Alkali aggregate reaction topic american concrete institute. E ect of alkaliaggregate reactions in concrete dams using. The latter is derived by reason of concrete nature as an artificial material. India till 1983, when its occurrence was diagnosed in two concrete dams. Alkaliaggregate reaction aar is a reaction in concrete between the alkali hydroxides, which originate. 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. A total of approximately,700 seismic waveforms were acquired across three upstreamdownstream cross sections during 9 days of data acquisition. The resulting concrete expansion has caused the crest to rise and the curved dam to tilt upstream, with downstream lift joints opening, one significantly. The ability to model timedependent deterioration processes is necessary in order to predict future performance and the associated change in risk or safety. This ability can, potentially, have a large impact on the decision. Construction standard on aggregates for concrete cs3, draft. International specification for dams and other hydro structures aar7. 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.
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. E ect of alkali aggregate reactions in concrete dams using finite element method m. It was a common belief that finland does not have asr. This alkali aggregate reactivity aar has two formsalkalisilica reaction asr and alkalicarbonate reaction acr, sometimes called alkalicarbonate. 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. Aar results in deleterious expansive cracking of concrete occurring at later. Alkali aggregate reaction is the expansive reaction that takes place in pcc between alkali contained in the cement paste and elements within an aggregate. Two forms of alkali aggregate reactions are recognized. Alkalisilica reaction in concrete understanding cement. Concrete swelling, associated with the alkali aggregate reactions in particular represents without doubt the major problem affecting concrete dams worldwide. The sulfate attack in concrete by degradation of iron.
Rilem recommendations for the prevention of damage by. Alkali silica reaction asr is of more concern because aggregates containing reactive silica materials are more common. Two models have been presented to assess the e ects of the aar in concrete dams. Proceedings of the 5th international conference on alkaliaggregate reaction in concrete, cape town, nbri of the council for scientific and industrial research, pretoria, s. Long term assessment of dams suffering from alkali. Concrete admixture is the material other than aggregate, water, and cement added to the concrete. Effects of concrete deterioration on safety of dams 4 snapshot of time used for the risk evaluation process. It is based on the nbri accelerated test method 14. 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.
Effects of concrete deterioration on safety of dams. I briefly appraise the problems and trends in aar research in. Cip 43alkali aggregate reactions aar what is alkali aggregate reactivity. Abstractalkaliaggregate reaction aar is one of the phenomena that during the life time of concrete, endangers. 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. A design guide for alkali silica reaction for concrete duration. Topics on alkalisilica reaction development bureau. Aci manual of concrete practice, aci, farmington hills.
Concrete technology diagnosis and control of alkali. 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. 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. 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. Managing the effects of alkali aggregate reaction on the. Seismic damagecracking analysis of concrete dams affected by. Concrete technology diagnosis and control of alkaliaggregate. Rilem recommendations for the prevention of damage by alkali aggregate reactions in new concrete structures. Alkali release from aggregates in longservice concrete.
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. D 583 addition of lightweight aggregate reduces expansion in concrete containing a highly reactive normal weight aggregate boyd, s. Pdf the alkaliaggregate reaction aar is a concrete pathology. In most concrete, aggregates are more or less chemically inert. Alkali carbonate reaction in concrete was not documented until 1957. The most common of these is the alkali silica reaction asr. Cip 43 alkali aggregate reactions aar what is alkali aggregate reactivity. The expansion causes cracking in the cement paste and aggregates, which adversely affects the mechanical properties of the material. 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. There were no known cases of alkalisilica reaction in. Alkaliaggregate reaction aar of concrete structures. Alkaliaggregate reaction in concrete containing fly ash. Alkaliaggregate reaction aar is a reaction in concrete between the alkali hydroxides, which originate mainly from the portland cement, and certain types of aggregate. 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. Alkaliaggregate reactions in concrete springerlink. Alsaffar university of colorado, boulder may 2019 saouma, hariri, al saffar university of colorado, boulder 123. The effects of alkali aggregate reaction can be severe cracking, distortion and loss of strength of the concrete mass. The reasons for this are that the aggregate commonly used originates from very high quality granitic rock. The construction of dam was completed in year 1962. 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. 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.
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. Heterogeneity modeling in concrete has received some, but limited attention. Diagnosis and control of alkali aggregate reactions in concrete. Alkali aggregate reactions aar are chemical reactions between alkalis in the pore solution of hardened concrete and some types of minerals within concrete aggregates. One outcome of this work was the development of the quick chemical test, astm c 289. Numerical simulation for the mechanical behaviors of a.
The product is a gel that expands in the presence of moisture. 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. After this reaction it is formed a gel that when imbibes water, increases in volume and expands hobbs. 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. Alkaliaggregate reaction portland cement association. E ect of alkaliaggregate reactions in concrete dams using finite element method m. Alkali silica reaction asr can cause serious expansion and cracking in concrete, resulting in major structural problems and sometimes necessitating demolition. 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. Progress in the evaluation of alkaliaggregate reaction in. Alkali aggregate reaction asr in concrete is one of the least dealt with concrete degradation mechanism in finland.
Pdf computational modeling of damage in concrete dams due. The pore water in concrete is an alkaline solution. However, some aggregates react with the alkali hydroxides in concrete, causing expansion and cracking over a period of many years. The types of coarse aggregate used were granite, gneiss. 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. Alkali silica reaction an overview sciencedirect topics. 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. The cement paste contains interconnected microscopic pores through which water or ions in solution can migrate. Introduction many old concrete structures are known to suffer from alkali aggregate reactions aar. While mostly inert, some concrete aggregates, can react in the highly. In most concretes, aggregates are more or less chemically inert. 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. Aar results in deleterious expansive cracking of concrete occurring at later ages after construction. Pdf modelling of alkali silica reaction in concrete structures for.
The varying nature of the aggregates used in concrete signifies that many different alkali aggregate reactions can be observed. Long term assessment of dams suffering from alkali aggregate. Ghaemian the e ect of alkali aggregate reactions aar in concrete dams was investigated using the nite element method. Pdf computational modeling of damage in concrete dams. A 593 evaluation of different measures to reduce the risk of alkali silica reaction in recycled aggregate concrete. It will trigger a progressive damage over time, and give rise to a network of. Today jon and david take the time to analyze and comment on alkali silica reaction attack on a concrete dam in canada. Use of the damage rating index as input for service life. The alkali aggregate reaction aar in concrete is considered as a. Divergence between performance in the field and laboratory. Check it out to see aggressive asr attack and hear from the experts.
This internal reaction causes gel formation inside the aggregate and the matrix and results in swelling of the concrete. 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. New concrete national and state specific research and development has eliminated asr concerns in todays concrete mixes through. Alkali aggregate reaction is from the surrounding cement paste or the caused by a. 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. 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. Case studies on alkaliaggregate reactions in concrete.
The reactivity is potentially harmful only when it produces significant expansion mather 1975. Shrp research on alkalisilica reactivity has contributed to an increased. Numerical simulation for the mechanical behaviors of a concrete dam with consideration of alkaliaggregate reaction. Computational modeling of damage in concrete dams due to alkali aggregate reaction.
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. The alkaliaggregate reaction aar affecting many civil engineering infrastructures is undoubtedly one of the major challenges for todays. In 1992 a first edition entitled the alkalisilica reaction in concrete, edited. Pdf this paper presents theoretical and applied stateoftheart information in the field of alkaliaggregate reactivity aar in concrete. Star 219acs rilem recommendations for the prevention. Introduction the varying aggregate properties, in particular those related to the rate of the alkali reaction, make it necessary. 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. Pdf case study on the impact of alkaliaggregate reaction on a. 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. Astm c1260 14 standard test method for potential alkali. 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. Alkaliaggregate reaction aar is the most common chemical reaction in concrete. The 16th icaar will be hosted by portuguese national laboratory for civil engineering lnec. This is a short introduction to asr for more information, see the understanding cement bookebook.
Whereas there can be adequate quality control for the cement and the mixing process, randomness is infused through the use of various aggregate. Term assessment of dams suffering from alkali aggregate reaction purpose. In 1992 a first edition entitled the alkalisilica reaction in concrete, edited by professor narayan swamy, was published in a. Stochastic analysis of concrete dams with alkali aggregate. Alkali silica reaction asr and alkali carbonate reaction acr. 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. Concrete is a mix of cement, crushed rock, sand, and water. Alkaliaggregate reactions can be either alkali carbonate reactions acrs or alkali silica reactions asrs. Alkaliaggregate reaction in concrete containing fly ash 16. He found that an alkali sensitive reaction had developed in concrete containing argillaceous. Alkali aggregate reaction aar dams and irrigation structures are often constructed in remote areas offering a limited choice of aggregates for the concrete mix. 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. 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. Its expansion can cause the concrete itself to expand.
Long term assessment of dams suffering from alkali aggregate reaction v. Alkalisilica reaction asr is of more concern because aggregates containing reactive silica materials are more common. 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. 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. This usually occurs between the highly alkaline portland cement and the various siliceous substances contained in the aggregate.
A gelatinous product is formed which imbibes pore fluid and. 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. The popularly known concrete cancer, is discussed in detail and the steps to prevent asr and its effects on concrete are also discussed. 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. Alkali aggregate reaction in concrete types, causes, and. Alkalisilica reaction in concrete containing glass. Numerical simulation of concrete expansion in concrete dams. Diagnosis and control of alkaliaggregate reactions in. Numerical simulation of concrete expansion in concrete. Aggregates containing certain constituents can react with alkali hydroxides in concrete. The nantymoch dam in 2011 no symptoms of asr after 50 years. Whereas there can be adequate quality control for the cement and the mixing process, randomness is infused through the use of various aggregate sources, the mixing.
Avoid the presence of a critical amount of reactive silica, e. Stress analysis of concrete structures subjected to alkali. 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. 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. Alkalisilica reaction mechanism of asr concrete consists of aggregatesstone or gravel and sand, in a matrix of cement paste. Abstract alkali aggregate reaction aar is one of the phenomena that during the life time of concrete, endangers. Different types of admixtures are used in concrete.
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