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 fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
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 , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
, which is found in many common
aggregates. This reaction can cause the expansion of the altered aggregate, leading to
spalling and loss of
strength
Strength may refer to:
Physical strength
*Physical strength, as in people or animals
* Hysterical strength, extreme strength occurring when people are in life-and-death situations
*Superhuman strength, great physical strength far above human c ...
of concrete.
More accurate terminology
The alkali–aggregate reaction is a general, but relatively vague, expression which can lead to confusion. More precise definitions include the following:
#
Alkali–silica reaction
The alkali–silica reaction (ASR), more commonly known as concrete cancer, is a deleterious swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (''i.e.'', non-crystalline) si ...
(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), 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 Mg( OH)2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and ...
(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 and
pozzolanic materials has also features similar to the alkali–silica reaction, mainly the formation of
calcium silicate hydrate
Calcium silicate hydrate (or C-S-H) is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials (e.g. concrete).
Preparation
When water is added to cement, each of the compounds ...
(C-S-H).
See also
*
Energetically modified cement (EMC)
*
Calthemite
Calthemite is a secondary deposit, derived from concrete, lime, mortar or other calcareous material outside the cave environment.Smith, G.K. (2016). "Calcite straw stalactites growing from concrete structures", Cave and Karst Science 43(1), 4 ...
*
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 ...
External links
Cement.org , Alkali-aggregate reactionAlkali-Aggregate Reactions (AAR) – International Centre of Research and Applied Technology
{{DEFAULTSORT:Alkali-aggregate reaction
Cement
Concrete
Chemical reactions
de:Alkali-Kieselsäure-Reaktion
fr:Réaction alcali-granulat
it:Reazione alcali aggregati
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