Academic literature on the topic 'Concrete microstructure ultrasound'

Locadiff, an innovative imaging technique based on diffuse waves, has recently been developed in order to image mechanical changes in heterogeneous, geological, or man-made materials. This manuscript reports the on-site application of Locadiff to locate several pre-existing cracks on an aeronautical wind tunnel made of pre-stressed concrete. Using 32 transducers working at ultrasonic frequencies (80–220 kHz) where multiple scattering occurs, we monitor during 15 min an area of 2.5 m×2.5 m of a 35-cm-thick wall. With the wind tunnel in its routine operation, structural changes around the cracks are detected, thanks to their closing or opening due to slight pressure changes. By mapping the density of such microstructure changes in the bulk of the material, locating three pre-existing cracks is properly performed in three dimensions.

Purpose Macro synthetic steel fibers were incorporated into the concrete material as a toughening agent to improve the corrosion and cracking resistances of concrete in a sulfate-containing service environment. Design/methodology/approach To study the basic mechanical properties of this system, an accelerated concrete degradation test was designed to evaluate the influence of the sulfate ions on the concrete. A three-point bending test was carried out in the laboratory to evaluate the fracture toughness. The thickness of the damaged concrete layer and changes of microstructure of the degraded concrete were monitored by using ultrasound, scanning electron microscopy and X-ray diffraction detection methods. Findings The results showed that compared to the performance of ordinary concrete, in an exposure environment containing sulfate ions, the structure compactness of macro synthetic steel fiber concrete was improved, degradation resistance to the sulfate solution was enhanced and the fracture resistance performance was improved significantly. Originality/value The thickness of the degradation layer on the macro synthetic steel fiber concrete was less than a half of that of ordinary concrete in the sulfate environment, and was generally unchanged with increase in the sulfate concentration. Through micro-structural analysis, it was confirmed that macro synthetic steel fiber improved the compactness of the concrete structure, inhibiting access of sulfate ions to the interior of the concrete and thereby reducing the degree of sulfate degradation to the concrete.

There are multiple references to sample cleaning methods prior to hydrogen content determination, or hydrogen spectroscopy analysis, but there is still no unified criteria; different authors use their own “know-how” to perform this task. The aim of this paper is to solve, or at least clarify, this issue. In this work, the most commonly used sample cleaning methods are compared. Then, five different methodologies are applied on certified hydrogen content calibration pins and on high strength steel concrete-prestressing strands and the three main situations regarding hydrogen content in the microstructural net (non-charged, charged, and charged and uncharged) are studied. It was concluded that the HCl solution C-3.5 cleaning method recommended by ASTM G1 introduces large amounts of hydrogen in the samples; but can be useful for eliminating superficial oxides if necessary. The rest of the methods had similar results; but the more complete ones that involve ultrasounds and last longer than 8 min are not appropriated when important diffusion may occur on the samples during their application. Simple methods that involve acetone or trichloroethylene and last around 1 min are preferable for almost all situations as these are faster, easier, and cheaper. As a final recommendation, as trichloroethylene is toxic, the simple acetone method is, in general, the most convenient one for regular hydrogen content analysis.

Journal of the Latin-American association of quality control, pathology and recovery of constructionhttp://www.revistaalconpat.orgWith great satisfaction, we present the first issue of the ninth year of the ALCONPAT journal.The aim of the journal is to publish case studies within the scope of the Association, namely quality control, pathology and recovery of constructions, including basic and applied research, reviews and documentary research.The V9 N1 issue begins with a work where Nicolle Christine Sotsek and colleagues provide, through a systematic review of the literature and focused on the quality control of buildings, a consistent database to present the most used criteria by the Building Performance Evaluation (BPE). It was possible to define 9 dimensions of analysis that are presented and discussed in this document.In the second work, Cristiano Corrêa et. al. present the computational simulation of a fire previously carried out as an experiment in a room that reproduced a single-family residence room, typically burnt down in the city of Recife (Pernambuco, Brazil). The objective of the article is to compare the results of the development of the temperatures of the gases obtained through computer simulation with the Fire Dynamics Simulator software (FDS) through the measurements obtained in the experiment. It was verified that the results obtained through the model developed in the FDS were coherent with those obtained experimentally.In the third article, Mauricio de Pina Ferreira et. al. evaluate the influence of anchoring on the flexural strength of beams reinforced with Carbon Fiber Reinforced Polymer (PRFC) blankets. The parameters affecting the performance and strength of the beams are evaluated, and the sizing criteria of FIB Bulletin 14 (2001) and ACI 440-2R (2008) are discussed. It was observed that, even with auxiliary devices in the anchoring of the PRFC, there is the possibility of premature failures, and that both recommendations lead to safe, but overly conservative estimates in cases where the anchoring of the PRFC blanket is carried out properly.In the fourth article, by Yagho de Souza Simões and Carol Ferreira Rezende Santos, we compare two techniques of structural reinforcement, carbon fiber and metal foil, used for the recovery of reinforced concrete structures degraded by fire. A deterioration of a beam in a fire situation is simulated from a thermal numerical modeling and, next, the reinforcements are calculated. It is concluded that carbon fiber has greater advantages regarding the reinforcement of beams.The fifth work in this issue is written by Ricardo José Carvalho Silva and colleagues, who analyze the efficiency of reinforcement in reinforced concrete beams by adding steel bars and epoxy adhesive. The tests showed that the clamps reduced the strength of the beams, compared to those that did not. The reinforced beams without clamps obtained better results, but the most important limiting factor was the adhesion between the epoxy and the beam. The use of clamps to try to solve the problem of adherence gave originality to this investigation.In the sixth work, Marcela Tavares de Araujo Silva and colleagues evaluate an ultrasound test to estimate the depth of cracks in the concrete, using a mathematical model of the literature, in addition to checking the depth with better results. The results show that the test is sensitive to detect the presence of cracks in the concrete. The mathematical model used allowed to estimate the most depths of fissures; but the results are scattered and with a high margin of error for the depths of 5 cm and 15 cm, since for 10 cm better results were observed.The seventh work in this issue is written by Renato Guilherme Pereira and colleagues, who present an experimental program to determine the residual strength of bi-supported reinforced concrete beams subjected to pure bending after fires. The beams presented, up to 120 minutes of exposure to fire, a good performance after the fire, not showing a significant reduction in their residual strength, and the numerical model was accurate in forecasting the temperatures and the residual rupture load when the experimental results were compared.The article that closes this edition is by Erick Maldonado et. al. they present the results of concrete manufactured with supersulfated cements (SSC) volcanic material bases. After 180 days, the concrete with a cementitious compound of 5% An-10% CP-10% CaO-75% PM exposed to the CaSO4 solution reached a compressive strength of 46 MPa and 44 MPa in dry conditions. laboratory. The microstructure was analyzed by scanning electron microscopy, energy dispersion spectroscopy and XRD, showed that the main hydration products are C-S-H and ettringite.We are confident that the articles in this issue will be an important reference for those readers involved with issues of modeling applications and service life, as well as inspections with modern and / or improved methodologies. We thank the authors participating in this issue for their willingness and effort to present quality articles and meet the established times.On behalf of the Editorial Board Pedro Castro Borges Editor in Chief

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.
Dr. Jennifer Michaels, Committee Member ; Dr. Jacek Jarzynski, Committee Member ; Dr. Jianmin Qu, Committee Member ; Dr. Laurence J. Jacobs, Committee Chair ; Dr. Kimberly E. Kurtis, Committee Co-Chair.

The goal of this work was to create a method for improving the dispersion of silica fumes for use in high performance concrete. Traditional methods used to design and manufacture high performance concrete emphasize the removal of coarse aggregates. Use of specially sorted fine aggregates at relatively low doses, the use of super-plasticizers and siliceous excrement. The low water content was achieved by using superplasticizer on a polycarboxylate basis. The standard ultrasound technology found in each laboratory was selected for the dispersion of silica fume. For experiments were we used dry silica fume powder and aqueous stabilized suspension. For comparison, were prepared different mixtures which showed the effects of the treatment prior to the use of silica fume.

Ce travail de thèse traite de la caractérisation de la microstructure du béton à l’aide des ondes ultrasonores. La structure hétérogène du béton entraine la diffusion multiple de ces ondes aux fréquences d’auscultation d’intérêt. Le signal reçu comprend alors une partie cohérente et une partie incohérente. Cette dernière est caractérisée par une longue coda qui correspond à des trajets longs à l’intérieur du milieu et qui est porteuse d’information sur la microstructure. Pour exploiter la coda, l’évolution de l’intensité moyenne est analysée. L’approximation de cette évolution par une équation de diffusion permet de mesurer la « diffusivité ». Celle-ci est sensible à l’évolution de la microstructure du béton. Des travaux le montrent par des évaluations qualitatives. Une analyse quantitative reste difficile du fait du biais entre les hypothèses et la réalité sur l’élément ausculté et les conditions de mesure. Plusieurs approches alternatives sont explorées afin d’analyser la coda : lorsque le régime de diffusion n’est pas établi ou lorsque la réverbération masque la diffusion multiple.Les simulations numériques constituent notre principal outil de travail car elles permettent d’aborder les différents cas de figures. Le béton est généralement considéré comme étant un milieu biphasique granulats/mortier, avec un contact parfait à leurs interfaces. Nous reconsidérons cette représentation en prenant en compte l’Interfacial Transition Zone (ITZ). Un modèle d’ITZ intégrant des caractéristiques réalistes est défini et implémenté numériquement. Les effets de l’ITZ sur les paramètres ultrasonores sont évalués et validés expérimentalement
This work deals with the characterization of the microstructure of concrete with ultrasonic waves. The high heterogeneity of concrete makes the ultrasonic waves multiply scattered at the frequency range of interest. The recorded signal is thus composed of a short coherent part and a long incoherent part called coda. The latter corresponds to long paths inside the medium and brings information about the microstructure.The averaged intensity’s evolution is analyzed in order to exploit the coda. Fitting this evolution with a solution of the diffusion equation allows to measure the diffusivity parameter. The diffusivity is shown to be sensitive to the concrete’s microstructure evolution, but those approaches are qualitative. A quantitative measurement of the diffusivity remains challenging because of the bias between assumptions generally used and reality about the material and the measurement. Many alternative approaches are explored in this work that aims to allow a characterization on a wide range of situations. Numerical simulations constitute an ideal tool because they allow to consider many cases without being expensive. Concrete is generally considered as a two-phase medium (aggregates/mortar) with a perfect contact at their interfaces. We reconsider this approach by taking into account the Interfacial Transition Zone (ITZ). A numerical model which accounts for realistic characteristics of ITZ is developed. The effects of ITZ on ultrasonic parameters are evaluated and validated with experimental data