Performance Engineered: Mixtures and AASHTO PP 84: It's Time for a Change
- 1. Image Here Office of Infrastructure MICHAEL F. PRAUL, PE SENIOR CONCRETE ENGINEER FHWA, OFFICE OF INFRASTRUCTURE Performance Engineered Mixtures and AASHTO PP 84: It’s Time for a Change All images FHWA unless otherwise noted. 2019 NCPA Concrete Paving Workshop
- 2. Timeframe for widespread use of SCMs 28-day strength testing Slump test We Are Horrible With Change Image Pixabay
- 3. 1920 198019601940 2000 ASTM C231ASTM C143 Evolution of Concrete Testing Slump Cone Pressure Meter 1981 Rapid Chloride Permeability Test 1922 1949 FHWA/PCA
- 4. Performance Engineered Mixture Concept Understand what makes concrete last and what failure mechanisms we see Specify critical properties to address those failure mechanisms and test for them Starting point for a performance-driven QA specification and acceptance program for owner agencies
- 5. PEM/PP 84 Specification Development The Team o Dr. Peter Taylor, Director, CP Tech Center/Iowa State o Dr. Jason Weiss, Oregon State University o Dr. Tyler Ley, Oklahoma State University o Dr. Tom Van Dam, NCE o Cecil Jones, Diversified Engineering o Tom Cackler/Gordon Smith, CP Tech Center o Mike Praul, FHWA ETG Participants/Reviewers o Champion States o ACPA National, ACPA Chapter Execs o PCA o NRMCA
- 6. AASHTO PP 84: A Better Specification Strength Shrinkage Freeze-thaw resistance Transport properties (Permeability) Aggregate stability Workability* Require the things that matter
- 7. AASHTO PP 84 A guide specification with tests completed either during mixture design or at placement or both that focus on concrete performance. Allows DOTs to take what they like from the document and make it their own. DOTs should not give up what they already know is important for them.
- 8. AASHTO PP 84 A commentary is included that gives the technical background behind the tests and limits. A tool to help you improve your concrete. The document is not designed to be used without modifying for local practice and experience.
- 9. PEM/PP 84: It’s our Superpave Most significant field-level advancement in decades Answers the question “With our loss of staff and resources, how are we going to be able to get the job done in the future?” Collaboration with industry (It’s more than just the tests!) Why We’re Excited Concrete Evolution Image Pixabay
- 10. Jerry Voigt, ACPA “It’s the agency’s responsibility to allow for innovation. It’s the contractor’s responsibility to deliver.” Image ACPA
- 11. How Do Contractors Deliver in a Performance Specification? Image Pixabay
- 13. Standard procedures (AASHTO, ASTM, state) Laboratory accreditation/qualification program Technician training and certification programs State Independent Assurance Program Calibrated equipment schedules Controlling Sampling and Testing Variability
- 14. Testing Variability Procedure 95% Lower Limit Test Result 95% Upper Limit Sieve analysis (% passing ½”) 24% 28% 32% Slump 2” 2 ½” 3” Air content 4.9% 5.5% 6.1% Rodded unit weight for aggregate 114.5 lb/ft3 120 lb/ft3 125.5 lb/ft3 Compressive strength 3,390 lb/in2 3,600 lb/in2 3,810 lb/in2 Flexural strength 602 lb/in2 700 lb/in2 798 lb/in2
- 15. Controlling Material and Process Variability Image Pixabay
- 16. Prescriptive vs. Performance Specifications Prescriptive Agency dictates how the material or product is formulated and constructed Based on past experience Minimal/uncertain ability to innovate Requires agency to have proper manpower and skill set to provide oversight Performance Agency identifies desired characteristics of the material or product Contractor controls how to provide those characteristics Maximum ability to innovate Reduced oversight burden on the agency
- 17. Agency Acceptance Contractor Quality Control Qualified (certified) Personnel Qualified Laboratories Independent Assurance Dispute Resolution for Test Results Quality Assurance Defined: 23 CFR 637 } State processes, independent of material
- 18. Quality Control PP 84 acknowledges the key role of QC in a performance specification Requires an approved QC Plan Testing targets, frequency, and action limits Equipment and construction inspection Mirror design-build experience Requires QC testing and control charts Unit weight Air content/SAM Water content Formation Factor (via Surface Resistivity) Strength Image Pixabay
- 22. Change State mind set that QC is not its business Gordon Smith example Change (some) industry mind set that QC is not its business Provide guidance on developing State specification language QC Testing Guide (very similar to guidance for the acceptance program but slanted to industry) QC test tech briefs and videos Frequency Control charts and usage QC Plan template and guidance Quality Control Evolution
- 23. 3% 4% 5% 6% 7% 8% 9% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 AirContent,% Test # Air content and Unit Weight Air Content Unit Weight Dual Axis Plot Example Air content plotted on the left vertical axis Unit weight plotted on the right vertical axis 136 137 138 139 140 141 142 143 144 145 1463% 4% 5% 6% 7% 8% 9% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 UnitWeight,pcf AirContent,% Test # Air content and Unit Weight Air Content Unit Weight
- 24. 0 5 10 15 20 25 2-2 3-1 3-2 3-3 5-1 5-2 6-1 6-2 SurfaceResistivity,KOhm-cm 56 Days Low Moderate High 0 5 10 15 20 25 2-2 3-1 3-2 3-3 5-1 5-2 6-1 6-2 SurfaceResistivity,KOhm-cm 28 Days Low Moderate High Unit Weight/Heat Signature/Permeability Unit Weight – Real Time Surface Resistivity – 56 DaysHeat Signature – Info in a day Field Data from an MCT project Real Time 28 / 56 days Surface Resistivity – 28 Days
- 25. Cements Widespread use of SCMs Advancements in chemical admixture technology De-icers Agency personnel and experience levels Industry knowledge base “But Mike, You’re Asking for a Lot of Change” Change has already happened!
- 27. PEM Pooled Fund Partners FHWA State Departments of Transportation (DOTs) Industry (American Concrete Pavement Association, Portland Cement Association, National Ready Mixed Concrete Association, others) Image Pixabay
- 28. Pooled Fund Participants 16 States + FHWA & Industry (July 2018)
- 29. Pooled Fund Emphasis Implementation Education and training Adjustments in specifications based on field performance Continued development of a knowledge base relating early age properties to performance
Editor's Notes
- #13: Introduction and Key Points There are four main sources of inherent variability. Variability exists in all construction materials. It is one of the key factors that is integral to Quality Assurance and must be clearly understood. Variability is defined as “differences in measured test values for a given Quality Characteristic within a stable pattern due to chance, or outside this normal pattern due to an assignable cause.” Variation can be controlled, but cannot be eliminated. The level of Quality of any material or product is associated with the level of Variability. There are four primary sources of Inherent Variability; Material Variability, Process (or Production/Construction) Variability, Sampling Variability and Testing Variability. Sampling and Testing Variability, combined, have been stated as comprising up to 50 percent of the total overall composite variation in test results from independent random samples. Instruction Review information on the slide. Engagement N/A
- #15: This table illustrates the variation associated with standard test procedures typically encountered in paving projects. Note that we are only interested in the actual materials variability and are constantly trying to improve the testing procedure to minimize all other sources of error. Precision and Bias considerations Established test procedures (ASTM, AASHTO) have accounted for test variability through precision and bias statements All physical tests have built in variability that must be accounted for in some manner
- #17: Performance based specifications for the following: Materials: Cementitious materials Aggregates Admixture Water Reinforcing Steel Dowel Bars Fibers Subbase materials Joint materials Designs and Systems: Pavement Life without major reconstruction Pavement Life with limited maintenance Pavement Life with cars only loads Pavement Life with heavy loads Prefabricated Pavement Systems
- #19: Welcome the audience
- #24: Same air content data that the class just plotted Note that the unit weight axis is in reverse order (heavier to lighter) – why would we do this? How are air content and unit weight related? What should the unit weight do as the air content increases? Unit weight should decrease