Surface of a concrete pillar with crack pattern of alkali–silica reaction Alkali–aggregate reaction is a term mainly referring to a reaction which occurs over time in

concrete Concrete is a composite material composed of aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...

between the highly alkaline

cement A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ( aggregate) together. Cement mi ...

paste and non-crystalline

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...

, which is found in many common aggregates. This reaction can cause the expansion of the altered aggregate, leading to

spalling Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...

and loss of

strength Strength may refer to: Personal trait *Physical strength, as in people or animals *Character strengths like those listed in the Values in Action Inventory *The exercise of willpower Physics * Mechanical strength, the ability to withstand ...

of concrete.

More accurate terminology

The alkali–aggregate reaction is a general, but relatively vague, expression which can lead to confusion. More exact definitions include the following: #

Alkali–silica reaction The alkali–silica reaction (ASR), also commonly known as concrete cancer, is a deleterious internal swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (''i.e.'', non-crystal ...

(ASR, the most common reaction of this type); # Alkali–silicate reaction, and; # Alkali–carbonate reaction. The alkali–silica reaction is the most common form of alkali–aggregate reaction.
Two other types are: * the alkali–silicate reaction, in which layer silicate minerals (

clay minerals Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay mineral ...

), sometimes present as impurities, are attacked, and; * the alkali–carbonate reaction, which is an uncommon attack on certain argillaceous dolomitic limestones, likely involving the expansion of the mineral

brucite Brucite is the mineral form of magnesium hydroxide, with the chemical formula Magnesium, Mg(hydroxyl, OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal Vein (geology), vein mineral in metamorphosed li ...

(Mg(OH)₂). The

pozzolanic reaction The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate between a pozzolan and Ca2+ or calcium hydroxide (Ca(OH)2) in the presence of water. The rate of the pozzolanic reaction is dependent on the intrinsic ...

which occurs in the setting of the mixture of

slaked lime Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula Ca( OH)2. It is a colorless crystal or white powder and is produced when quicklime ( calcium oxide) is mixed with water. Annually, approxim ...

and pozzolanic materials has also features similar to the alkali–silica reaction, mainly the formation of

calcium silicate hydrate Calcium silicate hydrates (CSH or C-S-H) are the main products of the hydration of Portland cement and are primarily responsible for the strength of cement-based materials. They are the main binding phase (the "glue") in most concrete. Only well de ...

(C-S-H).

External links

Cement.org , Alkali-aggregate reactionAlkali-Aggregate Reactions (AAR) – International Centre of Research and Applied Technology
{{DEFAULTSORT:Alkali-aggregate reaction Cement Concrete Inorganic reactions de:Alkali-Kieselsäure-Reaktion fr:Réaction alcali-granulat it:Reazione alcali aggregati pt:Reação álcali-agregado

More accurate terminology

See also

External links