Recycling and Reclamation of Asphalt Pavements Using In-Place Methods (2011)

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36 CHAPTER FIVE BENEFITS AND BARRIERS BENEFITS A number of advantages to using in-place recycling pro- cesses are routinely cited in the literature. Survey questions were included to assess state and contractor perceptions of benefits. The most frequently cited benefit is a savings of virgin materials (Table 37). Other benefits include shorter lane closures, reduced fuel consumption, and reduced emis- sions. Potential cost savings with recycling are addressed in the following section. TABLE 37 STATE AND CONTRACTOR RESPONSES FOR TYPE OF SURFACE TREATMENT USED Question: Environmental Benefits: Indicate environmental benefits, which you have documented on your projects Surface Treatments Agency Responses Saves Virgin Materials AK, AR, CA, DC, DE, FL, GA, IA, ID, IL, KY, MD, MN, MO, MT, NC, NE, NV, NY, ONT, OR, UT, VT, WY Reduces Fuel Consumption CA, DC, ID, KY, MN, NV, ONT, UT, VT Reduces Emissions CA, DC, ID, MN, NV, ONT, UT, VT Shortens Lane Closures CA, DC, FL, ID, IL, MN, NV, ONT, UT Other AZ, NV Contractors noted benefits associated with in-place recy- cling more frequently than did state agencies (Figure 30). The agency written responses suggest that agencies sub- jectively assume that benefits are achieved, but they do not specifically measure the benefits (Table 38). On the other hand, contractors provided a number of specific quantifiable examples of environmental benefits. Additional information on environmental benefits was found in the literature. Alkins et al. (2008) reported that CIR and CIR-expanded asphalt mixes (CIREAM) had twice the production rate compared with the traditional mill and over- lay option, reducing traffic disruptions and worker exposure to traffic. These processes generate less noise and conserve natural resources by using recycled materials on the road- way. An evaluation of emissions using PaLATE found a reduction in greenhouse gases. CIR and CIREAM programs in Ontario, Canada, reduced carbon dioxide by 52%, nitric oxide/nitrogen dioxide by 54%, and sulfur dioxide by 61% compared with the mill and overlay option. CIREAM also reduces the typical curing time from about 1 to 2 weeks for CIR to 2 days for CIREAM (Lane and Kazmierowski 2005b). FIGURE 30 Environmental benefits from in-place recycling reported by agencies and contractors. Percentages are based on the total survey respondents. The agency and contractor responses were used to rank and summarize the benefits gained from in-place recycling (Table 39). TABLE 39 BENEFITS FROM IN-PLACE RECYCLING Benefits from In-Place Recycling Frequency of Benefit Saves new materials Frequently Shortens lane closure times Often* Reduces fuel consumption Often* Reduces emissions Often* Rarely = lower than 10% average of agency and contractor with experience. Sometimes = between 10% and 25% average of agency and contractor with experience. Often = between 25% and 50% average of agency and contractor with experience. Frequently = greater than 50% average of agency and contractor with experience. *Contractor response was significantly higher than agency with experience. Contractor project records can be used to provide quan- tifiable environmental benefits from in-place recycling. Future research is needed to quantify benefits.

37 – Heater repaving averaged $2.17 per square yard, but the database contained only two projects con- structed over the 8-year period. • FDR costs vary with the selection of additives and sta- bilizers (Mallick et al. 2002): – Pulverized material with water and mechanical sta- bilization was $2.00 to $2.10 per square meter. – Emulsion stabilization was $3.50 per square meter. – Emulsion with lime (2%) additive was $3.75 to $3.85 per square meter. – Emulsion with cement (5%) was $3.25 to 3.35 per square meter. • FDR saved 25% of the project cost compared with stan- dard reconstruction (Rosenmerkel 2003). • Maine reported a cost savings by using FDR of $8.86 per square meter when compared with full conventional reconstruction, which included excavation, placement, grading, compaction, and paving (Harrington 2005). • Nevada projects showed that – Savings of $104,000 per centerlane-mile savings could be realized if a 75-mm (3-in.) CIR with dou- ble chip seal wearing course was used instead of the conventional HMA. – Savings of $38,000 to $93,000 per centerline mile could be realized with FDR, CIR, and CIR with stockpiled millings compared with conventional HMA approaches to address structural deficiencies. TABLE 38 WRITTEN RESPONSES FOR ENVIRONMENTAL BENEFITS Environmental Benefits: Can you quantify these environmental benefits? If so, please provide a summary of these quantified benefits. State Responses Contractor Responses FDR reduces pavement structure requirement 20%–50% CIP sometimes reduces overlay thickness required up to 50%. (IA) Less use of virgin materials and use of resources. (MD) No—varies by project. (WY) No Experience to quantify (DE) No. Information is not available. (ID) Not enough projects to quantify benefits. (AZ) The emission savings are quantified using PaLATE soft- ware. The emissions savings for using CIR or CIREAM are: 52% reduction in carbon dioxide; 54% reduction in nitrogen oxide; 61% reduction in sulfur dioxide com- pared to traditional HMA paving operation. (MTO) There also is a reduction in the hauling of material to the site. Actual quantities are hard to estimate as full imple- mentation has not been done. (UT) We have not documented any environmental benefits, but it is assumed that these projects use less virgin mate- rial then a non-recycled project. (ND) By virtue of the CIR process, the city estimates that over 840 truck trips were eliminated from traveling over city streets during the construction operation. In addition, the process saved 1,649 barrels of oil, while reducing the overall carbon emissions by approximately 80% com- pared with the alternative methods of rehabilitation the city considered. It reduced the entire project time by 5 working days and at the same time saved over $262,000 for the city CIR Foamed Asphalt Project I-80, Caltrans data show the CIR process saved 101,909 metric tons aggregate, 2,545 metric tons bitumen, 9,200 truck trips @ 80 km round trip, 736,000 truck traveled km, 204,000 liters of diesel, and 7200 kg of 0x emissions. On a 5.5 mile segment constructed in two sections, the existing HMA pavement 22 ft wide was widened to a 28-ft wide bituminous base course using an FDR process. The material from the widening trench was stockpiled to be used as shoulder material after the paving was completed. The widening material came from milling the existing surface, placing the mill- ings in the widening trench and processing the entire width—eliminating the longitudinal widening joint. This project saved 2,800 tons of aggregate that would have been used as shoulder material. This process also eliminated the need of providing 9,040 tons of a HMA widening material. Documented a 50% savings in CO2 emissions, 55% savings in 0x emissions, and 60% sav- ings in SO2. Other contractor savings noted, but without quantities included reductions in: • CO2 emissions • Collateral ESALs on adjacent roadways • Need for future maintenance (i.e., proven long-term solution) • Construction traffic congestion (i.e., fewer trucks) • Fuel consumption COST BENEFITS Cost savings reported in the literature include • Canadian research, which showed that the net present value of the CIR option was 13% higher than an over- lay; however, the cost–benefit ratio was 8 times greater (Cuelho et al. 2006). • North Dakota research showed that selecting the most appropriate surface treatment for traffic conditions can result in significant savings. One project evaluation showed that CIR–double chip overlay was $180,000/ mile for higher traffic sections, but changing to a CIR– single chip seal for lower traffic sections reduced the cost to $80,000/mile (costs also were lower because traffic control was provided by the county). • HIR costs vary with the type of HIR used for the proj- ect. The Colorado DOT experience with HIR recycling from 2000 to 2008 showed the following differences in cost (Fisher 2008): – Heater scarifier treatment averaged $1.55 per square yard for 19 projects, with quantities recycled from 50,000 to more than 350,000 square yards of old pavement surface. – Heater remixing averaged $3.74 per square yard for 37 projects 50,000 to more than 500,000 square yards in size.

38 – Estimated network-level savings of $8,400,000 per year could be realized if strategies other than con- ventional HMA are used (Maurer and Polish 2008). • Savings are achieved for FDR projects when the patch- ing level is below 15% to 20% (PCA 2005). Additional cost savings are obtained by using less fuel (energy) and by reducing disposal costs on recycling proj- ects (PCA 2009). Figure 31 summarizes the savings in con- struction zone traffic, use of new materials, disposal costs, and fuel consumption. FIGURE 31 Potential reduction in construction zone traffic, use of new materials, disposal volume, and fuel consumption (based on PCA 2009). Life-cycle costs are commonly achieved by increasing the service life of the pavement. The length of time a given pro- cess will delay the progression of pavement distresses and the deterioration of the overall pavement condition needs to be estimated when evaluating the potential reduction in life- cycle costs. The following life-cycle-related performance information was found in the literature. HIR performance characteristics have been reported as • Heater-scarified sections showed that the appearance of distresses had the following annual rates of progression: – International roughness index (IRI) increases of 15 in./mi annually, – Rutting increases of 1.5 mm (0.06 in.) annually, – Fatigue cracking increases of 22.3 m2 (240 ft2) annually, – Transverse cracking increases of 2 m (6.5 ft) annu- ally, and – Longitudinal cracking increases of 30 m (97 ft) annually (Shuler and Schmidt 2008). CIR performance characteristics have been reported as • Kansas DOT showed that CIR sections with – Fly ash additives had twice the total amount of crack- ing compared with emulsion–lime slurry sections. – Fly ash additives had longitudinal cracking in one or both wheel paths compared with little or no cracking in emulsion–lime slurry sections (Thomas et al. 2000). • An Arizona study by Mallela et al. (2006) evaluated the performance of 17 CIR projects: – CIR with double chip seal provided good performance for up to 20 years when traffic was below 5,000 AADT. – Overlays of 50 to 75 mm (2 to 3 in.) provided excel- lent performance for at least 7 years (maximum age of projects in study). • Life expectancies reportedly used in life-cycle cost assessments included CIR life of – 13 years in Pennsylvania (Cuelho et al. 2006), – 12 to 20 years in Pennsylvania (with overlay) (Cuelho et al. 2006), – 17 to 25 years in Iowa (Lee and Kim 2007a), – 18 to 22 years in Iowa when constructed on poor soil support (<5,000 psi) (Heitzman et al. 2007), – 26 to 34 years in Iowa when constructed on good soil support (±5,000 psi) (Heitzman et al. 2007), – 10 to 18 years for Arizona CIR with consistently more reliable performance if a 2- to 3-in. HMA overlay is used with the CIR (Mallela et al. 2006). FDR performance characteristics were not specifically separated out in the literature because this process provides only a stabilized base for the new HMA surface. Perfor- mance-related characteristics such as in-situ or laboratory base modulus are typically used in the structural design. Research conducted by the Ontario MTO (Kazmierowski 2008) compared the performance of CIR and FDR projects over 11 years of service (Figure 32). This research indicates that slightly more improvement can be achieved using FDR than CIR. This is expected given that FDR addresses defi- ciencies in all pavement layers. However, after about 8 years of performance, the FDR showed significantly slower losses in ride quality (i.e., IRI) and pavement condition. A well-designed experimental approach to evaluating the progression of pavement distresses and the overall decline in the pavement condition index for in-place recycling methods is needed to provide reliable life-cycle cost and life expectancy guidance. BARRIERS Both agencies and contractors were asked to indicate what they considered to be barriers that limit the use of in-place recycling methods (Figure 33). Agencies identified the lack of mix designs most frequently. Both agencies and contrac- tors identified the frequently encountered barriers as

39 • Unsuccessful experiences, • Competing industries, and • Lack of specifications. FIGURE 32 Ontario, Canada, experience with CIR and FDR performance as measured with IRI and PCI (based on Kazmierowski 2008). FIGURE 33 Perceived barriers to increased usage of in-place recycling by agencies and contractors. Percentages are based on the number of survey respondents. Barriers more frequently cited by agencies than contrac- tors are a lack of • Mix design methods, • Experienced contractors, and • Agency experience. The only barrier cited more often by contractors than agencies is a lack of project selection criteria. Barriers were identified by Cuelho et al. (2006), who noted the following top five preservation treatment selection decision factors that need to be overcome or considered as potential limitations: • Previous experience with a treatment, • ADT or number of trucks, • Urban versus rural roadway, • Availability of contractors/equipment/materials, and • Conclusive research in the state. Cuelho et al. also noted the three least important decision factors: • Weather, • Availability of design standard/manual, and • Availability of state equipment/workforce. These lists generally agree with most of the agency and contractor responses. The agency and contractor responses were used to rank and summarize the importance of various barriers to increased use of in-place recycling (Table 40). TABLE 40 BARRIERS TO INCREASED USE OF IN-PLACE RECYCLING Barriers to Increased Use Frequency of Benefit Lack of mix design Often** Unsuccessful experiences Frequently Lack of experienced contractors Often** Lack of agency experience Often** Lack of engineering design Often** Competing industries Often Lack of project selecting criteria Often** Lack of specifications Sometimes Sometimes = between 10% and 25% average of agency and contractor with experience. Often = between 25% and 50% average of agency and contractor with experience. Frequently = greater than 50% average of agency and contractor with experience. *Contractor response was significantly higher than agency with experience. **Agency response was significantly higher than contractor with experience. SUCCESSFUL EXPERIENCES The lack of successful experiences is a significant barrier to using in-place recycling processes. This section provides brief summaries of successful in-place recycling projects found in the literature. More detailed project descriptions can be found in the associated references and references for the case studies listed in Appendix C. Successful agency experiences with various in-place recycling projects are pro- vided for the following topics: • HIR cost benefits in Colorado, • HIR surfacing in Wisconsin,

40 • CIR additives used to minimize presurfacing traffic damage in Kansas, • CIR with foamed asphalt in Canada, • CIR use on steep grades in Nevada, • CIR surface treatment selection for traffic consider- ations in North Dakota, • CIR subgrade support in California, • FDR using emulsion stabilization for rehabilitation and lane widening FDR in Georgia, • FDR choice of additive in Mississippi, • FDR cement stabilization in Alabama, • FDR selection to meet environmental policy in Texas, and • FDR cost benefits in Georgia. HIR Cost Benefits in Colorado Denver, Colorado, has 5 years of experience using HIR on its 1,800 centerline miles of roadway network (Udelhofen 2006). Over the 5 years, Denver used HIR to preserve about 1.1 million square yards of HMA, saving the agency more than $5 million compared with conventional mill and fill. Most of the roadways were in residential streets with lim- ited truck traffic. The projects typically used a 50-mm (2-in.) recycled leveling course and a 25-mm (1-in.) overlay with 20% RAP in overlay HMA. A double screed allowed work to be completed in one pass, and most projects were finished within 1 to 2 days of the start of construction. Benefits noted by the agency included cost savings, shorter construction times than mill and fill, life extension of the roadways, and an improved bond between leveling course and overlay. HIR Surfacing in Wisconsin VanTimmeren (2009) summarized a project in the city of Mequon, Wisconsin, which needed to address more surface distresses than could be handled using crack sealing. Streets were evaluated to determine whether any drainage problems needed to be corrected before resurfacing. Culverts were replaced as needed and the roadways were patched with HMA as needed. One preheater and a preheater/scarifier were used to loosen the top 50 mm (2 in.) of existing HMA, and a rejuvenator was added to soften the oxidized HMA. Conventional equipment was used to place and roll the HMA, which was finished with a seal coat. Excess aggregate was swept off the surface treatment before opening to traffic. The benefits noted by the agency were that no shoulder- ing or driveway-matching work was needed and no waste material was produced in the process. Challenges noted by the agency included determining which streets were best suited for HIR. Coring was used to determine thickness and whether there was adequate base thickness to support the equipment. If there was insufficient base, an alternative recycling method was needed, such as FDR. It was impor- tant to make sure the excess aggregates were swept and the public was kept informed. CIR Additives Used to Minimize Presurfacing Traffic Damage in Kansas Thomas et al. (2000) documented a Kansas CIR project where the initial problem was rutting and raveling in the CIR under traffic and before the placement of the surface course. The agency used a Class C fly ash additive to solve this prob- lem. A subsequent problem resulting from the use of the fly ash was premature cracking. Alternative combinations of emulsion and additives were evaluated with test sections. Fly ash (10% by weight of millings) was used in the first section, and the second test section used a combination of solventless asphalt emulsion formulated for recycling and lime slurry (1.5% hydrated lime by weight of millings). The lime was used to improve early strength gain and moisture resistance. Equipment used on the project included one 3.6-m (12-ft) milling machine, a trailer-mounted screening and crushing unit, and a mixing unit with belt scale and computer control. A conventional asphalt paver with pickup device was also used. Rollers consisted of a heavy 30-ton, seven-tire pneu- matic roller for breakdown and a double drum vibratory roller for intermediate and finish rolling (static). The results showed that transverse cracking was twice as frequent in the fly ash section as in the emulsion–lime com- bination. No cracks were wider than 4.75 mm (¼ in.), with most cracks being about 1.6 mm (1/16 in.) wide. Longitudi- nal cracking was prevalent in the fly ash sections in one or both wheel paths; if only one wheel path was cracking, then the cracking usually occurred in the outside wheel path. In some cases, the longitudinal cracks were side-by-side in the outside wheel path. There were few longitudinal cracks in the emulsion–lime section. Rutting was either low or non- existent in either of the sections. Field results were substan- tiated with a laboratory-loaded wheel rut tester and shear modulus testing. The emulsion–lime combination with the CIR minimized cracking typically seen in CIR with fly ash. CIR with Foamed Asphalt in Canada Lane and Kazmierowski (2005b) reported on the use of CIREAM. The emulsion sections needed a minimum curing time of 14 days, with fixed requirements for maximum mois- ture and minimum compaction. The foamed CIREAM sec- tions needed a curing period of only 3 days, which was the time needed to achieve compaction and TSR requirements. The foamed asphalt binder curing time was less dependent on warm, dry weather conditions for placement to achieve the desired properties.

41 The equipment consisted of a milling machine, a mobile screening and crushing deck, and a mix paver where emul- sion was added and the material was placed. Rollers were pneumatic tire rollers for breakdown and a steel drum for finish rolling. For CIREAM, the mix paver was replaced with an onboard twin-shaft pugmill where the expanded foam was added and mixed. The mix was fed into a heavy- duty paver with dual tamping bards in the screed. Project requirements included compaction to 96% of the target density established by laboratory testing, with no sin- gle result below 95%, and moisture contents of less than 2%, with no sublot exceeding 3%. Results showed that the CIREAM sections were ready to cap within 2 days of placement. FWD testing immediately after construction showed slightly higher deflections for the CIR compared with the CIREAM sections, which was attributed to the CIR section not being fully cured. FWD testing after 1 year showed that the deflections were similar for both CIR (emulsion) and CIREAM sections (Chan et al. 2009). The IRI was used to measure ride quality. IRI val- ues were similar for both sections, but the CIR values were slightly lower than those for the CIREAM section. However, this section was micromilled before CIR for minor profile corrections, which could have helped improve the ride in this section. Both sections had little to no rutting after 1 year. Laboratory resilient modulus testing showed similar stiff- ness for both mixes. Benefits of using CIREAM were an extension of the con- struction season and reduced curing time. CIR Use on Steep Grades in Nevada VanTimmeren (2008) reported various strategy consider- ations for maintaining the roadway at the Pequop Summit on I-80 in Elko County, Nevada. The desired life expectancy for the project was 20 years. After evaluations, an 89-mm (3.5- in.) CIR with a 100-mm (4-in.) overlay was selected because other traditional options would have cost about $8 million dollars more for the same life expectancy. Challenges encountered, but overcome, included traf- fic control, length of time for lane closures (cure times), steep grades (up and down), and nonrecycling infrastruc- ture repair that needed to occur before paving. The pulling requirements uphill while milling to a depth of 89 mm (3.5 in.) slowed the process. Traffic speeds increase on the down- hill side of the interstate and can pose safety issues. Pipe work and other non-pavement-related work components in the project area were completed before the recycling process. The success of the project depended on constant communi- cation for planning work activities. CIR Surface Treatment Selection for Traffic Considerations in North Dakota Kronick (2009) reported on construction considerations of CIR equipment weights resulting in punch-through problems for a 100-mm (4-in.) milling depth on a 140-mm (5.5-in.) existing HMA layer. An alternative to the originally selected CIR with double chip seal was to use CIR with overlay, but this was considered less desirable because of rapidly increas- ing asphalt prices. A small portion of the project had higher traffic (1,800 AADT) compared with rest of the project (985 AADT); therefore, CIR plus a 37.5-mm (1.5-in.) overlay was kept as an alternative if the CIR and chipped sections showed too much early rutting. This option was eventually used in the higher traffic area. Advantages associated with the CIR and double chip seal compared with the CIR with overlay for the county roads were the elimination of edge dropoffs and minimal change in roadway elevations. The edge dropoffs in the overlay sections are because the lifts are placed in progressively narrower lane widths, resulting in a lip at the edge of the pavement that can catch car tires and send a vehicle out of control. The CIR with double chip had an acceptable ride, but it was not as good as the overlay. Some reflective cracking in a 1.5-mi section with overlay was seen, but it was much less than was typically seen in other overlay projects. Microsur- facing was planned for a later date to address any rutting in the CIR with double chip section. Benefits noted by the agency were a substantial cost sav- ings. The cost of the CIR plus double chip was $80,000 per mile (2007 prices), with the CIR plus overlay at $180,000 per mile. This was 56% less for CIR plus double chip. The costs did not include cost of traffic control, which was provided by the county. CIR Subgrade Support in California VanTimmeren (2009) reported the CIR experiences of the city of Santa Anna in Orange County, California. The project was to maintain 50-year-old streets for which a soils report showed the need for extensive full-depth base repairs. The desire to implement more environmentally friendly technol- ogies and reduce the cost of rehabilitating the roadways led to consideration of CIR as the best choice. The planned work included header cuts at the gutters, 75 mm (3 in.) of CIR, with 25 mm (1 in.) of HMA. Construction started on the two streets in the worst con- dition with respect to subgrade support for the heavy recy- cling equipment. Repeated problems and lost time because of punch-through problems were a significant concern. After

42 extensive discussion between the city and contractor, the agency decided that CIR, although a good option, was not applicable in all cases. The city and contractor developed a plan for evaluating the soil-support characteristics for each street by coring, then using DCP testing to determine the structural capacity of the subgrade and base. More than 90% of the remaining streets were considered acceptable for CIR work. For roads with low support values, an FDR process was used to provide a cement-stabilized 200-mm (8-in.) base with an HMA overlay. Benefits of this approach included a cost savings of 40% over conventional reconstruction, and that no waste materi- als were generated. FDR with Emulsion Stabilization for Rehabilitation and Lane Widening in Georgia In 2006, the Virlyn B. Smith Road in Fairburn, Georgia, needed significant repair and widening. Rather than install full-depth asphalt concrete patches for about 40% of the roadway, the agency chose to use FDR with EE for stabiliza- tion. The FDR project was approximately a mile of a 7-m (23-ft) wide, two-lane roadway that needed to be widened to 8.2 m (27 ft) and the base support improved (Besseche et al. 2009). About 0.6 m (2 ft) on either side of roadway was trenched, followed by pulverizing 240 mm (9.5 in.) of the existing HMA and base, which was spread over the new lane width. An extra 37.5 mm (1.5 in.) of prepulverized base was added to trenches using a motor grader. A second round of pulverization was made to a depth of 200 mm (8 in.), and emulsion was added as a base stabilizer for the new 27-ft- wide roadway. Two passes of the pulverizer were needed to complete the second round of pulverization. A motor grader was used to smooth the surface to grade, and additional roll- ing was completed with a pneumatic tire roller followed by a steel wheel roller. The FDR surface was covered with 37.5 mm (2.5 in.) of HMA 7 days later. The two methods of mix design evaluated for the project were standard Marshall stability and the SemMaterials mod- ulus. Cores were taken for determining the extracted grada- tion, which showed that 33% RAP and 66% gravel aggregate base were needed to achieve the FDR gradation. Preconstruction testing showed that the original gravel aggregate base had a modulus of about 62 MPa (9,000 psi), which was increased to about 1,241 MPa (180,000 psi) after FDR using emulsion stabilization. DCP data were used to determine the consistency of the base, sub-base, and sub- grade quality. In one area with 50 mm (2 in.) of sub-base silty clay soil, an additional 50 mm (2 in.) of aggregate was added before the emulsion. The average modulus value calculated from the DCP data showed an increase of 177% when com- paring preconstruction to postconstruction properties (11 months). The short-term DCP results are shown in Table 41. Both mix designs were ultimately compared at an opti- mum 4.5% of emulsion by weight. The criteria and results for these designs are shown in Table 42. TABLE 41 SUPPORT DETERMINED FROM DCP FIELD TESTING FOR GEORGIA FDR PROJECT (Besseche et al. 2009) Day of Testing DCP Results from Field Testing R-Value kPa (psi) Pulverizing Depth, mm (in.) Pre-construction 116 400 (58) 280 (11.0) Immediately after emulsion added 48 207 (30) 305 (12.0) End of 7 days of curing 71 400 (58) 261 (10.3) During construction, the moisture content was taken every 305 m (1,000 ft) to determine whether conditions to replicate mix designs could be met. Pre-emulsion moisture content was 1.7% immediately before the overlay, which increased to 3.2% to 3.5% after emulsion was mixed into the pulverized materials. Before placement of the overlay, the moisture content was reduced to 1.7%. Density was monitored every 500 ft per lane using modi- fied Proctor, nuclear gauge, and sand cone. The modified TABLE 42 SUMMARY OF MODULUS AND MARSHALL MIX DESIGN CRITERIA AND RESULTS FOR ENGINEERED EMULSION FDR (based on Besseche et al. 2009) Modulus Design, 4.5% emulsion content Marshall Design, 4.5% emulsion content Test Criteria Results Test Criteria Results Indirect Tensile Strength, psi (ASTM D 4867) 35 min 36 Coating Test, Modified, % Retained (LADOTD TR 317-87) 80 min 90 Indirect Tensile Strength Ratio, psi (ASTM D4867) 20 min 26 Initial Marshall Stability (ASTM D1559), lb 1,500 min 3,493 Resilient Modulus, ksi (ASTM D4123) 120 min 144 Cured Marshall Stability (ASTM D1559), lb 2,000 min 5,820 Short-term Strength Test, Modified Cohe- sion (ASTM D1560) 150 min 187 Conditioned Marshall Stability after Soaking (ASTM D1599), lb 1,000 min 4,590

43 Proctor was used as the reference density for developing nuclear density gauge correlations (Table 43). Cores taken 1 year after construction showed that the resilient modulus of the FDR layer ranged from 214 ksi to 474 ksi, with an average value of 349 ksi. The effective struc- tural number was calculated as 3.36. This is equivalent to a structural coefficient for the FDR layer of 0.24, compared with the original coefficient of 0.07 for the gravel aggregate base (GAB). The structural coefficient from laboratory test results of the cores was calculated as 0.31, which gives a structural number of 3.91. Problems encountered during construction included a subgrade that was too soft in a few locations in the south- bound lane. There were also a few soft spots because of excess moisture in the clayey sub-base, and the problem areas were dug out. Good base material was placed to the side and the soft sub-base was removed [about 0.6 to 0.7 m (2 to 2.2 ft) deep] and replaced with GAB. The GAB was compacted, the good sub-base material returned, a 1.5% emulsion was added, and the stabilized sub-base was the compacted. Problem areas were typically between 15 and 30.5 m (50 and 100 ft) long and were too short to capture in preconstruction testing. FDR Choice of Additive in Mississippi Prokopy (2003) reported details for an FDR project where the selection of additives was based on the desired properties for the base. The original plan was to use foamed asphalt as the stabilizer, which worked well for the first 457 m (1,500 ft). At that point, unexpected variances in soil and moisture needed further consideration. Hydrated lime was used for next 305 m (1,000 ft) to help dry soil, but durability and den- sity requirements were still not met. Portland cement was tried next and worked well. Portland cement (8,400 tons) was used for the remaining 30 mi of project. Previous agency experience with cement-stabilized soil showed problems with high levels of cracking because of the high percentage needed to meet the requirements. Dis- cussions with FHWA suggested that a low cement content of about 3.5% worked well, and this content was used. The project was successful and other projects were being con- sidered. Construction equipment was required to be moved off roadway and parked remotely overnight. Extra care was needed to avoid damage to surrounding foliage and soils. FDR Cement Stabilization in Alabama Prokopy (2003) reported the benefits of an FDR-stabilized base using cement for a 1.7-mi project. This project incor- porated 5% cement (440 tons) for stabilization, which pro- duced a base with a minimum unconfined strength of 2,413 kPa (350 psi). The base was topped with a double surface treatment. This project was constructed with county forces, which used a nuclear density gauge to monitor compaction during construction. A pulverizer was used to rip up the old asphalt and base course. A motor grader was used to provide the cross section and grade. A spreader truck was used to place the cement, which was mixed with water. Compaction was accomplished with standard rollers. Benefits associated with using the cement-stabilized FDR were a substantially reduced number of haul trucks, reduced fuel costs, no waste generation, and reduced project costs. This process allowed for recycling roadways with higher traffic than previously considered and required significantly less material. FDR Selection to Meet Environmental Policy in Texas PCA (2008) reported the construction of a cement-stabilized FDR where the main factor in the selection of the recycling process was defined by the waste management office in Dal- las, Texas. The project used FDR with cement stabilization, an underseal, and a 50-mm (2-in.) HMA overlay. Environmental benefits associated with this project included reduced use of new materials, complete recycling of existing materials with no generated waste, and a quick return of traffic to the roadway. FDR Cost Benefits in Georgia In 2005, Coweta County, Georgia, placed its first 1-mi FDR project to address reconstruction needs, as the county was experiencing accelerated damage from heavy construction equipment moving in and out of the area (Nickelson 2010). The initial county concerns were spread and cost of con- struction. Increasing use of FDR over the past few years has demonstrated that FDR with cement provides a stabi- lized base with significantly improved pavement life. By 2008, 35 major county roadways in Coweta County were completed, with another 10 mi of roadways planned for the next year. TABLE 43 CONSTRUCTION TESTING FOR GEORGIA FDR PROJECT (BESSECHE ET AL. 2008) Lane Moisture, % Modified Proctor Nuclear Gauge, lb/ft3 Sand Density, lb/ft3 Compaction, % Wet Dry Wet Dry Wet Dry North Bound 3.4 131.4 127.0 134.4 130.0 128.7 124.4 100 South Bound 3.7 132.2 127.5 136.0 131.3 133.8 129.1 101