Aggregates constitute about threequarter of the volume of concrete, and therefore their physical and chemical properties need to be correctly assessed before their use in concrete. Therefore, the correlation between reactivity of aggregates and free expansion. Alkalisilica reaction asr and delayed ettringite formation def, or combinations of the two, have been found to be the main causes of these problems. Alkaliaggregate reaction aar of concrete structures. Chapter 2 alkalisilica reaction guidelines for the use of. The susceptibility of alkaliactivated fly ash and slag concrete binders to deleterious asr was evaluated in accordance with relevant astm standards. Effect of multiaxial stresses on alkalisilica reaction damage of concrete by bishnu prasad gautam, daman k. Engineered for longterm durability, newcem slag cement helps structures achieve greater strength potential, reduced permeability, and increased resistance to sulfate attack and alkali silica reaction. The expansion of concrete through reaction between cement and aggregates was first studied by thomas e. Since the 1940s, considerable research has been developed to.
Alkalisilica reaction in concrete ice virtual library. The susceptibility of alkali activated fly ash and slag concrete binders to deleterious asr was evaluated in accordance with relevant astm standards. Alkali silica reaction gels are composed of twocomponent mixtures of alkali calciumsilicate hydrate and alkali silica sols of nearly fixed compositions. Use lithiumbased admixtures in the concrete mixture, the effectiveness of which is highly dependent on the type of aggregate, the alkali content in the concrete, and the form of lithium.
As one of the most challenging problems in concrete durability, alkalisilica reaction asr has received significant attentions over the past 80 years since its discovery in 1940s by stanton. It is based on the accelerated test method developed at the national building research institute. Ficks law which takes into account the concentration of free ions in the pore. Alkalisilica reaction and high performance concrete. 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 amorphous silica found in many common aggregates, given sufficient moisture. Alkali silica reaction article about alkali silica. Lithuanian quarry aggregates concrete effects of alkaline corrosion tests lietuvos karjeru uzpildu poveikio betono sarminei korozijai tyrimai. This is a short introduction to asr for more information, see the understanding cement bookebook. The use of reactive aggregates in concrete is necessary for asr to occur. Because of its slow reaction, damages of concrete structures caused by asr are usually observed after decades and are difficult to predict. Alkalisilica reaction wikipedia republished wiki 2. Alkali silica reaction in concrete a book for concrete users which provides an authoritative explanation of the alkali silica reaction asr, its effects and methods of minimizing the risk of danger in new construction. Alkalisilica reaction asr is a concrete pathology due to chemical reactions involving reactive silica. The alkali silica reaction mechanism catalysed by a soluble strong base as naoh or koh in the presence of caoh 2 alkalinity buffer present in the solid phase can be compared with the carbonation process of soda lime.
The expansive type cif alkalicarbonate rock reaction in concrete has now been estab lished as a phenomenon quite distinct from the better known alkalisilica reaction. 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. Multiscale homogenization analysis of alkalisilica. It also has one manual pressure relief valve and two pressure indicators. Quartz is the main mineral responsible for triggering the alkalisilica reaction asr in concrete structures 1,2,3. Alkalisilica reaction gels are composed of twocomponent mixtures of alkalicalciumsilicate hydrate and alkalisilica sols of nearly fixed compositions. National regulations for preventing alkalisilica reaction asr in concrete structures are based on. Concrete technology diagnosis and control of alkali. The reaction entails the dissolution of the silica, the formation of an alkalisilica gel, and interaction with calcium.
This reaction is called asr and initially forms a hygroscopic alkali silica gel e. Owing to hydraulic reaction with water, the gel expands and exerts swelling pressures inside the reactive aggregate particle, which are sufficient to induce and propagate fractures. Less reactive aggregates often expensive or difficult to find. Asr is a chemical reaction between the silica existing inside the aggregate. Effect of multiaxial stresses on alkalisilica reaction. Alkali silica reactivity, better known as asr, has openly been with us since the early1940s when it was discovered in california and publicized by t. Mechanism of alkalisilica reaction and the significance of. Alkalisilica reaction a wide range of materials were evaluated in this project, including seventeen different reactive aggregates from texas and some from other parts of the u. The asr mechanism and mitigation of asr within portland cement. The reaction product, an alkali silica gel, is hygroscopic, and will absorb water and swell if the concrete is in a moist environment. The silicic acid h 2 sio 3 or sio 2 is simply replaced in the reaction by the carbonic acid h 2 co 3 or co 2. Alkalisilica reaction in concrete civil engineering. Alkali aggregate reaction topic american concrete institute.
Synthesis, characterization, and water uptake property of alkalisilica. Alkalisilica reaction article about alkalisilica reaction. The role of calcium on the formation of alkalisilica. This report summarizes the findings of an experimental evaluation into alkali silica reaction asr in cement free alkali activated slag and fly ash binder concrete. Over seven decades later, occurrences of this reaction may actually be increasing, despite our vast knowledge about asr gained over these years. The factors involved are exceedingly complex, very interdependent and highly interactive. This usually occurs between the highly alkaline portland cement and the various siliceous substances contained in the aggregate. In asr, the reaction is between alkalies and certain siliceous rocks or minerals, such as opaline chert. Astm c1567 standard test method for determining the. Most of the others are stmcturally safe but the concrete might have failed as a protective barrier to the reinforcement. T he first guidance documents on ways of minimising the risk of damage due to alkalisilica reaction in concrete were published in the early 1980s by the concrete society technical report 304 and bre digest 330. Alkali aggregate reactions can be either alkali carbonate reactions acrs or alkali silica reactions asrs. Cracking may be initiated by swelling of aggregate particles before copious production of gel and large expansions of cracks caused by swelling of gel occurs. The alkalisilica reaction though not true is described as a concrete cancer.
Standard test method for determination of length change of. There is a strong indication that the mechanism by which the silica fume and slag. Possible asr damage on concrete retaining wall picture taken 12002. In this study, thermodynamic data for the synthesized asr products i. Avoid the presence of a critical amount of reactive. For alkali silica reaction to occur, three conditions must be present. Alkali silica reaction asr is of more concern because aggregates containing reactive silica materials are more common. The alkali silica reaction asr is a chemical deterioration of concrete that involves reactive forms of silica. High replacement levels of slag cement in properly proportioned mixes also help control shrinkage, creep and thermal cracking in mass concrete structures. Supplemental information should be developed to confirm that the expansion is actually due to alkalisilica reaction. Alkalisilica reaction in concrete a book for concrete users which provides an authoritative explanation of the alkalisilica reaction asr, its effects and methods. 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. The reaction involves interaction of hydroxyl ions associated with alkali in cement with certain siliceous constituents of the aggregate reactive silica the products of reaction such as sodium silicate gel called water glass form on the exterior surface of particles and can bring about excessive expansion, cracking, pop outs and general.
As the gel takes up water, it expands significantly, destroying the integrity of the weakened aggregate particle and the surrounding cement paste. Alkalisilica reaction the influence of calcium on silica dissolution and the formation of reaction products, journal of the american ceramic society 94. The term reactive refers to aggregates that tend to breakdown under exposure to the highly alkaline pore solution in concrete and subsequently react with the alkali hydroxides sodium and potassium to form asr gel. The alkali silica reaction though not true is described as a concrete cancer. 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 reaction mechanism of alkalisilica reaction asr is poorly understood due to the. The alkalisilica reaction asr is one of the major longterm deterioration mechanisms occurring in concrete structures subjected to high humidity levels, such as bridges and dams. The alkali silica reaction is an unusual and unpredictable phenomenon which occurs worldwide.
Predicting the conditions for alkalisilica reaction asr had been difficult for several decades due to the lack of indepth knowledge of the asr products. Asr is a chemical reaction between the silica existing inside the aggregate pieces and the alkali ions from the cement paste. Alkalisilica reaction how is alkalisilica reaction. 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. A human cancer, if untreated is terminal, whereas the alkalisilica reaction and the expansion it induces, if untreated, eventually stops. 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. Influence of the quartz deformation structures for the. Pdf concrete is one of the most widely used building materials since the nineteenth. Alkalisilica reaction and delayed ettringite formation.
No concreted structure or part of a concrete structure any where in the world has collapsed due to alkali silica reaction alone. Asr is a chemical reaction between the alkali hydroxides in the pore solution of concrete and certain forms of reactive silica minerals occurring in some aggregates. This reaction produces a hygroscopic gel, which absorbs water and swells, causing cracking to occur as tension builds in the concrete structure. A human cancer, if untreated is terminal, whereas the alkali silica reaction and the expansion it induces, if untreated, eventually stops. This report summarizes the findings of an experimental evaluation into alkali silica reaction asr in cement free alkaliactivated slag and fly ash binder concrete.
Alkalisilica reaction in portland cement concrete the university. Chapter 2 alkalisilica reaction guidelines for the use. The alkalisilica reaction is an unusual and unpredictable phenomenon which occurs worldwide. Alkali silica reaction article about alkali silica reaction. A variety of laboratory test methods were performed. Practices to mitigate alkalisilica reaction asr affected. The cementitious materials are composed of various proportions of hydraulic cement, pozzolans and ground granulated blastfurnace slag.
The alkalies, specifically sodium and potassium, do not actually attack the reactive silica. 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 term premature concrete deterioration pcd has been adopted to refer to problems associated with asr and def because it is often difficult to distinguish between them. The term alkali silica reaction is somewhat misleading the reaction itself is actually between the ohions in the pore solution and certain siliceous components of the aggregates. Alkali silica reaction in concrete alkali silica reaction asr can cause serious expansion and cracking in concrete, resulting in major structural problems and sometimes necessitating demolition. Multiscale homogenization analysis of alkalisilica reaction. 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 free powerpoint ppt presentation displayed as a flash slide show on id. Alkaliaggregate reactions can be either alkalicarbonate reactions acrs or alkalisilica reactions asrs. Alkalisilica reaction and high performance concrete by ferraris, chiara f.
The reaction entails the dissolution of the silica, the formation of an alkali silica gel, and interaction with calcium. The reaction product, an alkalisilica gel, is hygroscopic, and will absorb water and swell if the concrete is in a moist environment. Alkalisilica reaction in concrete containing glass. Petrographic examination of the concrete prisms should be conducted.
Volcanic glass is one of the potentially reactive forms of silica that can be. Preventing alkalisilica reaction and delayed ettringite. Alkali silica reaction asr and delayed ettringite formation def, or combinations of the two, have been found to be the main causes of these problems. The displacement of the crystalline structure of quartz leads to changing the. It may contain differences from the journals pdf version. Identifying the susceptibility of an aggregate to alkalisilica reaction asr. The alkalisilica reaction asr is a chemical deterioration of concrete that involves reactive forms of silica. No concreted structure or part of a concrete structure any where in the world has collapsed due to alkalisilica reaction alone. Effect of multiaxial stresses on alkali silica reaction damage of concrete by bishnu prasad gautam, daman k. More detailed information on the specific mechanisms governing aggregate breakdown and. Alkalisilica reaction asr is of more concern because aggregates containing reactive silica materials are more common. Alkali silica reaction the influence of calcium on silica dissolution and the formation of reaction products, journal of the american ceramic society 94. Alkaliaggregate reaction portland cement association.
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