Effect of Mixture Design on Densification

Transcription

1 Effect of Mixture Design on Densification Louay Mohammad Louisiana Asphalt Technology Conference February 23-24, 25 Shreveport, Louisiana

2 Outline - Background -Objective - Scope - Mixtures Evaluation -Results - Concluding Remarks 2

3 Objectives of Mix Design Resist permanent deformation. fatigue cracking repeated load low temperature cracking moisture induced damage Resist skid Workability 3

4 Steps Involved in the Mixture Design 1. Materials Selection 2. Design Aggregate Structure TSR 3. Design Binder Content 4. Moisture Sensitivity 4

5 Superpave Mixture Design Concerns: Minimum VMA Criteria Difficulties Differentiate sound from unsound mixtures higher VMA mixtures Cannot guarantee Durable rut resistant V T VOL V V VMA V EAC air asphalt agg MASS 5

6 Superpave Mixture Design Concerns: Aggregate Properties/Gradation selection 95 percent Aggregate Specification Consensus ETG Little research Aggregate Structure/Mixture Design and Performance 6

7 Superpave Mixture Design Improvement: Design Aggregate Structure Mixture stability Rational approach to design aggregate structure based on principles of aggregate packing concepts 7

8 Objective Critically examine Superpave mixture design criterion Effect of NMS Aggregate Gradation and type 8

9 Scope Aggregate Types Two ` Sandstone, Limestone Aggregate Structure 12.5 mm NMS 25 mm NMS Aggregate gradation Coarse, Medium, Fine Bailey Method analytical method that enables blending aggregates using engineering principles and packing theory concepts 9

10 Scope Compaction Level 125 gyrations Binder Type PG 76 22M 1

11 Methodology Superpave Gyratory Compactor Densification Indices, Slope Locking Point Pressure Distribution Analyzer Frictional Indices, Locking Loaded Wheel Tester PMW 11

12 Combined Blend Gradation Sieve % Passing 1 9 A 1 B 97 C 76 D E 39 F 25 % Passing % Passing 7 6 G 17 H 11 I 7 J K Fine Coarse K J I H G F E D C B A Sieve Size (mm) Raised to.45 Power

13 Combined Blend Gradation % Passing % Passing Sieve % Passing A 1 B 98 C 85 D 72 E 58 F 4 G 32 H 21 I 12 J 7 K Fine Coarse K J I H G F E D C B A Sieve Size (mm) Raised to.45 Power

14 3/4" 14 Aggregate Gradation ½ SS /2" 3/8" No. 4 No. 8 Sieve Size No. 16 No. 3 No. 5 No. 1 No. 2 Percent Passing

15 1.5" 15 Aggregate Gradation 1 LS Percent Passing " 3/4" 1/2" 3/8" No. 4 No. 8 No. 16 No. 3 Sieve Size No. 5 No. 1 No. 2

16 Mixture Design Coarse Medium Fine Specs VFA Coarse Medium Fine LS.5 LS.5 SS 1 LS.5 LS.5 SS Coarse Medium Fine %Gmm, Ni 6 4 %AC LS.5 LS.5 SS. 1 LS.5 LS.5 SS

17 SGC Pressure Distribution Analyzer 1 22 Ht, mm FR, psi 17 Coarse Medium Fine No. Of Gyration No. of Gyrations 17

18 Superpave Gyratory Compactor Locking Point Number of gyration Ht specimen remains constant for three consecutive gyrations Ht, mm No. Of Gyration N. Gyrations Height, mm

19 Superpave Gyratory Compactor Locking Point Locking Point N. Gyrations Height, mm

20 Superpave Gyratory Compactor Slope % Gmm@ Ndes % Gmm@ Nini Log( Ndes) Log( Nini) % Gmm No. of Gyrations 2

21 Superpave Gyratory Compactor Compaction Indices 1 N= % TDI % Gmm 9 85 CDI Traffic Densification Index 8 75 Compaction Densification Index N= No. of Gyrations 21

22 Pressure Distribution Analyzer Measures the frictional resistance of mixtures during compaction Double plate assembly with 3 load cells equally spaced on the perimeter 22

23 Pressure Distribution Analyzer LC1 LC2 LC

24 Pressure Distribution Analyzer Frictional Resistance 22 FR, psi 17 Coarse Medium Fine No. of Gyrations 24

25 Pressure Distribution Analyzer Locking Point -Maximum interlock in the aggregate structure FR, psi Number of gyrations corresponding to the point of minimum rate of change in FR Coarse Medium Fine No. of Gyrations Rate of Change of FR Rate of Change of Frictional Resistance FR Locking Point No. of Gyrations 25

26 Pressure Distribution Analyzer Indices Frictional Resistance, psi N=1 Compaction Force Index N@FR Locking Point 2 gyrations No of Gyrations Traffic Force Index 26

27 Loaded Wheel Tracking Test 27

28 Loaded Wheel Tracking Test Four parameters (indices) are measured from the data collected in the HWT test - Post Compaction Consolidation - Inverse Creep Slope - Stripping Inflection Point - Stripping Slope 28

29 Superpave Gyratory Compactor Locking Point Spec 1" LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

30 Superpave Gyratory Compactor Locking Point % of Ndes 1" LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

31 Superpave Gyratory Compactor Compaction Slope " LS F 1" LS M 1"LS C 1/2" SST 1/2" SST M 1/2" SST C 1/2"LS 1/2"LS M 1/2"LS C

32 Superpave Gyratory Compactor Compaction Indices -- CDI " LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

33 Superpave Gyratory Compactor Compaction Indices -- TDI " LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

34 Pressure Distribution Analyzer FR Locking Point N des = " LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

35 Pressure Distribution Analyzer FR Locking Point % of Ndes 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C 1" LS F 1" LS M 1"LS C

36 Frictional Resistance Locking Point FR, psi USB19 BC 1" LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

37 Pressure Distribution Analyzer FR -- CFI /2"LS F 1/2"LS M 1/2"LS C 1/2" SST M 1/2" SST C 1"LS C 1/2" SST F 1" LS F 1" LS M

38 Pressure Distribution Analyzer FR -- DFI " LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

39 Relationship: No. of Gyrations SGC LP vs. PDA LP FR Locking Point y = 1.x - 4. R 2 = SGC Locking Point 39

40 Relationship: VTM SGC LP vs. PDA LP VTM at FR Locking Point, % y =.7x R 2 = VTM at SGC Locking Point, % 4

41 Relationship: VMA vs SGC CDI & TDI CDI 2 TDI VMA VMA Trends Increase VMA Higher CDI Lower TDI Is there a Min. VMA? 41

42 Relationship: Compaction Indices SGC CDI vs PDA CFI R 2 = CFI CDI 42

43 Relationship: Compaction Indices SGC TDI vs PDA TFI 45 R 2 =.19 TFI TDI 43

44 Relationship: SCG Compaction Slope vs. CFI R 2 =.9 CFI Compaction Slope 44

45 LWT Test Results " LS F 1" LS M 1"LS C 1/2" SST F 1/2" SST M 1/2" SST C 1/2"LS F 1/2"LS M 1/2"LS C

46 Relationship: Rut Dept vs. CDI & CFI HWT Rut, mm CDI HWT Rut, mm CFI 46

47 Relationship: Rut Dept vs. TDI & TFI HWT Rut, mm TDI HWT Rut, mm TFI 47

48 Relationship: Rut Depth vs. FR HWT Rut Depth, mm FR at Locking Point, psi 48

49 Relationship: LWT Rut Depth & Compaction Slope HWT Rut, mm R 2 = Compaction Slope 49

50 Conclusions - SGC densification curves can provide valuable information about mixtures behavior during compaction - CDI, Slope Coarse-grades mixtures had higher SGC LP 5% - 7% of N design Coarse-grades mixtures had higher Compaction Slope: 6-1 SGC CDI and PDA CFI indices were higher for Coarsegrades mixtures PDA measured LP showed similar ranking as SGC LP Lower FR increased with an increased in the NMS 5

51 Conclusions Good correlation was observed B/W SGC LP and PDA LP SGC CDI and PDA CFI SGC Slope and CDI SGC Slope and LWT rut depth Poor correlation was observed B/W SGC TDI and PDA TFI Mixtures evaluated performed well in the LWT 51

52 Thank You 52