CASE STUDIES ON PROCESSES INVOLVED IN THE PRODUCTION AND PLACEMENT OF HIGH RAP ASPHALT CONCRETE MIXES IN 2007 ON SELECTED ROUTES IN VIRGINIA

Transcription

1 CASE STUDIES ON PROCESSES INVOLVED IN THE PRODUCTION AND PLACEMENT OF HIGH RAP ASPHALT CONCRETE MIXES IN 2007 ON SELECTED ROUTES IN VIRGINIA Todd Rorrer Assistant Asphalt Program Manager Materials Division Virginia Dept of Transportation 1401 East Broad Street Richmond, VA Alexander K Appea PhD PE Asphalt Program Field Engineer Materials Division Virginia Department of Transportation 1401 East Broad Street Richmond, VA Telephone (804) Alexander.Appea@vdot.virginia.gov Trenton Clark PE Asphalt Program Manager Materials Division Virginia Department of Transportation 1401 East Broad Street Richmond, VA Trenton.Clark@vdot.virginia.gov Corresponding Author: Alexander K Appea Word Count : Figures + 7 Tables = 8605

2 Rorrer, Appea, Clark 2 ABSTRACT This paper presents the documentation of Recycled Asphalt pavement processes in selected plants that were involved in the production of High RAP mixes for selected plant mix schedules which were placed in 2007 in the state of Virginia. A description of the processing of RAP at the different plants is given and how the production of the high RAP material (reclaimed asphalt pavement which make up 20% or more of the asphalt mix) was monitored at the plants and the field on the selected routes in the state of Virginia. The different types of asphalt plants operated by the different contractors are discussed showing how quality control processes are monitored in High RAP production. Process control charts were shown for the RAP materials in one of the selected plants in addition to laboratory testing results. Results show the placement of the High RAP went well and field monitoring mechanisms are being put in place to continue monitoring these sites for long term performance.

3 Rorrer, Appea, Clark 3 BACKGROUND In 2007, Virginia Department of Transportation (VDOT) decided to allow the higher percentages of recycled asphalt pavement (RAP), i.e. more than 20 percent, in hot mix asphalt with no change in binder grade. Because of this increase, one section of the contract provisions in certain plantmix overlay schedules around the state had to be rewritten to raise the limit on the proportion of recycled material to 30% from 20% (1). There has been a push from all over the states to increase RAP used in asphalt pavement. It was reported that about 140 million tons of asphalt concrete are recycled in the United States each year, according to the Construction Materials Recycling Association and it is also reported that market forces and project conditions not government mandates are driving reuse of materials in today s highway (2). At the current price of price of liquid AC above $700 a ton and the price of rock aggregates between $5 to $20 per ton, the economics of using RAP is an attractive choice to both producers and department, since recycling can make use of the aged asphalt binder in the recycled material in addition to the virgin binder added at the plant. In Virginia a high recycled asphalt pavement (RAP) concrete SM 12.5D mix with 25% RAP was incorporated in plant mix schedules that were placed on some selected secondary routes (Route 40 and 6) in Richmond and Dinwiddie respectively and 30% RAP was placed on Interstate 664 in the City of Chesapeake. The Route 40 in Dinwiddie County was supplied by an Asphalt Plant owned by B.P Short Inc located in Petersburg with capability for RAP processing. Route 6 (in Goochland County) was supplied with RAP processed at Branscome Inc plant in Powhatan and the Interstate 664 Route was supplied with RAP processed at the Branscome Plant in Hampton. This paper presents the documentation of RAP processing that occurred at the different plants and a brief description of the asphalt plants and some field monitoring issues. Rideability data on one of the routes show the contractor was able to improve the quality of the ride on the road even with the introduction of high RAP The process control charts were developed for one of the plants to determine whether the addition of RAP to the virgin mix affected the contractor s ability to control his process and meet VDOT specifications RAP Processing and Plant Capabilities at B.P. Short s - Jack Plant A total of 8006 tons of SM 12.5D mix made up of 25% RAP was produced and placed in Route 40 in Dinwiddie County. This mix was produced in BP Short and Sons plant based in Petersburg, Virginia. Most of the RAP material used at this plant is from dense graded surface and base courses. The RAP used in this project came mainly from millings off of the Battlefield Park project, which is not too far from the plant. B.P. Short manages several stockpiles of RAP: an unprocessed RAP stockpile which is comprised of construction waste that includes slabs of asphalt pavements, millings and plant waste as well as separate milling stockpiles. Millings from known sources are kept separate if they can be used with limited processing. The RAP processing used at this facility produces a fine graded RAP material with conglomerates up to 2 inches in diameter. Figure 1a shows the un-processed RAP stockpile on the left and the processed RAP on the right. This plant has the ability to produce either a 9.5 or 12.5 mm HMA mix containing more than 25% RAP. The plant used the PROTONGRIND (seen in Figure 1b) for initial processing. The Protongrind uses a standard milling head in an enclosed chamber to break the RAP down into a manageable consistency but does not reduce the size of the aggregates. The material is then

4 Rorrer, Appea, Clark 4 FIGURE 1a Un-Processed and Processed Rap Stockpiles. FIGURE 1b PROTOGRIND machine for grinding RAP Materials at the Plant. stockpiled and can be used as a component material for HMA or it can be processed further depending on the need. The plant has the ability to fractionate or scalp their stockpiled RAP with a separate screen deck and conveyor system (Figure 2a) before it enters the RAP feed at the plant. This system is employed to incorporate higher RAP contents and/or to control the max aggregate

5 Rorrer, Appea, Clark 5 size entering the mix. The plant s RAP feed bin can accept various RAP components, from straight millings to fractionated or scalped RAP. FIGURE 2a Separate screen deck and conveyor system. From the feed bin the RAP material is sent through a Hammer mill that breaks the RAP material down to a specific size. The screens can be set by the panels in the hammer mill to produce the desired size of RAP. The oversize RAP material is brought back through the Hammer mill to be reground and broken down into smaller sizes. The maximum RAP size that can be used in this plant is 2 inches. The Hammer mill equipment is shown in Figure 2b. As part of the quality control plan, tests samples are taken from the processed RAP stockpile to be checked for gradation and moisture and asphalt contents once a day. RAP Feed Bin Hammer mill and screen deck FIGURE 2b: RAP Feed and Hammer mill to supply RAP to the plant. The estimated maximum RAP capacity of the plant ranges from 35 to 40%. The HMA Plant at this facility installed in the late 1980 s is a single barrel counter flow type drum with a capacity of 250 tons per hour. The typical operating temperatures for this plant range from 325 to 330oF, the temperature also depends on the amount of moisture present in the component materials Job Mix Formula and Production The job mix formula for the SM-12.5D with 25% RAP (VDOT Mix ID ) was submitted and granted approval in August The mix proportions, as well as the material source data is given in Table 1a. The Contractor did not produce a conventional SM-12.5D from this plant in

6 Rorrer, Appea, Clark However they did produce 9 lots of a conventional SM-12.5D with 20% RAP in 2006 (VDOT Mix ID ) using the same mix components as the 25% RAP mix produced in Both mixes are detailed in Table 1b for comparison. The additional 5% RAP did not require a change to the aggregate structure, percent fines or the asphalt cement content. TABLE 1a Material Source Data for Different Mix Proportions Material Bin Percentage (%) Mix ID 722 Bin Percentage (%) Mix ID 612 Kind Source Aggregate #8 A Stone Vulcan Materials Jack Quarry Aggregate Washed Vulcan Materials Jack Quarry Screenings RAP RAP Various Sand 10 5 Concrete Sand Vulcan Materials Puddledock Screening 8 15 Dry Screenings Vulcan Materials Jack Quarry Asphalt Cement PG Valero Additives Kling Beta Akzo-Nobel TABLE 1b Conventional and High RAP Bin Percentages and Job Mix Formulas SM-12.5D w/ 25% RAP Total % Passing SM-12.5D w/ 20% RAP Total % Passing Job-Mix Lab JMF Sieves 19 mm mm mm mm mm mm 5.0. Asphalt (%) 5.5 Job-Mix Lab JMF Sieves 19 mm mm mm mm mm mm 5.0 Asphalt (%) 5.5 Plant Temperatures Mix 722 with 25% RAP had an average temperature leaving the plant of o F and was produced in the month of August. Mix 612 with 20% RAP had an average temperature of o F and was produced in the spring and fall of The difference in temperatures leaving the plant is mostly likely due to ambient temperatures and not related to the increased RAP percentage; both averages are within VDOT specifications for plant temperatures. Materials Acceptance and Variability VDOT accepts Hot Mix Asphalt based on individual lot averages and variability for AC content and gradation per the Road and Bridge Specifications Section 211 (3). Four full 2000-ton lots of the SM-12.5D with 25% RAP were produced for the Dinwiddie schedule and all lots were within specifications and no price adjustments were applied.

7 Rorrer, Appea, Clark 7 Mix Volumetrics Superpave volumetric properties were monitored throughout production by the contractor at a minimum rate of one sample per 1000 tons produced with at least one sample per production day. The Superpave properties of Voids in the Mineral Aggregate (VMA), Voids Filled with Asphalt (VFA) and Voids in the Total Mix (VTM) were measured from samples produced at 65 gyrations in the gyratory compactor. Figure 3 shows the results of the contractor s testing for the conventional and high RAP mixes, 612 and 722 respectively. Data points on the Chart represent the results of one sample and data points falling within the green and red boundaries meet VDOT specifications. B.P. Short measured the volumetric properties of mix 722 in every 500 Ton sub-lot, with the only discrepancies occurring on the VFA. These four samples came from lots 1 and 3. Both lots 1 and 3 had AC contents that were outside of the mix s established control limits but within the specification limits as can be seen in the following process control charts for the mix. 5.4% 4.9% Universal Volumetric Chart: Mixes & 722 SM-12.5D w/ 20% & 25% RAP VFA 65 Voids in Total Mix (%) 4.4% 3.9% 3.4% 2.9% VMA14 VFA 83 Mix ID 612 Mix ID % VMA 13 VMA15 1.9% 8.5% 9.5% 10.5% 11.5% 12.5% 13.5% 14.5% Volume Binder( % effective) FIGURE 3 Universal Volumetric Chart. Process Control and Capability Process Control Charts (Xbar and s) shown in Figures 4 and 5 were developed for both mixes in order to compare the production variability to current VDOT specifications. This was done to confirm that the additional RAP would not affect the contractor s ability to control his process and meet specifications.

8 Rorrer, Appea, Clark 8 Percent Asphalt (Avg/Lot) Control Chart: Asphalt Content/Lot USL (5.8%) UCL (5.67%) Mean (5.48%) LCL (5.30%) LSL (5.2%) Percent Passing (Avg/Lot) Control Chart: Percent Passing The 200 Sieve / Lot USL (6.0%) UCL (5.5%) Mean (5.2%) LCL (4.8%) LSL (4.0%) Percent Passing(Avg/Lot) Control Chart: Percent Passing The #8(2.36mm) Sieve USL (45.0%) UCL (43.2%) Mean (41.5%) LCL (39.8%) LSL (37.0%) Percent Passing(Avg / Lot) Control Chart: Percent Passing the 3/8in (9.5 mm)sieve FIGURE 4 SM-12.5 with 25% RAP Control Charts USL (93.0%) UCL (91.6%) Mean (90.3%) LCL (89.0%) LSL (85.0%) Control Chart: Asphalt Content/Lot Percent Asphalt (Avg/Lot) USL (5.8%) UCL (5.54%) Mean (5.39%) LCL (5.23%) LSL (5.2%) Percent Passing (Avg/Lot) Control Chart: Percent Passing The 200 Sieve / Lot USL (6.0%) UCL (5.5%) Mean (4.9%) LCL (4.3%) LSL (4.0%) Percent Passing(Avg/Lot) Control Chart: Percent Passing The #8(2.36mm) Sieve USL (45.0%) UCL (42.0%) Mean (40.3%) LCL (38.6%) FIGURE 5 SM-12.5 with 20% RAP Control Charts. LSL (37.0%) Table 2 shows how the process control values are obtained. Both mixes showed processes that were in control and capable of meeting the specifications. The mix with 25% RAP operated higher in the specification range for AC content and seems to be sensitive to VFA issues whenever the material fell outside of the established control limits. The 20% RAP would

9 Rorrer, Appea, Clark 9 approach the VFA limit but not exceed the established criteria. No single property of either mix exceeded using more than 62% of the established specification range. This gives the contractor the needed flexibility to make adjustments to the mix during production without risking price adjustments. The processing used for both mixes was capable of producing a controllable mix within specifications. TABLE 2 Control Chart Nomenclature Chart Nomenclature USL UCL Mean LCL LSL Upper Specification Limit Upper Control Limit Grand Average of all lots Lower Control Limit Lower Specification Limit Definition Job Mix Target + VDOT Specified Tolerance on Lot Averages Grand average + 3 standard deviations Grand average -3 standard deviations Job Mix Target VDOT Specified Tolerance on Lot Average Each point on a control chart is the average of 4 samples per 2000-ton lot. The blue error bars per lot represent one lot standard deviation in each direction. Rut Testing Samples for measuring the mix s susceptibility to rutting were taken for the SM-12.5 with 25% RAP. The conventional SM-12.5 (Mix ID 612) used for comparison was not sampled for rut testing in The testing was performed using the Asphalt Paving Analyzer (APA) using a 120lb point load, a hose pressure of 120psi, at 120 o F for 8000 cycles in accordance with VTM-110 (4). Table 3 shows the summary of the results. TABLE 3 APA Rut Testing Mix ID 722 SM-12.5D w/ 25% RAP Date Sampled 08/24/07 Lot # 2 Rut Depth [mm] Max Rut Depth per VDOT specs [mm] 7.7% Air Voids 5.5mm Field Operations and Monitoring Issues Materials inspection and quality/independent assurance testing was provided by the South Hill Residency in the Richmond District. VDOT accepts the field placement of Hot Mix Asphalt based on the average nuclear density reading on 5000 ft lots referred to as test sections. A nuclear target was established using the roller pattern and control strip method and this target must be

10 Rorrer, Appea, Clark 10 verified on a %Gmm basis by cores sawn from the control strip. The requirements for the placement of this mix for temperature and densities were: Minimum/Maximu m Lay-down temperatures Minimum Control Strip Target Density (% Gmm) 270 to 350 F to Minimum Production Density (% of Nuclear Target) The target control strip density of lb/ft 3 was determined and the average % Gmm of the target verification cores from the control strip was 93.3%. Densities of the test sections as a percentage of the nuclear target are shown in Table 4. The percent nuclear target densities obtained during production averaged 99.49% and ranged from 98.6% to 100.6% with a standard deviation of 0.62 and a coefficient of variation of 0.62%. TABLE 4 Field Acceptance Data Date % of Nuclear Target Density 8/23/ /23/ /24/ /24/ /25/ /25/ /27/ /27/ /28/ /28/ /29/ RAP Crushing Operations at Hampton Plant A total of 7093 tons of SM 12.5D material with 30% RAP was produced and placed on portions of Interstate 664 from milepost 3.81 to 5.23 in both north and southbound lanes in the city of Chesapeake. The facility at the plant where the asphalt concrete was produced was too small to handle a RAP processing operation so all the RAP was processed offsite and trucked to the facility. A layout of the facility with the processed RAP stockpile is shown in Figure 6. The HMA plant was located in the City of Suffolk and is a CMI parallel flow drum plant capable of producing asphalt at 400 tons per hour The RAP used at the Suffolk Plant is processed by Interstate Custom Crushing at the Branscome Hampton Plant off of Interstate-664 West.

11 Rorrer, Appea, Clark 11 FIGURE 6 Layout of Suffolk Plant owned by Branscome Inc. The main sources that go into the processed RAP produced at this site are dense graded surface millings, base millings, SMA plant waste, plant waste and asphalt construction waste. No effort is made to segregate the sources for normal processing operations. The surface millings are predominately the older VDOT specified S-5 and SM-2A mixes that have been used in the Hampton area since the 1990 s. Figure 7 shows a view of the unprocessed RAP stockpile Interstate Crushing uses a primary and a secondary crusher with a screen deck and an oversized return. The primary crusher is a Pioneer Impact crusher and has the ability to reduce aggregate size by crushing. This system operates at this site for two to three weeks, three times a year. In a typical operation the unprocessed RAP is removed from the stockpile at the Hampton Plant and dumped into a feed bin which is then sent to the primary crusher. The crushed RAP is sent by conveyor belt to the secondary crusher and screen deck. Between the primary crusher and the secondary crusher there is a magnetic belt used to remove metal objects. The screen deck uses a 9/16 inch size screen to scalp the final product sent to the processed stockpile. The oversized RAP FIGURE 7 Unprocessed RAP Stockpile at the Hampton Plant.

12 Rorrer, Appea, Clark 12 material is sent back through the secondary crusher by the oversized return to be re-crushed, scalped and sent to the processed RAP stockpile. This RAP operation has the capability of crushing about 300,000 tons a year. Figures 8 and 9 show the crushing operations as explained FIGURE 8a Interstate Crushing Equipment showing Primary Crusher location. FIGURE 8b Secondary Crusher Component in RAP processing. FIGURE 9 Screened RAP sent by conveyor belts to Processed RAP Stockpile. RAP Placement into HMA at the Suffolk Plant At the Suffolk plant the processed RAP stockpiles supplied from the crushing operation sites are not protected with any special covering. The Branscome quality control plan for the RAP involves sampling a quantity of processed RAP once a week for determining Asphalt Cement (AC) and moisture contents. The average AC content normally is between 5 and 5.2%. Moisture contents are normally in the range of 6 to 7%. In cases of high moisture contents resulting from heavy rainfall the percentage of RAP used in the plant is reduced to allow the plant operator better control of the mix. At the stockpile feed system before the processed RAP is introduced into the mix, the processed material is screened over a scalping screen to remove larger particles. The screen sizes may vary from 1/2 inch to 9/16 inch depending on mix type being produced. The screened RAP is then sent by a conveyor system to the RAP collar before it is introduced into the drum where it

13 Rorrer, Appea, Clark 13 meets the virgin aggregates and is mixed as shown in Figures 10 (a to c). The super hot virgin aggregates liquefy the asphalt in the recycled material and the asphalt in the RAP coats the virgin aggregates before fresh asphalt is injected into the mix.. FIGURE 10a Processed RAP is conveyed to the drum after going through screening units. FIGURE 10b Processed RAP enters the drum mixer through a RAP collar. FIGURE 10c Mixing chamber where RAP, virgin aggregates and asphalt are mixed. The amount of RAP introduced in the drum affects the operating temperatures in the plant. Higher plant operating temperatures are required when more RAP is added to the virgin mix. A summary of plant operating temperatures at this plant when there is no RAP in the mix and when RAP is added to the mix is shown in Table 5..

14 Rorrer, Appea, Clark 14 TABLE 5 Rap vs. Mix Temperature Amount of RAP in HMA Plant Operating Temperature ( F) 10% % % 350 No RAP Rut Testing Samples for measuring the mix s susceptibility to rutting were taken for the SM-12.5 with 30% RAP. The testing was performed using the Asphalt Paving Analyzer (APA) using a 120lb point load, a hose pressure of 120psi, at 120 o F for 8000 cycles in accordance with VTM-110. Table 6 breaks down the testing results. The mix met the VDOT specification where the maximum mix rut depth allowed is 5.5mm for an SM 12.5 surface mix. TABLE 6 APA Rut Testing Mix SM-12.5D w/ 30% RAP Date Sampled 07/16/07 Lot # 1 Rut Depth 7.7% Air Voids [mm] Max Rut Depth per VDOT 5.5mm specs [mm] Extraction, Recovery and PG Grading Samples for determining the Performance Grade of the asphalt in the mix were taken at the same time as the rut samples were taken. The asphalt cement was extracted from the mix in accordance with AASTHO T-164 Quantitative Extraction of Asphalt Binder from Hot-Mix Asphalt. The asphalt cement is then recovered from the extraction solution in accordance with AASHTO T-170 (5) Recovery of Asphalt from Solution by Abson Method. The asphalt cement was then sent to Virginia Transportation Research Council for grading in accordance with AASHTO R-29 Grading or Verifying the Performance Grade of an Asphalt Binder. The mix was comprised of a binder with 30% RAP, the extracted binder graded out to be a PG Field Acceptance and Observations The sub contractor, Dominion Paving, milled 2 inches of the pavement section under VDOT s performance milling specification, which allows the milled surface to be opened to traffic for approximately one week, before it was paved with the SM-12.D mix with 30% RAP by the main contractor Branscome Inc. Materials inspection and quality/independent assurance testing was provided by Hampton Roads District Materials Office. The requirements for the placement of this mix for temperature and densities were: Lay- Minimum/Maximum down temperatures Minimum Control Strip Target Density (% Gmm) 270 to 350 F to Minimum Production Density (% of Nuclear Target)

15 Rorrer, Appea, Clark 15 The target control strip density was determined to be lbs/ft 3 and the subsequent test values resulted in an average of %; reported as a percentage of target nuclear control strip density, with 101.6% and 99.3% being the maximum and minimum reported values respectively. The target nuclear control strip density is verified by determining the % Gmm of 6 cores taken from the three locations closest to the average nuclear density along the control strip. The average % Gmm of the cores for this control strip was 95.3% recorded. Most of the construction was done at night time. The highest ambient air temperature recorded on the project was 102 F on 7/19/07 during paving operations and the lowest temperature recorded was 66 F on 7/23/07. It was reported in the job records that the mix was placed and compacted by contractor in a professional manner and no placement and workability problems were encountered with this mix at the job site. A visual survey of this section of road built with 30% RAP, after eight months of service, indicates it is performing well though long term monitoring and performance will be done. Rideability and International Roughness Index The smooth paving operations resulted in the contractor earning an incentive cash bonus for the four lanes paved (approximately 1.4 miles each lane). This was an overall improvement of 40% in the pavement smoothness as reported in Table 7 below. TABLE 7 *IRI Improvements in the east and westbound lanes of I-664 IRI Before IRI After Route 664 % Improvement Construction Construction Eastbound Lane Eastbound Lane Westbound Lane Westbound Lane * IRI is in inches per mile RAP Processing and Plant Description at Branscome Powhatan A total quantity of 5,250.6 tons of SM 12.5D mix with 25% RAP was placed on Route 6 between May and September of The RAP material used for this project was processed at a site adjacent to the Branscome Asphalt Plant in Powhatan County on Route 60 in Richmond. Typically three sources of unprocessed RAP are stockpiled separately at this site. The sources are: 1) general asphalt construction waste which comes from private contractors who dump the asphalt waste at no charge, 2) plant waste which includes rejected HMA from plant production, plant calibration runs, and cleaning runs, and 3) milled asphalt from roads and parking lots. The material is almost exclusively dense-graded base and surface type mixes, there is currently no RAP from SMA (stone matrix asphalt) sources. The processing crews try to maintain a proportional combination of the three sources to create a consistent final product. The RAP is estimated to account for 35-40% of mixes on private jobs for surface and base mixes. Figures 11a,b and c emphasize the three distinct sources as managed at the Powhatan facility. The individual processed RAP stockpiles at the processing site were not covered with any protective covering, there were however discussions by the plant management on instituting methods to reduce the moisture content in the RAP stockpiles. The processed RAP is checked

16 Rorrer, Appea, Clark 16 once every 2,000 tons for moisture and asphalt contents. The amount of moisture in the RAP varies between 5 and 8%, while the typical AC content is about 5%.

17 Rorrer, Appea, Clark 17 FIGURE 11a Backhoe operations on unprocessed RAP stockpile at Powhatan. FIGURE 11b General asphalt construction waste to the left and Clean millings to the right are kept separate. FIGURE 11c Asphalt Plant waste is separated into a third distinct source. As part of the process control, the gradation of the RAP is checked to ensure 100% of the processed RAP is passing the 1/2 inch sieve. High amounts of minus #200 materials are generated in this process and can affect the amount of RAP incorporated into a mix. Therefore the percent passing the #200 sieve is monitored closely. Nine to ten percent passing the #200 sieve is the

18 Rorrer, Appea, Clark 18 limit set for the processed RAP. There is no attempt to fractionate the RAP material and the final product from this standard processing is used in all mix types. The unprocessed RAP is loaded onto the crusher, where a blow bar type crusher crushes or breaks the RAP materials into smaller pieces. This crusher can reduce the maximum aggregate size in the RAP. The crushed material passes over screens of size 9/16 inch and the oversized materials are returned through a loop in the mobile equipment to be re-crushed. Once or twice a day the rejected over sized particles, which may contain metals, cans and other non-rap objects, are removed and dumped as waste. The mobile crushing operation is detailed in Figure 12 a and b. The processed RAP material is then stockpiled nearby, and is then available to be trucked to the nearby asphalt plant or other facilities in the region FIGURE 12 a Mobile Crushing Equipment at the Powhatan Plant. FIGURE 12b Processed RAP material being produced from Mobile crushing equipment at the Powhatan Plant. The HMA plant located at the Powhatan facility is an ASTEC half barrel, counter flow drum plant, with a capacity of 400 tons per hour. RAP is introduced into two feed bins and sent by a single conveyor system through the scalping screens (3/4 size) in one passage. The oversized RAP aggregates are scalped/discarded and collected on site The screened RAP material is then sent to the drum and is introduced into the outer-half barrel where it meets the superheated virgin aggregates and the two materials are mixed. The super hot virgin aggregates melt the old asphalt in the recycle material and the aged asphalt coats the virgin aggregates before fresh asphalt is introduced into the mix at the pug mill. The total mixing time in the outer barrel and the pug mill is longer than a typical drum plant and may give

19 Rorrer, Appea, Clark 19 the opportunity for a more thorough blending of the aged and virgin binders. Parts of the plant is shown in Figure 13 a and b FIGURE 13a Half Barrel overview FIGURE 13b RAP transported through scalping screens to Drum QUALITY CONTROL AND PLANT OBSERVATIONS Mix Volumetrics Mix Volumetrics were monitored throughout production by the contractor at a minimum rate of one sample per 1000 tons produced with at least one sample per production day. The Superpave properties of Voids in the Mineral Aggregate (VMA), Voids Filled with Asphalt (VFA) and Voids in the Total Mix (VTM) are measured from samples produced at 65 gyrations in the gyratory compactor.

20 Rorrer, Appea, Clark 20 Extraction, Recovery and PG Grading Samples for determining the Performance Grade of the asphalt in the mix were taken at the same time as the rut samples. The asphalt cement was extracted from the mix in accordance with AASTHO T-164 Quantitative Extraction of Asphalt Binder from Hot-Mix Asphalt. The asphalt cement is then recovered from the extraction solution in accordance with AASHTO T-170 Recovery of Asphalt from Solution by Abson Method. The asphalt cement was then sent to Virginia Transportation Research Council for grading in accordance with AASHTO R-29 Grading or Verifying the Performance Grade of an Asphalt Binder. The mix was comprised of a binder with 30% RAP, the extracted binder graded out to be a PG Field Operations and Monitoring Issues Materials inspection and quality/independent assurance testing was provided by consultant inspectors for the Richmond District. VDOT accepts the field placement of Hot Mix Asphalt based on the average nuclear density reading on 5,000 ft lots referred to as test sections. A nuclear target for the test sections is established using the roller pattern and control strip method and this target must be verified on a %Gmm basis by cores sawn from the control strip. The requirements for the placement of this mix for temperature and densities were: Lay- Minimum/Maximum down temperatures Minimum Control Strip Target Density (% Gmm) 270 to 350 F to Minimum Production Density (% of Nuclear Target) Results for the SM 12.5D ranged from 99.0 to 100.7% of the established target. All test sections resulted in 100% pay for the contractor based on percentage of the target nuclear control strip density. The density of one core cut in Lot 1 for the SM 12.5D mix was verified and reported as 97.1% of Gmm. From the data obtained from the placement operations the mix performed adequately throughout the entire production period CONCLUSIONS The use of High RAP (Reclaimed Asphalt Pavement which make up 20% or more of the asphalt) were incorporated in the plant mix schedule and placed in Richmond, Dinwiddie County and the City of Chesapeake. Field monitoring is planned for these different high RAP mix that were placed and also comparing the performance to control mixes that were placed in other locations in the state. Field operations show that the high RAP mixes were placed with minimal problems in these routes mentioned in the paper and had satisfactory laboratory results. Continual monitoring will aid in coming out with life cycle cost savings. The continual success of the use of RAP will depend also on the quality after processing and the quality of good construction practices. ACKNOWLEDEMENTS The authors will like to express their gratitude to W.R Bailey III, Assistant State Materials Engineer of VDOT and Mourad Bouhajja (formerly of VDOT Materials Division) for being instrumental in organizing the planning of the evaluation of RAP sites throughout the state which resulted in documenting and collecting data for the projects in this publication. REFERENCES

21 Rorrer, Appea, Clark Maupin, G. W., Jr., Diefenderfer S., and Gillespie James Evaluation of Using Higher Percentages of Recycled Asphalt Pavements in Asphalt Mixes in Virginia.Final VTRC 08-R22. Virginia Transportation Research Council, Charlottesville, Kuennen T. Green Highways Now Part of Complete Package. Better Roads, February pp Roads and Bridges Specifications, Virginia Department of Transportation Virgina Department of Transportation. Virginia Test Methods. Richmond 5. American Association of State Highway and Transportation Officials. Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part 2B: Tests. Washington, D.C., 2006

22 Rorrer, Appea, Clark 22