Use of Additives and Fillers in Hot- Mix Asphalt

Transcription

1 Use of Additives and Fillers in Hot- Mix Asphalt Cassie Hintz, Ahmed Faheem, & Hussain U. Bahia University of Wisconsin Madison CUPGA 2010 WORKSHOP PROGRAM November 28, 2010, Edmonton, Canada

2 Research Team NCHRP Project 9-45 Results are based on NCHRP Project : Test Methods and Specification Criteria for Mineral Filler Used in HMA Research Team: MTE - Gerry Reinke and Erv Dukatz UIUC - Imad Al Qadi UW-Madison - Ahmed Faheem, Cassie Hintz & Hussain Bahia

3 Do binders or mastics control HMA perfromance? Fillers & modifiers affect all aspect of mastic behavior Stiff particle In Collaboration with Prof. Rod Lakes UW- Madison

4 Problem Statement: Predicting effects of fillers + modifiers Fillers vary in their effects on bitumen properties Einstein Model for Diluted Composites (1911): η r = 1 + K E ø η r = Viscosity of mastic/ viscosity of matrix (Binder) K E = Einstein Constant ~2.5 Ø: Filler volume fraction Many modification to this equation have followed based on the type of both the filler and binder. η r Ø Fillers Effects Vary

5 Basic Concept of Study: Fillers Interaction with Binders (Tunnicliff in 1960) Gradient of stiffening Important Filler Properties: 1.Geometry, and 2.Composition 1. Filler 2. Asphalt adsorbed layer 3. Asphalt layer affected by adsorption

6 Important Filler Properties 1. Geometry Fillers geometry can be defined by four measurements: Size, shape, angularity, & texture. Last 3 are difficult to measure individually. Two primary can be measured Fractional Voids (FV) Size Distribution and Surface Area Two Secondary Absorption Specific Gravity

7 Rigden Voids -- Fixed & Free binder Fractional voids content Volume percentage of voids in a dry, compacted filler sample fractional voids is a measure of the interactive effect of size, shape, texture, and angularity on stiffening of binders Higher Rigden voids leads to higher stiffening of binder

8 RIGDEN VOIDS (BS 812, EN )

9 New Rigden Voids Device by Gilson

10 Important Filler Properties 2. Composition There appears to be a small number of chemical compounds that affect asphalt-filler interactions. Two main properties are important: Reactivity Calcium compound. Water solubility. Harmful fines Active Clay Content. Organic Content.

11 Filler Mineralogical Types Selected Natural Fillers Imported Fillers Filler Type 1.Andesite 2.Basalt 3.Caliche 4.Dolomite 5.Granite 6. Limestone 1.Hydrated Lime 2.Fly Ash 3.Slag

12 Rigden Voids(%) Distribution of Rigden Voids Can be group by Minerlogy Average 25

13 Composition Variation of Fillers Filler Type Al2O3 CaO FeO K2O MgO SiO2

14 Asphalt Binders for Producing Mastics (a) PG with low asphaltenes (from a light crude source) (b) PG with high asphaltenes (from a heavy crude source) Binder (a) modified with PPA to a PG Binder (a) modified with SBS to a PG All mastics prepared at 1:1 ratio by mass

15 Volume Fraction (%) Distribution of Volume 1:1 ratio by mass One Standard Deviation (0.01) Average

16 G* Ratio Complex Modulus of Mastics Relative G* of Binder "A" Mastics Dolomite Hydrated Lime Fly Ash Limestone Granite Filler Volume Fraction (%)

17 Mastic & Mixture Testing and Analysis of Results

18 Mastic Properties Measured 1. Workability measure: 2. Rutting: 3. Fatigue: Viscosity: 135 C at 1 50 RPM Jnr, %Recovery, 58 C, 64 C, at 0.1, 3.2,10kPa G*.Sinδ, and Time Sweep, 25 C and 10Hz 4. Low Temp Cracking: S, m, at -12 C, Cracking temperature (ABCD) 5. Moisture Damage Pull Off Test, 24hr moisture conditioning at 60 C

19 Jnr (1/kPa) J nr at 58 C and 3.2kPa Compare effects of modifiers + fillers PG 64 PG 76 PPA SBS Valero 0.1 Increasing Rigden Voids

20 Jnr (1/kPa) J nr at 58 C and 3.2kPa Effect of Rigden Voids Increasing Rigden Voids Flint Hills PPA SBS Valero 0.1 Valero R² = 0.66 Flint Hills R² = 0.86 PPA R² = 0.88 SBS R² = 0.10

21 Prediction of Mastic Jnr The best fit regression equation at ( 1:1 binder to filler) is: Mastic Jnr = Binder Jnr Rigden Voids Predictor Coef SE Coef T P Constant Binder Jnr Rigden Voids S = R-Sq = 74.7% R-Sq(adj) = 72.7%

22 Mixture Flow Number Effects on Mixture Rutting Results Measured by FN (Coarse Mixtures) Coarse: Correlation Between Mixture and Mastic Rutting Indicators y = x R 2 = Mastic Jnr (1/kPa)

23 Deriving Mastic Jnr Limits For Acceptable Rutting Resistance Mixture (FN) Limits derived from NCHRP 9-33 Recommendations: Traffic Level (Million ESALs) Minimum Flow 200kPa < to < to < 30 1, ,400 Corresponding Mastic Jnr Limits: Mixture Gradation Maximum Mastic Jnr at 3.2kPa (1/kPa) Fine 0.41 Coarse 0.62

24 Limits on Measured or Predicted Mastic Jnr 3.2 Kpa) Propose limits on Mastic Jnr as measured or predicted. Jnr < 0.5 1/Kpa Best fit regression analysis: Jnr (mastic) = Binder Jnr Rigden Voids Volume Fraction Predictor T P Constant Binder Jnr Rigden Voids Volume Fraction S = R-Sq = 70.9% R-Sq(adj) = 69.5%

25 Effects on Low Temperature Cracking Measured 1.S, m for mastics 2. Creep Stiffness and Strength for mixtures

26 Stiffness at -12 C MPa Mastic Stiffness at -12 C Increasing Rigden Voids Flint Hills PPA SBS Valero

27 m-value at -12 C Mastic m-value at -12 C Increasing Rigden Voids R² = 0.03 Flint Hills PPA SBS Valero

28 Relative m-value at -12 C Relative m-value at -12 C 1.2 Increasing Rigden Voids Flint Hills PPA SBS Valero

29 ANOVA Analysis for Mixture Stiffness at -12 C Variable F-Value P-Value Gradation Binder Source Binder Modification Filler Mineralogy R 2 = 62.31% Binder type (source) & aggregate gradation are most important. Binder modification and fillers are insignificant. Some fillers may negate or even reverse the effect of the binder modification ( e.g. PPA binder with soft limestone).

30 ANOVA Analysis for Mixture Strength at -12 C Variable F-Value P-Value Gradation Binder Source Binder Modification Filler Mineralogy R 2 = 39.80% Binder modification is the most significant factor while filler effects are only marginal.

31 Summary of Rutting Results Mixture rutting resistance is highly affected by the following factors: Binder modification (Jnr), Filler Rigden voids and volume fraction. SBS has the strongest interaction with fillers, while PPA has the lowest. In some combinations, filler effects are higher than modification effects (e.g. PPA). Focusing on mastic Jnr could a better approach.

32 Summary of Low Temperature Stiffness and Strength For mixture stiffness, modification and filler properties are insignificant. For mixture strength, modification is important while filler properties are not.

33 So, What s New? Measure Rigden Voids Measure Specific Gravity Change mixture design procedure to include Volume fraction of fillers rather than dust to binder ratio Caution about modifiers and fillers combinations

34 Acknowledgment CUPGA Organizers Mr. Nabil Kamel for the invitation NCHRP Dr. Ed Harrigan and the Project Panel Asphalt Research Consortium- FHWA. WRI uwmarc.org

35 Strain (mm/mm) Binder Rutting: Repeated Creep Test Results 5.50 Jnr: Non-recoverable Creep Compliance = Strain (NR)/Stress B 6281 (PG74-28) B 6289 (PG74-31) Binder with high Jnr Limited Recovery ALF 15.7 mm rutting Time, sec Time (s) Binder with low Jnr High recovery ALF mm rutting (Delgadillo 2005, also MSRC- D Angelo s FHWA team)