Alkali-carbonate reaction
Encyclopedia
The alkali–carbonate reaction is a process suspected for the degradation of concrete
containing dolomite
aggregate
.
Alkali
from the cement
might react with the dolomite crystals present in the aggregate inducing the production of brucite
, (MgOH)2, and calcite
(CaCO3). This mechanism was tentatively proposed by Swenson and Gillott (1950) and may be written as follows:
Brucite (Mg(OH)2), could be the responsible of the volumetric expansion
after de-dolomotisation of the aggregate, due to absorption of water.
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
containing dolomite
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
aggregate
Construction Aggregate
Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined material in the world...
.
Alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
from the cement
Cement
In the most general sense of the word, a cement is a binder, a substance that sets and hardens independently, and can bind other materials together. The word "cement" traces to the Romans, who used the term opus caementicium to describe masonry resembling modern concrete that was made from crushed...
might react with the dolomite crystals present in the aggregate inducing the production of brucite
Brucite
Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg2. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites...
, (MgOH)2, and calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
(CaCO3). This mechanism was tentatively proposed by Swenson and Gillott (1950) and may be written as follows:
- CaMg(CO3)2 + 2 NaOH —> CaCO3 + Na2CO3 + Mg(OH)2
Brucite (Mg(OH)2), could be the responsible of the volumetric expansion
Swelling (medical)
In medical parlance, swelling is the transient enlargement or protuberance in the body and may include tumors. According to cause, it may be congenital, traumatic, inflammatory, neoplastic or miscellaneous....
after de-dolomotisation of the aggregate, due to absorption of water.