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Batching Effects on Properties of Recycled Aggregate Concretes for Airfield Rigid Pavements

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. O’Hare Modernization Program (OMP).

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Batching Effects on Properties of Recycled Aggregate Concretes for Airfield Rigid Pavements

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  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.

  3. O’Hare Modernization Program (OMP)

  4. Why Recycle? • 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.

  5. Challenges for using Recycled Concrete Aggregates • Resistance to change • Lack of experience • Inadequate codes, specifications and standards • Inconsistent aggregate grading • Lower and variable quality

  6. Recycled Concrete Aggregates at Airports • 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, 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 RCA

  8. Mixture Procedure (Two-Stage Mixing Approach) mix mix mix Recycled coarse + cementing material 50% water Virgin coarse + sand+ 50%water 1 min 1 min 2 min * Control concrete (VAC) was mixed following the commonly used mixing procedure

  9. O’Hare Aggregate Physical Properties

  10. Mixture Design • w/cm = 0.42 • The recycled aggregates sprayed to approximately fill 80% of the total absorption capacity.

  11. Fresh Properties Slump for 100% RA was higher than expected. Nearly saturated aggregates reduces effects of RA absorption

  12. Drying Shrinkage Results • Lower microstrain for 100% RA at 14 days age • RA soaked for 24 hrs while virgin aggregate in oven dry condition

  13. Summary Properties of RAC(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

  14. Issues to Consider for RAC • 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

  15. Field Testing

  16. Pouring Gate F7B at O’Hare Run #2 of VAC Run #1 of RAC • 2 strips of 25ft x 125ft x 17in were placed • Prairie supplied the materials • Rossi Construction was the contractor • SAM Consultants handled material testing

  17. Sensor Installation • 28 Sensors to measure RH and Temperature • 7 LVDT sensors to measure lift-off of the slab

  18. Placement and Finishing • After placement of the RAC • No bleeding was observed • Finishing took place almost immediately after placement • Very little effort required to finish

  19. Field Visits 10/29 VAC RAC (Run #1)

  20. Field Visit 11/12 VAC (Run #2) VAC RAC (Run #1) VAC

  21. Field Visit 3/18 VAC • Contraction joints remain unchanged • Some scaling observed in the test strips RAC

  22. 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 24

  23. 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!

  24. Acknowledgements

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