Andres salas batching effects on properties of recycled aggregate concretes for airfield rigid pavements
1. Batching Effects on Properties of
Recycled Aggregate Concretes for
Airfield Rigid Pavements
Dr. Andres Salas
Prof. David Lange
Prof. Jeff Roesler
2010 FAA Technology Transfer Conference and Exposition
April 22, 2010
2. O’Hare Modernization Program
(OMP)
The purpose is to reconfigure the intersecting
runways at O’Hare International Airport into a
more modern parallel layout.
Prior to this O’Hare had not added a new
runway since 1971.
Project budget of $6.6 billion.
4. Sustainable practices are desirable
Reuse and conserve natural resources
Cost savings over traditional methods
Use of RA in concrete and asphalt
showed comparable performance over
virgin aggregates.
Why Recycle?
5. Resistance to change
Lack of experience
Inadequate codes, specifications
and standards
Inconsistent aggregate grading
Lower and variable quality
Challenges for using RecycledChallenges for using Recycled
Concrete AggregatesConcrete Aggregates
6. Recycled Concrete Aggregates atRecycled Concrete Aggregates at
AirportsAirports
Commonly used for base and subbase
Not used on airport concrete surface before in
U.S.?
Technical issues for surface applications
Durability, shrinkage, premature cracking
7. Two-Stage Mixing Approach, TSMATwo-Stage Mixing Approach, TSMA (Tam et al. 2005):
Mixing process divided into two parts with required
water proportionally split and added at different timing.
Initial water used for the formation of thin layer of
cement slurry on the surface of RA.
Permeate into old porous cement mortar, filling up
the old cracks and voids.
Do the aggregates have to be dry, partially-saturated, or
saturated+surface moisture?
A new idea about mixing with RCAA new idea about mixing with RCA
8. Mixture ProcedureMixture Procedure
(Two-Stage Mixing Approach)(Two-Stage Mixing Approach)
Recycled coarse + cementing material 1 min 50% water 1 min Virgin coarse + sand+ 50%water 2 min
mix mix mix
* Control concrete (VAC)
was mixed following the
commonly used mixing
procedure
14. Drying Shrinkage ResultsDrying Shrinkage Results
Lower microstrain for 100% RA at 14 days age
RA soaked for 24 hrs while virgin aggregate in oven dry condition
0.0
50.0
100.0
150.0
200.0
250.0
300.0
0 10 20 30 40 50 60
FreeShrinkage(x10-6)
Age (days)
VA
30% RA
50% RA
100% RA
50% RA + SF
100% + SF
100% + FIBERS
0.0
50.0
100.0
150.0
200.0
250.0
300.0
0 10 20 30 40 50 60
FreeShrinkage(x10-6)
Age (days)
VA
30% RA
50% RA
100% RA
50% RA + SF
100% + SF
100% + FIBERS
15. Summary Properties of RACSummary Properties of RAC
(Two Stage Mixing Approach)(Two Stage Mixing Approach)
Similar or higher compressive strength
compared to VAC
Similar shrinkage to VAC at early ages
Reduced bleeding and segregation
Similar concrete workability
Low dosages of silica fume (2 to 3%) enhances
the behavior of RAC
16. Minimize old mortar attached to aggregate
Aggregate grain size distribution and proportions
Aggregate Absorption Capacity
RA should be nearly-saturated conditions to
avoid loss in slump and excessive shrinkage.
Two-Stage Mixing Approach (TSMA) and pre-
soaking treatment method for the production of
RAC are encouraged
Issues to Consider for RACIssues to Consider for RAC
18. Pouring Gate F7B at O’HarePouring Gate F7B at O’Hare
Run #1 of RACRun #2 of VAC
2 strips of 25ft x 125ft x 17in were placed
Prairie supplied the materials
Rossi Construction was the contractor
SAM Consultants handled material testing
20. Placement and FinishingPlacement and Finishing
After placement of the RAC
No bleeding was observed
Finishing took place almost
immediately after placement
Very little effort required to finish
23. Field Visit 3/18
Contraction joints remain unchanged
Some scaling observed in the test strips
VAC
RAC
24. 24
Compare Lab to Field
Mix designs and early age results for the Recycled Aggregate Concrete Mixes. Comparison
between U of I mix designs and Prairie Mix Design
Compressive Strength Design 4000psi
Prairie (RAC) Prairie (VAC) U of I (20%FA) 30% Class C FA 40% Class C FA 50% Class C FA
Water (gal) 28 ~26 ~26 ~26 ~26
Cement (lbs) 490 414 362 310 259
Fly Ash (lbs) 130 103 155 207 259
Air (%) 4.5-7.5 3% 3% 3% 3%
% WRA Variable dosage No No No No
Initial Slump (in) 3±1 4 7.5 8 8
Recycled Coarse (lbs) 1500 1688 1683 1677 1672
Extra Fines (lbs) 400 274 273 272 271
Natural Sand (lbs) 1093 1011 1007 1004 1000
Compressive strength at 3 days (psi) 3547 3581 - - - -
Compressive strength at 7 days (psi) 5190 4855 4700 3978 3830
Compressive strength at 28 days (psi) 6900/5858 5182 5751 5507 5435 5005
Flexural strength at 3 days (psi) 704.5 - - - -
Flexural strength at 7 days (psi) 760 - - - -
Flexural strength at 28 days (psi) 915/1052 826 - - - -
w/cementitious ~0.375 0.42 0.42 0.42 0.42
* Blod and blue represents testing results from SAM Consultants
25. Summary
• Lab test program helps us predict behavior of RAC using
recycled material sources at O’Hare
• Lab test program encourages us to use high(er) volume
of fly ash
• Lab test encourages lower cement than used in the field
RAC
• Testing underscores importance of keeping RA supply
near saturation to control shrinkage
• Field testing confirms that RAC slabs were well-
constructed and not experiencing high deformations
• So far, so good!