What is alkali aggregate reaction and how it can be controlled?

Alkali-silica reaction can be controlled using certain supplementary cementitious materials. In-proper proportions, silica fume, fly ash, and ground granulated blast-furnace slag have significantly reduced or eliminated expansion due to alkali-silica reactivity.

How will the alkali aggregate reaction effect the concrete properties?

The effects of alkali–aggregate reaction (AAR) on concrete and structures start at the microstructural level, that is, at molecular and microscopic levels, such as the formation of reaction products in concrete and associated microcracking, which ultimately leads to macro-level effects such as visual cracking.

What is alkali aggregate reactivity AAR?

Alkali-aggregate reaction (AAR) is a reaction in concrete between the alkali hydroxides, which originate mainly from the portland cement, and certain types of aggregate. Two types of AAR are currently recognized; these are alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR).

What causes alkali-silica reaction in concrete?

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.

Why alkali is used in cement?

An increase in the alkali content of cement delayed the time of final setting, reduced the compressive strength, and increased the rapid chloride ion permeability, drying shrinkage and volume of permeable voids of HPCM.

What causes 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.

Who promote 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 causes alkali-aggregate reaction?

What do you mean by Chlor Alkali reaction?

The term chlor-alkali refers to the two chemicals (chlorine and an alkali) which are simultaneously produced as a result of the electrolysis of a saltwater. In the mercury cell process, chlorine and sodium hydroxide are produced simultaneously by electrolyzing seawater (sodium saltwater or brine) in a mercury cell.

How do you prevent an alkali aggregate reaction?

A possible practice to prevent disorders due to alkali-silica reaction (ASR) in concretes containing reactive aggregates is the use of chemical admixtures (lithium salts) or, more commonly, mineral admixtures such as fly ash, silica fume, ground granulated slag or metakaolin.

What are the 3 products of chlor-alkali process?

The three products as ‘chlor-alkali’ process are :

• Sodium hydroxide (NaOH)
• Chlorine (Cl2)
• Hydrogen (H2)

What is chlor-alkali used for?

Chlor-alkali is an industrial process widely used to produce chlorine, caustic soda, and other chlorine and sodium derived/based products such as sodium hypochlorite, hydrochloric acid, chlorosulphonic acid, bleaching power, polyaluminium chloride, hydrogen gas, and chlorinated paraffin.

What is Alkali-Aggregate Reaction?

Alkali-Aggregate Reaction. In most concrete, aggregates are more or less chemically inert. However, some aggregates react with the alkali hydroxides in concrete, causing expansion and cracking over a period of many years. This alkali-aggregate reaction has two forms: alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR).

What is the chemical reaction between concrete and aggregates?

In most concrete, aggregates are more or less chemically inert. However, some aggregates react with the alkali hydroxides in concrete, causing expansion and cracking over a period of many years. This alkali-aggregate reaction has two forms: alkali-silica reaction (ASR) and alkali-carbonate reaction…

What is alkali in concrete?

Aggregate containing feldspars, some micas, glassy rock and glass may release alkali in concrete. Sea dredged sand, if not properly washed, may contain sodium chloride which can contribute significant alkali to concrete. 3. Admixtures Admixture in the context of AAR in concrete means chemical agents added to concrete at the mixing stage.

What is an ACI reaction in concrete?

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. Alkali-aggregate reactions can be either alkali-carbonate reactions (ACRs) or alkali-silica reactions (ASRs).