The Experts below are selected from a list of 42594 Experts worldwide ranked by ideXlab platform
M G Alexander - One of the best experts on this subject based on the ideXlab platform.
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Durability and service life prediction for Concrete structures developments and challenges
MATEC Web of Conferences, 2018Co-Authors: M G AlexanderAbstract:The paper reviews developments in service life prediction for Concrete structures. It indicates the difficulties inherent in rational service life design, in view of the multiple factors and variabilities involved in the process. The paper also emphasises the advantages of performance-based approaches to Durability prediction, and considers performance testing, which is critical to achieving intended service life. Such approaches allow service life modelling, which the current prescriptive approaches do not. The concept of ‘Durability indicators’ is covered, with a practical example showing how this can be used to improve Concrete Durability in construction. The paper also stresses the importance of an ‘integrated approach’ to Durability specifications, performance-based predictions, and site quality control.
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oxygen permeability of Concrete and its relation to carbonation
Construction and Building Materials, 2015Co-Authors: B G Salvoldi, Hans Beushausen, M G AlexanderAbstract:Abstract The corrosion of steel reinforcement due to carbonation of Concrete presents one of the major deterioration mechanisms in reinforced Concrete structures. The South African Concrete Durability design method for reinforced Concrete structures incorporates a performance based approach to evaluate the penetrability and quality of the Concrete cover. With respect to carbonation, the method relies on measurement of an index of the oxygen permeability of Concrete, which is used as an input parameter to a carbonation model. This paper presents a revised model for Concrete carbonation, which expands common carbonation models by accounting for the effect of relative humidity on both diffusion and chemical reactions. Using experimental data, oxygen permeability results are correlated with the carbonation coefficient as well as the carbon dioxide diffusion coefficient of Concrete. This correlation enables prediction of time-dependent carbonation depths of Concretes based on the environmental exposure, mix design and oxygen permeability of the Concrete.
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Durability design and specification for Concrete structures the way forward
International Journal of Advances in Engineering Sciences and Applied Mathematics, 2010Co-Authors: M G Alexander, Manu Santhanam, Yunus BallimAbstract:Much effort has been made in recent years to adopt suitable strategies for Durability design of Concrete. Most of this work has focused on the development of ‘performance specifications’ for Concrete. However, there are many barriers and limitations to successful implementation of these strategies for early-age control of reinforced Concrete Durability. This article reviews some of the recent efforts in the implementation of such strategies. It describes the South African approach to Durability design, which is based on performance specifications that are to be satisfied at the time of construction. Case studies are presented on approaches to reinforced Concrete design and the corresponding application of a Durability performance specification, to highlight the potential for adopting a probability-based methodology for Durability design. Finally, the paper attempts to provide a way forward towards successful utilization of such approaches, with particular emphasis on the construction industry in India.
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Durability performance of Concrete containing condensed silica fume
Cement and Concrete Research, 1999Co-Authors: M G Alexander, Bryan MageeAbstract:The paper describes a short-term study carried out to examine the Durability performance of various condensed silica fume (CSF) Concretes in comparison to portland cement (PC) and PC/ground granulated blast furnace slag (GGBS) controls up to the age of 28 days. Mix proportions were designed to provide 28-day strengths of 30, 40, and 50 MPa for the PC controls and these were used for all binder combinations considered. Concrete Durability was inferred from a suite of Durability index tests designed to measure Concrete resistance to gas, liquid, and ion transport mechanisms. It is shown that Concrete Durability is dramatically improved through the use of CSF. Optimum performance was achieved through the use of CSF as a 10% addition by mass to the initial binder content. The work also confirms CSF’s effectiveness when used in ternary binder blends with PC and GGBS, with these mixes out-performing the controls and selected binary-blended PC/CSF mixes.
Baoshan Huang - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of fly ash Concrete under sulfate attack
Construction and Building Materials, 2015Co-Authors: Qingke Nie, Changjun Zhou, Xiang Shu, Hongren Gong, Baoshan HuangAbstract:Portland cement Concrete (PCC) suffers sulfate attack in sulfate-rich environments. On the other hand, industrial by-products such as fly ash and slag are routinely added to PCC to improve its properties. However, the impact of fly ash on Concrete Durability is not always conclusive and it is time- and energy-consuming to test Concrete Durability in the laboratory or through field observation. This study presents a numerical simulation of the Durability of Portland cement Concrete made with fly ash. The simulation of sulfate attack on fly ash Concrete was performed based on ion transport mechanism. The chemical reactions among chemical compounds of hydrated cement paste and sulfate ions were considered. Additionally, the pozzolanic and hydration reactions of fly ash were incorporated as well to incorporate the impact of fly ash. The pozzolanic and hydration reaction were simulated through the extended version of an existing numerical procedure. Field observation data from the United States Bureau of Reclamation (USBR) was employed to validate the extended simulation program. After pozzolanic and hydration reactions of fly ash were incorporated, the prediction agreed well with the field measurements. The simulation shows that pozzolanic reaction of fly ash can significantly slow down sulfate attack on Concrete, thus increasing the sulfate resistance of PCC and extending the service life of Concrete infrastructures. The major factors that affect the sulfate resistance of Concrete were explored through the numerical simulation as well.
David O Nduka - One of the best experts on this subject based on the ideXlab platform.
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assessment of Concrete Durability in buildings the effects of the quality of cements available in lagos nigeria
International Review of Civil Engineering, 2019Co-Authors: Joshua Opeyemi, K O Olusola, Olabosipo I Fagbenle, Ayodeji Ogunde, David O NdukaAbstract:This paper presents an investigative research that aims to find the effects of the cements available in Lagos, Nigeria on the Durability of Concrete within the study area. This is in an attempt to stem the rate of building failures in Lagos, Nigeria. The physical, the mechanical and the microstructural properties of the cements have been determined and compared with the standard properties as specified in relevant standards. 150mm cubes have been cast with these cements and all the sources of aggregates within the study area. Laboratory findings have discovered that all the cements investigated have fallen short of the expected strengths specified in standards but the labelled brands had values close to the strength standards but the unlabeled ones have fallen far short of the standard strength. The chemical analysis has complied with standard requirements except for their loss on ignition (LOI) values and the chemical properties have been complemented by the microstructural morphology as determined with the Scanning Electron Microscope (SEM) though the unlabeled brands have tendencies for alkali silica reactivity due to higher levels of alkali present in them. In assessing their performance in Concrete, the Concrete cube strength has met the expected 20MPa except for the unlabeled brands that have fallen a little short of it. The effects of these cements have been discovered to be very significant on the Concrete Durability within the study area. It is thereby recommended that the Nigerian regulatory agencies on cements make more efforts in order to ensure that cement manufacturers in Nigeria improve the quality of their cement brands in order to standard strength specification. All cements should be temporarily used as a 32.5 strength class, despising the labelled 42.5, pending when the manufacturers would fully comply their products to standard. Copyright © 2019 Praise Worthy Prize S.r.l. - All rights reserved.
Qingke Nie - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of fly ash Concrete under sulfate attack
Construction and Building Materials, 2015Co-Authors: Qingke Nie, Changjun Zhou, Xiang Shu, Hongren Gong, Baoshan HuangAbstract:Portland cement Concrete (PCC) suffers sulfate attack in sulfate-rich environments. On the other hand, industrial by-products such as fly ash and slag are routinely added to PCC to improve its properties. However, the impact of fly ash on Concrete Durability is not always conclusive and it is time- and energy-consuming to test Concrete Durability in the laboratory or through field observation. This study presents a numerical simulation of the Durability of Portland cement Concrete made with fly ash. The simulation of sulfate attack on fly ash Concrete was performed based on ion transport mechanism. The chemical reactions among chemical compounds of hydrated cement paste and sulfate ions were considered. Additionally, the pozzolanic and hydration reactions of fly ash were incorporated as well to incorporate the impact of fly ash. The pozzolanic and hydration reaction were simulated through the extended version of an existing numerical procedure. Field observation data from the United States Bureau of Reclamation (USBR) was employed to validate the extended simulation program. After pozzolanic and hydration reactions of fly ash were incorporated, the prediction agreed well with the field measurements. The simulation shows that pozzolanic reaction of fly ash can significantly slow down sulfate attack on Concrete, thus increasing the sulfate resistance of PCC and extending the service life of Concrete infrastructures. The major factors that affect the sulfate resistance of Concrete were explored through the numerical simulation as well.
F Irassar - One of the best experts on this subject based on the ideXlab platform.
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effect of the marine environment on reinforced Concrete Durability in iberoamerican countries duracon project cyted
Corrosion Science, 2007Co-Authors: Troconis O De Rincon, M Sanchez, Valentina Millano, Rafael Fernandez, E De Partidas, C A Andrade, Isabel Martinez, M Castellote, M Barboza, F IrassarAbstract:Abstract This work presents some of the results from the project: “Effect of the environment on reinforcement Durability” (DURACON) in its first two-years period, which investigates the influence of urban and marine meteorochemical parameters on the performance of reinforced Concrete structures. The results presented in this investigation are from 21 marine test sites only (no urban environments are included), distributed among 11 countries (Argentina, Bolivia, Brazil, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal and Venezuela). The environment was evaluated using ISO Standard 9223 and the Concrete was characterized by measuring compressive strength, elastic modulus, total and effective porosity, chloride permeability according to ASTM standards, as well as the effective porosity and resistance to water absorption using the Fagerlund method. To that effect, Concrete specimens (with and without reinforcement) were prepared for electrochemical and physical/mechanical/chemical tests using the existing materials in each participating country, following strict procedures which enabled the preparation of similar Concrete samples. Two water/cement (w/c) ratios (0.45 and 0.65) were selected, where the Concrete with 0.45 w/c ratio had to have a minimum cement content of 400 kg/m 3 and the one with 0.65 w/c ratio a compressive strength of 210 kg/cm 2 . Type I Portland cement, siliceous sand, and crushed rock as coarse aggregates (13-mm maximum nominal size) were used. After a one-year exposure, the results of the corrosion potentiality and probability analysis of the reinforcement in the different test stations showed that, for marine atmospheres, the most aggressive environment to induce steel corrosion was at Portugal’s Cabo Raso station, and the least aggressive one was at Chile’s Valparaiso station. These results are comparable with the ones found using electrochemical measurements, after a two-year exposure.