2/5/2019 Mixture Design Part 1: Creating the Balance Shane Buchanan CRH Americas Materials Learning Objectives 1. Understand the concept of Balanced Mixture Design. 2. Review the most common performance tests (rutting and cracking) for BMD. Learn the current national state of practice for BMD. 3. 4. Understand how a BMD compares to a traditional volumetric design. 5. Discuss how acceptance testing can be conducted with a BMD system. 6. Learn how you can prepare for the future of asphalt mixture design. Discuss theory and reality pertaining to mix design. 7. What is Balanced Mix Design (BMD)? 1
2/5/2019 Balanced Mix Design Definition “Asphalt mix design using performance • tests on appropriately conditioned specimens that address multiple modes of distress taking into consideration mix aging, traffic, climate and location within the pavement structure .” • Use the right mix for the right job! Selecting the Correct Mix But if a Ferrari is needed, don’t Using the right mixture for the right job! provide a Pinto! Don’t design a Ferrari, if a Pinto will do the job! History of Mix Design • Barber Asphalt Paving Company B • Asphalt cement 12 to 15% / Sand 70 to 83% / Pulverized carbonite of lime 5 to 15% 1890 I N D • Clifford Richardson, New York Testing Company E • Surface sand mix: 100% passing No. 10, 15% passing No. 200, 9 to 14% asphalt R 1905 • Asphaltic concrete for lower layers, VMA terminology used, 2.2% more VMA than current day mixes or ~0.9% higher binder content C • Hubbard Field Method (Charles Hubbard and Frederick Field) O • Sand asphalt design Stability N 1920s •30 blow, 6” diameter with compression test (performance) asphaltic concrete design (Modified HF Method) T E • Francis Hveem (Caltrans) N • Surface area factors used to determine binder content; Hveem stabilometer and cohesionmeter used Stability + Durability T 1927 • Air voids not used initially, mixes generally drier relative to others, fatigue cracking an issue L • Bruce Marshall , Mississippi Highway Department O • Refined Hubbard Field method, standard compaction energy with drop hammer Stability + Durability W 1943 • Initially, only used air voids and VFA, VMA added in 1962; stability and flow utilized E R • Superpave 25 Years Without the Promised • Level 1 (volumetric) Performance Test! 1993 • Level 2 and 3 (performance based, but never implemented ) http://asphaltmagazine.com/history-of-asphalt-mix-design-in-north-america-part-2/ 2
2/5/2019 Why the need for BMD? Why the Need for a New Mix Design Approach? Problems: Dry mixes exist in some areas. Volumetrics alone can not adequately evaluate mix variables, such as recycle, warm-mix additives, polymers, rejuvenators, and fibers. Solutions: Recognize performance issues related to dry mixes in some 1. areas. (Note: Many performance issues are caused by factors outside the mix design.) Increase understanding of the factors which drive mix 2. performance Design for performance and not just to “the spec”. 3. Start thinking outside of long held “rules and constraints” 4. Innovate! 5. Importance of Quality Asphalt Mixtures Each day , approximately 1.4 Million tons of HMA are produced in the U.S. (M-F production basis) Equivalent to ~2500 lane miles @ 12’ wide and 1.5” thick Distance from New York to Las Vegas 3
2/5/2019 Pavement Performance General Overview Achieving Balanced Mixture Performance is Key to a Long Lasting Pavement What Type Distress Is Occurring? Source: Oldcastle Internal Survey Agencies are Searching for Solutions: Ndesign Many agencies are lowering design gyrations (Ndesign) Several states have selected one (1) Ndesign level for most all mixtures Alabama (60), Ohio (65), Tennessee (65), Virginia, (65, 50) Other states are still using excessively high Ndesign values (100+) Need to have sufficient gyrations for develop / engage aggregate blend structure. Too many gyrations result in breakdown and an unrealistically high target density (field compaction problems). Caution: Lower gyrations do not necessarily equate to more binder over the long term. 4
2/5/2019 What is the Main Key to Enhancing the Durability of Asphalt Mixtures? “ Volume of Effective Binder (Vbe) is the primary mixture design factor affecting both durability and fatigue cracking resistance .” Vbe = VMA – Air Voids “A number of state highway agencies have decreased the design gyration levels in an attempt to increase effective binder contents. However, decreasing the design gyrations may not always produce mixtures with higher Vbe.” Agencies Are Searching for Solutions: Spec Changes Which of the following specification changes has your DOT implemented Superpave system is becoming in the last 5 years? unrecognizable with specifications changing rapidly as agencies search for ways to improve durability Specifications have become convoluted and confounded Existing specified items compete against each other New requirements get added and nothing gets removed Establishing true “cause and effect” is impossible Source: Oldcastle Internal Survey What are the most common performance tests (rutting and cracking) for BMD? PERFORMANCE 5
2/5/2019 Main Pavement Distresses Observed in the Field Source: NCAT What Distress Does Your State Want to Address with Performance Testing? Source: NCAT Survey Test Mixtures in the Lab to Help Ensure Field Performance Mixtures need to be evaluated in the lab during design to help ensure the required field performance can be achieved. Lab Test (Hamburg Wheel Tracker) Lab Test Results Expected Field Performance 6
2/5/2019 Stability Testing (Rutting) Rutting Tests Rutting can be evaluated with several available tests based on the user preference. AMPT Flow Number / Hamburg Wheel Test (HWT) Asphalt Pavement Analyzer (APA) Dynamic Modulus Most commonly used tests. Hamburg gaining popularity due to moisture susceptibility analysis. Durability Testing (Cracking) 7
2/5/2019 Durability/Cracking Evaluation Durability/cracking evaluation is substantially more complicated than stability with aging being one main variable. No general consensus the best test(s) or the appropriate failure threshold. MANY different tests are available with more being developed. Main question is “ What is the anticipated mode of distress?” First Question for Durability Testing: What is the Anticipated Mode of Distress for Testing? Many test are available with each targeting a specific specimen response (i.e., field distress) Various empirical and mechanistic tests are available for use. Match apples to apples, not apples to oranges! = GOALS 1. MA TCH THE TEST TO THE DISTRESS 2. SET APPROPRIA TE FAILURE THRESHOLDS Fatigue (Bottom Up or Top Down) Related Cracking Tests Bottom Up / Bottom Up Bottom Up Bottom Up Top Down Bending Beam Fatigue Texas Overlay Test SCB Direct Tension Cyclic LTRC – Jc - Fatigue, S-VECD - IFIT 8
2/5/2019 Thermal Cracking Tests IDT Creep TSRST SCB at Low Temp Disk Shaped Compact Compliance Tension (DCT) Reflection (Reflective) Cracking Tests Disk Shaped Compact Texas Overlay Test SCB (IFIT) Tension (DCT) IFIT Overview Source: Brian Hill, Illinois Department of Transportation’s Implementation of I-FIT, NAPA Mid Year Meeting 2017 9
2/5/2019 IFIT Background Information IFIT 2 Americas Materials - Performance 8 IDEAL CT Background Information https://www.youtube.com/watch?v=OB 4pQDB2Yfs IDEAL CT - Similar to IFIT Time View: 0:40 to 1:40 - Uncut ! - 62 mm height specimen What is the current national state of practice for BMD? 10
2/5/2019 NCAT BMD Survey Results NCAT BMD Survey Results Illinois Balanced Mix Design • Phased implementation • Research started in 2012 • 26 Pilot projects 2016/2017 • All Interstate projects 2019 • Full implementation 2020 11
2/5/2019 Illinois BMD http://publish.illinois.edu/bituminous/files/2016/12/4.-Imad-Al-Qadi.pdf Louisiana Balanced Mix Design • Louisiana DOT has implemented BMD in the 2016 Standard Specifications for all DOT projects. + • Hamburg research began prior to 2000 • SCB research began in 2004 Hamburg Louisiana SCB New Jersey Balanced Mix Design • NJDOT High RAP Design incorporates BMD + Asphalt Pavement Texas Overlay Analyzer (APA) Tester 12
2/5/2019 Texas DOT Balanced Mix Design • TxDOT currently uses BMD for selected specialty mixes. • New SS 344 developed for Superpave BMD. • SS 344 allows TxDOT Districts to use on a case by case basis. + • Delta Tc (<6C) and Methylene Blue (<10) requirements • Grade “dumps” reduced • Simplified recycle material requirements Hamburg Texas Overlay Tester From Robert Lee (TxDOT, Now CRH) Texas DOT Balanced Mix Design Performance Crack Initiation Parameter Crack Propagation Parameter From Robert Lee (TxDOT, Now CRH) BMD Basic Example • Texas DOT • Volumetric design conducted • Hamburg Wheel Tracking Test (HWTT) AASHTO T 324 Overlay Tester (OT) Tex-248-F • Three asphalt binder contents are • used: optimum, optimum +0.5%, and optimum -0.5%. The HWTT specimens are short- • term conditioned. • The OT specimens are long-term conditioned. Within this acceptable range (5.3 to 5.8 percent), the mixture at the selected asphalt content must meet the Superpave volumetric criteria. 13
Recommend
More recommend
