The document discusses alkali-silica reaction (ASR) in concrete, which is a chemical reaction between alkalis in cement and certain reactive aggregates containing silica. This reaction forms an expansive gel that can cause cracking and deterioration in concrete structures over time. The document outlines factors that contribute to concrete durability against ASR, including aggregate type, cement content, water-cement ratio, and permeability. It also describes causes of ASR, defects caused by ASR, and techniques for mitigating ASR, such as limiting reactive aggregates or alkalis in cement and using mineral admixtures.

2. Presented To:
Dr. Ayub Elahi
Presented By:
Taseer Raza (17-CE-93)

3. Properties of Concrete

4. Durability aspects and factors contributing
towards durability
• What is durability?
• What is importance of durability?
• Alkali Silica Reaction (ASR) in Concrete.
• Reasons and remedial measures for alkali-silica reaction in concrete

5. Durability
• Durability is the ability to last a long time without significant deterioration. A
durable material helps the environment by conserving resources and reducing
wastes and environment impacts of repair and replacement.

6. Durability of concrete
• Ability to resist weathering action, chemical attack, abrasion, or any process
of deterioration.
• A durable concrete is one that performs satisfactorily under anticipated
exposure conditions during its life span. The materials and mixed proportions
used should be such as to maintain its integrity and, if applicable, to protect
embedder metal from corrosion. Even though concrete is durable material
requiring a little or no maintenance in normal environment but when
subjected to highly aggressive or hostile environments it has been founded to
deteriorate resulting in premature failure of structures or reach a state
requiring costly repairs.

7. Importance of durability
• Durability is vital with regards to a structure's lifespan. It is the characteristic
that dictates how long a structure can live to perform its desired function.
• Durability has a direct impact on strength. It cannot be underestimated. More
the structure is durable more it has strength.
• The durability is about the ability of the structure to resist action from the
weather over time, fire, and any chemical attack, while maintaining the
desired engineering properties. So, it is really vital.

8. Ancient durable structures

9. Colosseum of ROME

10. Pantheon in
Rome

11. Deteriorate structures

14. Factors contributing towards durability

15. There are many factors that contribute in durability of concrete, amongst
them few are following;
• Aggregate type
• Cement content
• Water cement ratio
• Cement type
• Air entrainment
• Carbonation
• Freeze thaw cycle

16. • Quality of mixing water
• Depth of cover to reinforcement
• Permeability

18. Alkali silica reaction(ASR) in concrete

19. Alkali silica reaction(ASR) in concrete
• The alkali silica reaction (ASR), more commonly known as "concrete
cancer", is a swelling reaction that occurs over time in concrete between the
highly alkaline cement paste and the reactive non-crystalline
(amorphous) silica found in many common aggregates, given sufficient
moisture.
• This reaction causes the expansion of the altered aggregate by the formation
of a soluble and viscous gel of sodium silicate. This hygroscopic gel swells
and increases in volume when absorbing water. It exerts an expansive
pressure inside the siliceous aggregate, causing spalling and loss of strength
of the concrete, finally leading to its failure.

20. • ASR can lead to serious cracking in concrete, resulting in critical structural
problems that can even force the demolition of a particular structure.
• There are many hydraulic as well as other structures that are demolished or
damaged due to ASR.These structure includes bridges, highways and dam
walls.
• ASR is mainly due to use of reactive aggregates.

23. Causes of ASR in concrete

24. Causes of alkali silica reaction are many but they are broadly classified into two
pats,
External causes:
• Alkalinity in the water to which the concrete is exposed may cause problems
if reactive aggregate was used in the concrete.
• The water may acquire its alkalinity from soil through which it passes.
• Deicing solutions may provide alkalis that could cause ASR if reactive
aggregate was used in the concrete
• Sea water and water from industrial processes may also introduce alkali to
concrete

25. Internal causes:
• Alkali in the cement and reactive aggregate in the concrete in sufficient
concentrations will cause ASR.
• Use of reactive aggregates that has high content of alkali.
• Internal humidity may cause ASR if the concrete is not permitted to dry
properly.
• Using mix water with high alkalinity will increase the concrete’s alkali
content

26. Defects produced due to ASR

27. The cracking caused by ASR can have several negative impacts on concrete,
including:
• Expansion:
The swelling nature of ASR gel increases the chance of expansion in
concrete elements.
• Compressive Strength:
The effect of ASR on compressive strength can be minor for low
expansion levels, to relatively higher degrees at larger expansions compressive
strength is not very accurate parameter to study the severity of ASR; however,
the test is done because of its simplicity.
• Fatigue:
ASR reduces the load bearing capacity and the fatigue life of
concrete.

28. ASR Mitigation techniques

29. • Limit the alkali metal content of the cement. Many standards impose limits on
the "Equivalent Na2O" content of cement.
• Limit the reactive silica content of the aggregate. Certain volcanic rocks are
particularly susceptible to ASR because they contain volcanic glass (obsidian)
and should not be used as aggregate.
• The use of calcium carbonate aggregates is sometimes envisaged as an
ultimate solution to avoid any problem.
• If no water is available for ASR reaction then it will never occur.

31. • The alkali-silica reaction will not take place in a concrete structure if the
internal relative humidity of the concrete is lower than 80%. As a result,
keeping the concrete dry will prevent the reaction from occurring. However,
this is practically impossible for exterior structures.
• Lowering the permeability of concrete by reducing the water-cement ratio
reduces the internal moisture and delays the reaction.
• Effective mineral admixtures include fly ash, silica fume, ground granulated
slag, and calcined clay reduce ASR expansions by either reducing the alkali
content of the concrete mix or reducing the pH of the pore solution

32. Questions?