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7 Research Approach Chapter 2 provides an overview of the work completed during this study. The objectives of the study were addressed through three phases. In Phase I, current and emerging test methods for quality assessment and process control of cold recycled materials where emulsified asphalt or foamed asphalt serves as the stabilizing/recycling agent were identified. The three primary sources of information used were a literature review, a review of agency specifications, and an online stake- holder survey. Phase II, a laboratory-based experiment, was conducted with test slabs of recycled materials fabricated in the laboratory using materials sampled from recycling proj- ects in the United States and Canada. Phase III, a field-based experiment, was conducted where the most representative tests identified in Phase II were used to assess the early-age properties of recycled materials on nine field projects in the United States. 2.1 Phase IâCurrent and Emerging Quality Tests From the literature review, agency specifications review, and stakeholder survey, the research team identified relevant material properties that were key to addressing the study objectives and candidate tests that could assess the relevant material properties of interest. Through these steps, the fol- lowing key properties were identified: product uniformity, moisture, compaction, thickness, curing, strength/stiffness, and raveling resistance. Assessing one or more of these proper- ties could then be used to determine if a recycled material was ready to be opened to traffic or ready to be surfaced. The work focused on identifying those tests that could assess these prop- erties, were relatively inexpensive, were easy to operate in the field, and were able to capture the anticipated material prop- erty trends associated with changes in stabilizing/recycling agent types, the presence of active fillers, and field curing. The review of agency specifications for asphalt-stabilized FDR, CIR, and CCPR and the stakeholder survey were con- ducted to identify and summarize current practices. The agency specifications review was completed with the goal of identifying current traffic opening and surfacing requirements and other material quality tests. The survey of academic, industry, and agency stakeholders was conducted to identify any additional tests not discovered during the literature review (such as those that might come from unpublished studies or from ongoing research) and to help the research team identify the curing time(s) from which the stakeholders would seek to use the results of any proposed tests. 2.1.1 Specification Review The standard specifications and special provisions for asphalt-based CIR, CCPR, or FDR from U.S. states and Canadian provinces were collected and reviewed. Of the 50 U.S. states, 41 states, in addition to FHWAâs Federal Lands Highway Division, had at least one of the relevant specifica- tions. Of the 10 Canadian provinces/territories, three included asphalt-based CIR, CCPR, or FDR in their standard speci- fications. In addition, the specifications from three munici- palities in the United States were collected and reviewed. In total, 83 specifications were reviewed. Of these, approximately 54% (45 specifications) governed CIR, 17% (14 specifications) governed CCPR, and 29% (24 specifica- tions) governed FDR. Figure 2.1 is a map of the United States and Canada that identifies the locations of all state/province/ municipal CIR, CCPR, and FDR specifications that were reviewed. 2.1.2 Stakeholder Survey An online stakeholder survey was conducted from October through December 2017. The objectives of this survey were to identify: â¢ Tests that were being assessed but had not yet been incor- porated in current agency standard specifications or special provisions, C H A P T E R 2
8 â¢ Procedures used by practitioners for process control that are not standardized or published, â¢ Potential hurdles that exist with implementation of current methods of product acceptance and specifications, â¢ Rankings of the most important test method characteris- tics by practitioners (e.g., time taken to perform the test, equipment required), â¢ Potential field projects that could be used in Phase III of the study for evaluating the testing procedures developed in Phase II, and â¢ Recommended improvements to existing tests from practitioners. The stakeholder survey questions are presented in Appendix A. The online survey link was distributed to the AASHTO Committee on Materials and Pavements, selected TRB committees in the pavements and asphalt materials sections, and in presentations at regional and national pave- ment recycling conferences. A total of 84 survey responses were received. 2.2 Phase IIâLaboratory Testing Using the information collected during the literature review and stakeholder survey, the research team developed a laboratory experiment conducted in Phase II of this study. The experiment was conducted on test slabs of recycled materials fabricated in the laboratory. The slabs were fabri- cated from loose recycled materials sampled during construc- tion of projects from across the United States and Canada, Alberta (AB) is the only municipality in the âMunicipality Specification Onlyâ category, and California is the only state in the âState/Province and Municipality Specificationâ category. Color figure can be viewed in the online version of this report. Figure 2.1. Location of all state, province, and municipality CIR, CCPR, and FDR specifications reviewed in this study.
9 as shown in Figure 2.2. For this work, loose materials were defined as the processed RAP and any other material required to produce an FDR, CIR, or CCPR layer but not including any stabilizing/recycling agent or active filler. Industry and agency partners assisted the research team with identifying relevant projects, obtaining the mix designs, and shipping approximately 500 lb to 600 lb of loose materials from each project. Along with the loose materials, the research team received the designated asphalt emulsion or binder to repli- cate the mix design in the laboratory. The research team followed the developed mix design, mixed the provided materials, and compacted slab specimens in the laboratory. These slabs were tested with the tests identified in Phase I to determine the testsâ ability to discern differences in material behavior related to curing time, type of stabilizing/recycling agent, and presence of active filler. 2.2.1 Objectives The objectives of the laboratory testing included assessing tests that could be conducted easily, quickly, and inexpen- sively in a field setting and could quantify material property differences resulting from changes in curing time, type of stabilizing/recycling agent, and presence of active filler. Preferably, tests would provide an immediate result. 2.2.2 Experimental Design To accomplish the objectives of the laboratory experi- ment, the research team chose to conduct the laboratory experiment using a partial factorial design. A partial factorial design was selected because of the high number of potential combinations given the possible factors (including recycling With Active Filler No Active Filler CIR CIR CCPR CCPR FDR FDR Figure 2.2. Project locations for Phase II materials sampling.
10 processes; stabilizing/recycling agent types; presence of active fillers; RAP, asphalt binder, and aggregate sources; and curing time), multiple levels of each factor, and number of tests. The experiment was designed using factors and levels that were expected to yield the greatest range of results for the testing conducted. For example, for a test that measures stiffness of a recycled material, rather than each possible com- bination of recycling process, stabilizing/recycling agents, chemical additives/active fillers, geographic location, and RAP type being tested, an experimental design could be developed that studied the combinations expected to produce the least and the greatest stiffness. From this, the effectiveness of each test (or more tests) could be studied in a way that was more efficient while still technically valid. Multiple sets of test slabs were fabricated to conduct all the tests. This was necessary given (1) the limited size of the test specimens, (2) the desire to conduct testing on undisturbed sections of the test specimens, and (3) the need to provide replication. Each test specimen was fabricated in accordance with the mix design, and the quantity of each ingredient was recorded. Subsequent test specimens from the same project were fabricated using the same ingredient quantities. 2.2.3 Source Projects and Materials Sampling With the help of industry and agency partners, the research team was provided with a mix design (which included an optimum density, a stabilizing/recycling agent content, and an active filler content [if used]) and materials from 14 recycling projects located across the United States and Canada. From each project, the supporting contractor or agency provided the research team with 10 to 12 5-gal buckets of the loose material (composed of RAP and sometimes unbound materials from underlying layers) and 4 to 6 gal of emulsified asphalt for those projects where emulsified asphalt was used. For those projects where foamed asphalt was used, a performance grade (PG) 64-22 binder already available in the laboratory was included. To help develop a more complete matrix of material types, 24 and 48 5-gal buckets of loose material were sampled from two ongoing research studies in California and Virginia, respectively. These extra materials were used to produce additional mixtures using both emulsified and foamed asphalt (each with and without an active filler) from the same source. Table 2.1 describes the projects from which the loose materials were obtained. The stabilizing/recycling agent dosage ranged from 1.2% to 4.5%, with 2.5% being the most common agent content. In addition, the active filler content ranged from 0% to 1.5%, with 0% and 1% being the most common. 2.2.4 Slab Specimen Fabrication Compacted slab specimens (500 mm Ã 400 mm Ã 110 mm) were manufactured from field-produced materials. The slabs were prepared with the loose materials sampled from each field project upon which the various laboratory tests were conducted. Following the mix design from (or devel- oped for) each project, the loose materials were mixed with stabilizing/recycling agents and active fillers (where used) in a Wirtgen WLM30 laboratory-scale twin-shaft pug mill. This equipment has the capacity to mix a batch of approx- imately 30 kg (66 lb). For those mixtures using emulsified Mix ID Stabilizing/ Recycling Agent Active Filler Process State Project Description Agent Content, % Active Filler Content, % Target Density, lb/ft3 1 Emulsified asphalt Cement CCPR IN SR 101 2.5 1.0 128.02 VA I-64 Segment II 2.5 1.0 128.0 3 FDR TX I-10 4.5 1.1 135.0 4 CA UCPRC Test Track 2.5 1.0 128.0 5 No cement CCPR NY Courtland 3.0 0.0 134.06 VA I-64 Segment II 2.5 0.0 128.0 7 CIR ON Huron County, Road 87 1.2 0.0 121.5 8 FDR IN Shelby County, SR 252 2.5 0.0 118.09 CA UCPRC Test Track 2.5 0.0 128.0 10 Foamed asphalt Cement CCPR VA I-64 Segment II 2.5 1.0 128.0 11 CIR CA Hayward, Soto Road 2.0 1.0 124.8 12 MA Southwick 2.5 1.0 129.5 13 FDR TX FM 1245, Groesbeck 2.4 1.5 124.814 CA UCPRC Test Track 2.5 1.0 128.0 15 No cement CCPR VA I-64 Segment II 2.5 0.0 128.0 16 CIR MI Jackson County, Rosehill Road 2.2 0.0 130.017 WI Douglas County, STH 35 2.0 0.0 121.5 18 FDR CA UCPRC Test Track 2.5 0.0 128.0 Table 2.1. Phase II source projects summary.
11 asphalt, the emulsion (kept at a temperature of 40Â°C) was added directly during the mixing process. For those mixtures using foamed asphalt, a Wirtgen WLB10S laboratory foam- ing unit produced the foamed asphalt at a temperature of 163Â°C. Once the emulsified or foamed asphalt, mixing water, and active filler (if used) were combined, the mixed materials were transferred to a slab compactor to fabricate the slab specimens. The following example calculations demonstrate how the quantities for mixing a batch of material were determined. Two examples are shown, one for foamed asphalt materials and the other for emulsified asphalt materials. For each example, 1.0% cement was included, the RAP had an âin-the-bucketâ moisture content of 2.4%, and the optimum moisture content was 4.0%. For the foamed asphalt example, a binder content of 2.0% was assumed. For the emulsified asphalt example, a binder content of 2.5% (2â3 residual binder, 1â3 water) was assumed. The actual mix design from each project was used when the test specimens were made. Foamed asphalt materials: 1. Weigh RAP (assume a batch weight of 25 kg) and account for existing moisture of 2.4% = 25,000 g + 2.4% = 25,600 g. 2. Add 1.0% cement based on mass of dry RAP = 25,000 Ã 1.0% = 250 g Ã 1.0% = 253 g. 3. Add water to reach an optimum moisture content of 4.0% = 25,600 Ã (4.0% â 2.4%) + 253 Ã 4.0% = 420 g. 4. Add 2.0% foamed asphalt based on mass of dry RAP = 25,000 Ã 2.0% = 500 g. Emulsified asphalt materials: 1. Weigh RAP (assume a batch weight of 25 kg) and account for existing moisture of 2.4% = 25,000 g + 2.4% = 25,600 g. 2. Add 1.0% cement based on mass of dry RAP = 25,000 Ã 1.0% = 250 g Ã 1.0% = 253 g. 3. Calculate 2.5% emulsion mass based on mass of dry RAP = 25,000 Ã 2.5% = 625 g. 4. Calculate water to reach an optimum moisture content of 4.0% and subtract the water proportion (assumed as 1â3) of emulsion = 25,600 Ã (4.0% â 2.4%) + 253 Ã 4.0% = 420 g â 625 Ã (1â3) = 166 g. 5. Add 166 g of water. 6. Add 625 g of emulsion. For foamed asphalt materials, the research team used the same PG 64-22 binder so that the foaming temperature and amount of foaming water would be the same. For emulsi- fied asphalt materials, the research team used the emulsion supplied by the agency/contractor. The day prior to mixing, approximately 1,000 g of loose material was taken from a sealed 5-gal bucket and placed in a forced-draft oven set at 40Â°C until a constant mass was reached, and then the mois- ture content was calculated. Each test slab had dimensions of 500 mm in length Ã 400 mm in width and a thickness of approximately 110 mm. To fabricate each slab, two batches of mixed materials were required. The batches were produced as follows: 1. Calculate the mass of parent material required for desired slab size and mix design density. 2. Using two mostly full 5-gal buckets of loose material, add one-half of each bucket to an 18-gal tub, and mix by hand. Transfer the contents of one 5-gal bucket into the other and empty the mixed contents of the 18-gal tub into the empty 5-gal bucket. Add the contents of the second 5-gal bucket to the 18-gal tub and mix by hand. Empty the 18-gal tub into the second 5-gal bucket. 3. Add and mix the contents of each 5-gal bucket in the pug mill for 1 minute. After mixing, empty the contents into a 50-gal tub. 4. Based on the desired slab density, calculate the amount of mixed material required. Place approximately equal portions of mixed material from the 50-gal tub into two 5-gal buckets. 5. Add enough loose material to the 5-gal buckets to account for the measured moisture content (determined as described previously). 6. Add the contents of one 5-gal bucket into the pug mill. 7. Add water if needed (calculated as described previously) and mix for 1 minute. 8. Add cement if needed (calculated as described previously) and mix for 1 minute. 9. If emulsion is used, add emulsion directly to the pug mill and mix for 1 minute. If foamed asphalt is used, spray the foam into the pug mill and mix for 1 minute. 10. Transfer contents to an empty 50-gal tub. 11. Repeat steps 6 through 10 for the second 5-gal bucket. The slab specimens were prepared using an IPC Global/ Controls Group Advanced Asphalt Slab Roller Compactor. The slab compactor used a roller head segment (having a radius of 535 mm) and applied the compaction load to the material by the specimen mold carriage moving back and forth under the roller head with the load applied in a pendulum-like action. The slab compactor was used since it could operate in a displacement control function so that the desired thickness of the test specimen could be set, and thus the approximate bulk density was controlled by adjust- ing the mass of material added. After mixing in the pug mill, the mixed materials were transferred to the slab mold. The mixed material was added by hand, filling the corners first and then the lower edges to reduce the chances of having lower density in these areas.
12 The mixed material was rodded using a concrete molding rod until the material surface was below the maximum that could be accommodated by the slab compactor. For certain mixtures having higher densities, the height of the loose material exceeded the maximum that could be accommo- dated by the slab compactor (approximately 155 mm prior to compaction), and thus all slabs (regardless of initial height) were rodded. Following rodding, a sheet of heavy- duty aluminum foil was used to cover the rodded material to prevent it from sticking to the compactor roller head segment. No other lubricants or bond breakers were used. The slab compactor was set to compact using a displacement rate of 1 mm per pass until the machine had compacted the slab to the desired height of 110 mm. Prior to the testing, the research team needed to deter- mine the best way to produce the slabs and then handle them without causing damage. It was originally planned to demold the slabs after compaction but prior to testing. After the first few slabs were fabricated, it was observed that the slabs tended to crack during handling when removed from the mold, as shown in Figure 2.3. To counter this, a metal base plate was placed in the slab mold before the mixed material was added. The idea was that the metal base plate would support the slab while the slab was removed from the mold. The plate did assist with reducing handling damage, but it was soon discovered that any testing away from the center of the slab (especially at early ages) caused the slab to crumble because of a lack of confinement. The research team next tried confining the slab by remov- ing the slab from the mold and using metal plates along the edges of the slab. The metal plates were held together with a tie-down strap and wood blocks to hold the plates tight to the slab, as shown in Figure 2.4. It was discovered that the confinement pressure was variable and difficult to replicate. In addition, exploratory testing with a lightweight deflectom- eter (LWD) showed a large difference in stiffness properties depending on the amount of pressure applied by the tie-down strap. For these reasons, all testing was conducted within the fabrication mold. 2.2.5 Slab Specimen Testing A series of existing and newly developed tests capable of assessing the early-age condition of recycled materials were identified in Phase I. These tests, listed in Table 2.2, were grouped into the following material property catego- ries: density, stiffness, penetration resistance, deformation Figure 2.3. CCPR slab with arrow showing crack that formed during the demolding process. Figure 2.4. LWD testing of slab confined using metal plates and confined with tie-down strap and wood blocks. Property Suggested Test or Device Density Mass of dry material divided by slab volume Stiffness Soil stiffness gauge Lightweight deflectometer Penetration resistance Dynamic cone penetrometer Deformation resistance Marshall hammer Shear resistance Long-pin shear test* Raveling resistance Short-pin raveling test* Moisture Electromagnetic moisture probe *Conceptual test proposed by the research team. Table 2.2. List of properties and tests for Phase II testing.
13 resistance, shear resistance, raveling resistance, and mois- ture. The density was assessed by dividing the mass of dry material by the slab volume. The stiffness of the recycled materials was assessed by using a commercially available LWD and soil stiffness gauge (SSG). The penetration and deformation resistance were assessed using a commercially available dynamic cone penetrometer (DCP) and a Marshall hammer (MH) assembly having a 4-in.-diameter foot, respec- tively. Shear and raveling resistance were assessed using custom-fabricated fixtures developed during the project. Moisture was assessed using an electromagnetic moisture probe. Tests were conducted on single or replicate slabs; the number of replicates varied depending on the test conducted. All tests were conducted within the slab specimen com- paction mold. This was necessary since recycled materials tend to be susceptible to damage during handling, especially at early ages and when unconfined. It was recognized that there were likely some unaccounted edge effects that could influence the magnitude of the test results. However, the purpose of the Phase II laboratory testing was to assess the response of the various test methods with respect to changes in material properties in the laboratory. It was expected that trends in the measured responses in the laboratory and during field testing would be similar. 188.8.131.52 Stiffness Tests Stiffness testing was completed using commercially avail- able LWD and SSG devices. Both devices were used to calcu- late the stiffness of the test slabs at 2 and 72 hours after slab fabrication. The time that the slabs were fabricated was used to denote the start of the curing time. For LWD testing, a known load pulse was applied to induce a deflection on a test slab surface, as shown in Figure 2.5. The vertical movement of the surface was measured directly under the LWD with a 6-in.-diameter load plate and a fixed center deflection sensor. The deflection measurements were then used to determine the surface deflection modulus (stiffness) of the test slabs using Equation 1: )( = â s â â â1 (1)0 0 2 E f a v d where E0 is a surface deflection modulus; f is a factor for stress distribution, taken as 2 for the measurements in this study; s0 is a stress under the LWD plate; Î½ is Poissonâs ratio (assumed to be 0.35); a is the radius of the plate; and d is the center deflection under the LWD. The test variability was reduced when a total of 10 drops were used for each test, with the average of the last three drops being reported. The drop height required to com- plete the test at early ages without plastically deforming the material was investigated, and it was found that drop heights ranging from 4 in. to 12 in. produced similar test results (using a 10-kg mass). All testing with the LWD was completed using a drop height of 12 in. This height/mass combination applied a force of approximately 800 lbf and a pressure of approximately 35 psi. The SSG uses an electromechanical vibration to impart a small dynamic load as low-frequency sound waves on the surface of a test slab. The resulting surface deflection as a function of frequency is measured. The test surface vibration is applied between 100 Hz and 196 Hz at 4-Hz increments, producing 25 steady-state frequencies. The magnitude of the applied force is about 9 N, and the induced deflections are less than about 0.00005 in. The stiffness of the test slab is determined for each of the 25 frequencies, and the average value from these measurements is reported as the stiffness. Three replicates of the SSG test were performed at the center of a test slab by rotating the device approximately 120Â° between tests, and the average stiffness value of the three replicates was reported. 184.108.40.206 Moisture Content Tests Moisture content testing was conducted using a recently developed commercial electromagnetic moisture device. The device was manufactured to be used in conjunction with a low-level NDG. Since the device could not be driven into the Figure 2.5. LWD test conducted at the center of a test slab.
14 test slab itself, the probe end was inserted into a hole created by driving a metal rod (like that used for nuclear density test- ing in the direct transmission mode) into the test slab or by using the hole that remained after dynamic cone penetrom- eter testing. Figure 2.6 shows the device and data collection unit. Not shown in Figure 2.6 is the probe sensor, which is inserted into the test slab and is the same size as the probe rod of an NDG. 220.127.116.11 Penetration Resistance Tests The penetration resistance of the recycled material was measured using an MH assembly and a commercially avail- able DCP (conforming to the requirements of ASTM D6951). DCP testing was conducted by placing the DCP on top of the recycled slab and then dropping the 8-kg mass 575 mm and recording the penetration after each drop. Testing was conducted at 2 and 72 hours after compaction using the same slabs used during stiffness testing, and again at 1 and 24 hours after compaction for the same test slabs used during raveling testing (discussed in the following sections). DCP testing was conducted by placing the tip of a fixed cone on the recycled slab. The penetrated depth was recorded with each blow, starting at a penetration of zero. An MH assembly with a 4-in.-diameter foot and a 17.6-lb sliding weight falling 22.6 in. was used, as shown in Figure 2.7. The test procedure included dropping the weight on a location 20 times with recording of the penetration depth every five drops. The penetration depth was measured using a digital caliper with an external depth blade. The penetration depth was measured at three locations along a line (at approximately a 1-in. spacing) across the full diameter of the penetrated area, as shown in Figure 2.7. MH testing was conducted at 2 and 72 hours after compaction on the same test slabs used during stiffness testing. Figure 2.6. Moisture testing. Figure 2.7. Marshall hammer testing of a recycled slab (left) and penetrated area measurement (right).
15 18.104.22.168 Shear and Raveling Tests Shear resistance was assessed using a developed fixture that could be driven using the upper assembly of a stan- dard DCP. The developed prototype shear fixture, shown in Figure 2.8, consisted of a steel base plate approximately 5 in. square with four outer pins (each 13â32-in. in diameter, extending 3.0 in. from the base plate) located along four points of a circle approximately 3.5 in. from a 1â2-in.-diameter, center pin that extended 3.0 in. from the base plate. The test performed with this fixture was termed a âlong-pin shear test.â The term âlong-pinâ is used to differentiate this fixture from a similar-looking fixture with shorter pins used to assess raveling resistance. To conduct the test, the shear test fixture was driven into the test slab until the plate seated on the surface, using the upper assembly of a DCP that fits over the center shaft on top of the fixture base plate, as shown in Figure 2.9. The center shaft had a diameter of 1.0 in. with a hexagonal head milled into it so that a 3â4-in. socket could be attached to the center to accommodate a handheld torque wrench. After the fixture was driven in and the number of blows until the base plate touched the slab surface was recorded, the operator used a torque wrench to apply a rotational force, as shown in Figure 2.10. The maximum torque reading was recorded. The length of pins was intentionally chosen to match the approximate minimum thickness of a recycled layer (approxi- mately 3 in.). Pins were included in the fixture design, rather than solid vanes, to reduce damage to the recycled layer caused by testing. The raveling resistance of the recycled materials was assessed using a modified version of the shear test fixture. The raveling fixture is similar to the shear test fixture, but the outer pins used for the raveling test extend 1.0 in. from the base plate, as shown in Figure 2.11. The test performed with this fixture is termed a âshort-pin raveling test.â The length of pins was chosen to be similar to the likely maximum par- ticle size of most recycled materials (approximately 1 in.). The test procedure was essentially the same as the long-pin shear test in that the upper assembly of a DCP was used to drive the raveling test fixture into the test slab, as shown in Figure 2.12. To maintain a constant normal force that kept the short pins from riding up onto the slab surface, two 10-lb plates were added on top of the raveling test fixture to apply a normal force. The operator used a torque wrench to apply Figure 2.8. Prototype long-pin shear test fixture. Figure 2.9. Upper assembly from a DCP used to drive the long-pin shear test fixture. Figure 2.10. Measuring torque with long-pin shear test fixture.
16 a rotational force, as shown in Figure 2.13, and the maximum torque reading was recorded. Since the raveling fixture pins were of different lengths, two separate blow counts were recorded for the short-pin raveling test, as described in the following. The number of blows required to drive the fixture to the tip of the shorter outer pins was counted and denoted N1. The cumulative number of blows required to drive the entire fixture to the level of the base plate was recorded and denoted N2. The number of blows to these various positions was recorded in case one measurement proved to be a more significant predictor of performance than another. 22.214.171.124 Other Tests Considered Several other tests were considered for the laboratory experiment but ultimately were not chosen by the research team. These tests included penetration resistance tests using a rapid compaction control device, a stiffness test using a Clegg hammer, stiffness assessment using an ultrasonic pulse velocity and portable seismic pavement analyzer, a raveling/abrasion test using the Wet Track Abrasion Test and cohesion testing (ASTM D3910), and a cohesion test with a field-portable pneumatic cohesion tester (based on the ASTM D3910 cohesion test). Ultimately, these tests were not selected because of issues such as limited device availability, incompatibility with early-age properties of the recycled material, and difficulties with demonstrating expected per- formance trends with changes in material properties. These tests, which were not part of the laboratory experiment, are not discussed further in this report. 126.96.36.199 Test Arrangement Three sets of test slabs from each project were fabricated to accommodate all the tests. For each project, single slabs or replicates were fabricated depending on the amount of loose material available. The first set of slabs was fabricated to facilitate moisture, stiffness, and penetration resistance Figure 2.11. Prototype short-pin raveling test fixture. Figure 2.12. Applying blows using DCP upper assembly with short-pin raveling test fixture. Figure 2.13. Applying torque to measure raveling resistance.
17 testing. The second set was used for stiffness (by LWD only) and shear resistance testing. The third set of slabs was used for stiffness (by LWD only), DCP, and raveling testing. The three sets of tests were conducted to maximize the amount of information that could be collected while reducing the potential for one test to influence another. Moisture, stiffness, and penetration resistance testing was conducted on the first set of slabs. The tests were arranged on the slab so that one slab could be used to support multiple tests at two curing times (2 and 72 hours after slab fabrication), as shown in Figure 2.14. At the 2-hour test, LWD and then the SSG tests were conducted at the center of the slab. Next, the MH was used for penetration resistance testing at two corner locations on one side of the slab (e.g., upper left and lower left, as shown in Figure 2.14). The tests were con- ducted such that the MH foot was approximately 2 in. from any edge of the slab. Following this, the DCP was used at approximately the midpoint between the two MH tests and approximately 4 in. from the edge of the slab. Moisture content measurements with the moisture gauge were taken in the hole left after the DCP test. At the 72-hour test, the LWD and SSG tests were again conducted at the center of the slab. The MH, DCP, and moisture tests were then conducted at the end of the slab opposite to the end used in the 2-hour test. Moisture contents at the 2-hour test were compared to the moisture content during mixing, and the moisture content at the 72-hour test was compared to the moisture content of a sample taken from the slab after all tests were completed and then dried in an oven. Stiffness and shear resistance tests were conducted on the second set of slabs. These tests were arranged differently since the shear test is destructive. Two or three replicate slabs were prepared from each source project. Tests were conducted on each slab at 1, 3, 6, and 24 hours after compaction. The LWD test was conducted first, followed by the shear test at the same location. At each curing time, a different corner of the slab was tested. Figure 2.15 is a schematic of the test locations. Stiffness, DCP, and raveling tests were conducted on the third set of slabs in a similar way to those performed on the shear test slabs. One or two replicate slabs were prepared from each source project. Tests were conducted on each slab at 1, 3, 6, and 24 hours after compaction. The LWD test was conducted first, followed by the raveling test at the same location. At each curing time, a single measurement using the LWD and raveling fixture were conducted in a different corner of the slab. The DCP test was conducted adjacent to the longest dimension of the slab at 1 and 24 hours only. Figure 2.16 is a schematic of the test locations. 2.3 Phase IIIâField Testing Testing to assess the short-term properties of recycled materials on nine field projects in the United States was conducted at the locations shown in Figure 2.17. The field projects included CIR, CCPR, and FDR using either emulsi- fied or foamed asphalt as the stabilizing/recycling agent with and without cement as an active filler. The projects were completed by multiple contractors using different source materials and were located in different climatic regions. 2.3.1 Objectives Phase III field testing was conducted to assess the most applicable tests from Phase II and to determine the appropriate 6-in.-diameter LWD 8-in.-outer-diameter SSG 4-in.-diameter MH DCP and Moisture Gauge MH Test Line Figure 2.14. Test locations for laboratory-fabricated slabs for stiffness and penetration resistance tests (400 mm Ã« 500 mm), shown to scale. 6-in.-diameter LWD Shear Fixture Figure 2.15. Test locations for laboratory-fabricated slabs for shear tests (400 mm Ã« 500 mm), shown to scale.
18 limits of the tests for identifying time to opening or surfacing. The research team tested multiple locations within the same project when changes in material properties were observed. In addition to the test assessment, a field-based preliminary interlaboratory study (ILS) was performed at one project location to obtain an indication of the precision of the test methods. It was impractical to ship (and receive undamaged) test slabs produced in the laboratory to other research team members while maintaining curing conditions. So the ILS was conducted in the field, as has been done with previous studies on the DCP and for fresh properties of Portland cement con- crete. Lessons learned, draft methods of test, and precision statements were developed from this Phase III testing. 2.3.2 Field Project Summary Table 2.3 shows a summary of the Phase III field projects. All testing was done during the 2019 construction season. The additive and filler contents shown in Table 2.3 were obtained from the material mix designs that were completed by the contractor or agency. Either a contractor or an agency representative used an NDG to measure the field density within or near the test location; the measured field densities are shown in Table 2.3. 2.3.3 Test Block Layout At each field project, the research team met with agency and contractor representatives to discuss the goals of testing and the specific locations available that day. All testing was conducted by members of the research team, but consider- able logistical support was provided by the local agency and contractor representatives. All tests were performed within test blocks that were approximately 4 ft (in the direction of traffic) by 2 ft (perpendicular to the direction of traffic), as shown in Figure 2.18. Within each test block, one field density test and three replicates of stiffness (LWD and SSG), DCP, shear (torque and number of blows), and raveling (torque and number of blows) were conducted. Based on the results of laboratory testing, MH testing was not conducted at the field projects. For several of the early projects, moisture tests were also conducted in the same hole following the DCP tests. Where possible, replicate test blocks were used to gain knowledge of test variability at multiple locations. An NDG was not available for every testing block, so selected test blocks were located near previously performed field density tests. All tests within each test block were completed within approximately 30 minutes. 2.3.4 Testing Details The research team conducted at least one test block at selected curing times ranging from 0.5 hour to 48 hours after the contractor completed the compaction process at the selected test location within the project. Table 2.4 shows the curing times and number of replicate test blocks for each field project. Table 2.5 shows the distribution of testing by process and material type. From Table 2.5, the total number of sections exceeds the number of sites visited since multiple sections were tested at some projects. A total of eight unique process and material combinations were assessed from testing 14 sections and 51 test blocks. 2.4 Repeatability and Reproducibility of Field Raveling and Shear Tests A preliminary evaluation of repeatability and repro- ducibility of the raveling and shear tests developed in this research was conducted by means of a ruggedness evaluation and an ILS in accordance with ASTM C802. In accordance with ASTM E1169 and ASTM C1067, the ruggedness eval- uation was needed prior to the ILS since the raveling and shear tests were newly developed. Once completed, a preci- sion statement was prepared for each test. A ruggedness evaluation is a controlled experiment where factors or test conditions are varied to evaluate their effect on the test response. Examples of factors that were initially con- sidered include test temperature, lift thickness, load/torque applied, and test equipment apparatus physical characteristic dimensions or rates. For each factor, variations or levels were determined at the expected extreme values for each level, and the respective test was conducted. If the impact of level variation due to operating conditions and tolerances proved 6-in.-diameter LWD DCP Raveling Fixture Figure 2.16. Test locations for laboratory-fabricated slabs for raveling tests (400 mm Ã« 500 mm), shown to scale.
3 6 2 With Active Filler No Active Filler CIR CIR CCPR CCPR FDR FDR FDR, CIR, and CCPR (ILS) Numbers in shapes indicate number of projects/processes tested if more than one. Figure 2.17. Project locations for Phase III. State Project Nearest Town Process Agent Agent Content, % Active Filler Active Filler Content, % Field Density, lb/ft3 NY Route 30 Andes CIR Emulsion 2.5 None 0.0 129.1 Route 28 Meredith Emulsion 3.0 141.0 Route 23A Prattsville Foam 2.8 131.9 MN 70th Street Albertville CCPR Foam 2.3 Cement 1.0 133.8Emulsion 3.5 None 0.0 131.3 CIR Foam 2.3 Cement 1.0 130.6Emulsion 2.8 None 0.0 129.0 FDR-HD Emulsion 3.0 Cement 1.0 133.0 FDR-LD Emulsion 3.0 Cement 1.0 117.3 SC SC 123 Clemson FDR Foam 2.3 Cement 1.0 119.4 IN SR 1 Ft. Wayne CIR-GS Emulsion 2.5 None 0.0 122.5CIR-PS Emulsion 2.5 None 0.0 122.5 CA SR 178 Ridgecrest CIR Emulsion 3.4 Cement 0.5 121.6 NM U.S. 491 Tohatchi FDR Foam 2.0 Cement 1.0 134.0 CA SR 22 Woodland CIR Foam 2.2 Cement 1.0 127.9 Notes: FDR-HD = full-depth reclamation, high density; FDR-LD = full-depth reclamation, low density; CIR-GS = cold in-place recycling, good support; CIR-PS = cold in-place recycling, poor support. Table 2.3. Phase III project summary.
20 to be too great, the test method needed to be refined further or the tolerance reduced prior to performing an ILS. Following the ruggedness evaluation, an ILS was con- ducted to generate precision statements for the newly devel- oped test methods in accordance with ASTM C802. For this study, multiple laboratories were represented by three institutions in the research team. Multiple materials were assessed at the field-testing site at the MnROAD test track in August 2019 (as shown in Figure 2.17). The ILS is termed âpreliminaryâ because it was not possible to fulfill all of the requirements of ASTM C802, Standard Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods for Construction Materials, which include a valid written test method, a rugged- ness test prior to the ILS, and a minimum of 10 participating laboratories. Proposed test methods were written for each test, ruggedness tests were conducted for each test, and at least six materials were used per test method. However, only three laboratories participated because the tests were new and commercially available equipment was not available. Also, the ILS was conducted in the field rather than in a laboratory. This was done because of the difficulty associated with pre- paring, shipping, and testing undamaged slabs. 2.4.1 Ruggedness Evaluation A ruggedness evaluation was performed using a single material for both the shear and raveling test methods in accordance with ASTM C1067-2, Standard Practice for Con- ducting a Ruggedness Evaluation or Screening Program for Test Methods for Construction Materials. The laboratory testing conducted as part of Phase II and engineering judg- ment by the research team were used to identify potentially influential factors. Optimally, a ruggedness evaluation would 2 Fe et 4 Feet Shear 1 LWD/SSG1 Shear 2 Raveling 1 LWD/SSG 2 Shear 3 NDG DCP 1 LWD/SSG 3 Raveling 2 DCP 2 Raveling 3 DCP 3 Figure 2.18. Phase III test block layout. State Project Process Curing Time No. of Replicate Test Blocks NY Route 30 CIR E-N 1 hour 224 hours 2 Route 28 CIR E-N 1 hour 148 hours 1 Route 23A CIR F-N 1 hour 118 hours 1 MN 70th Street CCPR F-C 1 hour 3 CCPR E-N 1 hour 3 CIR F-C 1 hour 3 CIR E-N 1 hour 3 FDR E-C HD 3 hours 3 FDR E-C LD 3 hours 3 SC SC 123 FDR F-C 1 hour 24 hours 1 IN SR 1 CIR E-N GS 1 hour 1 3 hours 1 6 hours 1 24 hours 1 IN SR 1 CIR E-N PS 1 hour 2 3 hours 1 6 hours 1 24 hours 1 CA SR 178 CIR E-C 1 hours 1 1.5 hours 1 3 hours 1 NM U.S. 491 FDR F-C 0.5 hours 2 2 hours 1 3 hours 1 4 hours 1 24 hours 2 CA SR 22 CIR F-C 2 hours 1 6 hours 1 24 hours 1 Notes: CIR E-N = cold in-place recycling, emulsion, no cement; CIR F-N = cold in-place recycling, foam, no cement; CCPR F-C = cold central-plant recycling, foam plus cement; CCPR E-N = cold central-plant recycling, emulsion, no cement; FDR E-C = full-depth reclamation, emulsion plus cement; FDR E-C HD = full-depth reclamation, emulsion plus cement, high density; FDR E-C LD = full-depth reclamation, emulsion plus cement, low density; CIR E-N GS = cold in-place recycling, emulsion, no cement, good support; CIR E-N PS = cold in-place recycling, emulsion, no cement, poor support. Table 2.4. Phase III project testing details. Process Agent and Filler No. of Sections No. of Test Blocks CCPR F-C 1 3 F-N â â E-C â â E-N 1 3 CIR F-C 2 6 F-N 1 2 E-C 1 3 E-N 4 18 FDR F-C 2 10 F-N â â E-C 2 6 E-N â â Total number of sections 14 Total number of test blocks 51 Total number of unique process/material combinations 8 Notes: F-C = foam plus cement; F-N = foam, no cement; E-C = emulsion plus cement; E-N = emulsion, no cement. Table 2.5. Phase III total number of sections and test blocks by process.
21 assess each influential factor both independently and inter- dependently using full factorial designs. However, this was not possible given the time and material resources required. Thus, a partial factorial experiment was designed in accor- dance with ASTM C1067. This standard provides clear direc- tion for the design of a ruggedness evaluation for construction materials using the Plackett-Burman design. 188.8.131.52 Ruggedness Evaluation Factors and Levels Eight specimens were prepared and tested using a single material for each evaluated test. Per a Plackett-Burman design, up to seven factors could be considered, with each factor having two levels. In the ruggedness evaluation experimental design, a partial factorial was developed by varying the com- binations of factor upper and lower levels among the eight specimens. Tables 2.6 and 2.7 show the factors and levels for the ravel- ing and shear tests, respectively. The factor and level com- binations were randomly assigned to different slabs as part of an experimental design. The factors investigated included length of the outer pins, pin tip angle, angular rate applied to the torque wrench, tip dullness, and outer pin diameter. The tip dullness was adjusted by first performing the tests with a sharp tip and then grinding off approximately 0.1 in. of the tip to a more flattened tip. Tables 2.6 and 2.7 indicate two levels, denoted with plus (+) and minus (â) signs. A plus (+) sign for a given factor indicates that the measurement was made with that factor at the high level, and a minus (â) sign indicates the factor was at a low level. The factors and values for each level were determined based on the results of concurrent laboratory testing in Phase II, limited field testing, and the engineering judgment of the research team. Tables 2.8 and 2.9 show the associated experimental Level Factor Outer Pin Length, in. Pin Tip Angle, Â° Applied Angular Rate, Â°/sec Tip Dullness Outer Pin Diameter, in. Level 1 (+1) 0.85 70 90 Sharp 1/2 Level 2 (â1) 0.65 50 60 Dull (0.1 in.) 13/32 Table 2.6. Raveling test factors and levels for ruggedness evaluation. Level FactorLength, in. Tip Angle, Â° Angular Rate, Â°/sec Tip Dullness Outer Pin Diameter, in. Level 1 (+1) 3.1 85 90 Sharp 1/2 Level 2 (â1) 2.9 65 60 Dull (0.1 in.) 13/32 Table 2.7. Shear test factors and levels for ruggedness evaluation. Specimen FactorLength, in. Tip Angle, Â° Angular Rate, Â°/sec Tip Dullness Outer Pin Diameter, in. Specimen 1 +1 +1 +1 â1 â1 Specimen 2 â1 +1 +1 +1 +1 Specimen 3 â1 â1 +1 +1 â1 Specimen 4 +1 â1 â1 +1 +1 Specimen 5 â1 +1 â1 â1 +1 Specimen 6 +1 â1 +1 â1 +1 Specimen 7 +1 +1 â1 +1 â1 Specimen 8 â1 â1 â1 â1 â1 Table 2.8. Raveling test experimental design for ruggedness evaluation. Specimen FactorLength, in. Tip Angle, Â° Angular Rate, Â°/sec Tip Dullness Outer Pin Diameter, in. Specimen 1 +1 +1 +1 â1 â1 Specimen 2 â1 +1 +1 +1 +1 Specimen 3 â1 â1 +1 +1 â1 Specimen 4 +1 â1 â1 +1 +1 Specimen 5 â1 +1 â1 â1 +1 Specimen 6 +1 â1 +1 â1 +1 Specimen 7 +1 +1 â1 +1 â1 Specimen 8 â1 â1 â1 â1 â1 Table 2.9. Shear test experimental design for ruggedness evaluation.
22 designs for the raveling and shear test methods, respec- tively. The ruggedness study was conducted in accordance with ASTM E1169, Standard Practice for Conducting Rugged- ness Tests. 184.108.40.206 Slab Preparation for Ruggedness Test Slabs prepared using RAP from Lockwood, Nevada, and PASS-R emulsified asphalt were used to conduct the rugged- ness evaluation. Oven-dried RAP was mixed with 3% water and 4% emulsion (2.4% residual bitumen) until uniformly coated. The optimum moisture content and emulsion content were selected by comparing strength test results for speci- mens prepared in a gyratory compactor. For the shear tests, a Vibroplate compactor was used to compact the mixture to a target density of 130 lb/ft3 in a mold having dimensions of 24 in. Ã 59 in. Ã 3.5 in. Test slabs for raveling tests were fabricated in the same manner, but the molds had dimen- sions of 24 in. Ã 30 in. Ã 3.5 in. For the shear test, the length of the mold was increased from 30 in. to 59 in. so that all the experiments could be performed on the same slab with minimum disturbance from previous tests. The molds were anchored to the concrete floor, as shown in Figure 2.19. All the shear and raveling tests were conducted after 4 hours of curing at ambient conditions. The slabs were cast outside and exposed directly to the sun. 2.4.2 Interlaboratory Study The research team conducted an ILS to develop pre- liminary precision statements for the shear and raveling tests developed in this study. The term âpreliminaryâ is used since only three laboratories participated in the ILS. The ILS was conducted in accordance with ASTM C802 and ASTM C670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials. During the ILS, DCP tests were conducted in addition to the shear and raveling tests, allowing precision statements to be prepared for this test. ASTM C802 outlines the following general requirements for an ILS: 1. A valid and well-written test method; 2. Established tolerances for various conditions in each test method (e.g., from a ruggedness study); 3. Clearly defined and an available apparatus for perform- ing the test; 4. Personnel in participating laboratories with adequate experience; 5. Preliminary knowledge of how changes in materials and conditions affect the test results; 6. Procedures and facilities for obtaining, preparing, and distributing test specimens; 7. Randomized selection of test specimens for distribution to laboratories; 8. Application of the test method on materials with a range of properties representative of the characteristics for which the method will be used; 9. Adequate number of participating laboratories, with at least 10 recommended; and 10. At least three materials or materials with three different average values of the measured test characteristic. For this study, the research team was unable to satisfy requirements 6, 7, and 9. Requirements 6 and 7 could not be satisfied because the research team could not distribute samples to participating laboratories without damaging the samples because of the nature of the material and the effects of transportation and aging. However, within ASTM C802, a provision exists that operators can convene at one location if material cannot be distributed. The research team incor- porated this provision by performing all testing near the MnROAD test track as part of another ongoing study on a portion of 70th Street in Albertville/Oswego, Minnesota. At this location, multiple recycling processes and stabilizing/ recycling agents were used on the roadway to better under- stand their performance as a pavement rehabilitation tech- nique. An example of the preconstruction condition is shown in Figure 2.20. Figure 2.19. Compacted slab for ruggedness evaluation.
23 220.127.116.11 Experimental Design The ILS was conducted on six unique pavement test sec- tions. The test sections included CIR, CCPR, and FDR using emulsified or foamed asphalt, and some contained cement as an active filler. Table 2.10 illustrates the planned test sec- tions; each test section was 500 ft long. Note that the larger MnROAD experiment included mill and fill and thinlay sections that were not tested by the research team. The ini- tial plan was to conduct testing on both the eastbound and westbound lanes for cells 1 through 6. Because of weather restrictions and construction challenges, this was not feasible. Table 2.11 shows the recycling work that was completed and the five sections that were used during the ILS. The beginning of one section (FDR E-C) was found to have lower density than the remainder of the section using the nuclear density Figure 2.20. Preconstruction view of 70th Street, Albertville/Otsego, Minnesota. Figure 2.21. Members of research team conducting ILS. The research team for this study was able to conduct the ILS during this unique opportunity. Requirement 9 was left unsatisfied since the number of member institutions on the research team was less than the required number and the developed tests were not yet commercially available. A photo- graph of the research team members conducting the ILS is shown in Figure 2.21. Direction Test Section1 2 3 4 5 6 7 8 Westbound FDR F-C FDR E-C CIR F-C CIR E-N CCPR E-N CCPR F-C Mill & fill thinlay Thinlay Eastbound FDR F-C FDR E-C CIR F-C CIR E-N CCPR E-N CCPR F-C Mill & fill thinlay Thinlay Notes: CIR E-N = cold in-place recycling, emulsion, no cement; CIR F-C = cold in-place recycling, foam plus cement. CCPR F-C = cold central-plant recycling, foam plus cement; CCPR E-N = cold central-plant recycling, emulsion, no cement; FDR F-C = full-depth reclamation, foam plus cement; FDR E-C = full-depth reclamation, emulsion plus cement. Table 2.10. Proposed ILS test sections. Direction Test Section1 2 3 4 5 6 7 8 Westbound â â â â â â CCPR F-C â Eastbound FDR E-C â CIR F-C CIR E-N CCPR E-N â CCPR F-C â Notes: CIR E-N = cold in-place recycling, emulsion, no cement; CIR F-C = cold in-place recycling, foam plus cement; CCPR F-C = cold central-plant recycling, foam plus cement; CCPR E-N = cold central-plant recycling, emulsion, no cement; FDR E-C = full-depth reclamation, emulsion plus cement. Table 2.11. Actual ILS test sections.
24 gauge. The research team completed testing in this area and considered it a sixth material type. The research team established three adjacent test blocks in a random location along the length of the test section and in the center of the lane. Each of the three laborato- ries was randomly assigned to one of the test blocks. The location of each test within the test block was arranged in a way similar to that shown in Figure 2.18. Three replicate LWD, SSG, DCP, shear, and raveling tests were performed in each test block as soon as the test section was available following compaction. After all testing was complete, the roadway was reopened to traffic. From the collected data, the single-operator and multi-laboratory precision values were calculated.