Risk of alkalisilica reaction when using recycled concrete. Deterioration due to the alkali silica reaction is more common and this paper refers to this aspect. The most common of these is the alkali silica reaction asr. Effects of alkaliaggregate reaction on concrete and. Free lime cao in cement 1 reacts with co2 in the atmosphere to precipitate caco3 around the cement grains. Concrete technology diagnosis and control of alkaliaggregate. Standard test method for determination of length change of. In asr, the reaction is between alkalies and certain siliceous rocks or minerals, such as opaline chert. Length change of concrete due to alkalisilica reaction. It was a common belief that finland does not have asr. I of the alkaliaggregate reaction in highalkali cements, 11 reactive and nonreactive experimental aggregates were examined by several procedures. The alkalisilica reaction forms a gel that swells as it draws water from the surrounding. The alkalisilica reaction forms a gel that swells as it draws water from the surrounding cement paste.
Alkaliaggregate reactions in concrete springerlink. A rapid method of test for alkaliaggregate reaction is investigated and described. This causes a gel to form within the cement paste matrix. Microscopic and chemical methods of diagnosis of alkali.
Pdf this paper presents theoretical and applied stateoftheart information in the field of alkaliaggregate reactivity aar in concrete. The coarse aggregate particles are usually crushed stone or crushed gravel, and the fine aggregate particles are usually natural sand. Alkaliaggregate reaction and structural damage to concrete. The alkali silica reaction was first recognized as a problem in north american in 1940, in.
Alkaliaggregate reaction in concrete is the name given to a group of reactions leading to expansion caused by a chemical reaction between the alkalis contained in the cement paste and certain reactive forms of usually silica containing minerals in the aggregates, see figure 4. 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. Supplemental information should be developed to confirm that the expansion is actually due to alkali silica reaction. Alkali aggregate reactions aar occur when aggregates in concrete react with the alkali hydroxides in concrete producing a hygroscopic gel which, in the presence of moisture, absorbs water and causes expansion and cracking over a period of many years. 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. Petrographic examination of the concrete prisms should be conducted.
This paper describes this problem with respect to indian aggregates and cement. The reasons for this are that the aggregate commonly used originates from very high quality granitic rock. Modelling of alkali aggregate reaction effects in reinforced concrete structures ancacristina jurcut master of applied sciences graduate department of civil engineering university of toronto 2015 abstract significant research has been performed worldwide on alkali aggregate reaction aar since its first deleterious effects on concrete. Alkali reaction of aggregates building materials concrete. Mitigation of alkali silica reaction in volcanic aggregate concrete using pfa and ggbs annual concrete seminar 2016 20 april 2016 ryan c. This gel is hydrophilic, hygroscopic, and expansive.
Physicochemical studies of the destructive alkaliaggregate. Avoid the presence of a critical amount of reactive silica, e. The effects of alkaliaggregate reaction aar on concrete and structures start at the microstructural level, that is, at molecular and microscopic levels, such as the formation of reaction product. 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 main conclusions of the thesis were summarised in five papers. In order to show that alkali aggregate reaction is the primary cause of concrete deterioration, the concrete cracking characteristics of alkali aggregate reaction was observed in saunders.
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. Selecting measures to prevent deleterious alkalisilica. Evaluating aggregate reactivity for alkali silica and alkali carbonate reactive aggregates. Acr is a serious, but fortunately rare, variety of. Alkali aggregate reaction in concrete types, causes, and. Alkali aggregate reaction asr in concrete is one of the least dealt with concrete degradation mechanism in finland.
The crushed stone or crushed gravel aggregate make the asphalt or concrete mix somewhat difficult to place. The product is a gel that expands in the presence of moisture. Moisture is necessary for the reaction to take place. D 583 addition of lightweight aggregate reduces expansion in concrete containing a highly reactive normal weight aggregate boyd, s. A 593 evaluation of different measures to reduce the risk of alkali silica reaction in recycled aggregate concrete. Pdf this chapter presents the susceptibility of alkaliactivated binders to alkaliaggregate reaction. Concrete technology diagnosis and control of alkali. Alkaliaggregate reaction in concrete containing fly ash 16. Alkaliaggregate reactions in concrete sciencedirect. The alkalisilica reaction in portland cement concretes can be found in various. 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. The occurrence of alkalisilica and alkalisilicate reactions causes damage in concrete. This is a short introduction to asr for more information, see the understanding cement bookebook. This reaction can cause expansion of the altered aggregate, leading to spalling and loss of strength of the concrete.
Pdf resistance to alkaliaggregate reaction aar of alkali. Three main types of alkali aggregate reaction aar have been identified depending on the aggregates. Factors affecting asr for alkali silica reaction to occur, three conditions must be present. In particular, a suitable test approach for testing aggregates with marginal to. This alkali aggregate reactivity aar has two forms alkali silica reaction asr and alkali carbonate reaction. The reaction is accelerated under conditions of alternate wetting any drying. In 1992 a first edition entitled the alkali silica reaction in concrete, edited. The aspects discussed include basic concepts of the reaction. The reactivity is potentially harmful only when it produces significant expansion. In 1992 a first edition entitled the alkalisilica reaction in concrete, edited by professor narayan swamy, was published in a.
I of the alkali aggregate reaction in high alkali cements, 11 reactive and nonreactive experimental aggregates were examined by several procedures. Cip 43 alkali aggregate reactions aar what is alkali aggregate reactivity. The ideal condition of temperature for the promotion of alkali aggregate reaction is the range of 10 to 38c. The varying nature of the aggregates used in concrete signifies that many different alkali aggregate reactions can be observed. In acr, the reaction is between the alkalies sodium and potassium and certain carbonate rocks, particularly calcitic dolomite and dolomitic limestones, present in some aggregates. Pdf investigating the alkali silica reaction of recycled. Alkalis include sodium and potassium that are minor constituents in portland cement but can be from other concrete ingredients or from external sources. Alkali aggregate reaction topic american concrete institute. Divergence between performance in the field and laboratory. Investigating the alkali silica reaction of recycled glass aggregates in concrete materials article pdf available in journal of materials in civil engineering 2212 december 2010 with 1,546. Alkali aggregate reaction aar in recycled concrete is more complicated than the aar of its original concrete since it is affected by many factors such as alkali reactivity of original aggregate oa, reaction extent of oa, presence of residual mortar rm and production procedure. Astm c1260 14 standard test method for potential alkali. Alkaliaggregate reaction portland cement association.
Alkaliaggregate reactions can be either alkali carbonate reactions acrs or alkali silica reactions asrs. I briefly appraise the problems and trends in aar research in the pacific northwest region. Alkali silica reaction asr is of more concern because aggregates containing reactive silica materials are more common. Alkalisilica reaction in concrete containing glass. 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. Alkalisilica reactivity continues to be a serious cause of deterioration of concrete in pavements, bridges and other highway structures in the united states. 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.
However, it is not known exactly what percentage of the aggregate sources in the u. Aar is a chemical reaction in the cement between the aggregates and the alkali. Alkali silica reaction, aggregate, alkali content, durability. On com paring t he results of each method with the standard expansionbar test, it appears that each. Alkali aggregate reaction aar of concrete structures. The effects of alkaliaggregate reaction aar on concrete and structures start at the microstructural level, that is, at molecular and microscopic levels, such as the formation of reaction products in concrete and associated microcracking, which ultimately leads to macrolevel effects such as visual cracking, differential movements. Alkali aggregate reactions can be either alkali carbonate reactions acrs or alkali silica reactions asrs. Alkaliaggregate reaction aar is a reaction in concrete between the alkali hydroxides, which. Mitigation of alkalisilica reaction in volcanic aggregate. 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.
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. A design guide for alkali silica reaction for concrete duration. Alkaliaggregate reaction in recycled aggregate concrete. The reaction can be visualized as a twostep process. If the aggregate is shown to be potentially reactive by the tests, some mitigation measure must be used to control the expansion and cracking. Alkali aggregate reaction mainly refer to a reaction which occurs over time in concrete bw the highly alkaline cement paste and noncrystalline silicon dioxide, which is found in many common aggregates. Alkali aggregate reaction is the reaction between the active mineral constituents of some aggregates and the sodium and potassium alkali hydroxide in the concrete harmful only when it produes significant expansion. Reaction products from asr have a great affinity for moisture. Chemical analysis of these exudations or deposits shows them to be composed mainly of silica and alkali often with varying amounts of lime. How to minimise aar risk in new concrete structures.
Asr involves reactions between alkali pore solution in the concrete and certain forms of alkali reactive silica. In 1992 a first edition entitled the alkalisilica reaction in concrete, edited. Diagnosis and control of alkaliaggregate reactions in. Alkali aggregate reaction aar is a term that is used to describe both alkali silica reaction asr and alkali carbonate reaction acr.
Alkali aggregate reaction is the expansive reaction that takes place in pcc between alkali contained in the cement paste and elements within an aggregate. Alkali silica reaction an overview sciencedirect topics. 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. Acr chemical reaction in either concrete or mortar between hydroxyl ions oh of the alkalies sodium and potassium from hydraulic cement or other sources. This reaction can cause expansion of the altered aggregate, leading to spalling and loss of strength of the concrete more accurate terminology. Alkalisilica reaction in concrete understanding cement. Alkali silica reaction asr can cause serious expansion and cracking in concrete, resulting in major structural problems and sometimes necessitating demolition.
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 silica found in many common aggregates, given sufficient moisture this reaction causes the expansion of the altered aggregate by the formation of a soluble and viscous gel of sodium. 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. Aar results in deleterious expansive cracking of concrete occurring at later ages after construction. Pdf this chapter presents the susceptibility of alkaliactivated binders to alkali aggregate reaction. Concrete aggregates and selecting appropriate measures for preventing deleterious expansion in new concrete construction. The aspects discussed include basic concepts of the reaction and expansion mechanisms, conditions conducive to the development and the sustainability of aar in concrete, field and laboratory investigation programs for evaluating the potential alkali. This paper presents theoretical and applied stateoftheart information in the field of alkali aggregate reactivity aar in concrete. New concrete national and state specific research and development has eliminated asr concerns in todays concrete mixes through. In absorbing water, these gels can induce pressure, expansion, and cracking of the aggregate and surrounding paste. Alkaliaggregate reaction is a term mainly referring to a reaction which occurs over time in concrete between the highly alkaline cement paste and noncrystalline silicon dioxide, which is found in many common aggregates. Mitigation of alkalisilica reaction asr of highly reactive.
To improve the workability, many mixes contain both angular and round particles. The alkali aggregate reaction aar in concrete is a group of chemical reactions that involves the reaction of certain minerals present in the aggregates with alkali and hydroxyl ions in the interstitial solution of cement paste in concrete. He found that an alkali sensitive reaction had developed in concrete containing argillaceous calcitic dolomite aggregate that appeared to be different than the alkali silica reaction. There are three types of alkali aggregate reactions, namely the alkali silica, alkali silicate and akalicarbonate reactions.
Asr is a chemical reaction taking place in concrete between reactive forms of silica in the aggregate and the alkalis in the cement pore solution stanton 1940. Even though the reaction has been known for some time, the progress. 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. Nov 12, 2015 asr is the most common form of alkali aggregate reaction aar in concrete. Concrete affected by the variety of alkali aggregate reaction known as alkali silica reaction often shows exudations of a watery gel which dries to a white deposit. The concrete prism test is considered to be a better test that correlates with the field performance of an aggregate in concrete. Jan 20, 2009 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. In 1992 a first edition entitled the alkali silica reaction in concrete, edited by professor narayan swamy, was published in a first attempt to cover this concrete problem from. Alkali aggregate reaction aar and its effects on concrete an overview 1. The necessity of the presence of caoh 2 also has been suggested. If it is assumed that 50 percent of all aggregate sources fail the concrete prism test. Pdf role of test method in detection of alkalisilica.
The alkalis in concrete are mainly supplied by the cement and, in some cases, by admixtures, aggregates, or the external environment. As the title suggests, these guidelines can be broken down into two steps as follows. It is based on the nbri accelerated test method 14. Aggregates three main types of alkali aggregate reaction aar have been identified depending on the aggregates. Differently from the alkali release from concrete aggregates, the. 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. Abstract identifying the susceptibility of an aggregate to alkali silica reaction asr before using it in concrete is one of the most efficient practices for preventing damage and failure. Alkaliaggregate reaction in concrete containing fly ash. Subsequent work by swenson 1957, swenson and gillott 1960, and gillott. The reaction demands an alkaline environment which is. Alkaliaggregate reaction aar of concrete structures. Proceedings of the 12th international conference on alkali. A major diagnostic symptom which confirms the occurrence of the alkali aggregate reaction is the presence of the reaction products alkali silicate gel in the concrete.
Progress in the evaluation of alkaliaggregate reaction in. The effects of alkali aggregate reaction aar on concrete and structures start at the microstructural level, that is, at molecular and microscopic levels, such as the formation of reaction products in concrete and associated microcracking, which ultimately leads to macrolevel effects such as visual cracking, differential movements, displacement and so on. Its expansion can cause the concrete itself to expand. Alkali silica reaction in portland cement concrete 16. Asr is a complex physical and chemical reaction between water, alkali in the concrete pore solution and reactivesilica minerals in aggregates 1. Alkali release from aggregates in longservice concrete.
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