Pub Date : 2019-09-23DOI: 10.21809/rilemtechlett.2019.92
K. Vasilic, A. Gram, J. Wallevik
Recent developments in concrete technology are advancing into a scientific-based approach, where both experimental and numerical simulations are utilised to achieve an optimum mix design and an effective placement into formwork at the jobsite. Since the load carrying capacity and service life of concrete structures is fully dependent on the success of the placement process, researchers all over the world have started to work on casting prediction tools using different numerical software. However, a lot of work is still to be done in order to properly model the large-scale flow processes. This is because fresh concrete is a very complex material and its simulations involve complex material models and extensive computations. An exact material model of fresh concrete does not exist, and the researchers use diverse approximations to depict concrete flow. In this paper, we identify the main challenges for modelling fresh concrete and review the existing simulation methods. The advantages, disadvantages and application fields are discussed, including future perspectives for having numerical tools for practical use.
{"title":"Numerical simulation of fresh concrete flow: insight and challenges","authors":"K. Vasilic, A. Gram, J. Wallevik","doi":"10.21809/rilemtechlett.2019.92","DOIUrl":"https://doi.org/10.21809/rilemtechlett.2019.92","url":null,"abstract":"Recent developments in concrete technology are advancing into a scientific-based approach, where both experimental and numerical simulations are utilised to achieve an optimum mix design and an effective placement into formwork at the jobsite. Since the load carrying capacity and service life of concrete structures is fully dependent on the success of the placement process, researchers all over the world have started to work on casting prediction tools using different numerical software. However, a lot of work is still to be done in order to properly model the large-scale flow processes. This is because fresh concrete is a very complex material and its simulations involve complex material models and extensive computations. An exact material model of fresh concrete does not exist, and the researchers use diverse approximations to depict concrete flow. In this paper, we identify the main challenges for modelling fresh concrete and review the existing simulation methods. The advantages, disadvantages and application fields are discussed, including future perspectives for having numerical tools for practical use.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45470170","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-08-25DOI: 10.21809/rilemtechlett.2019.62
Ali Riza Erbektas, O. Isgor, W. Jason Weiss
Microbially Induced Corrosion of Concrete (MICC) is a progressive three-stage deterioration process that is primarily associated with sulfur-oxidizing bacteria (SOB). One strategy for mitigating MICC is the use of antimicrobial additives. It is hypothesized that the performance of antimicrobial products is influenced by the pH of the environment, the bacterial population, and the level of bacterial activity. To test this hypothesis, three bacterial activity-population levels were tested in environments with different pH levels to evaluate the efficacy of a typical antimicrobial product against planktonic SOB. The ability of the antimicrobial product to prevent or delay the biogenic acidification was considered as the criterion for its efficacy. The tested antimicrobial product was successful in delaying or preventing MICC with low and moderate bacterial populations and activity for all pH levels greater than 4. Lower pH levels were not tested in this investigation. Antimicrobial products were successful in delaying or preventing MICC with severe bacterial populations and activity for all pH levels tested greater than 6. The results support the main hypothesis of the research; therefore, the selection of whether to utilize an antimicrobial product requires an understanding of the operational pH of the environment as well as knowledge on the target bacterial population and activity.
{"title":"Evaluating the efficacy of antimicrobial additives against biogenic acidification in simulated wastewater exposure solutions","authors":"Ali Riza Erbektas, O. Isgor, W. Jason Weiss","doi":"10.21809/rilemtechlett.2019.62","DOIUrl":"https://doi.org/10.21809/rilemtechlett.2019.62","url":null,"abstract":"Microbially Induced Corrosion of Concrete (MICC) is a progressive three-stage deterioration process that is primarily associated with sulfur-oxidizing bacteria (SOB). One strategy for mitigating MICC is the use of antimicrobial additives. It is hypothesized that the performance of antimicrobial products is influenced by the pH of the environment, the bacterial population, and the level of bacterial activity. To test this hypothesis, three bacterial activity-population levels were tested in environments with different pH levels to evaluate the efficacy of a typical antimicrobial product against planktonic SOB. The ability of the antimicrobial product to prevent or delay the biogenic acidification was considered as the criterion for its efficacy. The tested antimicrobial product was successful in delaying or preventing MICC with low and moderate bacterial populations and activity for all pH levels greater than 4. Lower pH levels were not tested in this investigation. Antimicrobial products were successful in delaying or preventing MICC with severe bacterial populations and activity for all pH levels tested greater than 6. The results support the main hypothesis of the research; therefore, the selection of whether to utilize an antimicrobial product requires an understanding of the operational pH of the environment as well as knowledge on the target bacterial population and activity.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42960854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-10DOI: 10.21809/RILEMTECHLETT.2019.77
V. Guihard, F. Taillade, J. Balayssac, B. Steck, J. Sanahuja
The study presents the development of a new two-dimensional FEM numerical model describing the operation of two large open-ended coaxial probes designed to investigate the permittivity of concrete, and its constituents. This numerical simulation, combined with a capacitive approach describing the behaviour of the probes, enabled to prove the suitability of such device to determine the permittivity of dispersive dielectrics. Finding back the permittivity of a specified material by calculation of the S parameters, change of the reference plane and use of the capacitive model is the key to the proof. Measurements performed onto different materials show good similarities with the numerical simulations. Special considerations are mentioned concerning the size of the probe and its ability to measure the permittivity of heterogeneous materials made of large inclusions. Combination of such numerical tool and measuring device can be used as a non-destructive testing technique to assess the near surface permittivity of concrete structures or as a calibration technique for GPR measurements.
{"title":"Permittivity measurement of cementitious materials and constituents with an open-ended coaxial probe: combination of experimental data, numerical modelling and a capacitive model","authors":"V. Guihard, F. Taillade, J. Balayssac, B. Steck, J. Sanahuja","doi":"10.21809/RILEMTECHLETT.2019.77","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2019.77","url":null,"abstract":"The study presents the development of a new two-dimensional FEM numerical model describing the operation of two large open-ended coaxial probes designed to investigate the permittivity of concrete, and its constituents. This numerical simulation, combined with a capacitive approach describing the behaviour of the probes, enabled to prove the suitability of such device to determine the permittivity of dispersive dielectrics. Finding back the permittivity of a specified material by calculation of the S parameters, change of the reference plane and use of the capacitive model is the key to the proof. Measurements performed onto different materials show good similarities with the numerical simulations. Special considerations are mentioned concerning the size of the probe and its ability to measure the permittivity of heterogeneous materials made of large inclusions. Combination of such numerical tool and measuring device can be used as a non-destructive testing technique to assess the near surface permittivity of concrete structures or as a calibration technique for GPR measurements.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41425069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-08DOI: 10.21809/RILEMTECHLETT.2019.84
J. Putten, G. Schutter, K. Tittelboom
The structural capacity of 3D printed components mainly depends on the inter-layer bonding strength between the different layers. This bond strength is affected by many parameters (e.g. moisture content of the substrate, time gap, surface roughness,..) and any mismatch in properties of the cementitious material may lead to early failure. A common technique to improve inter-layer bonding strength between a substrate and a newly added layer is modifying the substrate surface. For the purpose of this research, a custom-made 3D printing apparatus is used to simulate the printing process and layered specimens with a different delay time (0 and 30 minutes) are manufactured with different surface modification techniques (wire brushing, addition of sand or cement and moisturizing substrate layer). The surface roughness was measured and the effect of the modification technique on the inter-layer-bonding strength was investigated. Results showed that the most effective way to increase the inter-layer bonding is increasing the surface roughness by a comb. This creates a kind of interlock system that will provide a higher inter-layer strength. The compressive strength is most influenced by the addition of cement, where the changing W/C-ratio will create a higher degree of hydration and consequently a higher strength.
{"title":"Surface modification as a technique to improve inter-layer bonding strength in 3D printed cementitious materials","authors":"J. Putten, G. Schutter, K. Tittelboom","doi":"10.21809/RILEMTECHLETT.2019.84","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2019.84","url":null,"abstract":"The structural capacity of 3D printed components mainly depends on the inter-layer bonding strength between the different layers. This bond strength is affected by many parameters (e.g. moisture content of the substrate, time gap, surface roughness,..) and any mismatch in properties of the cementitious material may lead to early failure. A common technique to improve inter-layer bonding strength between a substrate and a newly added layer is modifying the substrate surface. For the purpose of this research, a custom-made 3D printing apparatus is used to simulate the printing process and layered specimens with a different delay time (0 and 30 minutes) are manufactured with different surface modification techniques (wire brushing, addition of sand or cement and moisturizing substrate layer). The surface roughness was measured and the effect of the modification technique on the inter-layer-bonding strength was investigated. Results showed that the most effective way to increase the inter-layer bonding is increasing the surface roughness by a comb. This creates a kind of interlock system that will provide a higher inter-layer strength. The compressive strength is most influenced by the addition of cement, where the changing W/C-ratio will create a higher degree of hydration and consequently a higher strength.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42051071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-05DOI: 10.21809/RILEMTECHLETT.2019.90
B. Isgor, U. Angst, M. Geiker, Ceki Halmen, C. Hansson, J. Pacheco, D. Tepke, D. Trejo, Pavan Vaddey
Experience has shown that many aspects of experimental design for studying steel corrosion in cementitious systems may significantly influence the obtained results. In the absence of standardized methods to study steel corrosion in concrete, researchers usually define their own test setups, which partially explains the large scatter and uncertainty in the aggregated published data. When the details of these setups are not provided adequately, experimental results cannot be interpreted in a wider context. Unfortunately, many scientific publications lack important experimental details. Therefore, this paper aims at improving the quality of reported experimental details, observations, and data in scientific publications, and raising awareness for relevant issues to improve the quality of research in the field. To this end, this paper provides a list of experimental details that have been found important by many decades of research, and which are, thus, recommended to be considered in conducting and reporting laboratory studies involving corrosion of steel embedded in cementitious systems. Finally, we propose a checklist for reporting experimental data in scientific publications.
{"title":"Recommended practice for reporting experimental data produced from studies on corrosion of steel in cementitious systems","authors":"B. Isgor, U. Angst, M. Geiker, Ceki Halmen, C. Hansson, J. Pacheco, D. Tepke, D. Trejo, Pavan Vaddey","doi":"10.21809/RILEMTECHLETT.2019.90","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2019.90","url":null,"abstract":"Experience has shown that many aspects of experimental design for studying steel corrosion in cementitious systems may significantly influence the obtained results. In the absence of standardized methods to study steel corrosion in concrete, researchers usually define their own test setups, which partially explains the large scatter and uncertainty in the aggregated published data. When the details of these setups are not provided adequately, experimental results cannot be interpreted in a wider context. Unfortunately, many scientific publications lack important experimental details. Therefore, this paper aims at improving the quality of reported experimental details, observations, and data in scientific publications, and raising awareness for relevant issues to improve the quality of research in the field. To this end, this paper provides a list of experimental details that have been found important by many decades of research, and which are, thus, recommended to be considered in conducting and reporting laboratory studies involving corrosion of steel embedded in cementitious systems. Finally, we propose a checklist for reporting experimental data in scientific publications.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46216091","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-05DOI: 10.21809/RILEMTECHLETT.2019.80
F. Bennai, C. E. Hachem, K. Abahri, R. Belarbi
The use of bio-based materials such as hemp concrete in the field of construction allows limiting environmental impacts and improving the energy performances of buildings. The aim of this paper is to understand the influence of adsorption and desorption of moisture in hemp concrete on its internal morphology and its dimensional variations. That’s why, the high porosity and the adsorption capacity of hemp concrete were discussed. Then, an experimental cell was developed to follow the geometric evolution over time of hemp concrete microstructure under hydric solicitations: humidification and drying. The digital image correlation was used to determine the strains fields on the surface of the material. This technique showed the behavior of this hygroscopic material subjected to different hygrometries. Indeed, the hemp shiv undergoes larger strains than the binder, thus affecting the morphology of hemp concrete. The results obtained highlighted the influence of the hydric state of hemp concrete on its very heterogeneous microstructure. It has also been revealed that the durability of the material can be affected by the dimensional variations caused by the relative humidity variations.
{"title":"Influence of hydric solicitations on the morphological behavior of hemp concrete","authors":"F. Bennai, C. E. Hachem, K. Abahri, R. Belarbi","doi":"10.21809/RILEMTECHLETT.2019.80","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2019.80","url":null,"abstract":"The use of bio-based materials such as hemp concrete in the field of construction allows limiting environmental impacts and improving the energy performances of buildings. The aim of this paper is to understand the influence of adsorption and desorption of moisture in hemp concrete on its internal morphology and its dimensional variations. That’s why, the high porosity and the adsorption capacity of hemp concrete were discussed. Then, an experimental cell was developed to follow the geometric evolution over time of hemp concrete microstructure under hydric solicitations: humidification and drying. The digital image correlation was used to determine the strains fields on the surface of the material. This technique showed the behavior of this hygroscopic material subjected to different hygrometries. Indeed, the hemp shiv undergoes larger strains than the binder, thus affecting the morphology of hemp concrete. The results obtained highlighted the influence of the hydric state of hemp concrete on its very heterogeneous microstructure. It has also been revealed that the durability of the material can be affected by the dimensional variations caused by the relative humidity variations.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47253513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-05-24DOI: 10.21809/RILEMTECHLETT.2019.82
Shamsuddoha, G. Hüsken, W. Schmidt, H. Kühne, M. Baessler
Grouts have numerous applications in construction industry such as joint sealing, structural repair, and connections in precast elements. They are particularly favoured in rehabilitation of structures due to penetrability and convenience of application. Grouts for repair applications typically require high-performance properties such as rapid strength development and superior shrinkage characteristics. Sometimes industrial by-products referred as supplementary cementitious materials (SCM) are used with neat cement due to their capabilities to provide binding properties at delayed stage. Micro silica, fly ash and metakaolin are such SCMs, those can modify and improve properties of cement products. This study aims at investigating long-term mass loss and linear shrinkage along with long-term compressive and flexural strength for grouts produced from ultrafine cement and SCMs. A series of mixtures were formulated to observe the effect of SCMs on these grout properties. Properties were determined after 365 days of curing at 23oC and 55% relative humidity. The effect of SCMs on the properties are characterised by statistical models. Response surfaces were constructed to quantify these properties in relation to SCMs replacement. The results suggested that shrinkage was reduced by metakaolin, while micro silica and fly ash had positive effects on compressive and flexural strength, respectively.
{"title":"Long-term mechanical and shrinkage properties of cementitious grouts for structural repair","authors":"Shamsuddoha, G. Hüsken, W. Schmidt, H. Kühne, M. Baessler","doi":"10.21809/RILEMTECHLETT.2019.82","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2019.82","url":null,"abstract":"Grouts have numerous applications in construction industry such as joint sealing, structural repair, and connections in precast elements. They are particularly favoured in rehabilitation of structures due to penetrability and convenience of application. Grouts for repair applications typically require high-performance properties such as rapid strength development and superior shrinkage characteristics. Sometimes industrial by-products referred as supplementary cementitious materials (SCM) are used with neat cement due to their capabilities to provide binding properties at delayed stage. Micro silica, fly ash and metakaolin are such SCMs, those can modify and improve properties of cement products. This study aims at investigating long-term mass loss and linear shrinkage along with long-term compressive and flexural strength for grouts produced from ultrafine cement and SCMs. A series of mixtures were formulated to observe the effect of SCMs on these grout properties. Properties were determined after 365 days of curing at 23oC and 55% relative humidity. The effect of SCMs on the properties are characterised by statistical models. Response surfaces were constructed to quantify these properties in relation to SCMs replacement. The results suggested that shrinkage was reduced by metakaolin, while micro silica and fly ash had positive effects on compressive and flexural strength, respectively.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44105204","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-05-16DOI: 10.21809/RILEMTECHLETT.2019.88
Arunita Das, J. Bošnjak, Akanshu Sharma
Reinforced concrete (RC) structures may be subjected to accidental fire loads during their service life. In such a case, it is essential to have appropriate methods for the estimation of post-fire performance. One of the vital aspects for the performance of RC structures is adequate steel-to-concrete bond. The bond behaviour under ambient conditions is very well established. However, an appropriate model for the assessment of the post-fire bond capacity is still lacking. In order to provide more insight into the bond performance after fire, a 3D FE numerical study using a thermo-mechanical model with temperature dependent microplane model for concrete is performed. The effects of concrete cover, confinement through stirrups, fire duration and exposure type on post-fire bond performance are investigated using beam-end specimen. The results show a strong degradation of post-fire bond capacity, which is primarily attributed to the irreversible damage of concrete cover resulting from heating and cooling.
{"title":"Numerical investigations on post-fire bond behaviour of reinforcement in concrete","authors":"Arunita Das, J. Bošnjak, Akanshu Sharma","doi":"10.21809/RILEMTECHLETT.2019.88","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2019.88","url":null,"abstract":"Reinforced concrete (RC) structures may be subjected to accidental fire loads during their service life. In such a case, it is essential to have appropriate methods for the estimation of post-fire performance. One of the vital aspects for the performance of RC structures is adequate steel-to-concrete bond. The bond behaviour under ambient conditions is very well established. However, an appropriate model for the assessment of the post-fire bond capacity is still lacking. In order to provide more insight into the bond performance after fire, a 3D FE numerical study using a thermo-mechanical model with temperature dependent microplane model for concrete is performed. The effects of concrete cover, confinement through stirrups, fire duration and exposure type on post-fire bond performance are investigated using beam-end specimen. The results show a strong degradation of post-fire bond capacity, which is primarily attributed to the irreversible damage of concrete cover resulting from heating and cooling.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44586458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-04-18DOI: 10.21809/RILEMTECHLETT.2018.69
Alexis Simons, A. Bertron, C. Roux, A. Laborel-Preneron, J. Aubert, C. Roques
The impact of building materials on the environment and the health of occupants is nowadays a priority issue. Ecological construction materials such as earthen materials are currently experiencing a regain of interest due to both ecological and economic factors. The microbial proliferation on indoor materials can induce a deterioration of the building air quality and lead to an increase of health risks for the occupants. The issue of indoor air quality raises questions about the use of earthen building materials and their possible susceptibility to fungal development. The microflora of earthen materials and their ability to grow on such support are indeed poorly studied. This study focused on the quantification of both bacterial and fungal microflora along the manufacturing process. The impact of extreme humidity, simulating a hydric accident, on microflora development was analyzed on the surface and inside earthen bricks. The initial microflora of these materials was dramatically reduced during the manufacturing process, especially after heat treatment for drying. Proliferation of remaining microorganisms was only observed under high humidity condition, in particular for earthen materials with vegetal aggregates. Moreover, in situ samplings were performed on naturally dried earthen materials used in buildings. The characterization of the microbial density revealed a higher microbial density than on manufactured specimens, while microbial concentration and detected taxa seemed mainly related to the room use and building history. These results provide a better understanding of microbial proliferation on these materials.
{"title":"Susceptibility of earth-based construction materials to fungal proliferation: laboratory and in situ assessment","authors":"Alexis Simons, A. Bertron, C. Roux, A. Laborel-Preneron, J. Aubert, C. Roques","doi":"10.21809/RILEMTECHLETT.2018.69","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2018.69","url":null,"abstract":"The impact of building materials on the environment and the health of occupants is nowadays a priority issue. Ecological construction materials such as earthen materials are currently experiencing a regain of interest due to both ecological and economic factors. The microbial proliferation on indoor materials can induce a deterioration of the building air quality and lead to an increase of health risks for the occupants. The issue of indoor air quality raises questions about the use of earthen building materials and their possible susceptibility to fungal development. The microflora of earthen materials and their ability to grow on such support are indeed poorly studied. This study focused on the quantification of both bacterial and fungal microflora along the manufacturing process. The impact of extreme humidity, simulating a hydric accident, on microflora development was analyzed on the surface and inside earthen bricks. The initial microflora of these materials was dramatically reduced during the manufacturing process, especially after heat treatment for drying. Proliferation of remaining microorganisms was only observed under high humidity condition, in particular for earthen materials with vegetal aggregates. Moreover, in situ samplings were performed on naturally dried earthen materials used in buildings. The characterization of the microbial density revealed a higher microbial density than on manufactured specimens, while microbial concentration and detected taxa seemed mainly related to the room use and building history. These results provide a better understanding of microbial proliferation on these materials.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43933668","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-03-18DOI: 10.21809/RILEMTECHLETT.2018.73
D. Breysse, J. Balayssac
The non-destructive assessment of concrete strength in existing structures is a complex issue which has been analyzed by a recently closed RILEM committee (TC ISC 249) whose Guidelines and Recommendations are to be released soon. This committee has considered the state of practice, the yet existing standards and most recent innovative research results, in order to write recommendations that would improve the reliability of strength assessment with non-destructive techniques (NDT). These recommendations are based on a paradigm change: the challenge is not that of finding the true local strength, but that of estimating its value with a controlled tolerance interval and a limited risk of being wrong. Three levels of requirements are defined which correspond to different tolerance intervals on the assessed parameters and to a different amount of resources devoted to the investigation. While most of research had been devoted until now to the identification of relevant conversion models between NDT test results and strength, we have shown that the priority had to be put on other items, including the assessment of the NDT test results repeatability, the relevant definition of core locations and the checking of the final predictive error. This paper briefly describes the main innovations included in these recommendations.
{"title":"Reliable non-destructive strength assessment in existing structures: myth or reality?","authors":"D. Breysse, J. Balayssac","doi":"10.21809/RILEMTECHLETT.2018.73","DOIUrl":"https://doi.org/10.21809/RILEMTECHLETT.2018.73","url":null,"abstract":"The non-destructive assessment of concrete strength in existing structures is a complex issue which has been analyzed by a recently closed RILEM committee (TC ISC 249) whose Guidelines and Recommendations are to be released soon. This committee has considered the state of practice, the yet existing standards and most recent innovative research results, in order to write recommendations that would improve the reliability of strength assessment with non-destructive techniques (NDT). These recommendations are based on a paradigm change: the challenge is not that of finding the true local strength, but that of estimating its value with a controlled tolerance interval and a limited risk of being wrong. Three levels of requirements are defined which correspond to different tolerance intervals on the assessed parameters and to a different amount of resources devoted to the investigation. While most of research had been devoted until now to the identification of relevant conversion models between NDT test results and strength, we have shown that the priority had to be put on other items, including the assessment of the NDT test results repeatability, the relevant definition of core locations and the checking of the final predictive error. This paper briefly describes the main innovations included in these recommendations.","PeriodicalId":36420,"journal":{"name":"RILEM Technical Letters","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-03-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45241274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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