Numerical simulation of concrete expansion in concrete dams. The latter is derived by reason of concrete nature as an artificial material. The pore water in concrete is an alkaline solution. Alkali aggregate reaction aar is a twopart reaction that occurs when alkalies in the cement react with siliceous aggregate to form a silica gel, which then absorbs water and expands. Dams are the quintessential examples of concrete structures with random heterogeneous properties as large volume of concrete is cast in layers bordered by vertical expansion joints laterally, and lift joint horizontally, fig. Alkali aggregate reaction aar dams and irrigation structures are often constructed in remote areas offering a limited choice of aggregates for the concrete mix.
Different types of admixtures are used in concrete. Alkali aggregate reaction topic american concrete institute. Alkali silica reaction asr this reaction occurs when the reactive silicas present in the aggregates react with the hydroxyl ions present in the concrete structure. Alkaliaggregate reaction aar is a reaction in concrete between the alkali hydroxides, which originate. The use of surplus waste glass in concrete has been avoided on the grounds that it is known to undergo harmful alkali silica reaction asr. The reasons for this are that the aggregate commonly used originates from very high quality granitic rock. Term assessment of dams suffering from alkali aggregate reaction purpose. While mostly inert, some concrete aggregates, can react in the highly.
Alkaliaggregate reaction in concrete containing fly ash 16. It was a common belief that finland does not have asr. The dinas arch gravity dam was constructed in the early 1960s, and alkali aggregate reaction aar in the concrete was confirmed in the late 1980s. Rilem recommendations for the prevention of damage by alkali aggregate reactions in new concrete structures. Alkalisilica reaction in concrete containing glass. This paper presents an overview of the alkali aggregate reaction in brazil, focusing in cases reported in dams, hydroelectric power plants and in the brazilian standards for aar. A gelatinous product is formed which imbibes pore fluid and. There were no known cases of alkalisilica reaction in. Avoid the presence of a critical amount of reactive silica, e. Aar results in deleterious expansive cracking of concrete occurring at later ages after construction.
Abstract alkali aggregate reaction aar is one of the phenomena that during the life time of concrete, endangers. Two models have been presented to assess the e ects of the aar in concrete dams. Diagnosis and control of alkaliaggregate reactions in. The types of coarse aggregate used were granite, gneiss. Introduction many old concrete structures are known to suffer from alkali aggregate reactions aar. Star 219acs rilem recommendations for the prevention. Alkaliaggregate reactions in concrete springerlink. D 583 addition of lightweight aggregate reduces expansion in concrete containing a highly reactive normal weight aggregate boyd, s.
Numerical simulation of concrete expansion in concrete. The alkali silica reaction asr is the most studied alkali aggregate reaction, and it commonly occurs when the alkali present in the concrete pore solutions react with low crystallinity siliceous aggregates. Heterogeneity modeling in concrete has received some, but limited attention. It is based on the nbri accelerated test method 14.
Aj,1troet the main objective of this study was to determine the influences of the constituents of portland cement, aggregates, and mineral admixtures on alkali silica reaction. Rilem recommendations for the prevention of damage by. This usually occurs between the highly alkaline portland cement and the various siliceous substances contained in the aggregate. Aci manual of concrete practice, aci, farmington hills. Alkali aggregate reaction in concrete types, causes, and. Concrete swelling, associated with the alkali aggregate reactions in particular represents without doubt the major problem affecting concrete dams worldwide. Cip 43 alkali aggregate reactions aar what is alkali aggregate reactivity. I briefly appraise the problems and trends in aar research in. Alkali silica reaction asr study of the asr potential of aggregates from geological point of view study of asr in hardened concrete from geological point of view c. In 1992 a first edition entitled the alkalisilica reaction in concrete, edited. Concrete technology diagnosis and control of alkali. Alkali aggregate reactions aar are chemical reactions between alkalis in the pore solution of hardened concrete and some types of minerals within concrete aggregates.
The alkali aggregate reaction aar in concrete is considered as a. Effects of concrete deterioration on safety of dams. Divergence between performance in the field and laboratory. The expansion causes cracking in the cement paste and aggregates, which adversely affects the mechanical properties of the material. The effects of alkali aggregate reaction can be severe cracking, distortion and loss of strength of the concrete mass. We are glad to announce the 16th international conference on alkali aggregate reaction in concrete, which will take place in lisboa, portugal, from to 15 october 2020. Some aggregates react with the alkali hydroxides in concrete, causing expansion and cracking over a period of many years, affecting the structural integrity of the concrete. Alkali silica reaction asr is of more concern because aggregates containing reactive silica materials are more common. Alkali silica reaction an overview sciencedirect topics. Meissners findings generally corroborated those of stanton, and lent further credence to the importance of cement alkali level, aggregate composition, and environmental requirements in the development of expansion due to asr. Alkaliaggregate reaction aar of concrete structures. The resulting concrete expansion has caused the crest to rise and the curved dam to tilt upstream, with downstream lift joints opening, one significantly. Aggregates containing certain constituents can react with alkali hydroxides in concrete.
Progress in the evaluation of alkaliaggregate reaction in. Pdf the alkaliaggregate reaction aar is a concrete pathology. Alkali silica reaction alkali silica reaction asr in concrete is a reaction between certain silicious constituents in the aggregate and the alkali sodium and potassium hydroxide which are released during the hydration of portland cement. Two forms of alkali aggregate reactions are recognized. Alkali release from aggregates in longservice concrete. Stochastic analysis of concrete dams with alkali aggregate. Concrete technology diagnosis and control of alkaliaggregate. E ect of alkali aggregate reactions in concrete dams using finite element method m. This is a short introduction to asr for more information, see the understanding cement bookebook.
Alkalisilica reaction mechanism of asr concrete consists of aggregatesstone or gravel and sand, in a matrix of cement paste. Alkali silica reaction is a chemical reaction between the available reactive silica in certain types of aggregates and the alkali hydroxides in the pore fluid of the concrete. Most notable is the recent work of ghannoum who addressed tensile strength heterogeneity of concrete and ensuing size effects with application to nuclear containment structures. Pdf a number of hydraulic structures such as dams and hydropower plants in the world and in particular, in south africa which have been designed and.
Microp ores in concrete are highly basic with ph value generally greater than 12. The alkalis in concrete are mainly supplied by the cement and, in some cases, by admixtures, aggregates, or the external environment. Rilem recommendations for the prevention of damage by alkali aggregate reactions in new concrete structures this publication has been published by springer in september 2015, isbn 9789401772518. In most concrete, aggregates are more or less chemically inert. Alkalisilica reaction, the cause of the major issues in new brunswick, occurs when alkalis in the cement pore solution encounter reactive forms of silica in the rock used to make the concrete. In most concretes, aggregates are more or less chemically inert. Seismic damagecracking analysis of concrete dams affected by.
Aar is a chemical reaction within hardened concrete, which causes it to expand over time. Cip 43alkali aggregate reactions aar what is alkali aggregate reactivity. Alkali aggregate reaction asr in concrete is one of the least dealt with concrete degradation mechanism in finland. Abstractalkaliaggregate reaction aar is one of the phenomena that during the life time of concrete, endangers. Concrete admixture types of admixture used in concrete. Pdf this paper presents theoretical and applied stateoftheart information in the field of alkaliaggregate reactivity aar in concrete. The alkaliaggregate reaction aar affecting many civil engineering infrastructures is undoubtedly one of the major challenges for todays. Alkaliaggregate reactions can be either alkali carbonate reactions acrs or alkali silica reactions asrs. E ect of alkaliaggregate reactions in concrete dams using finite element method m. If still 30 years ago the international community was convinced that the problem was confined to certain regions of the planet, it is now accepted that the phenomenon affects all. The product is a gel that expands in the presence of moisture. India till 1983, when its occurrence was diagnosed in two concrete dams.
Concrete is a mix of cement, crushed rock, sand, and water. Alkali aggregate reactions aar occur in concrete as a result of chemical reactions between the alkali sodium and potassium hydroxides in the concrete pore solution, which are supplied mainly by the cement, and certain mineral components found in some aggregates. Alkali silica reaction asr and alkali carbonate reaction acr. Construction standard on aggregates for concrete cs3, draft. The ability to model timedependent deterioration processes is necessary in order to predict future performance and the associated change in risk or safety. Alkaliaggregate reaction portland cement association. Effects of concrete deterioration on safety of dams 4 snapshot of time used for the risk evaluation process. Pdf case study on the impact of alkaliaggregate reaction on a. Numerical simulation for the mechanical behaviors of a. The damage rating index dri was developed in the 1990s as a petrographic examinationbased tool to assist in characterizing the amount of damage present in concrete caused by the effects of alkali silica reaction asr, specifically in dams. Pdf computational modeling of damage in concrete dams due. This alkali aggregate reactivity aar has two formsalkalisilica reaction asr and alkalicarbonate reaction acr, sometimes called alkalicarbonate.
This reaction, which occurs to some extent in most pcc, can result in map or pattern cracking see figure 1, surface popouts and spalling if. After this reaction it is formed a gel that when imbibes water, increases in volume and expands hobbs. Long term assessment of dams suffering from alkali aggregate. This guide addresses the process of identifying both potentially alkali silica reactive asr and alkali carbonate reactive acr aggregates through standardized testing procedures and the selection of mitigation options to minimize the risk of. Interest in the alkaliaggregate reaction aar in concrete structures has increased in recent times because of the risk for dam safety and the high cost of. One outcome of this work was the development of the quick chemical test, astm c 289. A design guide for alkali silica reaction for concrete duration. This ability can, potentially, have a large impact on the decision. Alkaliaggregate reaction aar is the most common chemical reaction in concrete. The former is of higher concern since aggregates containing various forms of silica materials are very common whereas the latter occurs rarely because of the unsuitability of carbonates for use in concrete.
Alkalisilica reaction in concrete understanding cement. Ghaemian the e ect of alkali aggregate reactions aar in concrete dams was investigated using the nite element method. International specification for dams and other hydro structures aar7. Alkaliaggregate reaction in concrete containing fly ash. Introduction the varying aggregate properties, in particular those related to the rate of the alkali reaction, make it necessary. Use of the damage rating index as input for service life.
In asr, aggregates containing certain forms of silica will react with alkali hydroxide in concrete to form a gel that swells as it adsorbs water from the surrounding cement paste or the environment. The varying nature of the aggregates used in concrete signifies that many different alkali aggregate reactions can be observed. E ect of alkaliaggregate reactions in concrete dams using. Alkali aggregate reaction is from the surrounding cement paste or the caused by a. Alkalisilica reaction asr is of more concern because aggregates containing reactive silica materials are more common. Alkaliaggregate reaction aar is a reaction in concrete between the alkali hydroxides, which originate mainly from the portland cement, and certain types of aggregate.
Its expansion can cause the concrete itself to expand. This internal reaction causes gel formation inside the aggregate and the matrix and results in swelling of the concrete. A 593 evaluation of different measures to reduce the risk of alkali silica reaction in recycled aggregate concrete. The popularly known concrete cancer, is discussed in detail and the steps to prevent asr and its effects on concrete are also discussed. Case studies on alkaliaggregate reactions in concrete. The cement paste contains interconnected microscopic pores through which water or ions in solution can migrate. He found that an alkali sensitive reaction had developed in concrete containing argillaceous. It will subsequently analyse the efforts thus far in understanding and modelling this reaction, and the experimental methods and tests which have been carried out in pursuit of this goal. Concrete admixture is the material other than aggregate, water, and cement added to the concrete. Diagnosis and control of alkali aggregate reactions in concrete. The reactivity is potentially harmful only when it produces significant expansion mather 1975. The effect of concrete industries have contributed to this first edition of temperature and humidity on expansion, and the diagnosis and control of alkaliaggregate reactions in significance of. Astm c1260 14 standard test method for potential alkali. Computational modeling of damage in concrete dams due to alkali aggregate reaction.
Topics on alkalisilica reaction development bureau. Pdf computational modeling of damage in concrete dams. The 16th icaar will be hosted by portuguese national laboratory for civil engineering lnec. Alkali carbonate reaction in concrete was not documented until 1957. A total of approximately,700 seismic waveforms were acquired across three upstreamdownstream cross sections during 9 days of data acquisition. Alkalisilica reaction asr is a reaction between alkali, hydroxyl ions from concrete pore solution and amorphous siliceous minerals present in reactive aggregates mehta and monteiro, 2006. The alkali silica reaction asr, more commonly known as concrete cancer, is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive noncrystalline amorphous silica found in many common aggregates. Whereas there can be adequate quality control for the cement and the mixing process, randomness is infused through the use of various aggregate. Proceedings of the 5th international conference on alkali aggregate reaction in concrete, cape town, nbri of the council for scientific and industrial research, pretoria, s.
Mandatinguse of class f fly ash limiting alkali content of cement existing concrete ne continues to resurface or rebuild affected concrete pavements alkali silica reaction asr. The sulfate attack in concrete by degradation of iron. As part of a research project to develop draft specifications for glass in concrete, a major asr testing programme was undertaken to establish appropriate use of glass in concrete which avoided harmful asr. Managing the effects of alkali aggregate reaction on the.
Alkali silica reaction asr can cause serious expansion and cracking in concrete, resulting in major structural problems and sometimes necessitating demolition. Long term assessment of dams suffering from alkali. Numerical simulation for the mechanical behaviors of a concrete dam with consideration of alkaliaggregate reaction. The construction of dam was completed in year 1962. Aar results in deleterious expansive cracking of concrete occurring at later. Shrp research on alkalisilica reactivity has contributed to an increased. Alsaffar university of colorado, boulder may 2019 saouma, hariri, al saffar university of colorado, boulder 123. In 1992 a first edition entitled the alkalisilica reaction in concrete, edited by professor narayan swamy, was published in a.
It will trigger a progressive damage over time, and give rise to a network of. Stress analysis of concrete structures subjected to alkali. New concrete national and state specific research and development has eliminated asr concerns in todays concrete mixes through. The most common test methods used to evaluate alkali silica reaction asr are the concrete prism test cpt and the accelerated mortar bar test ambt. The most common of these is the alkali silica reaction asr. Check it out to see aggressive asr attack and hear from the experts. Proceedings of the 5th international conference on alkaliaggregate reaction in concrete, cape town, nbri of the council for scientific and industrial research, pretoria, s.
Today jon and david take the time to analyze and comment on alkali silica reaction attack on a concrete dam in canada. The nantymoch dam in 2011 no symptoms of asr after 50 years. Many concrete dams and other concrete structures in canada, and throughout the world, are suffering from deteriorations induced by alkali aggregate reaction aar that impair the durability and serviceability, and might also affect, in the long term, the safety of the installation. The alkalisilica reaction asr, more commonly known as concrete cancer, is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive noncrystalline silica found in many common aggregates, given sufficient moisture. Alkali aggregate reaction is the expansive reaction that takes place in pcc between alkali contained in the cement paste and elements within an aggregate. Pdf modelling of alkali silica reaction in concrete structures for. This alkali aggregate reaction has two forms, namely. However, some aggregates react with the alkali hydroxides in concrete, causing expansion and cracking over a period of many years. A methodology to distribute the observed concrete expansion in proportion to the compressive stress state, temperature, moisture, and the reactivity of the concrete constituents is proposed in this paper as a first step to rationalize the numerical modelling of the aar concrete swelling process in concrete dams. Alkali aggregate reactions can be either alkali carbonate reactions acrs or alkali silica reactions asrs.
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