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W P Boshoff - One of the best experts on this subject based on the ideXlab platform.
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the response of cracked steel Fibre reinforced concrete under various sustained stress Levels on both the macro and single Fibre Level
Construction and Building Materials, 2017Co-Authors: P D Nieuwoudt, Adewumi John Babafemi, W P BoshoffAbstract:Abstract If Fibre reinforced concrete structures are to be accurately designed, an understanding of the time-dependent response under sustained loadings and in the cracked state must be well understood. It is known that the Fibres pull-out with time under sustained loadings. However, the quantification of the pull-out creep is still understudied, particularly under uniaxial tensile loading. In this study, the tensile creep response of cracked steel Fibre reinforced concrete under varying sustained stress Levels has been performed. Furthermore, single Fibre pull-out and pull-out creep tests were also undertaken to describe the mechanisms responsible for the crack widening of steel Fibre reinforced concrete. The influence of Fibre orientation angle, Fibre mechanical anchorage, stress Level, and Fibre pre-slipping on the pull-out response at the single Fibre Level was also investigated. X-ray computed tomography (CT) scans of specimens subjected to pull-out creep tests are also shown to demonstrate the prominent mechanisms causing the time-dependent pull-out of steel Fibres. All tests were performed under a controlled environment. The results of the investigations have revealed that the tensile creep of cracked steel Fibre reinforced concrete increases as the stress Level increases. X-ray CT scan images have shown that instantaneous pull-out is caused by the collapse of the interface between the Fibre and the matrix. This damage to the interface also increases with time under sustained loading and increased load Levels. At higher stress Levels, pull-out creep increases due to micro-cracking at the region of the hooked end of the Fibre.
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tensile creep of cracked steel Fibre reinforced concrete mechanisms on the single Fibre and at the macro Level
2017Co-Authors: W P Boshoff, P D NieuwoudtAbstract:This paper reports on tests done to investigate the mechanisms causing the increased tensile creep of cracked Fibre reinforced concrete (FRC) members when a sustained load is applied. It is important to understand the mechanisms as this will pave the way for improvements that can be made to reduce this creep and will also assist in creating prediction models as it will be based on the fundamental mechanisms involved. This paper presents results of uni-axial tensile creep tests of cracked steel Fibre reinforced concrete (SFRC) and also tests at the single Fibre Level. Single Fibres were embedded in the matrix and pull-out at different rates and sustained loading was also applied to the single, embedded Fibres. It was found that the single Fibre pull-out creep test results can be directly linked to the uni-axial tensile tests. It was also shown that the pull-out creep is proportional to the load up to at least 50 % of the ultimate load after which the pull-out creep increases non-linearly. This can be ascribed to micro-cracking around the hooked-end of the Fibre. Lastly, it is postulated that the interfacial transition zone between the Fibre hooked-end and the concrete matrix plays a significant role in the pull-out creep behaviour.
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characterising the time dependant behaviour on the single Fibre Level of shcc part 2 the rate effects on Fibre pull out tests
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the single Fibre Level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports single Fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the Fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of Fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length.
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characterising the time dependant behaviour on the single Fibre Level of shcc part 1 mechanism of Fibre pull out creep
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:SHCC (Strain Hardening Cement-based Composite) has been designed and optimised to overcome the main weaknesses of ordinary concrete, which is its brittleness. SHCC shows a high tensile ductility and can resist the full load at a tensile strain of more than 4%. An in depth investigation into the time-dependant behaviour is still lacking for SHCC. This paper is the first part of a two paper series about the time-dependant behaviour on the single Fibre Level. In this paper, the tensile creep behaviour of SHCC is studied to distinguish mechanisms of creep. Tensile creep and shrinkage test results are reported for dumbbell type SHCC specimens. The specimens are pre-cracked to simulate in-service conditions, with subsequent sustained load at various Levels, here chosen as 30%, 50%, 70% and 80% of the ultimate resistance. To distinguish the sources of significant creep deformation under these sustained loads, single Fibre pull-out tests are performed under sustained load. It is shown that the time-dependent Fibre pull-out is a significant source of time-dependent deformation, along with the formation of new cracks in SHCC under sustained load.
Gideon P A G Van Zijl - One of the best experts on this subject based on the ideXlab platform.
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characterising the time dependant behaviour on the single Fibre Level of shcc part 2 the rate effects on Fibre pull out tests
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the single Fibre Level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports single Fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the Fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of Fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length.
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characterising the time dependant behaviour on the single Fibre Level of shcc part 1 mechanism of Fibre pull out creep
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:SHCC (Strain Hardening Cement-based Composite) has been designed and optimised to overcome the main weaknesses of ordinary concrete, which is its brittleness. SHCC shows a high tensile ductility and can resist the full load at a tensile strain of more than 4%. An in depth investigation into the time-dependant behaviour is still lacking for SHCC. This paper is the first part of a two paper series about the time-dependant behaviour on the single Fibre Level. In this paper, the tensile creep behaviour of SHCC is studied to distinguish mechanisms of creep. Tensile creep and shrinkage test results are reported for dumbbell type SHCC specimens. The specimens are pre-cracked to simulate in-service conditions, with subsequent sustained load at various Levels, here chosen as 30%, 50%, 70% and 80% of the ultimate resistance. To distinguish the sources of significant creep deformation under these sustained loads, single Fibre pull-out tests are performed under sustained load. It is shown that the time-dependent Fibre pull-out is a significant source of time-dependent deformation, along with the formation of new cracks in SHCC under sustained load.
P D Nieuwoudt - One of the best experts on this subject based on the ideXlab platform.
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the response of cracked steel Fibre reinforced concrete under various sustained stress Levels on both the macro and single Fibre Level
Construction and Building Materials, 2017Co-Authors: P D Nieuwoudt, Adewumi John Babafemi, W P BoshoffAbstract:Abstract If Fibre reinforced concrete structures are to be accurately designed, an understanding of the time-dependent response under sustained loadings and in the cracked state must be well understood. It is known that the Fibres pull-out with time under sustained loadings. However, the quantification of the pull-out creep is still understudied, particularly under uniaxial tensile loading. In this study, the tensile creep response of cracked steel Fibre reinforced concrete under varying sustained stress Levels has been performed. Furthermore, single Fibre pull-out and pull-out creep tests were also undertaken to describe the mechanisms responsible for the crack widening of steel Fibre reinforced concrete. The influence of Fibre orientation angle, Fibre mechanical anchorage, stress Level, and Fibre pre-slipping on the pull-out response at the single Fibre Level was also investigated. X-ray computed tomography (CT) scans of specimens subjected to pull-out creep tests are also shown to demonstrate the prominent mechanisms causing the time-dependent pull-out of steel Fibres. All tests were performed under a controlled environment. The results of the investigations have revealed that the tensile creep of cracked steel Fibre reinforced concrete increases as the stress Level increases. X-ray CT scan images have shown that instantaneous pull-out is caused by the collapse of the interface between the Fibre and the matrix. This damage to the interface also increases with time under sustained loading and increased load Levels. At higher stress Levels, pull-out creep increases due to micro-cracking at the region of the hooked end of the Fibre.
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tensile creep of cracked steel Fibre reinforced concrete mechanisms on the single Fibre and at the macro Level
2017Co-Authors: W P Boshoff, P D NieuwoudtAbstract:This paper reports on tests done to investigate the mechanisms causing the increased tensile creep of cracked Fibre reinforced concrete (FRC) members when a sustained load is applied. It is important to understand the mechanisms as this will pave the way for improvements that can be made to reduce this creep and will also assist in creating prediction models as it will be based on the fundamental mechanisms involved. This paper presents results of uni-axial tensile creep tests of cracked steel Fibre reinforced concrete (SFRC) and also tests at the single Fibre Level. Single Fibres were embedded in the matrix and pull-out at different rates and sustained loading was also applied to the single, embedded Fibres. It was found that the single Fibre pull-out creep test results can be directly linked to the uni-axial tensile tests. It was also shown that the pull-out creep is proportional to the load up to at least 50 % of the ultimate load after which the pull-out creep increases non-linearly. This can be ascribed to micro-cracking around the hooked-end of the Fibre. Lastly, it is postulated that the interfacial transition zone between the Fibre hooked-end and the concrete matrix plays a significant role in the pull-out creep behaviour.
Thierry Gidenne - One of the best experts on this subject based on the ideXlab platform.
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Post-weaning maturation of rabbit caecal microbial communities: impact of live yeast intake
2006Co-Authors: Thierry Gidenne, Nadia Bennegadi-laurent, Corinne Bayourthe, Valérie Monteils, Gérard FontyAbstract:The aims of this work were first to evaluate nutritional requirements of early weaned kits (23 days of age), more especially Fibre (experiment 1) and protein (experiment 2) needs. In experiment 1, 276 early weaned rabbits were offered from 23 to 50 days of age one of the three experimental diets containing increasing acid-detergent Fibre Level (160, 190 or 220g/kg). Fibre was substituted by starch and fat to obtain three isoenergetic diets. In experiment 2, 306 early weaned rabbits were offered from 23 to 50 days of age one of the three experimental diets containing increasing crude protein (CP) Level (150, 180 or 210g/kg). Protein was substituted by starch and fat to obtain three isoenergetic diets. These studies revealed no effect of the dietary Fibre Level and the dietary CP Level on health status. But from 23 to 36 days of age rabbits given diets containing a Fibre Level over 190g/kg or a CP Level under 180g/kg showed the lowest growth rate as compared with other respective treatments. Secondly, this research aimed to evaluate the interaction between age at weaning (23 days or 35 days of age) and food (RD and RY diets) on digestive health and performances of young rabbits (experiment 3). RD diet was formulated to contain (per kg) 170g starch, 160g Fibre and 180g CP (according to the nutritional requirements of does) and RY diet was formulated to reach 110g starch, 160g Fibre and 210g CP (according to the results of experiments 1 and 2). 39 litters of nine pups per litter were assigned at 18 days of age to one of four experimental groups in a 2×2 factorial design: RD23 (no. =84 rabbits), RY23 (no. =85 rabbits), RD35 (no. =86 rabbits) and RY35 (no. =74 rabbits). Food intake and live weight were not influenced by feeding strategy. Between 23 and 35 days of age, mortality was higher in RY than in RD group (20·4 v. 6·8% respectively; P
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Fibre and protein requirements of early weaned rabbits and the interaction with weaning age : effects on digestive health and growth performance
Animal Science, 2006Co-Authors: Alexandre Feugier, Miranda Smit, Laurence Fortun-lamothe, Thierry GidenneAbstract:The aims of this work were first to evaluate nutritional requirements of early weaned kits (23 days of age), more especially Fibre (experiment 1) and protein (experiment 2) needs. In experiment 1, 276 early weaned rabbits were offered from 23 to 50 days of age one of the three experimental diets containing increasing acid-detergent Fibre Level (160, 190 or 220g/kg). Fibre was substituted by starch and fat to obtain three isoenergetic diets. In experiment 2, 306 early weaned rabbits were offered from 23 to 50 days of age one of the three experimental diets containing increasing crude protein (CP) Level (150, 180 or 210g/kg). Protein was substituted by starch and fat to obtain three isoenergetic diets. These studies revealed no effect of the dietary Fibre Level and the dietary CP Level on health status. But from 23 to 36 days of age rabbits given diets containing a Fibre Level over 190g/kg or a CP Level under 180g/kg showed the lowest growth rate as compared with other respective treatments. Secondly, this research aimed to evaluate the interaction between age at weaning (23 days or 35 days of age) and food (RD and RY diets) on digestive health and performances of young rabbits (experiment 3). RD diet was formulated to contain (per kg) 170g starch, 160g Fibre and 180g CP (according to the nutritional requirements of does) and RY diet was formulated to reach 110g starch, 160g Fibre and 210g CP (according to the results of experiments 1 and 2). 39 litters of nine pups per litter were assigned at 18 days of age to one of four experimental groups in a 2×2 factorial design: RD23 (no. =84 rabbits), RY23 (no. =85 rabbits), RD35 (no. =86 rabbits) and RY35 (no. =74 rabbits). Food intake and live weight were not influenced by feeding strategy. Between 23 and 35 days of age, mortality was higher in RY than in RD group (20·4 v. 6·8% respectively; P
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effects of age and dietary Fibre Level on caecal microbial communities of conventional and specific pathogen free rabbits
Microbial Ecology in Health and Disease, 2003Co-Authors: Nadia Bennegadi, Thierry Gidenne, G Fonty, Liliane Millet, Dominique LicoisAbstract:Caecal community structure in conventional and specific pathogen-free (SPF) rabbits was assessed by performing dot-blot hybridization with 16S rRNA targeted oligonucleotide probes. The variation of the caecal flora was analysed according to age (18–70 days old), nutritional status (acid detergent Fibre=19% in standard and 9% in Fibre-deficient diet) and rabbit health (healthy vs diarrhoeic). Caecal flora was stabilized at around 25–28 days. Bacteria and archaea represented 73% and 22%, respectively, of the total microbial communities at weaning (28 days). Cellulolytic bacteria ( Ruminococcus albus, R. flaefaciens, Fibrobacter succinogenes and F. intestinalis ) represented <7% of total bacteria, with a predominance of R. flaefaciens and R. albus , respectively, for conventional and SPF rabbits. Bacterial and archaeal rRNAs were twofold higher in conventional than in SPF rabbits, fed standard diet (p<0.001). In conventional rabbits, archaeal community was twofold higher with standard diet than with Fibre-deficient diet. In both types of rabbits, quantities of Flexibacter-Cytophaga-Bacteroides rRNA were twofold higher with Fibre-deficient diet than with standard diet. In diarrhoeic conventional rabbits, the proportion of eukaryal rRNA increased 4-fold, but proportions of bacterial and archaeal rRNA decreased by 1-, 2- and 6-fold, respectively. The quantities of rRNA of F. succinogene s and F. intestinalis in conventional rabbits were, respectively 17 and 5 times higher in sick than in healthy animals, and decreased by 7-fold for R. albus . This study shows some microbial interactions according to nutrition and health of the rabbit. Key words : rabbit, caecal flora, Fibre deficiency, oligonucleotide probes, enteropathy, specific pathogen-free, microbial community balance.
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microbial activity in the caecum of the rabbit around weaning impact of a dietary Fibre deficiency and of intake Level
Animal Feed Science and Technology, 2002Co-Authors: Thierry Gidenne, N Jehl, M Segura, B MichaletdoreauAbstract:Abstract The current study was designed to evaluate the caecal microbial activity in the young rabbit, as influenced by dietary Fibre concentration and feed intake Level. Caecal fermentative activity and bacterial fibrolytic activity were measured before and after weaning (28-day old) in young (six litters of eight per diet) fed before weaning a Fibre deficient diet “DF” (92 g acid detergent Fibre (ADF) kg −1 ), or a standard Fibre diet (165 g ADF kg −1 ) containing either a standard (diet SF) or an excessive methionine Level (diet MSF). The effect of the dietary Fibre Level on microbial activity was evaluated by comparing DF and SF groups. The Fibre effect itself, without change in intake Level, was estimated by comparing DF and MSF groups, since a high Level of methionine reduces the intake Level in rabbits. Feed intake (from 28 to 42 days) was 13% lower for MSF than for SF group, but was similar to DF group. Between 21 days of age and weaning, caecal volatile fatty acid (VFA) concentration doubled and then slightly increased until 42 days of age. A linear reduction for propionate and, conversely, an increase in butyrate molar proportions were observed with age. Until weaning, VFA concentrations were similar between the three diets, although it tended to be lower for DF ( P =0.067). Subsequently, VFA concentration of SF group increased, while for DF it decreased (respectively, 72 mM l −1 versus 40 mM l −1 at 42 days, P
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Impact of Fibre deficiency and sanitary status on non-specific enteropathy of the growing rabbit
Animal Research, 2001Co-Authors: Nadia Bennegadia, Thierry Gidenne, Dominique LicoisAbstract:—The effects of a sharp reduction in dietary Fibre Level (19 to 9% ADF resp. for “S” and “D” diet) were studied on the health status and performances of two groups of rabbits with different sanitary statuses: conventional “C” (n = 224) and specified pathogen free ‘SPF’ (n = 72) from 28 to 70 days of age. Digestive pathology was monitored daily and individually along the whole fattening period (28–70 d old) to precisely quantify the impact of a Fibre deficiency on rabbit health. Diarrhoea was the most common symptom of enteritis due to Fibre deficiency (90% of cases). The major diges- tive lesions were dilatation of the caeco-colic segment (30%) and a watery intestinal and caecal digesta (60%). The digestive troubles had a similar expression with respect to sanitary status or diet effect. The mortality and the Health Risk index (HRi = mortality + morbidity rate) respectively reached 25 and 60% with the Fibre deficient diet “D” (28–70 d period) compared to 9 and 41% for the standard diet “S” (P < 0.05). The digestive disturbances appeared mainly during the period 28–42 d for SPF rabbits, and later for the C rabbits (43–56 d). Morbidity, HRi and the duration of diarrhoea were respectively 7, 2 and 3 times higher for C rabbits as compared to the SPF rabbits. A syner- getic effect of Fibre deficiency and conventional sanitary status was observed on the incidence and inten- sity of digestive troubles. For individually caged rabbits, morbidity seemed to be mainly linked to the sanitary status of the animal (SPF or conventional), while the mortality Level was enhanced by a Fibre deficiency. The Fibre supply thus seemed to prevent morbidity from evolving into mortality. In conclusion, non-specific enteropathy depends jointly on sanitary and nutritional status of the animals
Viktor Mechtcherine - One of the best experts on this subject based on the ideXlab platform.
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characterising the time dependant behaviour on the single Fibre Level of shcc part 2 the rate effects on Fibre pull out tests
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:This paper is the second part of a two paper series about the time-dependant behaviour of Strain Hardening Cement-based Composite (SHCC) on the single Fibre Level. Having dealt with mechanisms of creep in SHCC in the first part, this paper reports single Fibre pull-out tests that were done to investigate the effect of the pull-out rate on the mechanical response of the interface between the Fibre and the matrix. It was found that not only the pull-out resistance increased with an increase of the pull-out rate but the probability of Fibre rupture during pull-out as well. Another important finding was that the interfacial shear resistance and slip-hardening coefficient are not only dependant on the pull-out rate, but also the embedment length.
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characterising the time dependant behaviour on the single Fibre Level of shcc part 1 mechanism of Fibre pull out creep
Cement and Concrete Research, 2009Co-Authors: W P Boshoff, Viktor Mechtcherine, Gideon P A G Van ZijlAbstract:SHCC (Strain Hardening Cement-based Composite) has been designed and optimised to overcome the main weaknesses of ordinary concrete, which is its brittleness. SHCC shows a high tensile ductility and can resist the full load at a tensile strain of more than 4%. An in depth investigation into the time-dependant behaviour is still lacking for SHCC. This paper is the first part of a two paper series about the time-dependant behaviour on the single Fibre Level. In this paper, the tensile creep behaviour of SHCC is studied to distinguish mechanisms of creep. Tensile creep and shrinkage test results are reported for dumbbell type SHCC specimens. The specimens are pre-cracked to simulate in-service conditions, with subsequent sustained load at various Levels, here chosen as 30%, 50%, 70% and 80% of the ultimate resistance. To distinguish the sources of significant creep deformation under these sustained loads, single Fibre pull-out tests are performed under sustained load. It is shown that the time-dependent Fibre pull-out is a significant source of time-dependent deformation, along with the formation of new cracks in SHCC under sustained load.