1. ALKALI-SILICA REACTION MITIGATION STATE-OF-THE-ART
Dr. L. Javier Malvar
NFESC, 10 October 2001

2. Airfields already identified as having ASR problems:
15 Air Force airfields
Air Combat Command: Seymour-Johnson AFB, NC, Langley AFB, VA, Offut AFB, NC, Holloman AFB, Cannon AFB, NM
Pacific Air Force : Osan AB, Korea, Plant 42, CA, Kirtland AFB, NM, Wright-Patterson AFB, OH
Air Mobility Command: Andrews AFB, MD, Travis AFB, CA
Air Force Space Command: Warren AFB, WY
U.S. Air Force Europe: Torrejon AB, Spain, Aviano AB, Italy
Air National Guard: Pease AFB, NH
3 Army airfields
Biggs, Ft Bliss, TX, Ft Campbell, KY
6 Navy airfields
NAS Point Mugu, CA, NAS Fallon, NV, NOLF San Nicolas Island, CA, MCAS Iwakuni, Japan, MCAS Beaufort, SC, MCAS Cherry Point, NC

3. Public Law
In 2001, Congress passed Military Authorization Bill - Public Law (HR 4205) (Section 389), and Military Construction Appropriations Bill - Conference Report for Public Law , 2001 (page 88).
The Conference Report directs the Under Secretary of Defense for Acquisition, Technology, and Logistics to assess the overall condition of Department of Defense (DOD) facilities and infrastructure with respect to Alkali-Silica Reaction (ASR).
Public Law directs the Secretary of Defense, through the Service Secretaries, to assess the damage caused to aviation facilities by ASR, and explore available technologies capable of preventing, treating, or mitigating ASR.

4. ASR State-of-the-Art report
Purpose is to:
Assess worldwide status of ASR mitigation
Derive best current set of mitigation techniques
Determine areas that need further investigation
In addition to report, we need to:
Provide in-house training to recognize ASR
Determine ASR problems at all airfields
During PCI assessments
Prepare proposal, determine funding source

5. Beneficial Admixtures
The following admixtures have been shown to mitigate ASR to various degrees:
Fly Ash Classes F, N, C
GGBFS
Lithium
Silica Fume
Each of these admixtures has to be added within specific minimum and maximum amounts, otherwise they may create problems, including worse ASR
Improper admixture dosage or usage can exacerbate the ASR problem !

6. Pessimum Effects

8. Effect of CaO
Because of the pessimum effect due to CaO content
Class C fly ash should not be used
Class F or N fly ash with CaO < 8% should be used at minimum replacements of 25%
Class F or N fly ash with 8% < CaO < 10% can be allowed at minimum replacements of 30%
Unless the CaO < 2%, a strong pessimum effect may be found for replacements below 25% - this is a problem for current practice which often uses 15%.
Previous Class F 15% cement replacements may have resulted in WORSE expansion !

9. Other Restrictions on Class F and N Fly Ashes
In addition to limiting the CaO content of the fly ash, other limitations are needed:
The maximum available alkalies should be less than 1.5% per ASTM C 618 (as Na2O equivalent)
The loss on ignition should be less than 6%
Although Class N fly ash has been less used than Class F, a CALTRANS study shows that it works equally well in reducing expansion

10. Other Benefits of Class F and N Fly Ashes
Reduced construction costs.
Savings in Portland cement production (~ $2B/year)
Reduced heat of hydration and reduced permeability.
Enhanced durability of waterfront structures.
Higher long term strengths.
Reduction in CO2 generation (40% of Kyoto Protocol)
Higher fly ash recycling.
Conformity with Resource Conservation and Recovery Act (RCRA) affirmative procurement regulations and DoD affirmative procurement policy.
Increased resistance to high temperatures from jet blast

11. Maximum Class F or N Cement Replacement
Several entities recommend 35%
Beyond 35% it is more difficult to finish, e.g. Pier D:
Bull floating was very difficult, very thick and sticky consistency.
After bull floating, mud was very soft at the edges.
Not much cream to fill imperfections with.
Mud does not move well requiring the use of frezno and hand tools to fill imperfections, which is very time consuming.
However, more than 35% replacement has other advantages (more durable, environmentally friendly..)
Should the maximum allowed replacement be higher ?

12. What do we do with Class C Fly Ashes
A list of providers of all types of fly ashes is being gathered
Class C fly ash information is included
Class C fly ash should be avoided in concrete – due to its high CaO content, it will worsen the ASR problem unless used at very high (typically impractical) volume replacements
However, Class C fly ash can be helpful in soil stabilization
At typical replacement levels, Class C fly ash will result in worse ASR expansion due to its high CaO content !

13. Effect of Replacement on Strength Gain
GGBFS
Ground granulated blast furnace slag is found in the East Coast
ASTM C 989 shows 3 Grades: only Grades 100 and 120 recommended
Minimum replacement for ASR mitigation is 40%
Maximum recommended replacement is 50%
GGBFS has cementitious properties, hence 28-day strength is often increased
Effect of Replacement on Strength Gain
GGBFS Grade 100

14. Lithium
Lithium Nitrate is being used and has shown to be successful in new construction
Can be expensive (add $5 to $15 per yard3)
Benefits from application to existing pavements are not well defined

15. Strength Specification
GGBFS stronger at 28 days
Class F, N less strong if direct replacement
Use partial replacement
e.g., replace 1 bag cement with 1.5 bags fly ash
Still need to have 25% fly ash
It is possible to get the same strength at 28 days
SouthDiv and LantDiv use 28-day specification
Navy to specify strength at 28 days

16. But it is expensive (10 times more than cement) And it can PRODUCE ASR
Silica Fume
Silica fume can prevent ASR with low cement replacement amounts (around 10%)
But it is expensive (10 times more than cement)
And it can PRODUCE ASR
A bridge in NAVSTA Pearl Harbor

17. Documenting ASR in PCI Reports
ASR can be counted as Scaling (close to D-cracking)
But ASR has to be reported separately
GOAL = assessing ASR extend at all airfields by 2006
What we need to do:
Learn to recognize ASR
Agree on reporting strategy
Include in separate Appendix

18. Conclusions
A state-of-the-art report has been completed that gives guidelines for ASR mitigation
All concrete will have 25-35% Class F or N fly ash, or 40-50% GGBFS
Also LOI < 6%, available alkalies <1.5%, CaO < 8%
Allow use of 8% < CaO < 10% for Class F or N fly ash > 30%
UFGS and NFGS are being updated to include the report recommendations
PCI reports need to include section on ASR