1. Alkali-Silica Reaction: “The Cancer of Concrete”
Courtney Collins . Jason Ideker . Gayle Willis . Jessica Hurst

2. Outline What is ASR and why is it important? How does ASR work?
How can ASR damage be prevented?

3. What is ASR?
Alkali Silica Reaction (ASR)
Alkalis +
Reactive Silica
Moisture
ASR Gel which expands
Concrete cracking

4. Concrete failure due to ASR
AASHTO Innovative Highway Technologies
AASHTO Innovative Highway Technologies
AASHTO Innovative Highway Technologies
Georgia Tech School of CEE - Courtney Collins

5. Why is it important to study ASR?
Concrete quality
Loss of strength, stiffness, impermeability
Premature failure of concrete structures
Economic/Environmental impacts
ASR lowers concrete lifetime
Less reactive aggregates often expensive or difficult to find
Cement production creates 7% of the world’s
CO2 emissions (a greenhouse gas).

6. Case Study: Parker Dam, California
Alkali-Aggregate Reactions in Hydroelectric Plants and Dams:
Hydroelectric dam built in 1938
180 mm of arch deflection due to alkali silica gel expansion
Cracking and gel flow in concrete

7. Case Study: I-85 - Atlanta, Georgia
Possible ASR damage on concrete retaining wall - picture taken 1/2002

8. How does ASR work? What we know: What we don’t know:
Which reactants involved and their sources
How alkali-silica gel is created
ASR prevention can be achieved by using low alkali cement and non-reactive aggregate
Additives such as lithium compounds and pozzolanic material help prevent ASR damage
What we don’t know:
Mechanism of gel expansion
Lithium: it’s mechanism of inhibition, which compounds work best, how much of each compound is needed to prevent expansion

9. Creation of alkali-silica gel

10. Creation of alkali-silica gel
Reactants: alkalis, reactive silica, and water
Alkalis
Main cations:
Sodium (Na+)
Potassium (K+)
Common sources:
Portland cement
Deicing agents
Seawater

11. Creation of alkali-silica gel
Reactive Silica
Silica tetrahedron:
Amorphous Silica
Crystalline Silica

12. Creation of alkali-silica gel
Reactive Silica
Amorphous silica = most chemically reactive
Common reactive rocks:
opal
obsidian
cristobalite
tridymite
chelcedony
cherts
cryptocrystalline volcanic rocks
strained quartz

13. Creation of alkali-silica gel
Water
Found in pore spaces in concrete
Sources:
Addition of water to concrete mixture
Moist environment/permeable concrete

14. Creation of alkali-silica gel
1. Aggregate in solution, pre-ASR damage

15. Creation of alkali-silica gel
2. Surface of aggregate is attacked by OH-
H20 + Si-O-Si
Si-OH…OH-Si

16. Creation of alkali-silica gel
3. Silanol groups (Si-OH) on surface are broken
down by OH- into SiO- molecules
Si-OH + OH-
SiO- + H20

17. Creation of alkali-silica gel
4. Released SiO- molecules attract alkali cations
in pore solution, forming a gel around the
aggregate

18. Creation of alkali-silica gel
5. Alkali-silica gel takes in water, expanding and
exerting a force against surrounding concrete.

19. Creation of alkali-silica gel
6. When the expansionary pressure exceeds
the tensile strength of the concrete, the
concrete cracks

20. Creation of alkali-silica gel
7. When cracks reach the surface of the structure,
“map cracking” results

21. Images of ASR damage

22. Images of ASR damage

23. Images of ASR damage

24. How to prevent ASR damage

25. Alkalis + Reactive Silica + Moisture
How to prevent ASR damage
Alkalis + Reactive Silica + Moisture
ASR Gel
Avoid high alkali content:
use low alkali portland cement
replace cement with pozzolanic admixtures
Avoid reactive aggregate (amorphous silica)
Control access to water
Use lithium additives prior to placement of concrete or as a treatment in already existing concrete

26. ANY QUESTIONS?