Origin. Characterization of Stone Matrix Asphalt Mixtures and Comparisons to Hot Mix Asphalt Mixtures. Acknowledgements. SMA in the United States

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1 Characterization of Stone Matrix Asphalt Mixtures and Comparisons to Hot Mix Asphalt Mixtures Brian Pearson Washington State Department of Transportation Origin Europe introduced Stone Mastic Asphalt in the 1960 s To combat rutting caused by studded tires 48 th Idaho Asphalt Conference October 23, Acknowledgements SMA in the United States Washington State Department of Transportation Dr. Laith Tashman Dr. Balasingham Muhunthan Tim Moomaw Dr. Fouad Bayomy 1990 European Asphalt Study Tour. SMA = Stone Matrix Asphalt In 1991 the Wisconsin DOT was the first state in the U.S to implement SMA pavements. Today SMA is used by more than 28 states. 2 4

2 SMA in Washington State Characteristics of SMA (cont.) 1999 ~ SR th Ave West to I-5 in Lynnwood Performing well 2000 ~ I-90 Ritzville to Tokio (East of Ritzville) Extreme flushing in first year of service Removed and replaced with superpave 2001 ~ I-90 SR 21 to Ritzville (West of Ritzville) Performing well 2004 ~ I-90 Dodson Rd to Moses Lake (West of Moses Lake) Performing well 5 Stone-on-Stone Coarse Aggregate Skeleton Mechanical interlock to resist shearing Load transfer network SMA Asphalt Rich Mastic High Asphalt Content (>6.0%) High PG Grade Binders Small Percentage of Fines (< 30%) Mineral Filler (Fly Ash) Stabilizing Additive HMA 7 Characteristics of SMA Stone Matrix Asphalt Gap-Graded aggregate gradation Typically >70% retained above No. 4 High Quality Aggregates Percent Passing Power Chart for WSDOT ½ SMA Disadvantages Initial Costs 76% more than HMA Higher grades & percentages of binder Better aggregates Additional Materials (Flyash, Fiber) Longer mixing & placing times Labor intensive quality control. Advantages Lasts 25% to 50% Longer than HMA Rut-Resistant Increased Durability Better Skid Resistance 0 #200 #40 #8 #4 3/8" 1/2" 3/4" 6 8

3 SMA Mixture Design Specifications The Problem? Method is based on an Assumption from prior research and is an Indirect measure of the existence of a stone-onstone coarse aggregate skeleton Method Voids In Coarse Aggregate () Method is the current mix design procedure used to ensure the stone-on-stone coarse aggregate skeleton exists within SMA mixtures. DRC Perform AASHTO T-19 & T-85 MIX Calculate from volumetric properties of mix When Stone-on-Stone Contact Exists 10 Objective and Scope Experimentally verify current SMA mix design. Quantify existence of the stone-on-stone coarse aggregate skeleton using imaging technology (Direct Measure). Quantify the mechanical response (Performance-Based). Investigate the mix design inequality. Comparatively investigate differences in the mechanical response between SMA and HMA mixtures. 12

4 To help protect your privacy, PowerPoint prevented this external picture from being automatically downloaded. To download and display this picture, click Options in the Message Bar, and then click Enable external content. Asphalt Mixes I-90 Moses Lake West Paving Contract 6687 Constructed in 2004 SMA vs. HMA Gradation 100 EASTBOUND SMA ½ PG Mill & Fill 21,617 tons $41.50/ton WESTBOUND HMA ½ PG Mill & Fill 37,040 tons $23.50/ton Percent Passing Sieve Size (mm) SMA HMA MDL Materials and Mixture Design Experimental SMA Mixture Designs Stone Matrix Asphalt Gradation blended from 4 aggregate stockpiles 3/4 No.4 3/8 0 1/2 No. 4 Type F Flyash Optimum AC of 6.3% PG % Fiberand Mineral Road Fibers Hot Mix Asphalt Gradation blended from 2 aggregate stock piles 3/4 No.4 3/8 0 Optimum AC of 6.0% PG Modified SMA JMF to produce two alternative gradations Gradation simulate possible variations that could be experienced during construction. From the 3 gradations, 5 mixtures were designed 14 *Optimum asphalt content for the gradation 16

5 SMA Mixture Design Gradations Method Conduct method and present results as the Ratio Ratio MIX DRC Quantitatively characterizes the Method Provides insight towards the extent of contact ratio > 1: Insufficient skeleton ratio < 1: Stone-on-stone skeleton exists Specimen Preparation X-Ray CT and Image Analysis 10 SMA specimens prepared 2 of each mixture design X-Ray images every 0.25 mm 600 images/specimen Compacted Specimen 150 mm diameter 170 mm height Target %AV 9.5% Measure the area of each air void within each image Analyze the air void size distributions Cut/Cored Test Specimen 150 mm height 100 mm diameter %AV of 7.5%0.5% 18 Air Void 20

6 Packing of Granular Materials Granular materials achieve higher degrees of packing when smaller air voids exist within the microstructure (Watson et al., 2004). Asphalt mixtures with high degrees of packing have increased particle interlock. Simple Performance Tests Unconfined Dynamic Modulus Test 6 loading frequencies and 4 temperatures: Frequency: 25, 10, 5, 1, 0.5, 0.1 Hz Temperature: 4.4, 21.1, 37.8, 54.4C Master curve constructed at 21.1C. Unconfined Static Creep Test Static load applied until strain reached 70,000 microns. Poorly Packed Well Packed Characterization of Packing Dynamic Modulus Characterization Weibull distribution model approximates air void size distribution within asphalt mixtures (Masad, 2002). Least square method was used to fit the Weibull distribution model and quantify the packing of the material. F( x) 1 e x Sigmoidal function approximates master curves of asphalt mixtures (Witczak et. al 2002). Least square method was used to fit the sigmoidal function and quantify the performance of the material. log( E*) (logt ) 1 e r 22 24

7 Static Creep Characterization Method Typical static creep analysis of the viscoelastic compliance was used to fit the power model and quantify the permanent deformation behavior of the material. V > 0 V = 0 D' m t D t D at 0 D (t) = D(t) - Do Primary Zone Secondary Zone D' t m at Tertiary Zone FT 25 Time 27 Air Void Size Distribution The Results 28

8 Relationship with Ratio F( x) 1 e x Relationship with Ratio log( E*) (logt ) 1 e r If, Packing Ratio MIX 1 DRC If, Performance If, Performance 29 Ratio MIX 1 DRC 31 Dynamic Modulus Master Curves Static Creep Ratio MIX 1 DRC D' t at m 30 If a, Rutting Performance If m, Rutting Performance Flow time, Rutting Performance 32

9 Combine Packing & Performance Dynamic Modulus Comparison Packing HMA SMA Performance High Temperature Low Temperature SMA vs. HMA Performance Static Creep Comparison SMA JMF6.3-R1 HMA S1-100/150C a, Rutting Performance m, Rutting Performance F t, Rutting Performance HMA SMA 34 36

10 Conclusions (cont.) Quantifying the method with the Ratio was advantageous as it provided the relative amount of stoneon-stone coarse aggregate contact. Ratio MIX DRC X-Ray CT successfully quantified the microstructure to give direct measures of packing. Conclusions (cont.) The performance of SMA and HMA to resist fatigue and thermal cracking were found to be nearly identical. SMA lived up to its reputation of being superior to resisting rutting over its opposition (HMA). Dynamic Modulus and Static Creep provided critical measurements of SMA performance and the adequacy of the stone-on-stone coarse aggregate skeleton Conclusions (cont.) Questions? method is a simple way to reasonably identify mixtures with a stone-on-stone coarse aggregate skeleton. However Ratio MIX 1 DRC 0.98? SMA mixture design lacks a performance test to complement the methodology, i.e. the existence of the skeleton does not necessarily ensure good load carrying capacity. Contact Information Brian Pearson Washington State Department of Transportation pearsob@wsdot.wa.gov