The alkali-aggregate reaction (AAR) in concrete occurs when alkalis from cement react with reactive minerals in aggregates, leading to swelling and possible cracking of structures. There are two main types: alkali-silica reaction (ASR) and alkali-carbonate reaction (ACR). Prevention methods include using low-alkali cement, testing aggregates, and utilizing chemical admixtures, while repair involves assessment, removal of damaged concrete, and application of repair materials.

1. WHAT IS ALKALI-AGGREGATE REACTION
IN CONCRETE? PREVENTION AND
REPAIR METHODS
WHAT ARE THE EFFECTS OF ALKALI-AGGREGATE REACTIONS IN CONCRETE
AND WHY DOES IT OCCUR?

2. ALKALI-AGGREGATE REACTION IN CONCRETE
The alkali-aggregate reaction (AAR) occurs when alkalis,
typically sodium and potassium ions from cement, reacts
with minerals present in aggregates within concrete.This
reaction can lead to the formation of a gel, which can induce
swelling and exert pressure on the concrete, ultimately
resulting in the expansion and, in severe cases, the cracking
of the structure.

3. TYPES OF ALKALI-AGGREGATE REACTION IN
CONCRETE
• Alkali-Silica Reaction (ASR)
Alkali-Silica Reaction (ASR) is a prevalent form of alkali-aggregate that
occurs when certain reactive forms of silica minerals present in aggregates,
such as opal, chert, and strained quartz, react with the alkalis, namely
sodium and potassium, in the cement.
• Alkali-Carbonate Reaction (ACR)
Alkali-Carbonate Reaction (ACR) is a type of alkali-aggregate reaction that
occurs between alkalis present in the cement and carbonate minerals found
in specific aggregates.

4. WHERE DOES ALKALI-AGGREGATE REACTION
OCCUR?
• Buildings
• Bridges
• Dams and Water Retaining Structures
• Highway Pavements
• Tunnels
• Hydropower Plants
• Ports and Harbors etc

5. CAUSES OF ALKALI-AGGREGATE REACTION
IN CONCRETE
• High Alkali Content in Cement
• Reactive Minerals in Aggregates
• Moisture Availability
• Elevated Temperatures
• Inadequate Concrete Mix Design

6. IMPACTS OF ALKALI-AGGREGATE REACTION
IN CONCRETE
• Cracking
• Reduced Durability
• Loss of Load-Bearing Capacity
• Surface Disintegration
• Efflorescence
• Structural Distress
• Crushed or Fractured Aggregates
• Map Cracking on Exposed Surfaces

7. HOW TO AVOID AN ALKALI-AGGREGATE
REACTION IN CONCRETE?
• Use low-alkali cement.
• Test aggregates for reactive minerals.
• Consider blended cements (fly ash, slag).
• Control water-cement ratio.
• Utilize chemical admixtures for AAR control.
• Incorporate air-entraining agents.
• Avoid reactive aggregates.
• Use pozzolanic materials in the mix.
• Opt for lithium-based admixtures for AAR prevention.

8. HOW TO REPAIR ALKALI-AGGREGATE
REACTIONS IN CONCRETE?
• Assessment
• Remove Damaged Concrete
• Clean the Surface
• Apply Bonding Agent
• Mix Repair Material
• Place Repair Material
• Cure the Repair
• Apply Protective Coating
(Optional)
• Documentation

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