118,672 research outputs found
Evaluation of Fly Ash Concrete Durability Containing Class II Durability Aggregates, July 1986
Fly ash was used in this evaluation study to replace 15% of the cement in Class C-3 concrete paving mixes. One Class "c" ash from Iowa approved sources was examined in each mix. Substitution rate was based on 1 to 1 basis, for each pound of cement removed 1.0 pound of ash was added. The freeze/thaw durability of the concrete studied was not adversely affected by the presence of fly ash. This study reveals that the durability
of the concrete test specimens made with Class II durability aggregates was slightly increased in all cases by the substitution of cement with 15% Class "c" fly ash.
In all cases durability factors either remained the same or slightly improved except for one case where the durability factor decreased from 36 to 34. The expansion decreased in all cases
Concrete Pavement Mixture Design and Analysis (MDA): Assessment of Air Void System Requirements for Durable Concrete, TPF-5(205), 2012
Concrete will suffer frost damage when saturated and subjected to freezing temperatures. Frost-durable concrete can be produced if a specialized surfactant, also known as an air-entraining admixture (AEA), is added during mixing to stabilize microscopic air voids. Small and well-dispersed air voids are critical to produce frost-resistant concrete. Work completed by Klieger in 1952 found the minimum volume of air required to consistently ensure frost durability in a concrete mixture subjected to rapid freezing and thawing cycles. He suggested that frost durability was provided if 18 percent air was created in the paste. This is the basis of current practice despite the tests being conducted on materials that are no longer available using tests that are different from those in use today. Based on the data presented, it was found that a minimum air content of 3.5 percent in the concrete and 11.0 percent in the paste should yield concrete durable in the ASTM C 666 with modern AEAs and low or no lignosulfonate water reducers (WRs). Limited data suggests that mixtures with a higher dosage of lignosulfonate will need about 1 percent more air in the concrete or 3 percent more air in the paste for the materials and procedures used. A spacing factor of 0.008 in. was still found to be necessary to provide frost durability for the mixtures investigated
Sustainable Concrete for the 21st Century Concept of Strength through Durability
The world is passing through difficult and troubled times, and we live in a rapidly changing world. The construction industry is facing many challenges – global warming, climate change forces, and the capability to achieve sustainable development and economic progress without damaging our environment. The concrete industry in particular faces further challenges. There is extensive evidence to show that concrete materials and concrete structures all over the world are deteriorating at a rapid rate, and that we are unable to ensure their long-term durable service life performance. To confound this situation, we are also faced with an urgent need to regenerate our infrastructure systems if we are to eradicate poverty and provide a decent Quality of Life for all the peoples of the world. This paper shows that the current emphasis on high strength and very high strength, and the design philosophy of Durability through Strength for concrete materials and concrete structures is fundamentally flawed. It is this misleading concept and vision that is primarily responsible for the lack of durable performance of concrete in real life environments. To change this scenario, this paper advocates that concrete materials must be manufactured for durability and not for strength. It is shown that this concept of Strength through Durability can be achieved through careful design of the cement matrix and its microstructure. If concrete is to be an eco-friendly, and sustainable driving force and construction material for social change, the need is to produce durable concrete with strengths of 30 to 60 to 80 MPa rather than very high strength concrete without an assured durable performance
Influence of concrete composition on chloride ingress and carbonation : analysis by means of an extended data-set
In 2015 an IWT-TETRA project, called DurOBet, was initiated focusing on service life
design assessment according to different chloride diffusion and carbonation models applied on
Belgian concrete mixtures. The main purpose of this research project is to develop a quantitative
method for a service-life based design of concrete structures, more particular applicable for the
Belgian concrete industry. In this way an improvement of the deemed-to-satisfy approach of the
EN206-1 code can be established which is more reliable with regards to service life predictions of
concrete structures.
In the framework of this DurOBet project it was decided to develop an extensive database
incorporating concrete related results on i) fresh properties, ii) hardened properties and iii) durability
related properties such as porosity, permeability and more specifically on chloride ingress and
carbonation. The data originate from numerous journal articles and conference papers, doctoral
research projects and master thesis studies. At this time more than 100 papers or studies were
investigated, reported between 1992 and 2016, generating a dataset of over a thousand unique
concrete recipes, geographically spread but with focus on the concrete mixes applicable for the
Belgian industry. Both traditional and self-compacting concrete mixes are incorporated into the
database.
This database is being used for the analysis of the durability related properties, such as the chloride
diffusion and carbonation coefficient, and their relation with mix proportioning parameters of the
concrete mixtures (cement or binder content, type of binder, water-to-binder ratio,…). The main
focus of this paper is to highlight the framework of the database: the mix proportioning of the
concrete mixes is being discussed and the origin of the concrete data (country, reference info, etc.).
By means of data mining and some known relations with respect to the durability related properties,
e.g. correlation between w/b-ratio and chloride diffusion coefficient, are being evaluated
Strength prediction and durability performance of concrete containing coal bottom ash as supplementary cementitious material under aggressive environment
Strength prediction and durability of concrete under aggressive environment requires serious attention for all kind of significant concrete structures. However, concrete built with Ordinary Portland Cement (OPC), when exposed to the aggressive environment tends to deteriorate much faster than their projected service life. Therefore, Supplementary Cementitious Material (SCM) need to be introduced to improve the strength and durability performance of concrete. Besides that, prediction of concrete compressive strength is also an important aspect for the safety and quality control of concrete structures. Thus, this study aims to evaluate strength and durability performance of concrete containing Coal Bottom Ash (CBA) as a SCM and to develop empirical equation to predict compressive strength of concrete under normal as well as in aggressive environment. CBA was considered as SCM because it is a huge waste that produced by a coal-based power plants, which creates environmental problems for the global society. Initially, raw CBA was grinded for various periods, to get different particle fineness, then CBA was incorporated as replacement of OPC in concrete at various percentages 10%, 20% and 30% by weight of cement. The optimum percentage replacement and suitable grinding period were determined based on concrete strength performances and it was found that 10% proportion of CBA gives the optimum results at the age of 28 days. Next, the performance of concrete containing 10% CBA was further evaluated in terms of compressive strength, change in weight and degree of damage under aggressive environment such as 5% sodium sulphate (Na2SO4), 5% sodium chloride (NaCl), combination of both (5%Na2SO4+5%NaCl) and seawater at the exposure period of 28, 56, 90 and 180 days. Additionally, microstructural changes in concrete due to aggressive environment were also assessed through Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) techniques. Besides that, the durability performance of concrete containing CBA were also evaluated using Rapid Chloride Permeability Test (RCPT). Moreover, influence of CBA on the drying shrinkage of concrete was also evaluated up to age of 180 days. The experimental results reveal that Control Mix (CM) delivers worst performance when exposed to seawater. However, the incorporation of 10% CBA in concrete enhances its strength performance under seawater exposure. Strength performance of concrete containing 10% CBA exhibits satisfactory in all aggressive environment conditions except 5% NaCl. It was also evaluated that concrete containing 10% CBA exhibits around 45.4% reduction in chloride penetration as compared to CM at 180 days, which indicated its potentiality as durable SCM. Besides that, it was experimentally and theoretically verified that the proposed Bolomey’s Modified Equation (BME) can be used for the prediction of compressive strength of concrete containing ground CBA exposed to normal as well as aggressive environment that particularly represents the marine environment. Hence, this study declared 10% ground CBA as optimum that can be used for future research
Predicting concrete durability from its absorption
This paper discusses the current approach for specifying the durability of concrete in structures. The shortcomings of the use of bulk parameters such as strength, water/binder ratio and binder content to specify durability are discussed. Studies carried out over the last 10 years at Dundee University, using simple permeation tests, which are sensitive to curing, cement type and grade of concrete, have shown close association between permeation properties and the durability of concrete. This paper deals with the measurement of concrete durability by the Dundeemodified Initial Surface Absorption Test (ISAT). A wide range of concrete mixes made with ordinary portland cement and blends with pulverized-fuel ash (PFA) and ground-granulated blastfurnace slag were designed. The duration of moist curing was varied from 0 to 28 days, and the maximum aggregate size from 5 to 40mm. All mixes were tested for absorptivity and aspects of durability including freeze/thaw resistance, carbonation, chloride ingress and mechanical wear. The results show that the absorptivity of concrete, measured with the ISAT, could be used as an accurate specification for concrete durability, irrespective of curing, grade or mix constituents. A tentative surface absorptivity classification for durability has been proposed
Improving durability through probabilistic design
In order to obtain a more controlled durability and long-term performance of concrete structures in chloride containing environment special care is needed in the design phase of reinforced concrete structures. The recent development of probability-based procedures has proven to give a more realistic basis for both durability design and condition assessment of reinforced concrete structures. Although there is still a lack of relevant data, this approach has been successfully applied to several new concrete structures, where requirements to a more controlled durability and service life have been specified.
Since parameters both for concrete durability and environmental exposure typically show a high scatter, a probability-based approach has shown to give a very powerful basis for durability analysis. This approach is primarily being applied for obtaining a more controlled durability and
long-term performance of new concrete structures, but it also provides a very valuable basis for
condition assessment of existing concrete structures in chloride containing environment.
In the present paper, the probability-based durability analysis is briefly described and used in order to demonstrate the importance and sensitivity of the various parameters affecting and controlling
the durability of concrete structures in chloride containing environment. The results show that this procedure provides valuable information concerning the design options, making
the decision process more reliable.(undefined
Durability Evaluation of Cactus-infused M25 Grade Concrete as a Bio-admixture
The durability of concrete incorporating cactus extract as a bio-admixture is the focus of this study, which is the first of its kind in the literature. Cactus-infused concrete is a novel type of concrete with exceptional fluidity, strength, and durability. In this project, cactus was employed as an addition to M25(3626 psi) concrete, which was designed to Indian standards. Cactus extract (1% to 9% of the total weight) was used to replace the water in the mix. In order to look into the durability properties of cactus concrete, durability experiments such as drying shrinkage test, water absorption, porosity, sorptivity, accelerated carbonation, acid, and alkalinity tests were carried out on the material. ETC concrete enhances the fluidity of the mixture, making it more workable. To determine the particle distribution in concrete, scanning electron microscopy (SEM) was used to investigate the material. According to experimental research, polysaccharides and fats in concrete have increased their durability properties by 30% when used at their optimal level. However, a high level of durability is attained, which encourages concrete voids to be effectively filled
Improving the durability of pozzolan concrete using alkaline solution and geopolymer coating
Durability is a major concern for concrete, therefore initiatives are needed to improve the durability of concrete. One way to
improve concrete durability is improving its surface quality. This study focuses on the improvement of the surface durability of
pozzolan concrete by applying coating of alkali solution or geopolymer paste. There were two different pozzolanic materials used
to manufacture the pozzolan concrete, i.e. class-F fly ash and calcined volcanic mud with two different particle sizes. The
alkaline solution was a combination of NaOH and sodium silicate solution. Fly ash-based geopolymer paste was prepared for the
geopolymer coating. Concrete specimens were exposed to 10% sulphuric acid solution by applying the wet�dry cycles to
accelerate the damage process, and to chloride solution to evaluate its penetration depth. The results show that applying the
alkaline solution and geopolymer coating improves the durability of pozzolan concrete
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