SEAUPG 2004 Conference - Baton Rouge Polymer Modified Asphalts

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1 SEAUPG 24 Conference - Baton Rouge Investigation of the Use of Recycled Polymer Modified Asphalt in Asphaltic Concrete Pavements Chris Abadie for Dr. Mohammad Louisiana Transportation Research Center Presentation Outlines Background Objective Laboratory Testing Discussion of Test Results Conclusions 24 SEAUPG Annual Meeting November 5-8, 24 Baton Rouge, Louisiana Background Polymers modification of asphalt binders increases fatigue life of mixture reduces the extent of permanent deformation improves thermal cracking resistance improves moisture sensitivity and reduces age hardening Initial success prompted LA DOTD and other states to require that polymers be incorporated into asphaltic pavements. Background Late 98s: PMAC pavements were built 994: LDOTD adopted the use of PMAC in most of its HMA pavements Rehabilitation stage Residual polymer additives Concentration Characterization Contribution Evaluate the fundamental characteristics of recycled polymer modified asphalt pavements Objective is to answer the question, can you recycle polymer modified asphalt? Characterize the rheological properties virgin polymer modified asphalt cement (PMAC) field aged PMAC (RPMAC) Blends Evaluate mixture performance properties containing various percentages of RPMAC Materials (a) Binder Types A SBS elastomeric polymer-modified asphalt cement (PMAC) - AC-3 + 3% SBS by weight. - meeting Louisiana DOTD specifications for PG A reclaimed PMAC binder (RPMAC) - eight year old PMAC binder wearing course from Highway US 6 4 binder blends Blend : % PMAC Blend 2: 8% PMAC + 2 % RPMAC Blend 3: 6% PMAC + 4 % RPMAC Blend 4: 4% PMAC + 6% RPMAC Page

2 SEAUPG 24 Conference - Baton Rouge Materials (b) Asphalt Mixtures Four 9 mm-superpave Mixtures with different binder types but same crushed limestone aggregate and gradation Aggregate Structure 25% No. 67 LS 25% No. 78 LS 45% No. LS Percent Passing % Sand.75 (2) 4.75 (4) 9.5 (3/8) 2.5 (/2) 9. (3/4) 25. (.) mm (inches) Sieve Sizes 9 mm Superpave Volumetric Properties Properties %AC 4.2 %AV 3.8 %VMA 3.7 %G mm, Ni 85.5 %G mm, Nf 97.5 Aggregate Properties FAA 48 SE 74 F & E 2 CAA Spec 3 5 > 3 < 89 > 89 45%, min 45%, min %, max 95/ Gyrations N i 9 N d 25 N f 25 Asphalt Binder Test and Results Asphalt Binder Tests Extraction process: Soxhlet Extraction Apparatus Binder Tests Extraction Dynamic Shear Rheometer (DSR) Bending Beam Rheometer (BBR) Condenser Extractor Core sample Toluene Flask Page 2 2

3 SEAUPG 24 Conference - Baton Rouge Material characterization - DSR Thermal Transitions of Asphalt Binder G*/sind, Pa 6 TANK PAC 4 EXTRACTED BINDER FROM AGED MIX CONTAINING PAC-4 PAV-AGED PAC-4 BINDER B 5 A Temperature, o C SAMPLE AC-3 PMAC PAV-PMAC US6 Binder 2% US6 4% US6 6% US6 Tg C < Binder Test Results (Table) DSR Test Results G*/sin(delta), kpa Original Binder G*sin(delta) at 25C, kpa PAV-Aged Binder 2% 4% 6% 2% 4% 6% BBR Test Results BBR Stiffness (-2C), MPa PAV-Aged Binder 2% 4% 6% BBR Mvalue (-2) PAV-Aged Binder 2% 4% 6% Mixture Test Results Page 3 3

4 SEAUPG 24 Conference - Baton Rouge Mixture Performance Tests Repeated Shear at Constant Height (RSCH), 6C Indirect Tensile Creep (ITC) test, 4C Indirect Tensile Strength (ITS) test, 25C Semi-Circular Bend (SCB) test, 25C Indirect Tensile Strength Test Test Protocol Cylindrical Specimen: mm x 63.5mm 5.8 mm/min vertical deformation rate Temperature: 25C Analysis: ITS ITS S T 2 Pult = π t D Indirect Tesile Strength, PSI Strain, % Indirect Tensile Creep Test Test Protocol Cylindrical Specimen: mm x 63.5mm Creep Load: 2.5 N (25lb) Compressive load Creep Time: 6 min. or failure. Temperature: 4C Creep Slope Creep Modulus CS ( T ) = 3.59 P t δv ( T ) Where: C(T) creep modulus at time T, MPa, P applied vertical load, N, t sample thickness, mm, and δv(t) vertical deformation at time T, mm. Log of Creep Modulus, C(t).. Creep Slope IT Creep Test-A-3 Creep Slope =.52 Time to Failure (Hdef=. in) = 46 sec log(c(t)) = -.52 * log(t) Coef of determination, R-squared = Log of time (t) seconds Repeated Shear at Constant Height Test Protocol (AASHTO TP7) Cylindrical Specimen: 5mm x 5mm Stress-controlled test Haversine load: 68kpa,.s load time, and.6s rest time Up to 5 cycles Temperature: 6C 68 Cumulative Permanent Shear Strain γ 2 = δ h / d Where: δ h - the cumulative permanent shear displacement at 5, cycles d - the distance over which shear deformation is measured or gage length. Shear Stress, kpa. Axial Stress, kpa..7.4 variable magnitude to keep specimen height constant.7.4 Time, sec T Semi-Circular Bend (SCB) Test Sample Geometry 5mm X 57mm Four specimens Three notch depths 25.4 mm 3.8 mm 38 mm SCB Test (Contd( Contd ) Loading rate.5 mm/min load and deformation are recorded Test temperature 25 o C Triplicate Deflection (mm) notch a notch a2 Page 4 4

5 SEAUPG 24 Conference - Baton Rouge Determination of J c 35 Determination of J (Contd ) c J c = U 2 U U b Deflection (mm) U 2 b a a 2 2 notch a notch a2 U is the total strain energy to failure Jc: the critical strain energy release rate 3 25 U mm notch mm notch 5 38 mm notch Deflection (in.) Notch (mm) Indirect Tensile Strength Indirect Tensile Strain IT Strength(Kpa) % 2% 4% 6% Percent of US6 Binder Strain (mm/mm)% % 2% 4% 6% Percent of US6 Binder Compliance Slope, log(psi)/log(sec) IT Creep Test % 2% 4% 6% Percent of US6 Binder Permanent Shear Starin, mm/mm Repetitive Shear at Constant Height (RSCH) % 2% 4% 6% Percent of US6 Binder Page 5 5

6 SEAUPG 24 Conference - Baton Rouge SCB Test Results Jc vs. Percent of RPMAC.4.2 % 2% 4% 6% y=-.34x+.5 y=-.7x+.97 y=-.28x x y = R 2 =.8988 R 2 =.8225 R 2 =.996 R 2 = Notch (mm) Critical Fracture Resistance, Jc, (kj/m 2 ) % 4% 6% Percent of RPMAC J c (kj/m 2 ) Comparison of the Critical Jc for various asphalt mixtures % 2% 4% 6% Current RPMAC Study PG CRA PG Mull et al., 22 AC-5 + 9% SEBS.42 AC-5 + 2% Elvaloy.4 Bhurke et al., 997 Summary and Conclusions Use of RPMAC in HMA was investigated Field aged binder was extracted from 8 year HMA WC mixture Blends: -, 2-, 4-, 6-percent RPMAC Procedures were developed to separate the PMAC into its asphalt resin and polymer additive components Impact of the extraction and recovery process on binder properties has been found to be minimal Summary and Conclusion Conclusion US6 binder exhibited higher extent of oxidation than the PAV-aged PMAC Increasing of the percentages of US6 binder in mixtures increased the rutting resistance, as evidenced by RSCH, APA and IT Creep test results. SCB test provides a simple means to obtain fracture resistance characterization of asphalt mixtures The critical Jc values are found fairly sensitive to changes in binder stiffness. As more RPMAC added, its stiffening effect overcame that of the new control modified binder. This has resulted in an increase in the values of strain energy to the failure, U, and the critical value of fracture resistance, Jc, which represents an improved fracture resistance of the RPMAC mixtures. Page 6 6

7 SEAUPG 24 Conference - Baton Rouge Summary and Conclusion Future Work It appears that the 6% RPMAC mixtures have a better fracture resistance than %, 2% and 4% RPMAC mixtures Similarly, the % RPMAC mixtures seems to have a better fracture resistance than 2% and 4% RPMAC mixtures The ranking order based on Jc values is different from that based on ITS test results. Produce blends with softer binders Sufficient polymer impact Validate blending charts Durability Acknowledgement Louisiana Education Quality Support Fund Louisiana DOTD Koch Materials Thank You Possible Explanation The sudden drop of the J c value from % to 2% could be due to, the RPMAC at low concentrations may be incompatible with the controlled elastomeric modified binder PMAC discontinuity in binder blend could be created, which can weaken the adhesive and cohesive properties of the binder and promoted the crack propagation in the mixtures. As more RPMAC added, its stiffening effect overcame that of the new control modified binder, which is accompanied by an increase in the maximum sustained load and slight decrease in the deflection at maximum load. The increased load and small decrease in deflection will result in an increase in the values of strain energy to failure, U, and eventually a higher Jc value. Page 7 7