Why Does Alkali-Silica Reaction Occur In Concrete?

Why Does Alkali-Silica Reaction Occur In Concrete?

What Is Alkali-Silica Reaction In Concrete?

Alkali-silica reaction (ASR) is an expansive chemical reaction occurring in concrete between alkalis present in the cement and silica present in the aggregates.

This reaction results in a gel-like substance, referred to as “ASR gel”, which absorbs water from the environment, swells, and exerts pressure on both hardened and freshly placed concrete causing cracking.

The expansion of ASR causes severe damage to concrete structures by significantly reducing their service life span.

To minimize the risk of ASR problems, it is important to perform proper material selection and mix design along with appropriate tests to verify that reactive materials are not being used in the production of concrete.

Why Does Alkali-Silica Reaction Occur In Concrete?

The alkali-silica reaction (ASR) occurs when certain types of reactive silica in concrete react with excessive amounts of alkalis typically found in cement.

The resulting expansion can cause cracking, loss of strength, and unacceptable deterioration in the concrete structure. This is a major issue as it can become costly over time to repair affected structures.

ASR is caused by several factors such as the presence of reactive silica in aggregates, low w/c ratio, high alkaline cement content combined with high pH levels and higher curing temperatures allowing for accelerated chemical reaction.

How Do You Fix Alkali-Silica Reaction In Concrete?

The most effective way to fix alkali-silica reaction in concrete is by using a chemical injection process.

This involves injecting a solution of silica-fume and hydrophobic silicate into the cracks that have been caused by the reaction.

The silica fume will act as a barrier, preventing the alkaline solution from further reacting with the aggregate while the hydrophobic silicate will coat it, sealing off any excess water and other contaminants.

Once injected, the solution will expand, which provides additional compressive strength while also filling any existing voids in the concrete.

In addition to this chemical injection process, repairing damaged concrete can be done by resurfacing or replacing sections of concrete that have already been affected.

What Is Alkali-Silica Reactivity And How Is It Avoided?

Alkali-silica reactivity (ASR) is a phenomenon that occurs in concrete when reactive aggregates, usually consisting of certain types of silica, react with the alkalis present in cement paste causing the formation of an expansive gel.

This expansive gel increases the volume and causes cracking, leading to weakening and possible collapse of the structure.

It can be avoided by using nonreactive aggregates in concrete mixes and selecting cements with low alkali content.

Additionally, good curing practices can also help reduce ASR by creating an environment where reaction between alkalis and silica is minimized.

What Kinds Of Problems Are Caused By Alkali-Silica Reactivity?

Alkali-silica reactivity (ASR) is a deterioration process that occurs in concrete structures due to the reaction between alkaline components of cement and certain types of reactive siliceous aggregates.

This chemical reaction causes the formation of expansive gel, which as it grows exerts destructive physical pressure on the surrounding concrete, causing cracks, swelling and disintegration.

Additionally, ASR can be responsible for reducing bond strength within a structure and increasing porosity, resulting in increased water penetration and decreased durability.

How Does ASR Cause Deterioration In Concrete?

Alkali-silica reactivity (ASR) is a reaction between alkalis present in the cement and siliceous aggregates which leads to expansion of the concrete, resulting in cracking, spalling of concrete surface and ultimately degradation of the structure.

This occurs when reactive silica bearing aggregates are used with cement containing high concentrations of soluble alkalis; it is most commonly caused by excessive amounts of sodium or potassium hydroxide generated from hardening Portland cement.

When exposed to moisture, these alkalis diffuse into the aggregate where they react with certain types of non-crystalline siliceous material such as opal, chalcedony, chert and volcanic glasses; this reaction produces an expansive gel which causes swelling and internal pressure on the surrounding concrete matrix leading to cracking along with loss of bond between the paste and aggregate particles.

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