What happens when an alkali reacts with a carbonate?

What happens when an alkali reacts with a carbonate?

The alkali–carbonate reaction is an alteration process first suspected in the 1950s in Canada for the degradation of concrete containing dolomite aggregates. Alkali from the cement might react with the dolomite crystals present in the aggregate inducing the production of brucite, (MgOH)2, and calcite (CaCO3).

What do you mean by alkali aggregate reaction?

Definition: chemical reaction in either mortar or concrete between alkalies (sodium and potassium) from portland cement or other sources and certain constituents of some aggregates.- ACI Concrete Terminology.

What is the function of alkali aggregate reaction?

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 cracking over a period of many years.

What are the two types of alkali aggregate reaction?

This alkali-aggregate reaction has two forms: alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). Alkali-silica reaction (ASR) is of more concern because aggregates containing reactive silica materials are more common.

What are alkali carbonates?

A general term referring to the carbonate of an alkali metal. Historically, ‘alkali’ referred just to hydroxides and carbonates of sodium and potassium. It was later extended to refer to water soluble compounds of other alkali metals and ammonium ion.

What is carbonate reaction?

Acids and metal carbonates When acids react with carbonates, such as calcium carbonate (found in chalk, limestone and marble), a salt, water and carbon dioxide are made. acid + metal carbonate → salt + water + carbon dioxide.

What causes ASR?

The primary cause of ASR is a reaction between the alkaline cement’s hydroxyl ions and some aggregate’s reactive forms of silica. This produces a hygroscopic gel which expands on the absorption of water, imposing pressure on the surrounding concrete and weakening it in a way similar to a freeze-thaw action.

How does alkali silica reaction occur?

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.

How does alkali-silica reaction occur?

What promotes the alkali-aggregate reaction?

The alkali-aggregate reaction is greatly promoted by a relative humidity of 80 % or more. Like all chemical reactions, AAR is affected by temperature. In general the rate of reaction and formation of gel will increase as the temperature rises.

What are the factors promoting the alkali-aggregate reaction explain any two of them?

Factors promoting the alkali aggregate reaction. 1) High alkali content in cement. 2) Availability of moisture. 3) Optimum temperature condition. 4) Reactive type of aggregate.

What do carbonates do?

The main uses of carbonates is as raw materials in different industrial processes such as drug development, glass making, pulp and paper industry, sodium chemicals (silicates), soap and detergent production, paper industry, water softener, clay and concrete production, among others.