— Alkali–silica reaction (ASR) is a chemical reaction within concrete which can lead over time to cracking and spalling. Due to the complexity of the problem, it still causes damage to concrete …
— Creation of alkali-silica gel 4. Released SiO- molecules attract alkali cations in pore solution, forming a gel around the aggregate. Creation of alkali-silica gel 5. Alkali-silica gel takes in water, expanding and exerting a force against surrounding concrete. Creation of alkali-silica gel 6. When the expansionary pressure exceeds the tensile ...
— The alkali–silica reaction is a universally known destructive mechanism in concrete that can lead to the premature loss of serviceability in affected structures.
1 Alkali-Silica Reaction: "The Cancer of Concrete" Courtney Collins . Jason Ideker . Gayle Willis . Jessica Hurst. 2 Outline What is ASR and why is it important? How does ASR …
— At later ages the alkali–silica gel reacts with calcium, and alkalis will be released into the pore solution and increase the alkalinity of the pore solution after 28 days up to 2 or 3 years [111]. Alkali recycling starts after a fixation phase, at least part of the alkalis eventually become available for alkali–silica reaction.
However, the main worry with using RCA as a sustainable construction material is its potential for Alkali-Silica Reaction(ASR), shrinkage, freezing-thawing. The objective of …
Alkali-silica reaction (ASR) is the chemical reaction that occurs between alkali cations and hydroxyl ions in the pore solution of hydrated cement paste and certain reactive silica phases present in the aggregates used in concrete. The product of that reaction, called ASR gel, can expand by imbibing water and thus lead to the expansion and ...
The durability of concrete for marine construction. M. Thomas, in Marine Concrete Structures, 2016 6.2.6 Alkali–aggregate reaction. Alkali– aggregate reaction (AAR) is a reaction between the alkali hydroxides in the pore solution of the concrete (supplied predominantly by the PC) and certain aggregates; alkali–silica reaction (ASR) involves …
— The alkali-silica reaction in cementitious composites occurs through the chemical association of the solution contained in the matrix pores, which is strongly basic and rich in alkalis, and the reactive phases of some aggregates. For the process to begin, high relative humidity and a high concentration of total alkalis are required. The …
International Conference on Alkali-Aggregate Reaction Proceedings Alkali-Aggregate reaction is a an umbrella term for two types of premature concrete deterioration: alkali-silica reaction (most common) and alkali-carbonate reaction (less common). These forms of deterioration encompass a chemical reaction between CERTAIN aggregate types and …
— 3. TYPES OF ALKALI-AGGREGATE REACTION IN CONCRETE • Alkali-Silica Reaction (ASR) Alkali-Silica Reaction (ASR) is a prevalent form of alkali-aggregate that occurs when certain reactive forms of silica minerals present in aggregates, such as opal, chert, and strained quartz, react with the alkalis, namely sodium and potassium, in …
— Alkali-silica reactions (ASR) occur when aggregates containing certain forms of silica react with hydroxyl ions in the alkaline cement pore solution. The reaction produces a gel, which absorbs water from the surrounding environment and expands. The expansion of the gel exerts pressure on the concrete and causes the concrete to crack and fail.
— In the last few decades, the alkali–silica reaction (ASR) has been reported as one of the major concrete concerns regarding durability, leading to hig…
The document provides an overview of alkali silica reaction (ASR) in concrete, including its mechanism, effects, symptoms, factors that influence it, diagnosis, testing, and mitigation techniques. It describes how a …
— Among the many concrete distress mechanisms, alkali-silica reaction (ASR) is one of the most harmful which affects the durability and serviceability of concrete infrastructure worldwide [7, 8]. This shortens the service life of concrete, resulting in an inefficient use of the non-renewable resources and material that previously emitted CO …
the deterioration of concrete, alkali–silica reaction (ASR) is the one that involves the aggregates. Aggregates con-stitute about three-quarter of the volume of concrete, and therefore their physical and chemical properties need to be correctly assessed before their use in concrete. Since the 1940s, considerable research has been developed to
alkali-aggregate reaction. There are three types of alkali-aggregate reactions, namely the alkali-silica, alkali-silicate and akali-carbonate reactions. Deterioration due to the alkali-silica reaction is more common and this paper refers to this aspect. The alkali-silica reaction was first recognized as a problem in North American in 1940, in
— a Concrete pore solution is dominated by Na, K, and OH (with minor amounts of Ca). If the silica in the aggregate is reactive — the OH and then the Na and K will react with the SiO 2.. b The product of …
— Alkali aggregate reaction (AAR), also known as alkali silica reaction (ASR), is a major form of concrete deterioration for older structures. AAR will eventually weaken the concrete, induce cracking, and can jeopardize the integrity of dams and nuclear structures to the point of having them decommissioned.
Alkali-Silica Reaction: - Less reactive aggregates often expensive or difficult to find ... exerting a force against surrounding concrete. Creation of alkali-silica gel ... | PowerPoint PPT presentation | free to view
— Alkali–silica reaction (ASR) is a deleterious reaction between the alkaline pore solution of concrete and various metastable forms of silica contained in many natural and synthetic aggregates [1], [2].The silica structure is dissolved by the nucleophilic attack of OH − ions, and the highly degraded silica structure behaves as a hygroscopic silica gel.
— Concentrating mainly on alkali–silica reaction (ASR), the mechanisms are elucidated, and the necessary requirements for ASR to occur are described. Assessing potential aggregates for use in concrete in terms of their alkali-reactivity is always crucial, and this aspect receives considerable attention. Lastly, practical measures to avoid or ...
— The alkaline solution reacts with amorphous silica to produce a viscous alkali silicate gel. As the reaction proceeds Ca 2+ ions are dissolved into the pore water. These react with the gel to form solid calcium silicate hydrate whereas the alkaline solution converts the remaining siliceous minerals into bulky alkali silicate gel.
— This paper presents a comprehensive review of modeling of alkali-silica reaction (ASR) in concrete. Such modeling is essential for investigating the chemical expansion mechanism and the subsequent influence on the mechanical aspects of the material. The concept of ASR and the mechanism of expansion are first outlined, and …
This attack, which in wet conditions produces a hygroscopic gel, can cause cracking and disruption of the concrete. The deterioration mechanism is termed alkali aggregate …
— Ferrara et al. [7] also suggested the processing of pozzolanic reactions promoted by CAs, based on the identification of C–S–H by SEM/EDS. Likewise, Esgandani et al. [16] attributed the refinement of the concrete pore to the replacement of CH by C–S–H based on the presence of active silica in CAs by the FTIR spectrum.
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 …
— Alkali-silica reaction is one of the most recognized deleterious phenomena in concrete. Various types of silica present in aggregates react with the hydroxyl ions present in the pore solution in …
The reaction process may take years, but once the reaction is underway, the forces from expansion cause cracking to appear on the surface. This blog post will focus on ASR and tests to detect the potential in aggregates and aggregate-mortar mixes. Photo Credit: ASR Identification Handbook The Effect of Alkali-Silica Reaction on Concrete
Alkali-silica reaction (ASR) can lead to premature failure of concrete elements and structures including pavements, bridges, tunnels, power plants, dams, and others. ASR is a chemophysical reaction within the concrete's microstructure occurring between certain alkalis, typically from the cement, and specific aggregates. ...
