Alkali-aggregate Reaction In Concrete Research Articles

Experimental Identification of Alkali-Aggregate Reaction in Concrete

Several advanced and time-consuming methodologies have been developed to detect Alkali-Silica Reaction (ASR) in suspected structures. The main objective of this research study was to identify a reliable experimental procedure for detecting ASR in existing concrete. A simple staining solution is used here to detect ASR in concrete specimens. The staining reagent employed here is Sodium Cobaltinitrite, which is used in the Los Alamos staining method to detect ASR. Sodium Cobaltinitrite can identify potassium-rich ASR gel by staining it yellow for rapid field screening purposes. Reactive and control concrete specimens were cast to get some experience with this test and to verify whether this test can be used in a suspected concrete structure. Waste white soda-lime glass aggregate was used to cast reactive concrete specimens, whereas natural coarse aggregates were used to cast non-reactive concrete specimens. Testing was carried out in two batches. Each batch consisted of six reactive and six control concrete specimens which were cured in the above-mentioned solutions. The first batch was examined after 44-days and the second batch was tested after 60-days of casting. Results of this test showed that reactive concrete specimens cast using glass displayed yellow stains as expected, demonstrating the presence of potassium-rich ASR gel on the concrete surface. Employing NaOH as a curing medium had accelerated ASR. There is a limitation in the method when utilizing KOH as a curing agent. It is concluded that Sodium Cobaltinitrite can be used as a method for rapid identification of ASR in the preliminary stages of experimental identification of the alkali-aggregate reaction in an existing concrete structure. KEYWORDS: Alkali-Silica Reaction, Sodium Cobaltinitrite, Aggregates, Waste glass, Cement, Potassium hydroxide, Sodium hydroxide

Evaluation of Current ASTM Standards for ASR Prevention When Fine Lightweight Aggregates Are Used

Abstract Previous research has shown that using fine lightweight aggregate (FLWA) can be a promising strategy to mitigate alkali-silica reaction (ASR) in mortar and concrete. However, limited studies focused on assessing current ASTM standards for their applicability in evaluating the efficacy of ASR mitigation using FLWAs. In this study, three commercially used FLWAs (expanded shale, clay, and slate) were investigated in mortar and concrete mixtures with reactive aggregates of different levels of reactivity. ASTM test methods, including ASTM C289-07, Standard Test Method for Potential Alkali-Silica Reactivity of Aggregates (Chemical Method) (Withdrawn 2016); ASTM C1260-14, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method) (Superseded); and ASTM C1293-18, Standard Test Method for Determination of Length Change of Concrete due to Alkali-Silica Reaction (Superseded), were completed. Fine normal-weight aggregates were replaced by the FLWA at 25 % and 50 % by volume in the concrete mixtures, and 25 %, 50 %, and 100 % in mortar mixtures. Results showed that ASTM C1260-14 and ASTM C1293-18 can be used to evaluate the mitigation efficacy when pre-wetted FLWAs were used. The ASTM C289-07 test is not a reliable test method to study the reactivity of the FLWAs, but the results can be used to indicate the alkali-consuming ability of the FLWAs. All three FLWAs were effective in reducing ASR-induced expansion in both ASTM C1260-14 and ASTM C1293-18. The investigated FLWAs were especially effective in the concrete when moderately reactive aggregates, as classified by ASTM C1778-14, Standard Guide for Reducing the Risk of Deleterious Alkali-Aggregate Reaction in Concrete (Superseded), were used. For concrete with a highly reactive aggregate or very highly reactive aggregate, other mitigation strategies may need to be combined with FLWAs to effectively mitigate ASR.

Material, structural and modelling aspects of alkali aggregate reaction in concrete

Concrete nuclear structures have been identified as suffering from alkali aggregate reaction (AAR) in both Canada and the United States. Although much research effort has been directed toward understanding its effect on reinforced concrete structures, unresolved issues still remain. Among them are the effect of multiaxial stress states, commonly developed in nuclear structures, on the response of AAR-affected concrete; also of concern is the possible invalidity of conventional methods of analysis for structural assessment due to the induced anisotropy in the mechanical properties of concrete. The Canadian Nuclear Safety Commission initiated and funded an extensive study aimed to reveal the implications of concrete deterioration due to AAR on structural integrity, which included material and structural testing and modeling. This paper presents an overview of the entire research program and discusses the key results.

Evaluating the effect of recycled aggregate on damaging AAR in concrete

A study examining damaging alkali–aggregate reaction (AAR) in concretes containing recycled aggregate is described. This considered masonry units, concrete, demolition waste, road planings, slate and plasterboard. Alkali release tests indicated that masonry units tended to release more alkali than recycled concrete (with higher levels generally obtained from recently produced materials), with slate and plasterboard giving least. Accelerated mortar expansion (reactivity) test results suggested there was a low risk of AAR for the materials. Concrete tests were then made using BS 812-123 exposure conditions. The concretes were proportioned (i) following the standard mixes (Na2Oeq = 7·0 kg/m3) with recycled materials replacing fine or coarse aggregate in a low-reactivity aggregate combination and (ii) at high alkali level (Na2Oeq = 5·4 kg/m3) with the materials as fine aggregate in a normal-reactivity aggregate combination. The tests for (i) gave results for the recycled materials indicating low reactivity, with classifications of non-expansive or probably non-expansive to BRE Digest 330. For (ii), expansions for the materials were mainly similar/slightly higher than those found for (i). However, recycled concrete that previously exhibited damaging AAR had greater expansions. Selected concretes were exposed at an external site for up to 8·5 years, during which observations by microscopy were carried out. These gave general agreement with the laboratory tests. The practical implications of the study are reviewed.

Can Sensors Solve the Deterioration Problems of Public Infrastructure?

Various deteriorations are detected in public infrastructures, such as bridges, viaducts, piers and tunnels and caused fatal accidents in some cases. The possibility of the applications of health monitoring by using sensors is the issues of this lecture. The inspection and diagnosis are essential in the maintenance works which include appropriate rehabilitations and replacements. The introduction of monitoring system may improve accuracy and efficiency of inspection and diagnosis. This seems to be innovation of maintenance, old structures may change smart structures by the installation of nerve network and brain, specifically. Cost- benefit viewpoint is also important point, because of public infrastructures.The modes of deterioration are fatigue, corrosion, and delayed fracture in steel, and carbonization and alkali aggregate reaction in concrete. These are like adult disease in human bodies. The developments of Infrastructures in Japan were concentrated in the 1960th and 1970th. These ages are approaching 50 and deterioration due to aging has been progress gradually. The attacks of earthquakes are also a major issue. Actually, these infrastructures have been supporting economic and social activities in Japan and the deterioration of public infrastructure has become social problems. How to secure the same level of safety and security for all public infrastructures is the challenge we face now.The targets of monitoring are external disturbances such as traffic loads, earthquakes, winds, temperature, responses against external disturbances, and the changes of performances. In the monitoring of infrastructures, 3W1H(WHAT, WHERE, WHEN and HOW) are essential, that is what kind of data are necessary, where sensors place, when data are collected, and how to collect and process data. The required performances of sensors are accuracy, stability for long time. In the case of long term monitoring, the durability of systems needs more than five years, because the interval of regular bridge inspection works are five years. The supply of powers sometimes becomes serious problem. Some case studies will be presented here.

Alkali-Aggregate Reactions in Concrete: Methodologies Applied in the Evaluation of Alkali Reactivity of Aggregates for Concrete

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. These reactions form an alkaline hygroscopic gel that absorbs water and expands causing internal stresses with cracking [1]. The AAR mitigation measures oblige the correct evaluation of the alkali reactivity of the aggregates. This is normally assessed by petrographic, chemical or expansion test methods. Several studies regarding alkali reactivity of aggregates for concrete structures in Portugal, including bridges and dams, indicated that their field performance does not correspond to the previously performed evaluation. Presently, Portuguese methodology is based on the LNEC Specification E461-2007, which shows some limitations regarding rock types such as granitoids [2]. This situation motivated the development of a research project, involving medium and long term expansion tests in different conditions, under accelerated and natural exposure conditions, as well as petrographic evaluation of the main Portuguese aggregates used/to be used in concrete. This paper presents the preliminary results of this research.

コンクリートのエトリンガイトの遅延生成（DEF）とアルカリ骨材反応

コンクリートのエトリンガイトの遅延生成（DEF）とアルカリ骨材反応

A reply to the discussion by Mingshu Tang of the paper “Laboratory assessment of alkali contribution by aggregates to concrete and application to concrete structures affected by alkali–silica reactivity”

The determination of available alkalis from aggregates is very important for design of durable concrete. This brief article answers comments on the authors original research study in which the researchers used 0.7 M NaOH or KOH solution to extract K or Na in a variety of aggregates at a solution-to-aggregate ratio of 1; the study found that the alkalis released by the aggregates in these alkali solutions can be up to 12.7 kilograms per meter cubed Na2Oe depending on the nature of the aggregate. In the commentary, Mr. Shu contended that the alkali solution extraction procedure presented in the paper is an ion-exchange test in nature and seems incorrect to be used to evaluate the available alkalis from aggregate for alkali-aggregate reaction in concrete. In this reply, Mr. Berube et al explain why their study utilized appropriate tests that measured not only ion exchange but other chemical reactions as well. The researchers discuss the reliability of immersion tests in NAOH and KOH solutions and consider the role of solution-to-aggregate ratio.

Effect of Slag on Expansion Due to Alkali Aggregate Reaction in Concrete

The efficacy of ground granulated blast furnace slag in controlling expansion caused by alkali-aggregate reaction was evaluated using both concrete prism and accelerated mortar bar testing. Six aggregates were included in the program; four of these were classified as alkali-silica reactive (siliceous limestone, sandstone, greywacke, and granite), one as alkali-carbonate reactive (dolomitic limestone), and one as nonreactive (dolostone). The partial replacement portland cement with slag in the range of 25-65% was effective in retarding the rate of expansion and limiting the ultimate expansion at 2 years in concrete prisms cast with all four alkali-silica reactive aggregates. However, the minimum level of slag required to control expansion to an acceptable level, (for example, 0.04% at 2 years) was found to vary depending on the nature of the aggregate and the amount of alkali present in the concrete. There appears to be a reliable correlation between the expansion of mortar bars after 14 days storage in 1M NaOH at 80 deg C and the expansion of concrete prisms after 2 years storage over water at 38 deg C. The accelerated mortar bar test appears to be an appropriate tool for determining the minimum safe level of slag required for a particular reactive aggregate source. The use of slag also reduced the initial rate of expansion of concrete prisms containing the alkali-carbonate reactive (ACR) aggregate. However, the expansion at 2 years exceeded 0.20% for all slag levels tested (25-65%), and this final expansion was actually greater for concretes with 25-50% slag than for the control concrete. The expansion of mortar bars was less than 0.10% at 14 days for all the mixes tested, which confirms the unsuitability of this test for detecting ACR aggregates.

On the mechanical behaviour of concrete subjected to alkali-aggregate reaction

A simple continuum theory is presented for the description of mechanical effects of alkali-aggregate reaction in concrete. The formation of alkali-silica gel leads to a progressive expansion of the material. The rate of expansion depends, in general, on the chemical composition of concrete mix, in particular on the available alkali content of the cement matrix. The progress in the reaction is assumed to be coupled with the degradation of mechanical properties, the latter described within the framework of elastoplasticity. The formulation is illustrated by some numerical examples evaluating the influence of the reaction on the mechanical characteristics of the material.

Review of Expansive Alkali-Aggregate Reactions in Concrete

Expansive alkali-aggregate reactions (AAR) are a frequent and worldwide cause of poor durability in Portland cement concrete. In plain concrete, deleterious AAR generally results in expansion and map-cracking, but in reinforced or prestressed concrete cracks may show a linear relationship to reinforcement. Expansion may lead to buckling, extrusion of joint filler, and displacement of equipment set in concrete. White deposits of silica gel, rims surrounding aggregate particles, pop outs, loss of strength, and decrease in modulus of elasticity may occur. Damage may be so severe that concrete has to be replaced, but less drastic remedial measures have been tried when the damage is less severe. Aggregates likely to cause expansive AAR may be identified by petrographic methods, length-change tests, and examination of deteriorated concrete made with similar materials and exposed to similar conditions. Potential expansion due to AAR may be minimized by reduction of the available supply of alkalies in concrete, use of mineral and chemical admixtures, design to limit wetting and the beneficiation of aggregates. Classification of the types of reaction and mechanisms of expansion are reviewed.

Some applications of the gel fluorescence test for alkali-aggregate reaction in concrete

The gel fluorescence test has been used to determine the presence of alkali-silica reaction products from two field structures and laboratory mortar bars made with reactive opaline aggregate. It is shown that the fluorescence test identifies clearly the products of the reaction between alkalis and reactive silica. A comparison of the expansions of the mortar bars and the amount of gel products in the bars suggests that the fluorescence test cannot be used as an indicator of potential expansion; however, it can be used successfully to determine the presence or absence of products of alkali-silica reaction and thus provide clues to the probable causes of deterioration observed in concrete.

Effect of Fly Ash on Alkali-Aggregate Reaction in Concrete

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Physicochemical studies of the destructive alkali-aggregate reaction in concrete

Physicochemical studies of the destructive alkali-aggregate reaction in concrete

Effect of blast furnace slag cement on alkali-aggregate reaction in concrete

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