough resistance against slip.
Biosystems Engineering.
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ABSTRACT: Inadequate properties of concrete floors in cattle houses seem to be the primary cause of most claw problems, resulting in economic losses and impaired animal welfare. Many claw diseases are sequels of an extreme local overload. In this paper, the mechanical strength of bovine claw horn is studied.The average Young's modulus E determined in bending and compression using a test velocity of 1 mm/min was 382 MPa for horn from the dorsal wall of the bovine claw, 261 MPa for horn from the abaxial wall and 13·6 MPa for bulb horn. There is a significant difference in Young's modulus, hence in stiffness, between dorsal and abaxial wall horn. The average yield stress was 14·3 MPa for dorsal wall horn and 10·7 MPa for abaxial wall horn in a three-point bending test, and 56·0 MPa for bulb horn in a compression test on samples with 100 mm2 surface area and 4 mm height. The registered average Poisson's ratio ν was 0·38. Histological observations could not explain the biomechanical differences between the dorsal and abaxial wall horn. The number of horn tubules per mm2 was smaller and the diameter of the tubules larger in bulb horn than in wall horn.In future research, the yield stress of the horn will be related with the maximum pressures that can occur between cattle claw and concrete floor.
Biosystems Engineering.
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ABSTRACT: Biogenic sulfuric acid corrosion is often a problem in sewer environment: it can lead to a fast degradation of the concrete structures. Since the involvement of bacteria in the corrosion process was discovered, considerable microbiological research has been devoted to the understanding of the corrosive process. Mechanical engineers have focused on experiments comparing the resistance of several concrete mixes against biogenic sulfuric acid corrosion. Because of a lack of standardised methods, different test methods have been used, and various parameters have been modified to evaluate the resistance of the materials. The research done on sulfuric acid corrosion of concrete can roughly be divided in three groups: chemical tests, microbial simulation tests, and exposure tests in situ. In this article, an overview of the recent developments in the test methods for biogenic sulfuric acid corrosion and the obtained results are presented. Possible differences between biogenic sulfuric acid corrosion and chemical sulfuric acid corrosion are delineated.
Cement and Concrete Research.
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ABSTRACT: Concrete is a construction material that is used world-wide because of its first-rate properties. However, the drawback of this material is that it easily cracks due to its low tensile strength. As large costs are involved in crack repair, the potential of self-healing of these cracks by means of calcium carbonate (CaCO 3) precipitating bacteria was investigated in this study. First, the survival of the bacteria was tested. Next, the optimal concentrations of bacterial cells, urea and Ca 2+ were determined in order to obtain a maximum amount of CaCO 3 precipitation. Finally, self-healing of cracks in mortar specimens, by means of bacteria, was investigated. Glass tubes, containing the healing agent were provided inside the mortar matrix. Upon crack occurrence, the tubes break and the healing agent, consisting of a filler material and bacteria, is released into the crack and can cause crack repair. Strength regain up to 60% was thus observed due to self-healing.
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ABSTRACT: In certain industrial activities sulfuric acid is used during the production process, which may cause degradation of concrete structures. Another important phenomenon where sulfuric acid is responsible for concrete corrosion is biogenic sulfuric acid corrosion, which occurs often in sewer systems. Because previous investigations have already pointed out the difference between purely chemical sulfuric acid corrosion and biogenic sulfuric acid corrosion two different tests were performed: a chemical test and a microbiological test. Five different concrete compositions were used in the tests, including a reference mixture with high sulfate resistant portland cement and four different polymer cement concrete with a styrene–acrylic ester polymer, an acrylic polymer, a styrene butadiene polymer and a vinylcopolymer, respectively. The concrete composition with the styrene–acrylic ester polymer showed in both tests a higher resistance than the reference mixture while the compositions with the acrylic polymer and the styrene butadiene polymer had a lower resistance than the reference mixture. The concrete composition with the vinylcopolymer did not induce the same results in both tests. The results of the chemical test indicated a slight increase in resistance compared with the reference mixture while the opposite was noticed for the microbiological test.
Cement and Concrete Research 31(9):1359-1365. · 2.78 Impact Factor
