Circular and Square Concrete Columns Externally Confined by CFRP Composite: Experimental Investigation and Effective Strength Models

The use of fiber reinforced polymers (FRP) jackets as an external mean to strengthen existing RC columns has emerged in recent years with very promising results [1-13], among others. Several studies on the performance of FRP wrapped columns have been conducted, using both experimental and analytical approaches. Such strengthening technique has proved t

The confinement of concrete in compression using CFRP composites – effective design equations

This paper presents the results of an experimental study on the behaviour of axially loaded short concrete columns, with different cross sections that have been externally strengthened with carbon fibre-reinforced polymer (CFRP) sheets. Six series, forming the total of 60 specimens, were subjected to axial compression. All the test specimens were loaded to failure in axial compression and investigated in both axial and transverse directions. According to the obtained test results, FRP-confined specimen failure occurs before the FRP reached the ultimate strain capacities. Thus, the failure occurs prematurely and the circumferential failure strain is lower than the ultimate strain obtained from the standard tensile testing of the FRP composite. In existing models for FRP-confined concrete, it is commonly assumed that the FRP ruptures when the hoop stress in the FRP jacket reaches its tensile strength from either flat coupon tests, which is herein referred to as the FRP material tensile strength. This phenomenon considerably affects the accuracy of the existing models for FRP-confined concrete. On the basis of the effective lateral confining pressure of the composite jacket and the effective circumferential FRP failure strain, new equations were proposed to predict the strength of FRP-confined concrete and corresponding strain for each of the cross section geometry used, circular and square. The estimations given by these equations were compared with the experimental ones and general conclusions were drawn

Modeling of CFRP strengthened RC beams using the SNSM technique, proposed as an alternative to NSM and EBR techniques

In this paper, an analytical and numerical study in FEM finite element by the ABAQUS software was conducted. Which aims to study the behaviour of RC beams bending strengthened with SNSM side near surface mounted technique, proposed as a solution to avoid the failure mode by debonding of the strengthening, the disadvantage of the EBR externally bonded reinforced technique, and the failure mode by separation of the concrete cover relative to the NSM near surface mounted technique, by comparing the behaviour of the three techniques, the effect of the quantity of strengthening and confirm the results with the literature. The results of this study show that the numerical and analytical model can predict the behaviour of strengthened RC beams according to the three techniques, a clear improvement of the bending capacity of beams strengthened is noticed. A good preservation of the ductility of SNSM beams with a better failure mode

Elaboration of geopolymer cement based on dredged sediment

This work aims to study the feasibility of making a geopolymer cement based on dredged sediments, from the Fergoug dam (Algeria). Sedimentary clays were characterized before and after calcination by X-ray diffraction, ATG / ATD, spectroscopy (FTIR) and XRF analysis. The reactivity of the calcined products was measured using isothermal calorimetric analysis (DSC) on pastes prepared by mixing an alkaline solution of sodium hydroxide (NaOH) 8 M in an amount allowing to have a Na / Al ratio close to 1. Also, cubic mortar samples were prepared with a ratio L / S: 0.8, sealed and cured for 24 hours at 60 ° C and then at room temperature. The results obtained allowed to optimize the calcination time of 5 hours for a better reactivity of these sediments, and a concentration of 8M of sodium hydroxide and more suitable to have the best mechanical performances

Contribution à l'Étude des Matériaux Composites Dans le Renforcement et la Réparation Des Éléments Structuraux Linéaires en Béton

International audienceCe travail concerne, l'étude du comportement axial et radial résultant de l'effet du confinement externe procuré par une enveloppe en matériau composite à base de fibres de carbone (PRFC) ou de fibre de verre (PRFV). Pour l'ensemble des spécimens testés, l'augmentation de la rigidité du confinement entraîne à la fois une augmentation de la résistance à la compression et de la ductilité. L'effet de la résistance du béton non confiné f'co sur l'efficacité du confinement été remarquable pour les deux type de sections étudiées (à savoir les sections circulaires et carrées). Les spécimens en B.A endommagés après avoir été renforcés par 3 couches de composite PRFC, se comportaient d'une manière tout à fait comparable à celle des spécimens similaires non endommagés. Comparés aux spécimens de références, le confinement par composite PRFC été très efficaces pour tous les spécimens quelque soient leurs taux d'endommagement initial (40, 60, 80 ou 100 % de la charge de rupture). A travers ce travail, nous espérons présenter pour les futurs chercheurs une modeste contribution à la compréhension du comportement mécanique du béton confiné avec des composites PRF

Contribution of the Blast Furnace Slag on the Behavior of HPC in a Hydrochloric Environment

Most mechanical properties and durability of cementitious materials are related to the performance of the hydrated cement that coats the granular skeleton. However, different mineral additions are currently used in concrete. They are used as addition or substitution to cement. The use of these supplementary cementitious materials provides to concrete a denser matrix that will be more resistant to aggressive environments such as sulphates, chlorides and other aggressive agents. In mixtures containing finely ground of slag, 15% of cement by weight was replaced with finely ground of slag of El-Hadjar (Algeria). The main objective of this study is to investigate the effect of curing in the hydrochloric environment by subjugating its granular effect on the performance of concrete. Density, compressive strength, concrete surface, internal microstructure and ultrasonic pulse velocity were investigated in this research. The damage mechanisms of concrete have been related to the development of the microstructure of the material. The degradations were observed using a scanning electron microscope (SEM) and quantified by x-ray diffraction (XRD). The microstructural study concerns both the surface layer and the internal structure of the samples. The results have shown that slag of El-Hadjar present a pozzolanic activity and hence it affects favorably the microstructure of the paste which becomes denser and less permeable

Elective cancer surgery in COVID-19-free surgical pathways during the SARS-CoV-2 pandemic: An international, multicenter, comparative cohort study

PURPOSE As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19–free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19–free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19–free surgical pathways. Patients who underwent surgery within COVID-19–free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19–free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score–matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19–free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION Within available resources, dedicated COVID-19–free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Elective Cancer Surgery in COVID-19-Free Surgical Pathways During the SARS-CoV-2 Pandemic: An International, Multicenter, Comparative Cohort Study.

PURPOSE: As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19-free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS: This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19-free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS: Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19-free surgical pathways. Patients who underwent surgery within COVID-19-free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19-free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score-matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19-free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION: Within available resources, dedicated COVID-19-free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Influence du type d'addition minérale sur le comportement physico-mécanique et sur la durabilité des bétons autoplaçants

En raison des spécificités relatives à la formulation des bétons autoplaçants (BAP) et en particulier ce qui concerne leur volume élevé en pâte et la présence d ajouts minéraux en grande quantité, leur comportement à l état frais et à l état durci ainsi que leur durabilité sont fortement influencés par ces deux paramètres. Ce travail de recherche vise à apporter une contribution à la valorisation de la pouzzolane naturelle de Béni-Saf (Algérie) en tant qu addition minérale dans la composition de bétons autoplaçants économiques. Il s agit de comparer l influence de la nature des ajouts minéraux (pouzzolane naturelle, cendre volante et filler calcaire) sur les caractéristiques physicomécaniques et sur la durabilité de ces bétons à court terme (28 jours), à moyen terme (90 jours) et à long terme (360 jours). Au total, douze formulations ont été étudiées, elles couvrent trois différentes classes de résistances (30 MPa, 50 MPa et 70 MPa) et quatre types de bétons : un béton ordinaire vibré (BOV), un BAP à base de pouzzolanes naturelles (BAP PZ), un BAP à base de fillers calcaires (BAP FC) et un BAP à base de cendres volantes (BAP CV). Les résultats de la résistance à la compression obtenus sont très proches selon la classe de résistance pour les trois additions minérales utilisées dans les BAP. Les résultats des essais d arrachement (pull-out test), de l absorption capillaire, de la porosité accessible à l eau et au mercure, du coefficient de diffusion des ions chlorures, de la perméabilité à l hélium, de l attaque acide (HCl et H2SO4) et de l attaque sulfatique Na2SO4, montrent que la nature de l addition minérale dans les BAP influe considérablement les propriétés physico-mécaniques et la durabilité de ces bétons. Les BAP contenant de la pouzzolane naturelle (BAP PZ) représentent non seulement un intérêt économique, mais aussi des performances très comparables à celles obtenues sur des BAP à base de cendres volantes (BAP CV) et bien meilleures que celles sur des BAP formulés avec du filler calcaire. Par ailleurs, Les BAP PZ et les BAP CV présentent des valeurs de retrait acceptables mais légèrement supérieures à celles des autres bétons.Because of the specificities of self-compacting concrete (SCC), especially regarding their high volume paste content and the presence of large amounts of mineral admixtures, the behavior in fresh and hardened state and the durability of these concretes are strongly influenced by these two parameters. This research aims to contribute to the valorization of the natural pozzolan of Beni Saf (Algeria) as a mineral admixture on the composition of an economic self-compacting concrete. The influence of the nature of different mineral admixtures (natural pozzolan, fly ash and limestone filler) on the physical, mechanical behavior and durability of these concretes in the short-term (28 days), medium-term (90 days) and long-term (360 days) were investigated. In total, twelve formulations were studied, thus covering three various strength classes (30 MPa, 50 MPa, and 70 MPa), as well as four types of concrete: ordinary vibrated concrete (OVC), SCC with limestone filler addition (SCC LF), SCC with natural pozzolan (SCC PZ), and SCC with fly ash (SCC FA). The results obtained of the compressive strength are very close by strength classes for the three mineral admixtures used in the SCC. The results of the different following tests : pull-out test, capillary absorption, accessible water and mercury porosity, chloride ion diffusion, helium permeability, carbonation, acids attack (HCl and H2SO4) and sulfate attack (Na2SO4), show that the nature of the mineral admixture influence greatly the physico-mechanical behavior and durability of the SCC. Also, shrinkage measurements and analysis show that SCC PZ and SCC FA present acceptable values slightly higher than those of other concretes. The SCC containing natural pozzolan represents not only an economic SCC but also performances quite comparables to those obtained on SCC containing fly ash and better than those of SCC made with limestone filler.RENNES-INSA (352382210) / SudocSudocFranceF

Strength model for square concrete columns confined by external CFRP sheets

International audienc