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Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1 (2013)

Chapter: Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements

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Suggested Citation:"Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements ." National Academies of Sciences, Engineering, and Medicine. 2013. Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1. Washington, DC: The National Academies Press. doi: 10.17226/22552.
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Suggested Citation:"Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements ." National Academies of Sciences, Engineering, and Medicine. 2013. Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1. Washington, DC: The National Academies Press. doi: 10.17226/22552.
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Suggested Citation:"Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements ." National Academies of Sciences, Engineering, and Medicine. 2013. Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1. Washington, DC: The National Academies Press. doi: 10.17226/22552.
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Page 33
Page 34
Suggested Citation:"Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements ." National Academies of Sciences, Engineering, and Medicine. 2013. Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1. Washington, DC: The National Academies Press. doi: 10.17226/22552.
×
Page 34
Page 35
Suggested Citation:"Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements ." National Academies of Sciences, Engineering, and Medicine. 2013. Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1. Washington, DC: The National Academies Press. doi: 10.17226/22552.
×
Page 35
Page 36
Suggested Citation:"Chapter Seven - Asphalt Concrete Pavements and Recycled Asphalt Pavements ." National Academies of Sciences, Engineering, and Medicine. 2013. Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1. Washington, DC: The National Academies Press. doi: 10.17226/22552.
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Page 36

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31 Recycled concRete AggRegAtes Background The types of PCC byproducts that were evaluated for use in highway applications included: • RCA (FHWA definition) • CDW RCM • PCC manufacturing byproducts: – Fresh concrete reused in other loads of fresh concrete – End of day hardened PCC, fractured (washed or unwashed for fines control) – Washed fresh concrete to recover the original com- ponents (primarily aggregates). FHWA (2004) limits the definition of RCA as PCC byprod- uct obtained from the removal of old PCC pavements. The specific definition is: Recycled concrete aggregate: is a granular material manufac- tured by removing, crushing, and processing hydraulic-cement concrete pavement for reuse with a hydraulic cementing medium to produce fresh paving concrete. The aggregate retained on the 4.75 mm sieve is called coarse aggregate and the material pass- ing the 4.75 mm sieve is called fine aggregate. Some states have expanded the definition to include bridge structures and decks, sidewalks, curbs, and gutters that have had the steel removed from the old concrete. One of the main advantages to using these sources for RCA is that state projects historically used high-quality aggregates with consistent properties defined in state specifications. High- quality and durable old concrete may be useful in new structural PCC applications, whereas lower-quality old concrete may be more useful in subbase or fill applications (ACPA 2008). RCA from old highway projects has five main steps: 1. Removal of as many potential contaminates as possible prior to demolition of PCC 2. Demolition of structure 3. Crushing and sizing RCA 4. Secondary removal of contaminates 5. Removal of dust and fines (air blowing or washing). An alternate source of RCA is from commercial construc- tion debris. However, state agencies prefer to reuse material recovered from either state projects or known sources of sup- ply because general CDW RCA can have contaminates such as bricks, wood, steel, ceramics, and glass. RCA from the demolition of other structures is not currently allowed in the United States; however, international research has explored methods for obtaining construction demolition debris for use in highway applications. Suppliers of fresh PCC have other potentially useful PCC byproducts. At the end of the day, leftover unused PCC mix is off-loaded. This mix can be dumped into a solid mass that can then be broken up and used as RCA at a later time. Alternatively, it can be washed to recover the aggregates for future use. There has been some experimentation with using the leftover mix to form an irregular block of PCC to be used as rip-rap. This is time-consuming and not currently a com- mon practice. Once the trucks are unloaded, they need to be cleaned. This process uses water to rinse out the trucks and produces water with an elevated pH. The reuse of both the water and the solids (usually aggregates) has to be considered. Unused fresh PCC mix may occasionally be remixed with a fresh batch of PCC. These recycled materials, while potentially useful in high- way applications, will have different physical and chemical properties than those of old recycled concretes. literature Review summary When RCA was used in PCC mixes, the water-to-cement, or cementitious materials, ratio may require adjustment to maximize workability. Alternatively, water reducers or super plasticizer was used to maintain strength requirements while achieving a workable mix. The PCC mix design test- ing included evaluations of freeze/thaw and alkali silica reactivity (ASR) resistivity, as well as volume changes, as a result of drying, and thermal contractions and expan- sions. High shrinkage characteristics are to be considered carefully so that early cracking failures are avoided. The use of fly ash with the RCA will improve the ASR resistivity and decrease the volume changes in RCA PCC. If the water demand-related workability issue was adequately addressed during the mix design then construction processes were not changed. The best way to control the variability within and between stockpiles of RCA was to maintain constant moisture content. chapter seven AsphAlt concRete pAvements And Recycled AsphAlt pAvements

32 tion to include reclaimed bridge PCC. Little work has been done until very recently in the United States on the use of construction demolition byproducts in highway applications. Most of the information found on this byproduct was located in international research publications. The three separate steps needed to recover CDW concrete byproducts are the demolition of the original structure, pro- cessing of the mixed waste stream, and sorting of the indi- vidual byproducts for recycling. The efficiency in recovering the byproducts can be enhanced by using organized demoli- tion of specific structural components, initial processing, and sorting of each byproduct (Lauritzen 2004). Optimal sorting of materials starts with the development of the demolition process and technologies (selective demolition) and correct handling of the recyclable materials. This takes more time and planning than traditional demolition and until recently demolition has been considered a low tech process, with rapid removal and disposal being the main focus. Quality standards for CDW recycled materials are needed along with education and technology transfer. Additional information can be found at the following web- site: Construction Materials Recycling Association (CMRA): www.cdrecycling.org. Agency survey Responses for Recycled concrete Aggregate Byproducts The survey contained questions about the use of all of the identified types of byproducts except the CDW RCA. The most commonly used highway application for RCA was as embankment and drainage material followed by use in PCC applications (Table 11). Most states used RCA washed or unwashed (Table 12). Six states recycle the end of day waste and water. Only one state indicated it allowed fresh PCC to be added to a new batch. The states with experience using recycled concrete in highway applications are shown in Figure 12. Sprinkling systems were recommended along with increased testing for stockpile moisture contents. Stockpiles of RCA should be constructed so that nearby water sources are not affected by alkali. Washing of the RCA was used to improve the fines content of the RCA byproducts. Another good prac- tice for improving quality and minimizing RCA variability was to keep stockpiles of RCA from different sources sepa- rate if at all possible. Structural design was occasionally influenced by the lower specific gravities, compressive and tensile strengths, and resilient moduli values. RCA PCC typically had higher water demands, creep, drying shrinkage, permeability, coef- ficients of thermal contraction/expansion, corrosion rate, and carbonization. When RCA was used in drainage systems, it was to be used below the drainage lines to minimize altering the ground-water properties. Filter fabrics could be selected to prevent clogging by the fines and carbonation byproducts. The costs of recycling PCC byproducts varied by source, region of country, and the quality needed for a given highway application. It was economically desirable to use RCA when the tipping fees were less than the charges for landfilling PCC waste. Use of RCA was also promoted when the cost could compete with the cost of purchasing new aggregates. In some cases, the contractor achieved cost savings when using RCA because of the reduced number of haul trucks and reduced fuel consumption. Agencies reduced project costs because of reduced needs to alter existing highway features such as curbs, gutter, and overhead clearances. construction and demolition Waste concrete The FHWA definition of recycled concrete aggregate nar- rowly limits the sources of old PCC to reclaimed highway pavements; however, some states have expanded the defini- Embank. = embankment. Byproducts Number of States Using Byproduct in Given Highway Application Asphalt Cements or Emulsions Crack Sealants Drainage Materials Embank. Flowable Fill HMA Pavement Surface Treatments (non- structural) PCC Soil Stability Concrete, Plant, End of Day Waste, and Water 0 0 1 2 0 0 0 3 0 Returned Fresh Mix Added to New Batch 0 0 0 0 0 0 0 1 0 RCA, Crushed and Washed 0 0 8 12 1 2 1 9 0 RCA, Crushed but Unwashed 0 0 7 18 0 0 1 6 2 RCA, Unknown Type 1 1 2 4 1 1 2 1 1 TAbLE 11 NUMbER OF STATES USINg RCA byPRODUCTS IN HIgHWAy APPLICATIONS

33 Number of Applications States Concrete, Plant, End of Day Waste and Water Returned Fresh Mix Added to New Batch RCA, Crushed and Washed RCA, Crushed but Unwashed RCA, Unknown Type 9 — — — — ID 4 — — IL — — 3 — — CO, ND FL, GA — 2 IL — LA, MD, NC, VA, VT, WA IL, KY, MN, ND, WA, WI — 1 MO, NC, NE, VA,TX NC AL, DE, FL, MN, MS, NJ, OR, OK, SC, WI AZ, CO, CT, DC, HI, IN, ME, MO, NC, NE, NH, NJ, NY, OH, OK, PA, TX, VA GA, MO, ND, NV, VT TAbLE 12 STATES USINg RCA byPRODUCTS IN HIgHWAy APPLICATIONS Reclaimed Concrete Materials 2009 Concrete Plant - End of Day Waste and Water 1 1 1 1 2 1 2009 Reclaimed Concrete Aggregate, Crushed and Washed 1 1 3 4 2 1 1 2 3 NJ - 1 DE - 1 MD-2 1 1 1 2 VT-2 1 2 2009 Reclaimed Concrete Aggregate, Crushed but Unwashed 1 1 1 1 1 1 CT-1 DC -1 NJ-1 1 1 1 1 3 3 2 1 2 2 2 2 2 1 1 1 1 NH-1 2009 Reclaimed Concrete Material, Unknown Type 9 1 1 1 1 VT-1 FIGURE 12 Agency survey results for recycled concrete aggregate byproducts (numbers indicate the number of applications that use the byproduct).

34 literature Review summary guidance was found in the literature for minimizing embrittle- ment of the mix binder when using high levels of RAP, improv- ing consistency of mix properties with stockpiling practices, using RAP in mechanically stabilized earth (MSE), and cost considerations. The use of rejuvenators had the potential for allowing for a higher RAP content in an HMA mix while still achieving the desired combined binder properties needed for good long-term performance. In addition, using crumb rubber and RAP in HMA had some potential for mitigating increased brittle behavior of the mix. Material preparation included frac- tionation of the RAP to make it easier to control the final mix gradation. RAP stockpiles were commonly tested to determine the asphalt content, aggregate gradation, and other aggregate properties as required by specifications. The use of warm mix asphalt technologies improved the workability of RAP HMA. Cold mixes with the proper moisture contents were placed with conventional paving equipment and operations. Mix prop- erty variability tended to increase with increased RAP con- tent; therefore, adjustments to sampling frequency needed to be increased so that the design properties were achieved dur- ing construction. Care needs to be taken during the mixing of cold RAP mixes so that overmixing is avoided. Density measurements of RAP backfill were accom- plished with standard nuclear gauges as long as the read- ings were correlated with a standard laboratory compaction measurement. However, the nuclear gauge readings tended to report higher than actual densities. It is important that correlation curves be established for each project. When RAP was used as backfill in an MSE, it was well-compacted so that deformation was minimized and adequate contact with the reinforcement was obtained. The lower angle of internal friction is to be considered when calculating the pullout capacity of the reinforcement. Fuel costs are a major component in producing and plac ing asphalt concrete mixes. When warm mix technolo- gies were used to produce HMA the energy consumption decreased by 4%. Increasing the use of RAP to 10% resulted in a 6% reduction in energy consumption. At 50%, RAP reduced energy consumption to an equivalent of energy needed to produce CMA. Increasing the amount of RAP in HMA increasingly reduced energy use. Conflicting information with regard to cost savings was found in the literature. One study showed that increasing the allowable RAP content from 20% to 30% did not result in a statistically significant cost savings, and at least three bids were needed to notice cost savings in the bids. That is, com- petition was necessary to pass the savings on to the agency. More benefits were seen when higher RAP contents were con- sidered as value engineering. Also, a minimum threshold of cost savings to the contractor was required before increased RAP content was considered economically attractive. ReclAimed AsphAlt pAvement Background Asphalt concrete is removed during maintenance or rehabili- tation activities by grinding (milling) the surface, pulverizing the old pavement along with a portion of the base or subgrade, or ripping up the old pavement. Milled or post-processed old asphalt concrete pavement is referred as reclaimed asphalt pavement, or RAP. RAP can be processed on-site using in- place recycling technologies or it can be removed from the job site and stockpiled at a contractor’s plant site (central plant recycling). In-place recycling includes hot in-place, cold in- place, and full-depth reclamation and is covered in a separate NCHRP synthesis. Central plants can be either HMA or cold mix asphalt (CMA) plants. Regardless of whether in-place or central plant recycling is used, it is advisable that preconstruc- tion testing include an evaluation of moisture susceptibility (Scullion et al. 1997, 2003). Hot central plant recycling combines RAP with new aggre- gates and fresh asphalt in the presence of heat and is the most common method used by contractors (Santucci 2007). The amount of RAP used in the new mix varies between agen- cies with the layer of the pavement being constructed. The use of RAP by agencies varies between 0% and 30% in the upper layers to up to 50% in shoulders and stabilized bases (TFHRC 2009). RAP can be added to HMA at either batch or drum mix plants. Cold mix central plant recycling combines RAP with new aggregate (if needed) and emulsified asphalt or an emulsified recycling agent without the use of heat in a central plant. Other additives can be used to help regulate the emulsion rate of set, early strength gain or improved mois- ture resistance. In-place recycling includes hot in-place, cold in-place, or full-depth reclamation. both hot and cold in-place recycling only addressed the top 1 to 4 in. of the old pavement surface. Asphalt concrete pavements pulverized in-place along with a portion of the unbound materials (i.e., full-depth reclama- tion) provides a stabilized base material that is covered with a wearing surface. In-place recycling of asphalt concrete pave- ments is covered in a separate NCHRP synthesis currently in production. RAP can be used as backfill material (TFHRC 2010); how- ever, most RAP is reused in the production of fresh HMA either in-place or stockpiled and added during central plant production processes. Another smaller source of recycled asphalt concrete material is the rejected or leftover fresh mix at the end of a day’s production. Additional information can be found at the following websites: • National Asphalt Pavement Association (NAPA) www. hotmix.org • American Recycling and Reclaiming Association (ARRA) www.arra.org

35 Byproducts Number of States Using Byproduct in a Given Highway Application Asphalt Cements or Emulsions Crack Sealants Drainage Materials Embank. Flowable Fill HMA Pavement Treatments (non-structural) PCC Soil Stability Baghouse Fines (HMA plant) 2 0 0 0 0 36 0 0 0 HMA, Unmilled (chunks) 0 0 2 11 0 3 0 0 2 HMA, Plant/Project Fresh Left-Over Mix 0 0 0 1 0 18 1 0 1 RAP, as Milled and Stockpiled 0 0 4 9 0 36 3 0 5 RAP, Separated into Sized Stockpiles 0 0 3 2 0 34 3 0 1 RAP, Unknown Type 1 0 1 3 0 13 0 0 3 Embank. = embankment. TAbLE 13 NUMbER OF STATES USINg RECyCLED ASPHALT PAvEMENTS IN HIgHWAy APPLICATIONS Agency survey Results for Recycled Asphalt pavements All agencies responding to the survey indicated they have used RAP byproducts in at least one application. The major- ity of the states reused HMA baghouse fines in the produc- tion of fresh HMA. The majority of the states also used either as-received or fractionated RAP in fresh HMA (Table 13; Figure 13). Fewer states reused fresh HMA left-over mix in fresh HMA. The most common use of unground RAP (i.e., chunks) was in the construction of embankments. A limited number of states used RAP in pavement surfaces, soil stabili- zation, or drainage materials. Only a few states used RAP in more than one highway application (Table 14). No distinction was made in this survey with regard to use in either in-place or central plant recycling. Asphalt Concrete FIGURE 13. (Figure continued on next page) 2009 Asphalt Concrete Baghouse Fines 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 MA-1 CT-1 NJ-1 DC-1 DE-1 1 1 1 1 1 1 1 1 NH-1 VT-1 1 1 1 1 1 2009 Asphalt Concrete, Chunks 1 3 1 1 VT-1 2 1 2 1 1 1 MD-1 NJ -1 1

36 Number of Applications States Baghouse Fines (HMA plant) HMA, Unmilled (chunks) HMA, Plant/Project Fresh Left- Over Mix RAP, As-Milled and Stockpiled RAP, Separated into Sized Stockpiles RAP, Unknown Type 3 — ND — FL, IL, MD, VT IL — 2 VA IL, WA VA AZ, CO, LA, MN, ND, NE, NM, OH, PA, TX, UT, WA CO, LA, MD, NE, NM, OH, SC, VA AK, MD, MO, ND, NM, TX 1 AL, AR, AZ, CO, CT, DC, DE, FL, GA, HI, IL, IN, IA, KS, KY, MA, ME, MN, MO, MS, NC, ND, NE, NH, NJ, NM, NV, NY, OK, OR, PA, SC, TX, VT, WA, WI AZ, CO, GA, IA, MD, MO, NJ, NV, OH, PA, VT AL, CO, CT, GA, IL, IA, KS, MD, MO, NC, ND, NH, NJ, NM, NY, OK, PA, SC, VT, WA, WI AL, AR, CT, GA, IN, IA, KS, KY, ME, MO, MS, NC, NH, NJ, NV, NY, OR, OK, SC, VA, WI, WV AL, AZ, CT, DC, DE, FL, GA, HI, ID, IN, IA, KS, KY, ME, MO, MS, NC, ND, NH, NJ, OR, OK, PA, TX, VA, WA, WI AL, AR, GA, IL, IA, MA, VT, WA, WI TAbLE 14 STATES USINg RECyCLED ASPHALT PAvEMENT IN HIgHWAy APPLICATIONS 2009 HMA Plant/Project Fresh Left-Over Mix CT-1 NJ-1 MD-1 NH-1 VT-1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 2 1 CT-1 NJ-1 DC-1 DE-1 MD-2 1 1 1 1 1 2 2 NH-1 2 2 1 2 1 1 1 1 1 2009 RAP, Separated into Sized Stockpiles 1 2009 RAP, Unknown Type VT-1 MA-1 MD-22 1 1 1 1 1 2 2 2 1 2 2 1 FIGURE 13 (continued ) Agency survey results for recycled asphalt pavement byproducts (numbers indicate the number of applica- tions that use the byproduct). 2009 RAP, As-Milled and Stockpiled 1 1 1 1 2 1 3 2 1 1 3 2 1 CT - 1 NJ-1 DC-1 MD-3 1 1 1 1 1 1 2 2 2 2 2 1 1 1 1 2 2 2 2 1 NH-1 VT -3

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 435: Recycled Materials and Byproducts in Highway Applications—Summary Report, Volume 1 summarizes the results of a project that describes the experiences of transportation agencies in determining the relevant properties of recycled materials and industrial byproducts and the beneficial use for highway applications.

NCHRP Synthesis 435 is presented in eight volumes and is designed to help serve as a guide to states revising the provisions of their materials specifications to incorporate the use of recycled materials and industrial byproducts.

Volume 1 is available in print and electronic versions. Volumes 2 to 8 are in electronic format only. The eight volumes are:

Volume 1 Recycled Materials and Byproducts in Highway Applications—Summary Report

Volume 2 Coal Combustion Byproducts

Volume 3 Non-Coal Combustion Byproducts

Volume 4 Mineral and Quarry Byproducts

Volume 5 Slag Byproducts

Volume 6 Reclaimed Asphalt Pavement, Recycled Concrete Aggregate, and Construction Demolition Waste

Volume 7 Scrap Tire Byproducts

Volume 8 Manufacturing and Construction Byproducts

A NCHRP Synthesis 435 website with links to all 8 volumes is available.

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