EVALUATION OF USING RECLAIMED ASPHALT PAVEMENT (RAP) AS UNBOUND BASE AGGREGATE LAYER

Transcription

1 EVALUATION OF USING RECLAIMED ASPHALT PAVEMENT (RAP) AS UNBOUND BASE AGGREGATE LAYER Burak Tanyu (Associate Professor at George Mason University) Saad Ullah (Graduate Research Assistant at GMU) Edward Hoppe (Associate Principal Research Scientist at VTRC) Dec. 06, 2018 (Presented at the 2018 Virginia Asphalt Conference & Expo)

2 Base layer intended in this study Base Layer Free Draining Strong Unbound Aggregate Asphalt Layer Subgrade (or subbase) (not to be confused with the base of the asphalt layer) 2

3 Introduction RAP is currently being used in VA. Principally for the production of new asphaltic mixtures. Reclaimed Asphalt Piles Recycling/Processing Reclaimed Asphalt Degraded Asphalt Pavement New Pavement with Recycled Asphalt 3 VDOT allows up to 30% RAP content in new HMA mixtures. However there is still excess RAP within the State.

4 According to VTRC study in 2015, there is approximately 4.7 million tons of excess RAP stockpiled in VA. Stockpiles require maintenance and real estate Both of these aspects have economical implications 4 Approximate locations of RAP Stockpiles in VA

5 Recommendation for additional RAP usage: Use of RAP as base material in pavement structure (VTRC Report No. 15-R6, 2015) Up to 30% in material cost savings if approximately 50% RAP is allowed for use as unbound base material (after 2015 VTRC report) 5 5

6 Research Objectives Main Objective To evaluate the means to be able to use RAP as an unbound base course aggregate. If successful, the over arching goal is to provide an additional means to recycle RAP in VA to help deplete the stockpiles and be able to apply the findings to the entire asphalt industry in VA. 6

7 Research Objectives Important to note: To objective is not: to restrict the use of RAP to only one mode and to develop set of road maps that only apply to some asphalt plants but not all 7

8 Research Approach Characterize the make-up of the reclaimed asphalt stockpiled in VA Develop guidelines to be able to use the reclaimed asphalt to construct unbound base layer Evaluate tools to provide means for quality control during construction/implementation Demonstrate the use so that it can lead into revising VDOT specifications for State wide implementation 8

9 Necessity to Conduct this Research Not all asphalt mixtures created the same way RAP is a reclaimed asphalt (original properties of the asphalt shapes up the properties of the RAP) Previous studies: primarily focus on mixing RAP with virgin aggregate (do not include an evaluation based on binder content) evaluate different gradations of RAP (particle size distribution) and mixing approaches. Results are conflicting. How much of those findings really apply to the asphalt produced in VA? do not provide a good path for quality control during construction and without this ability, it is not possible for the material to be constructed in DOT projects in VA 9 A demonstration that is well documented under VDOT s jurisdiction is needed to evaluate the suitability of using RAP in the base course

10 Evaluating the Make-up of the RAP Piles in VA 10

11 Met with VA Asphalt Association members. Discussed details of processing RAP to be recycled in re-creating asphalt. To minimize complexities to the industry, it is agreed that this research will focus on evaluating fine processed RAP (100% passing 0.5 inches). Fourteen different plants (owned and operated by different entities and located at different parts of VA) have been visited to obtain RAP samples. All samples have been evaluated for the variation of binder content, grain size distribution, and specific gravity (provides clues about the differences of geological composition of the aggregate in RAP). 11

12 Locations visited Loc. 8: Ashburn Loc. 6: Herndon Loc. 5: Chantilly Loc. 2: Gainseville Loc. 9: Alexandria Loc. 1: Manassas 1 Loc. 3: Manassas 2 Loc. 4: Warrenton Loc. 7: Bealton Loc. 10: Stafford Loc. 13: Mitchells Loc. 11: Fredericksburg Loc. 14: Southern Virginia 1 Loc. 12: Southern Virginia 2 12

13 Percent Passing (%) 1 1/2" 3/4" 1/2" 3/8" Gradation of all RAP samples Mechanical Sieve Analysis Coarse Fine Coarse Medium Fine Silt Clay Gravel Sand Fines 3" 2" 1" #4 #10 #20 #40 #60 #100 # RAP 1 RAP 2 RAP 3 RAP 4 RAP 5 RAP 6 RAP 7 RAP 8 RAP 9 RAP 10 RAP 11 RAP 12 RAP 13 RAP Particle Size (mm)

14 Binder Percent (%) Specific Gravity Binder content and specific gravity of all RAP samples Binder Content & Specific Gravity Test Results Mean Specific Gravity (RAP) Mean Specific Gravity (Parent Rock) RAP Sample Locations 0

15 Findings Binder contents varied from one location to another The median range for binder content throughout the State is found to be between 4.53 and 5.86 % Considering the variation of the piles from one location to another, overall grain size distributions throughout the State appeared to be fairly uniform Specific gravity and evaluation of the make-up of the aggregates after ignition of binder revealed that majority of the RAP in VA contains diabase 15

16 Developing Guidelines To Use RAP in Unbound Base Layer 16

17 Bases for this evaluation Design the pavement structure as usual based on 100% virgin aggregate for the base course Compare the engineering properties of the virgin aggregate that will be used in construction to the RAP/virgin aggregate (V.A.) blend Determine a threshold for blending RAP based on comparison of the engineering properties of the virgin aggregate 17

18 Challenges with this evaluation Typically the design parameters for virgin aggregate base course is obtained from CBR test (not very accurate method) Alternatively, resilient modulus tests may be conducted. Only considers the elastic properties and with RAP, the more RAP is blended with V.A. the better the modulus becomes. Does this mean we should keep adding RAP to virgin aggregate? No, because as the RAP percentage increases, the blend becomes more prone to deformations (displacements). 18

19 Method to compare virgin aggregate and RAP blends Permanent deformation test GMU testing protocol Simulated typical wheel load pulse Stress conditions associated middle of base course for a pavement profile of 3-in HMA and 8-in base Evaluated conditions based on 100,000 load cycles Cyclic load test No ASTM standard (need to be custom designed) May evaluate both elastic and plastic deflections Deviator stress, confining stress, load pulse type, number of cycles all can be adjusted 19

20 Method to compare virgin aggregate and RAP blends In addition to permanent deformation tests, all blends have also been evaluated based on: Compaction tests (both proctor and vibratory tests) California bearing ratio (CBR) Resilient modulus 20

21 Materials used in this evaluation Three different types of fine-processed RAP evaluated High binder content: 5.6 to 5.8% Middle range content: 5.1 to 5.3% Entire range in Virginia Low binder content: 4.5 to 4.7% Virgin aggregate with VDOT 21A gradation (V.A.) Blends of V.A. and RAP for each binder content created based on: 20% RAP 30% RAP 40% RAP 50% RAP 60% RAP 21

22 Blending RAP with virgin aggregate Two different blending approaches followed: Approach 1: Mixing RAP and V.A. based on weight (As-Is Gradation) Approach 2: Mixing RAP and V.A. based on target gradation regardless of the RAP / V.A. content (Engineered Gradation) 22

23 As-is Gradation (Each blend have unique gradation) 23

24 Engineered Gradation (All blends have the same gradation) Based on Fuller and Thompson approach % Passing at given sieve = 100 ( aperture sizeτmax particle size ) 24

25 Findings Engineered gradation is a better approach to study the effect of binder content and RAP percentage, because in all samples the gradation is the same Engineered gradation is not practical to create in the field Engineered gradation results showed: increase in RAP percentages increases deformations and in all cases, deformations of RAP blends are higher than 100% VA. This would limit the use of RAP completely As-is gradation results showed: it is possible to develop a limit that allows the use of RAP but both binder content and RAP percentages have to be evaluated 25

26 Findings Application of implementing as-is gradation in the field is confirmed Two different mixing approaches are used in the field: Mixing the material with front-end loader and pugmill (more relevant for aggregate producers to create RAP blends) Mixing the material using cold feed bins and stack of sieves (more relevant for asphalt producers to create RAP blends) 26

27 Findings Pugmill mixing RAP V.A. 27 Mixing by toss and turn process by loader Blend then mixed in the pugmill

28 Findings Mixing with cold bins RAP and V.A. placed in bins Blend then mixed in the shaker 28 Blends created by the release Conveyor belt takes it to shaker

29 Percent Passing (%) 1 1/2" 3/4" 1/2" 3/8" Findings Mechanical Sieve Analysis Coarse Fine Coarse Medium Fine Silt Clay Gravel Sand Fines " 2" 1" #4 #10 #20 #40 #60 #100 #200 30% RAP - 70% VA (Field) 30% RAP - 70% VA (Lab) Particle Size (mm) (Results from feed bins: field vs. lab) (Results from pugmill: field vs. lab)

30 Findings All performance tests (CBR, resilient modulus, and permanent deformation) then compared based on blends created with as-is gradation method Two variables: Variation of RAP percentage Variation of binder content In all compaction tests, adding RAP decreased the maximum dry density compared to the max. dry density of the V.A. alone In all resilient modulus tests, adding RAP improved the elastic modulus compared to the modulus of the V.A. alone 30

31 % Strain Findings Correlation between Binder Content and Permanent Deformation 0.85 RAP 1 (100% RAP binder: %) RAP 2 (100% RAP binder: %) 0.75 RAP 5 (100% RAP binder: %) 100% VA 0.65 Based on 100,000 load cycles % VA BAD GOOD Blue: 20% RAP Red: 30% RAP Green: 40% RAP Orange: 50% RAP Violet: 60% RAP Binder Content (%) 31 Permanent deformation tests showed a threshold

32 % Strain Findings Correlation between Binder Content and Permanent Deformation 0.85 RAP 1 (100% RAP binder: %) RAP 2 (100% RAP binder: %) 0.75 RAP 5 (100% RAP binder: %) 100% VA Results from CBR tests were not as accurate but did not contradict the findings % VA If the V.A. is created from a rock other than diabase, this threshold could be re-evaluated Binder Content (%) Based on permanent deformation evaluation, following recommendations obtained: For low binder content (i.e., 4.5 to 4.7%) Keep RAP percentage in a blend to ~ 20% For mid binder content (i.e., 5.1 to 5.3%) Keep RAP percentage to ~ 25% For high binder content (i.e., 5.6 to 5.8%) Keep RAP percentage to ~ 30% 32 For binder contents in between the above ranges Use the design chart (shown in previous slide)

33 Evaluating tools to provide means for quality control during construction/implementation 33

34 Bases for this evaluation Nuclear density gauge and oven drying methods do not work with RAP Presence of hydrogen ions in RAP affects the total count, which affects the moisture content estimation, which affects the dry density estimations Heat generated in a regular oven partially melts binder content of the RAP, which affects the moisture content estimations 34

35 Methods used to test quality control Light weight deflectometer - modulus Dynatest Model No used H 1 E 1, 1 Top Layer H 1 E 1, 1 Top Layer H 2 E 2, 2 Bottom Layer H 2 E 2, 2 Bottom Layer 35 H 1 > LWD Depth of influence not an issue H 1 < LWD Depth of influence is an issue

36 Large scale model experiment (LSME) 3 feet 4 feet 18 inch LWD conducted in the middle (Conducted by Mr. Emre Akmaz) All layers compacted in accordance with VDOT specifications associated with moisture content and relative compaction 36

37 Evaluation of LWD depth of influence in LSME LWD s depth of influence is an issue LWD CMU 6 in. E 1 Concrete Foundation E con 37

38 LWD s depth of influence is an issue LWD 6 in. E 2 CMU 6 in. E 1 Concrete Foundation E con 38

39 LWD s depth of influence is not an issue Good LWD 6 in. E 3 6 in. E 2 CMU 6 in. E 1 Concrete Foundation E con 39

40 LSME correlated to tests conducted on compaction mold Not everybody has GMU s test pit 40

41 41 Relating the modulus values from LSME to Compaction Mold

42 Quality control in the field based on LWD E LSME is considered as the target value for the field E FIELD is then compared to E LSME E FIELD E LSME : Good E FIELD < E LSME : Bad Methods to account for depth of influence based on multi-layer theory are also developed (not presented here) In the case where base layer is < 13 inches thick, both the modulus of subgrade and base layer must be measured in the field 42

43 Methods used to test quality control Speedy moisture test moisture RAP is a hydrophobic material (does not like to observe water) Specific deviations from AASHTO T217 developed A relationship developed between air drying and speed moisture contents 43

44 44 Relating moisture content from speedy test with air dry method

45 Quality control in the field based on Speedy Moisture test Optimum moisture content from laboratory is used to set target value (w target ) Speedy moisture obtained from the field (w speedy-field ) w speedy-field then converted to air dried moisture (w air-field ) w air-field is then compared to w target w air-field is within the range of specified w target : Good w air-field is not within the range of specified w target : Bad 45

46 Demonstrating the Use (Construction of an Actual Road) 46

47 Purposes of the field demonstration To document field performance based on blending up to 30% RAP with V.A. to create an unbound base layer To confirm the suitability of envisioned quality control methods Consisted of 6 sections 2 sections with low binder content (20% and 30% RAP blends) 2 sections with high binder content (20% and 30% Rap blends) 2 sections with virgin aggregate (control) 47

48 Location of the test sections Woodbridge, VA (NOVA District) Minnieville Test Sections at Woodbridge, VA Total of 900 ft (each section 150 ft long) 48

49 49 Instrumentation layout

50 Purpose of the instrumentation To determine changes in stress and strain conditions at: the boundary between subgrade and base course the boundary between base course and asphalt layer Pressure cell Soil strain gauge Asphalt strain gauge 50 Water content reflectometer

51 Each section had instrumentation Construction completed end of November 2018 Road still not opened to traffic Road profile 10.5 inch asphalt layer 6 inch base layer Monitoring will continue for one year 51

52 Trailer attached to Van moves the equipment LVDTs capturing road profile for IRI Laser Rut Measurement IRI test after construction FWD test after construction Performance evaluations will be conducted five times (Right after construction, following winter, spring, summer, and fall) LWD test after construction 52

53 Findings Test site constructed without any issues Blending RAP handled by one asphalt plant but RAP produced by two different plants Both LWD and speedy moisture tests were very effective for quality control Initial field data shows no signs of distress 53

54 Overall Conclusions To Date Developed guidelines for blending RAP and V.A. that yields performance level similar to V.A. Developed a laboratory testing methodology to determine an optimal RAP content to be mixed with V.A. Developed QC method for RAP-V.A. base course using LWD and speedy moisture test Field demonstration is initiated to confirm findings When all done, changes/modifications to existing specifications will be suggested 54

55 Acknowledgements This research has been funded by VDOT. We would like to thank all VDOT/VTRC TRP members for their active involvement in research and decision making. Special thanks to Mr. David Shiells and Mr. John Schuler from VDOT for their leadership. Special thanks to Dr. Hoppe from VTRC for his involvement in research. We greatly appreciate the support of the RAP industry and Asphalt Association in VA (especially Mr. Ed Dalrymple, Mr. David Branscome, and Mr. Trenton Clark). Thanks to Chantilly Crushed Stone (CCS) (Mr. Joe Fitterer) for their endless support of virgin aggregate material. 55

56 List of Relevant Publications Hoppe, E., Lane, S. D., Fitch, G. M., and Shetty, S. (2015). Feasibility of Reclaimed Asphalt Pavement (RAP) - Use as Road Base and Subbase Material, VDOT Report No. VCTIR 15-R6. Ullah, S., Tanyu, B. F., and Hoppe, E. J. (2018). Optimizing the Gradation of Fine Processed Reclaimed Asphalt Pavement and Aggregate Blends for Unbound Base Courses, Transportation Research Record Publication. Ullah, S. and Tanyu, B. F. (2018). Methodology to Develop Design Guidelines to Construct Unbound Base Course with Reclaimed Asphalt Pavement (RAP), Journal of Construction and Building Materials, In review. Akmaz, E. (2018), Evaluating the Methodology of Light Weight Deflectometer (LWD) for Construction Quality Control of Unbound Reclaimed Asphalt Pavement (RAP) Aggregates, Masters Thesis (GMU) 56

57 QUESTIONS? 57 Contact information: Burak Tanyu