Evaluation Plan for Investigation of In- Place Recycling of Asphalt Concrete as Unbound Base Material

Transcription

1 November 2004 Evaluation Plan for Investigation of In- Place Recycling of Asphalt Concrete as Unbound Base Material PPRC Strategic Plan Item Prepared by Partnered Pavement Research Center Caltrans District 2 Materials Branch 1

2 1.0 INTRODUCTION, OBJECTIVES, DELIVERABLES, SCHEDULE 1.1 Purpose The purpose of this forensic investigation project, Item in the Partnered Pavement Research Center (PPRC) Strategic Plan, is to evaluate a rehabilitation strategy that consists of in-situ recycling of existing failed asphalt concrete and a portion of the aggregate base and placement and compaction on the road as a new granular layer, followed by an asphalt concrete overlay. For convenience, this rehabilitation strategy is referred to as the pulverization strategy in this document. This evaluation plan documents the process and specific tasks that will be performed by the Partnered Pavement Research Center and Caltrans District 2 Materials Branch (District 2) to evaluate this strategy. 1.2 Background Historically, a great deal of engineering judgment has been used in the development of material structural contribution factors for pavement design. In the 1950s and 1960s, Caltrans developed gravel factors for aggregate base and subbase materials and emulsion and cement treated materials based on the Brighton Test Road results and laboratory cohesiometer measurements. A general relationship of the structural contribution for the different materials was determined from the accelerated pavement test results of the Brighton Test Road, and was expanded using the laboratory cohesiometer measurements. The values for the materials were related to the contribution of the aggregate subbase which was given a gravel factor of 1.0. (The cohesiometer provides a measurement of flexural strength). Gravel factors for conventional asphalt concrete were developed based on the results of the AASHO Road Test ( ), and the values for the aggregate and cement treated materials were also reevaluated at that time based 2

3 on the accelerated testing results from the test road. The actual data used for many of these calculations were not documented, and the general approach is primarily retained in summary documents prepared by the PPRC from discussions with the original participants. Looking at the AASHO Road Test data itself, and the approach used to develop material coefficients for the original AASHO Design Method, it can be seen that there is a great deal of scatter in the statistically determined structural contribution of the different layers. The ratios of the structural contribution factors for aggregate base, asphalt concrete and cement treated base developed from the AASHO Road Test for both the AASHO Design Method and the Caltrans design method are not the same, although in part they were developed from the same data. Differences were investigated in a previous PPRC report (1). A different approach was used to develop gravel factors for asphalt treated permeable base (ATPB) materials in the early 1980s. This was the last gravel factor development for material. Test sections were built on SR36 with and without ATPB, and the gravel factor (1.4) was estimated based strictly on the vertical deflections for the two types of structural sections using the Dynaflect. There was a great deal of variability or scatter in the data.(2, 3) The approach used to develop gravel factors for the original Caltrans design method materials is not feasible or desirable for the pulverization strategy because the basis is not well documented, the cohesiometer is not used today, and accelerated pavement test data is not currently available for the pulverization strategy. The strategies used to develop gravel factors for aggregate materials and asphalt concrete can be more accurate with the more sophisticated equipment that is now available. The approach that will be used to develop gravel factors for the pulverization strategy is to perform field and laboratory testing to characterize the materials and pavement produced by 3

4 the rehabilitation process by current Caltrans test methods and also by methods that provide input for mechanistic-empirical analysis. Mechanistic-empirical analysis will be used to develop ratios of structural contribution for the pulverized material and for current Caltrans granular materials for asphalt concrete fatigue and unbound layers rutting distress mechanisms. The results of this analysis will be used in conjunction with the results of the standard Caltrans materials properties to develop an appropriate gravel factor for the materials produced by the pulverization strategy for use in the current Caltrans pavement design method. 1.3 Objectives The objectives of the study are: 1. Perform a literature survey to determine the state-of-the-practice for this strategy outside of California, summarize lessons learned and specific design, specification and construction approaches used elsewhere, and summarize any performance data that might be available. 2. Perform field testing and materials sampling on three to five pilot projects to be conducted in District 2. Field testing will include dynamic cone penetrometer, and falling weight deflectometer on the original pavement before construction and after construction of the structural sections incorporating pulverization strategy. Sampling will include coring, and collection of loose samples of original asphalt concrete pavement and base, and pulverized materials. 3. Perform laboratory testing on the original and pulverized materials, and on other Caltrans granular materials with currently accepted gravel factors. Conventional laboratory testing will include gradations, characteristic compaction curves, permeability tests and R-values. Mechanistic-empirical input laboratory tests include 4

5 repeated load triaxial tests for stiffness and permanent deformation. The pulverized materials will be tested as produced in the projects, and with the addition of lime. The purpose of experimenting with lime is to investigate the increase of stiffness of the pulverized material without cementing the particles. Cement will not be tested, to avoid creating a cemented material that may cause reflective cracking over several years. 4. Perform field pavement condition surveys for up to five years after the completion of construction (dependent on continued funding). 5. Perform mechanistic-empirical analysis to estimate performance of the pavements with the pulverization strategy and compare with estimated performance of conventional pavements, and empirical data for performance of Caltrans overlay strategies (to the extent possible, dependent on the availability of data). 6. Recommend gravel factor(s) for the pulverization strategy based on the results of objectives 1-3 and 5 and preliminary results of objective Develop estimates of life cycle cost based on cost data from the pilot projects and the results of the other objectives of this project, and compare with life cycle cost of current rehabilitation strategies. 1.4 Assignment of Work for Objectives The PPRC will perform the work to complete objectives 1 through 6, except for R-value tests. R-value tests will be performed by private laboratory, due to schedule limitations at District 2 and TransLab. Characteristic compaction curves will be developed by both the PPRC and District 2. The life cycle cost analyses will be developed jointly by both PPRC and District 2. 5

6 District 2 will perform the cost analyses and PPRC will estimate the life. District 2 will aid the PPRC in arranging and completing field testing and materials sampling. 1.5 Deliverables The interim deliverables for objectives 1-3 will be technical memorandums summarizing results after completion of testing of materials from each project. A final report will cover the results of all objectives except objective 4 which is extended testing over 5 years (dependent on continued funding). A technical memorandum will cover the results of objective 4 at an appropriate time. All data collected in the project will be included in the PPRC Research database, available to Caltrans. 1.6 Schedule Literature review will be completed by the end of March Technical memorandums will be completed approximately 9 months after completion of each project. Mechanistic analysis will be performed as information becomes available. The draft final report will be delivered in February, 2006, 12 months after the completion of the Poison Lake project on Lassen 44. This completion date will be pushed back to 12 months after the completion of the last project, if additional projects are added to the scope. 2.0 LITERATURE REVIEW Literature review will be performed to determine the state-of-the-practice for this pulverization strategy outside of California, summarize lessons learned and specific design, specification and construction approaches used elsewhere, summarize any performance data that 6

7 might be available, understand the determination of gravel factor, and summarize the use of additives such as lime or cement by others. 3.0 FIELD TESTING PROGRAM The field testing program includes: 1. coring of the existing and new pavement, 2. dynamic cone penetrometer (DCP) testing of the existing and pulverized base materials, 3. falling weight deflectometer (FWD) testing, and 4. field pavement condition survey Items 1, 2, and 3 are conducted before and after the rehabilitation strategy. Items 3 and 4 are regularly conducted every year after the rehabilitation. 3.1 Coring Coring of the asphalt concrete (AC) layer will be conducted to obtain asphalt concrete thickness profiles along the pavement section. Asphalt concrete thicknesses will be used during the pavement analysis for estimating pavement layer moduli. Coring will be conducted before and after the recycling process. 3.2 Dynamic Cone Penetrometer (DCP) Testing After the asphalt concrete cores are removed from pavement, DCP testing will be conducted to obtain field measurements of thickness and strength of unbound layers. The DCP equipment and test procedure is relatively simple (see Figure 1). It consists of a 60 metal cone attached to a rod, and an 8-kilogram hammer dropped from a height of 575 mm to drive the cone 7

8 Figure 1. DCP device. into the in-situ base material, typically through a core hole. A measuring tape is secured to the rod in order for the technician to record the depth of penetration with the increasing blow count. The associated DCP penetration in the base is plotted against the number of blow counts. Changes in the penetration rate (DN = slope of the penetration-blow count relationship in mm/blow count) will be used to determine thickness of unbound layers. The penetration rate at a given layer is also used to define its strength. In general, lower penetration rates are indicative of stronger materials. Typical DCP data are presented in Figure Falling Weight Deflectometer (FWD) Testing The Dynatest Model 8082 Heavy Weight Deflectometer (HWD) test system (see Figure 3) will be used to generate the required non-destructive load-deflection data for this evaluation. The HWD is similar to the FWD although the loading range of the HWD is significantly greater than the FWD. 8

9 South Bound - Dynamic Cone Penetrometer Data After Recycling Process Pavement Depth, mm Sta 500-s Sta 1000-s Sta 1500-s Sta 2000-s Sta 2500-s Sta 3000-s Blow Counts Figure 2. Typical DCP data (Alturas project). Figure 3. Heavy Weight Deflectometer. 9

10 The HWD generates a transient, impulse-type load of msec duration, at any desired (peak) load level between 27 and 245 kn (6,000 and 55,000 lbf.), thereby approximating the effect of a km/h (30-50 mph) moving wheel load. For this evaluation, test loads will be ranged from 27 to 67 kn (6,000 to 15,000 lbf.). The sensor spacing is at: 0, 200, 300, 400, 610, 910 and 1525 mm from the center of the load plate. Tests will be performed every 50 meters in each lane. The FWD/HWD-generated load-deflection data will be used to estimate pavement layer modulus using available mechanistic tools for pavement analysis. The software package used for analysis will be the Dynatest ELMOD4.5 and Calback. 3.4 Field Condition Survey The Pavement Condition Survey (PCS) is an inventory of the existing pavement surface condition for the entire state highway network. Pavement condition is established by observing the severity and extent of surface distress. In order to understand performance of existing pulverized recycled pavement, regularly scheduled pavement condition surveys will be performed. Caltrans Pavement Management System survey evaluation will be used for condition surveys (4), or a more detailed condition survey that is compatible with the Caltrans Pavement Management System survey. Field condition surveys and FWD tests will be performed every year for up to five years after the completion of construction. If there is little change from year to year in the first three years, the testing schedule may be reduced to deflection testing every other year and condition survey every year until annual condition surveys indicate that damage is accelerating. The PPRC in consultation with the Caltrans technical lead will determine an appropriate long-term deflection testing and condition survey schedule after analysis of the first three years of data. 10

11 3.5 Sampling Program Samplings and reporting will be conducted during the construction to investigate the variability of recycled products and its effect on the performance. To get the enough material for conducting standard and triaxial tests, at least 1000 kgs of material are required from each project, or from each section of a project if they are more than one materials or treatment used within a project. 4.0 LABORATORY TESTING PROGRAM Laboratory tests will be conducted to characterize the recycled asphalt concrete materials using standard and repeated loading tests. The laboratory results will be compared to establish the relative response and performance of the recycled asphalt concrete material to standard base materials that meet California specifications for aggregate base Class Standard Tests Particle Size Distribution Mechanical sieving will be conducted following California Test Method (CTM) 202 for determining particle size distributions. Samples from the field will be prepared following California Test Method (CTM) R-value Test The R-value test will be conducted to characterize materials within the conventional Caltrans design method. The test procedure expresses a material s resistance to deformation as a function of the ratio of transmitted lateral pressure to applied vertical pressure. Materials tested 11

12 are assigned an R-value. The test procedure to determine R-value requires that the laboratory prepared samples are fabricated to a moisture and density condition representative of the worst possible in situ condition of a compacted subgrade Moisture Density Relationship Compaction tests will be conducted to determine the moisture-density relationships of the recycled materials according to ASTM 1557 (modified compaction tests) and California Test Method (CTM) 216. The results of the compaction tests will be used for preparing materials for dynamic testing Permeability Test Permeability tests will be performed to test the permeability of the as-compacted aggregate base according to ASTM D (constant head permeability test) and ASTM D (permeability measured with a compaction-mold permeameter). 4.2 Static and Dynamic Tests Static and repeated loading triaxial tests will be conducted on prepared 152-mm diameter by 304-mm high cylindrical specimens. The specimens will be tested on a closed-loop servohydraulic testing equipment capable of applying various sequences of stress levels. LVDTs and load cells are used to monitor load, and displacement measurements. Measurements are recorded and processed using a high-speed data acquisition system. Figure 4 illustrates the system. The materials will be tested untreated and treated with lime. No mix design for lime treatment will be conducted. 12

13 Figure 4. UC-PRC triaxial system. Static stress-strain triaxial tests and repeated loading tests (resilient modulus) will be conducted on specimens compacted at optimum moisture content and at 95 percent maximum wet density according to CTM Stress-Deformation-Strength Characteristics Displacement-controlled stress-strain triaxial tests will be conducted on the specimens at confining pressures of 0, 35, 70, and 105 kpa. Stress-strain triaxial test results will be used to define the shear strength of the materials using Mohr-Coulomb failure criteria. 13

14 4.2.2 Resilient Modulus Tests The resilient modulus (M R ) is an elastic modulus based on the recoverable strain under repeated loads. It is defined as: M R ( kpa) = σ ( kpa) d ε r where σ d is the applied deviatoric stress (σ l - σ 3 ) and ε r is the recoverable strain. A number of factors affect the M R of a base material, some of which are moisture content, density, stress history, aggregate type, gradation, temperature, percent fines, and degree of saturation. The resilient modulus tests will be conducted following the Strategic Highway Research Program (SHRP) test protocol P Permanent Deformation Resistance Permanent deformation resistance of the recycled aggregate base materials will be assessed based on the stress-strain characteristics of the materials. Researchers have shown that aggregate materials tested under stress-strain triaxial tests that reached a deviatoric stress of at least 620 kpa at 2 percent strain under a confining pressure of kpa had a low potential for rutting. Conversely, materials that did not reached a deviatoric stress of at least 620 kpa by 2 percent strain underwent a rapid accumulation of permanent deformation (5). 5.0 DETERMINATION OF GRAVEL FACTOR To develop a gravel factor (G f ) to be used by Caltrans within the current design method, a series of analyses will be performed on structural sections containing untreated aggregate base and compared with structural sections containing recycled AC used as unbound aggregate base. To arrive at the gravel factors, the tensile strain in the asphalt concrete will be used to estimate 14

15 fatigue performance, and the vertical stress at the top of the unbound layers and vertical compressive strain at the subgrade will be used to estimate unbound layers long-term rutting performance. The gravel factor will be developed based on comparison of the thicknesses required to obtain similar performance for the pulverized strategy and conventional Caltrans pavement designs. A similar method was used to evaluate the gravel factor for ATPB in Reference (3) as an example, an approximate equation for estimating the gravel factor from these performance estimates can be determined from the following expression: G f Re AB G f = T AB T Re AB AB where: G f = AB gravel factor of Recycled aggregate base = gravel factor of aggregate base G f AB T Re AB = thickness of recycled aggregate base to achieve a given life (mm) = thickness of aggregate base to achieve a given life (mm) T AB 6.0 PILOT PROJECTS The following pilot projects will be used for evaluation of the rehabilitation strategy: (Alturas Project): located on California State Highway (CSH) 395. A technical memorandum dated 11/6/01 was submitted to Ms. Lerose Lane at the Redding Materials Laboratory, Caltrans District (Beckwourth Project): located on Plu 70 in Plumas County. Referred to in technical memorandum dated 11/6/ (Cayton Creek Project): located on Sha 89 in Shasta County. This project was postponed and an emergency overlay was placed on it to preserve until the project can be completed. 15

16 (Poison Lake project): located on Las 44 will be completed during Summer District 2 may include one or two more projects within the next 12 to 18 months. 6. It has been suggested that a control section with the current standard overlay or overlay with digouts strategy be placed within future projects for long term monitoring and comparison. District 2 will investigate this option. 7.0 REFERENCES 1. Harvey, J., and F. Long. CAL/APT Program Comparison of Caltrans and AASHTO Pavement Design Methods. Report prepared for the California Department of Transportation. Pavement Research Center, CAL/APT Program, Institute of Transportation Studies, University of California, Berkeley. November Mann, G. Determining the Gravel Factor for Asphalt Treated Permeable Asphalt Concrete and Open-Graded Asphalt Concrete with the Use of Deflections. Transportation Laboratory Memorandum, File No , California Department of Transportation, Sacramento, 9 March Harvey, J., B-W Tsai, F. Long, and D. Hung. CAL/APT Program: Asphalt Treated Permeable Base (ATPB), Laboratory Tests, Performance Predictions and Evaluation of Caltrans and Other Agencies Experience. Report prepared for the California Department of Transportation. Pavement Research Center, CAL/APT Program, Institute of Transportation Studies, University of California, Berkeley. Draft submitted July Final submitted June Massey, S. and Poppe, J. Caltrans Pavement Condition Survey (Pavement Evaluation Manual). California Department of Transportation, January Garg, N. and Thompson, M.R. Triaxial Characterization of Minnesota Road Research Project Granular Materials. Transportation Research Record No Washington, D.C.,