Estimating the effect of warm mix additives on workability of asphalt mixtures

Transcription

1 Estimating the effect of warm mix additives on workability of asphalt mixtures Hussain U. Bahia, Andrew Hanz, & Enad Mahmoud University of Wisconsin, Madison ISAP Workshop, Fortaleza, CE, Brazil, October 5 th 2009

2 Two Main Objectives Evaluate claims about how Warm Mix Additives (WMA) work. Reducing viscosity Micro-foaming Lubrication Determine how much is needed. WMA content versus temperature reduction Cost is based on content, justify use by saving heat energy

3 Experimental Design - Materials Five Warm Mix Additives: Two surfactants: Revix and Rediset, One wax additive (Sasobit), and Two foaming processes. Two base binders: Unmodified d PG64-22 and SBS modified PG Two Mixture Gradations: Fine and Coarse

4 Aggregates and Mixtures Mixture testing Fine and Coarse graded mixes 10 million ESAL, mix design (N des =100) Granite aggregate source

5 Experimental Plan - Testing Binder Workability: Asphalt Binder Viscosity Rotational Viscometer Asphalt Binder Lubricity New DSR test Mixture Workability: Aggregate Coating: Percent Coated Gyratory Compaction Indices: > Construction Force Index using he PDA - (CFI) > Number of Gyrations to 92 % Gmm- N92

6 Effects on Viscosity PG ,00 PG76-22 Viscosity vs. Shear Rate 90 C 10,00 Change in η due to temperature. Visc cosity [Pa.s] 1,00 Change in η due to additive relatively small. 125 C 150 C PG76 Control Sasobit - 2% Surfactant - 0.5% 0,10 0,10 1,00 10,00 100,00 Shear Rate [1/s]

7 Asphalt Lubricity Test Based on ASTM D for lubricants (Determination of the Coefficient of Friction of Lubricants Using the Four Ball Wear Test Machine) Assumed Mixture Regime Friction as a function of viscosity (Z), pressure (P), and speed (N). Measurement Tool

8 Asphalt Lubricity Test: - Photo of new fixture for DSR Tip of Rotating Chuck Clamped Ball Assembly Coefficient of Internal Friction Entire Assembly (no clamping)

9 Effects on Asphalt Lubricity Initial Results 0.17 Coeffice ent of Fric ction Neat Neat PG Neat PG Revix PG Neat PG Revix PG Rediset Temperature [C]

10 Aggregate Coating (coarse mix) (the AASHTO T195 procedure ) PG 64-22

11 Aggregate Coating (fine gradation) Δ T = 30+ degc 40% More coating Neat 76-22

12 Coating of Aggregates as a function of Binder Viscosity it Vi it R i d f 95% C ti ~ 350 P Viscosity Required for 95% Coating ~= 350 cps (This is for 90 secs (1.5 min) mixing )

13 Use of the Gyratory Compactor with the PDA to Measure Resistance to Compaction 13

14 Use of the Pressure Distribution Analyzer to Calculate Resistance to Densificatuon Mold R e Ram r y P 1 e y x HMA Sample o 1.25 GLPA P o O e e x P 3 R = P 1 + P 2 + P 3 M(t) = R * e(t) x e = M M y e = 0y e = 0 e 2 x + (r y y x e y ) 2

15 Mixture Compaction- Densification Measured in Gyartory + PDA Mold R e Ram HMA Sample GLPA PDA Plate CFI o 1.25 N R = P 1 + P 2 + P ini Gyr. to 92% 3 Gmm M(t) = R * e(t) Pressure Distribution Analyzer (PDA) allow for Calculating resistive forces in the mix during compaction (w) Construction Force Index (CFI) : area under the Resistive Force (w) vs. Gyration curve

16 Effects of WMAs on CFI (Mixture Workability) HMA Major WMA effects are measured only below 100 ο C for foaming and Revix. Rediset (2% by wt. of binder) shows higher effects at all temperatures.

17 Regression Results (Compaction Force Index) Regression Analysis: CFI = F(Coef Fric, Visc, Bet a) CFI = Coef Fric Visc Beta Predictor Coef SE Coef T P Constant Coef Fric Binder Lubricity Visc Bet a Agg. Gradation

18 Gradation Analysis and Modeling Higher β Weibull distribution

19 Regression Results (CFI)

20 Interim Findings Warm Mix Additives affect coating and compaction. Minor reduction in viscosity Important effects on lubricity (Internal resistance to flow) Main effects are at lower temperatures ( Below 100 C). Cost need to be justified by energy savings or environmental impact.

21 Warm Mix Additives Effective Range Fuel /T Ton Emissi ons/to Ton Source: FHWA

22 Acknowledgments Organizing Committee Professor Soares and Sponsors Federal Highway Administration Western Research Institute Suppliers of additives

23 Thank you for attending UW-Madison Chicago X