National Academies Press: OpenBook

Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures (2016)

Chapter: Chapter Four - State Construction Engineer Survey

« Previous: Chapter Three - State Materials Engineers Survey
Page 65
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 65
Page 66
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 66
Page 67
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 67
Page 68
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 68
Page 69
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 69
Page 70
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 70
Page 71
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 71
Page 72
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 72
Page 73
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 73
Page 74
Suggested Citation:"Chapter Four - State Construction Engineer Survey ." National Academies of Sciences, Engineering, and Medicine. 2016. Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Washington, DC: The National Academies Press. doi: 10.17226/23641.
×
Page 74

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

66 • No excess supply of RAS (four agencies). • RAS is plentiful in cities and urban areas (two agencies). • RAS less available in the southern part of the state. • RAS is available, but contractors do not use. • Have not used RAS yet; unsure of availability. RECYCLED MATERIALS PROCESSING AND STOCKPILING PRACTICES This section outlines the State Construction Engineer survey responses about stockpiling and processing practices used by their state. RAP and RAS information is presented in sepa- rate sections. RAP Processing and Stockpiling The State Construction Engineers indicated that contractors frequently process the RAP at the asphalt plant site and occa- sionally process the RAP off site, but rarely have it processed by a third party (Table 64; n = 36 for this table). Only 25% of the agencies require the contractor to have sufficient RAP pro- cessed and stockpiled at the start of a project to complete the project, and 36% have no requirements for having sufficient quantities of RAP on hand at the beginning of the project. Large quantities of RAP are typically collected and stock- piled prior to processing, but unprocessed or processed RAP is rarely covered. Less than 10% of the agencies frequently fraction coarse and/or fine RAP fractions. The 19-mm (¾-in.) sieve size is typically used to scalp the oversize RAP, and the definition of coarse and fine RAP fractions varies between agencies: • 4.75-mm (No. 4) sieve is the most common (Table 65). • 2.36-mm (No. 8) or 9.5-mm (3⁄8-in.) sieve sizes are used less frequently. Additional respondent comments about fractionating stock- piles included: • The ¼ in. can be used in lieu of No. 4 sieve (bottom sieve), ¾ and 9⁄16 in. are commonly used to scalp top size and recrush. • In general, contractors do not fractionate unless it is necessary to meet volumetric requirements or control the properties. The State Construction Engineer survey (Appendix B) focused on topics that can are beneficial to the production and place- ment of high RAP, RAS, and a combination of RAP and RAS mixtures. A total of 45 responses were received; a response rate of 88% (50 states and the District of Columbia), includ- ing agencies that indicated they do not currently use at least 25% RAP or RAS in their mixtures, which are the focus of this synthesis. The main survey topics and the organization of this chapter are as follows: • Availability of recycled materials • Recycled material processing and stockpiling practices • Recycled materials properties and testing (as they are used in production) • Asphalt mixture production and placement • Volumetric quality control testing • Key points for field inspectors. AVAILABILITY OF RECYCLED MATERIALS Which types and percentages of recycled materials used in asphalt mixtures can be limited by the availability of materials? The potential economic benefits that can be achieved when using recycled materials can be offset by increased trans- portation costs when materials are only available in limited areas within the state. At least 80% of the responding State Construction Engineering surveys noted that RAP supplies are generally available across the state. However, only about one-third of these agencies have excess supplies of RAP either statewide or in limited locations in one or more state (Table 63). Additional respondent comments about RAP included: • No excess supply of RAP (four agencies). • RAP is plentiful in cities and urban areas (three agencies). • Some districts keep millings for other uses and that cre- ates a local low supply, and the urban districts have an oversupply. • Industry would like access to more RAP. There is significantly less availability of RAS that is, if available, typically limited to only one or more districts or local areas within the state. When RAS is available, there appears to be an excess of RAS in those areas. Additional respondent comments about RAS included: chapter four STATE CONSTRUCTION ENGINEER SURVEY

67 TABLE 63 AVAILABILITY OF RAP AND RAS THROUGHOUT STATE Survey Question: Supply and Demand: Also, indicate if there is any excess of recycled materials (i.e., more supply than demand). Locations Materials RAP Shingles (RAS) % n % n General Availability Statewide 81 29 17 6 In One or More Districts 3 1 33 12 Limited to Local Areas 0 0 25 9 Excess of Recycled Materials Statewide 28 10 0 0 In One or More Districts 28 10 11 4 Limited to Local Areas 11 4 33 12 Not all survey respondents answered all questions. n = 36. Survey Question: Indicate how frequently each of the following RAP processing and stockpiling practices is used in your state. Statement Frequently Occasionally Rarely Not Applicable % n % n % n % n Processing RAP RAP is processed at the asphalt plant site 47 17 17 6 3 1 6 2 RAP is processed elsewhere by asphalt mixture contractor and stockpiled at plant 8 3 39 14 25 9 0 0 RAP is processed by third party and delivered to asphalt mixture contractor 0 0 8 3 39 14 14 5 Asphalt mixture contractor required to have sufficient processed RAP material stockpiled at the beginning of the construction project 25 9 0 0 6 2 36 13 Stockpiling RAP Large quantity of RAP collected, then processed 33 12 31 11 0 0 0 0 Unprocessed stockpiles are covered 0 0 6 2 39 14 19 7 Stockpiles are stored in covered areas only covered after processing 3 1 8 3 42 15 11 4 *Coarse RAP stockpile is fractionated 8 3 22 8 22 8 17 6 Fine RAP stockpile is fractionated 6 2 17 6 25 9 17 6 Impact of Weather and Processing Times *Weather impacts RAP crushing and sizing operations (e.g., clumping, blinding screens, etc.) 0 0 17 6 22 8 6 2 *We have time limitations between RAP processing and using 0 0 3 1 11 4 53 19 *Respondents were asked to provide additional information about these statements. Not all survey respondents answered all questions. n = 36. TABLE 64 RAP PROCESSING AND STOCKPILING PRACTICES • Contractors have the option of fractionating and gen- erally they only do so if it is necessary to control mix design volumetrics. Consistency in the RAP is often maintained with milling and stockpiling procedures. Most of the time RAP from different sources is stock- piled separately. If multiple layers must be milled from a roadway, these layers may be milled up individually and stockpiled separately. • One large contractor that works nearly state-wide does fractionate on high-profile projects. All of our other con- tractors use inline crushers to process RAP at the plant. • RAP from cold-milling (used immediately) is screened to remove oversized partials. Occasionally, RAP is used from either state- or contractor-owned stockpiles. Pro- cessing of these can be as simple as remixing and screen- ing for oversized, to crushing, and screening.

68 Weather conditions and the time between processing and using the RAP may influence RAP processing; how- ever, 53% of the responding agencies do not have any time requirements in their state. Additional respondent com- ments about the influence of weather on RAP processing included: • Typically, contractors will not process RAP during bad weather. • Moisture and speed of processing affect crushing and sizing operation; do not focus on tons/h, but on quality of finished RAP screened product. • Not to an extent that it cannot be accomplished. Rain has a greater impact. • This is rarely a problem. Sometimes have problems when RAP comes from a thin cold-milling operation (e.g., chip seals) and the percentage of oil is high. In these cases, water or water with a surfactant is sprayed on the belt to prevent sticking. Additional respondent comments about time constraints between processing and using RAP included: • Currently we do not have any time constraints specified, but we prefer to keep time between processing and using RAP to a minimum. • We do not have time limitations, but prefer to use RAP that is not more than a year old. If there is a problem with HMA/WMA consistency or compliance with proj- ect specifications, additional efforts are taken to achieve acceptable levels of consistency and compliance with contract specifications at contractor’s discretion. RAS Processing and Stockpiling The State Construction Engineers noted that RAS is occa- sionally processed at the plant site, off-site by the contractor, or by third parties and supplied to the contractors (Table 66; n = 21 for this survey question). Manufacturer waste RAS are stockpiled separately from tear-off RAS and large quantities of RAS is frequently or occasionally stockpiled and then pro- cessed. Most agencies have no requirements for having suf- ficient RAS stockpiled for the entire project at the beginning of the project. Only four agencies cover unprocessed and/or Survey Question: Select the “retained on” sieve size used to define the coarse RAP fraction. Sieve Size % n +9.5-mm (3/8 in.) 28 5 +4.75-mm (No. 4) 61 11 +2.36-mm (No. 8) 11 2 This question was only provided to respondents indicating a frequent or occasional use of fractionating. n = 18. TABLE 65 SIEVE SIZE USED TO DEFINE “COARSE” RAP FRACTION TABLE 66 RAS PROCESSING AND STOCKPILING PRACTICES Survey Question: Indicate how frequently each of the following shingles (RAS) processing and stockpiling practices are used in your state. Statement Frequently Occasionally Rarely Not Applicable % n % n % n % n Processing RAS RAS is processed at the asphalt plant site 14 3 33 7 10 2 33 7 RAS is processed elsewhere by asphalt mixture contractor and stockpiled at plant 5 1 38 8 5 1 33 7 RAS is processed by third party and delivered to asphalt mixture contractor 19 4 38 8 5 1 29 6 Stockpiling RAP Manufacturing waste and tear-offs are kept separate 57 12 0 0 5 1 29 6 Large quantity of RAS collected, then processed 29 6 19 4 0 0 29 6 Asphalt mixture contractor required to have sufficient processed RAS material stockpiled at the beginning of the construction project 10 2 0 0 0 0 81 17 Unprocessed stockpiles are covered 5 1 0 0 29 6 33 7 Stockpiles are stored in covered areas only covered after processing 14 3 14 3 24 5 29 6 Sand is added during processing or after processing to prevent clumping 10 2 10 2 14 3 43 9 Impact of Weather and Processing Time *Weather impacts RAS crushing and sizing operations (e.g., clumping, blinding screens, etc.) 24 5 14 3 5 1 29 6 *We have time limitations between RAS processing and using 0 0 0 0 0 0 90 19 *Respondents were asked to provide additional information about these statements. Not all survey respondents answered all questions. n = 21.

69 TABLE 67 MAXIMUM PARTICLE SIZE ALLOWED FOR RAS Survey Question: Select the maximum shingle (RAS) particle size allowed. Sieve Sizes % n 12.5-mm (1/2 in.) 12 2 9.5-mm (3/8 in.) 35 6 4.75-mm (No. 4) 12 2 2.36-mm (No. 8) 12 2 Other 29 5 Not all survey respondents answered all questions. n = 17. TABLE 68 NEED TO ADJUST RAP PROCESSING AND STOCKPILING PRACTICES Not all survey respondents answered all questions. n = 26. Survey Question: Do your current processing and stockpiling practices need to be adjusted or changed so that higher percentages of RAP can be used? If yes, please indicate what changes are needed in the comment box below. Answer % n Yes 50 13 No 50 13 processed RAS and four agencies either frequently or occa- sionally blend processed RAS with sand to help minimize clumping. Eight agencies (38% of those agencies answering this ques- tion) believe that weather conditions are likely to impact the processing or handling of the RAS. Additional respondent comments about the impact of weather on RAS processing included: • Clumping occurs and recrushing or lump breaking is necessary almost daily. • Some RAS processing plants use water to mitigate heat generation. Most only process during good weather. • RAS has seen limited use for highway work; however, it appears to best fit commercial work when the asphalt is subsidiary to mixture. Currently the most commonly used maximum RAS size is 9.5 mm (3⁄8 in.) (Table 67); however, additional comments about “Other” sizes noted that RAS is sized: • As needed for total gradation (two agencies), and • Use maximum of 6.35-mm (¼-in.) sieve. Suggested Changes to Current RAP and RAS Processing Requirements Respondents were asked to comment about any potential changes to their current RAP or RAS processing and stock- piling practices that can increase the percentage and/or type of recycled material used in their state. Thirteen agencies provided suggestions for useful changes when processing and stockpiling RAP (Table 68). The comments provided included: • Fractionate RAP (six agencies): – Need to fractionate to meet mix design volumetrics. – Regularly approve mix designs incorporating 30% RAP in all mixture types and currently specify a maximum 40% RAP in drum mix plants, and pro- ducers are beginning to push to that limit. Those producers who have evaluated using more than 40% or 50% have indicated that fractionating would be necessary. • Occasionally millings from projects are used with no additional processing. Higher RAP content mixtures necessitate more advanced processing. • Covering the stockpiles (three agencies). • Most contractors are unable to incorporate more that 25% RAP. Most RAP comes from micro-milling in our state, which makes it mostly a fine-graded material. Fractionating is difficult because of the large amount of rejected material [i.e., passing 0.075-mm (No. 200)] that would be created. • Increase QC testing. • Currently conducting research into required adjustments. Five agencies provided suggestions for improving RAS processing and stockpiling practices (Table 69) that included: • RAS asphalt availability factor (two agencies): – A better determination of (RAS) asphalt contribution. – Adopt rule on amount of effective asphalt that is avail- able from the RAS. • Sand is sometimes blended into RAS to keep it from clumping. • Stockpiles must be kept in the shade. The fifth comment, related to the economic incentives associated with using RAS, noted that “more than anything, TABLE 69 ADJUSTMENTS NEEDED FOR PROCESSING AND STOCKPILING RAS Survey Question: Do your current processing and stockpiling practices need to be adjusted or changed so that RAS or combinations of RAP/RAS can be more widely used? If yes, please indicate what changes are needed in the comment box below. Answer % n Yes 28 5 No 72 13 Not all survey respondents answered all questions. n = 18.

70 the processing and storage costs for RAS prohibit their use in rural areas.” Recycled Material Processing and Stockpiling—Section Summary RAP processing and stockpiling • RAP is fractionated for better control of mix design volumetrics when using higher percentages. – The sieve size used to fractionate coarse and fine sizes is usually the 4.75-mm (No. 4) sieve, although the 9.5-mm (3⁄8-in.) and, less frequently, the 2.36-mm (No. 8) sieves can be used. – The 19-mm (¾-in.) or (9⁄16-in.) sieves are typically used for scalping the top size RAP. – RAP from micro-millings is mostly fine-graded materials and is most efficiently used at lower percent- ages. Fractionating the micro-millings would likely result in an overabundance of rejected materials [i.e., too much passing the 0.075-mm (No. 200) sieve]. • Increased QC testing may be necessary when using higher percentages of RAP. • Moisture (e.g., rain) can influence quality and speed of crushing and sizing operations. • If there is a high asphalt binder content in the RAP, water or water with a surfactant may have to be sprayed on the conveyor belt to prevent sticking. RAS processing and stockpiling • The majority of the agencies keep separate stockpiles for RAS manufacturer waste and RAS tear-offs. • Clumping and recrushing or lump breaking may be necessary. RECYCLED MATERIAL PROPERTIES AND TESTING Asphalt contents and aggregate gradations of the individual recycled material, as well as the final asphalt mixture, are deter- mined using the ignition by most of the agencies responding to this question (Table 70; n = 18). More than 70% of the agencies measure RAP asphalt contents and RAP aggregate gradations of both the individual recycled materials and the total asphalt mixture. At most, 33% of the agencies use sol- vent extraction to determine asphalt content and aggregate TABLE 70 TESTS AND ASSUMPTIONS USED TO DETERMINE RECYCLED MATERIAL PROPERTIES DURING PRODUCTION Survey Question: Indicate what tests or assumptions are used to determine asphalt content, aggregate properties, and other material or mixture properties are determined. (Check all that apply.) Testing RAP Shingles (RAS) Recycled Material Properties Certified by Supplier Recycled Material Properties Estimated Asphalt Mixture with Recycled Materials Is Tested % n % n % n % n % n Asphalt Content Ignition oven asphalt content 76 16 38 8 14 3 10 2 71 15 Solvent extraction asphalt content 33 7 19 4 10 2 5 1 24 5 Gradations Ignition oven gradation 71 15 29 6 14 3 14 3 71 15 Solvent extraction gradation 33 7 14 3 10 2 5 1 29 6 Consensus Aggregate Properties Flat and elongated aggregate properties from recycled materials 19 4 5 1 5 1 0 0 24 5 Fine aggregate angularity of aggregates from recycled materials 29 6 5 1 5 1 0 0 19 4 Specific Gravities Bulk specific gravity 52 11 33 7 14 3 24 5 76 16 Theoretical maximum specific gravity (i.e., Rice method; AASHTO T209) 57 12 33 7 5 1 14 3 90 19 Moisture and Contaminates Moisture content 52 11 33 7 19 4 0 0 33 7 Contaminates 29 6 24 5 14 3 5 1 14 3 Not all survey respondents answered all questions. n = 21.

71 gradations. Only a limited number of agencies determine flat and elongated coarse aggregate and fine aggregate angularity shape for either the individual RAP or total asphalt content mixture. More than 50% measure both the RAP bulk specific gravi- ties and RAP theoretical maximum specific gravities, and almost all of the agencies (90%) measure the theoretical maxi- mum specific gravity of the total asphalt mixture. The moisture content is a key factor in how hot the vir- gin aggregate needs to be to dry the RAP; however, only 52% of the agencies measure the RAP moisture content and 33% measure the moisture content of the total asphalt mixture. Contaminates in the RAP are evaluated by 29% of the agencies. No additional comments were received about testing for contaminates. Eight agencies provided information about RAS in response to this question. RAS asphalt content and grada- tion is most frequently determined using the ignition oven method, although some agencies do use solvent extractions. RAS aggregate shape is only determined by one agency. RAS bulk and theoretical maximum specific gravities, as well as moisture content, are almost always determined by the agencies that responded to this question. Contamination in the RAS is also frequently measured. Additional respon- dent comments about RAS contaminates included: • Mixture is visually evaluated. The RAS suppliers han- dle RAS testing for contaminants using limits of 1.0% for delirious materials and 0.1% for metals. • Visual inspection is used by four agencies that noted: – The use material retained on the 2.36-mm (No. 8) sieve. – A search for steel contaminates. – RAS processors have methods to remove metal and other materials during the grinding and screening process. The moisture content is determined for both RAP and RAS; however, the method used to dry the material is agency- dependent. Additional information was provided by respon- dents about drying recycled materials and included: • Oven drying: – Moisture content by the oven method (AASHTO T329, three agencies). – Oven dried (no test method information supplied) (four agencies). – Oven at 230°F (110°C); constant mass is defined as less than 0.1% change in mass between two dry all samples to a constant mass at 122°F (50°C) so as not to overheat. – Use intervals of 15 minute weights (two agencies). • Dried in a microwave oven to a constant mass. • Air dried. • Rapid drying technology is used. Recycled Material Properties and Testing—Section Summary • Asphalt content and gradations are most frequently determined for individual recycled material and asphalt mixtures with recycled materials using the ignition oven. – Solvent extraction is used by some agencies; how- ever, about the same number of agencies mentioned that they no longer use any extraction method in their laboratory. • Bulk specific gravities are measured for individual recycled material and asphalt mixtures with recycled materials; however, several agencies estimate these val- ues from other test results. • Theoretical maximum specific gravities are determined for individual recycled materials and the total asphalt mixtures. • Flat and elongated as well as fine aggregate angularity properties are determined by some agencies for RAP, but rarely determined for RAS. • Moisture contents are measured for both RAP and RAS recycled materials; however, agency drying methods and times and definitions of “dry to a constant mass” vary widely. • Recycled materials, both RAP and RAS, are checked for contaminates by some agencies. ASPHALT MIXTURE PRODUCTION AND PLACEMENT The survey included questions about how recycled materi- als are handled and fed into the asphalt plant, and potential changes that may be needed to the plant operations. The fol- lowing observations are made with the caveat that there are about as many responses indicating there is no difference between recycled and conventional mixtures as there are agen- cies noting differences owing to the recycled material content (Table 71). Handling recycled materials that tend to form a crust over the surface of the stockpiled materials, clump in the stock- pile, and bridge over belt weigh scales are more difficult to uniformly feed into the plant. The majority of the eight agen- cies that consistently answered questions about RAS con- sidered this a concern. Five agencies also considered this an issue when using more than 25% RAP. Asphalt plant options for feeding recycled materials into the plant include adding more cold feed bins, in-line crushing and sizing, and screening and sizing. Screen and sizing or in-line crushing and screening methods are used

72 for producing mixtures with more than 25% RAP. Plant production rates are to be slowed and temperatures raised when producing mixtures with more than 25% RAP and mixtures with a combination of RAP and RAS. Additional respondent comments about plant temperature constraints included: • Temperatures required to be ±15°F of the job mix for- mula temperature. • Mixture temperatures cannot reach more than 325°F. • Kept lower than 325°F to 330°F. • Not more than 10% than the target temperatures spec- ified in the mix design • Disincentives: – Not to exceed 90% pay for “hot-leg” (discharge) tem- peratures between 350°F and 400°F. – 40% pay or removal for “hot-leg” temperatures 400°F, 350°F for HMA mixtures, and not to exceed 275°F for WMA mixtures. General comments about the uniformity of mixtures with either RAP and/or RAS included: • Weigh recycled materials separately—separate weigh bridges for RAP and RAS (two agencies). • Test regularly to account for nonuniformity (two agencies): – Spend more time on selection and processing of recycled materials. – Use more cold feed bins. • Specific to RAP: – Use good stockpiling procedures (five agencies) – Different RAP sources are stockpiled separately, and if multiple layers are being milled from the road- way then the individual layers may be milled-up and stockpiled separately. – Fractionate RAP (three agencies). – Use consistent milling processes. – Age of the plant and flighting is important to ability to produce high RAP mixtures. • Specific to RAS: – Blend RAS with manufactured sand. One set of seven statements was presented to the respon- dents for each of the three types of mixtures that are the focus of this survey (i.e., more than 25% RAP, RAS, and combination RAP and RAS mixtures). Respondents were asked to indicate their level of agreement or disagreement about how mixtures behave when they are transferred from the haul truck to the paver, flow through the paver, any defects or difficulties behind the paver, and how difficult the mixtures are to work once placed. Mixtures with more than 25% RAP are more likely to form a crust on the mixture in the paver wings, somewhat more likely to segregate, and it can be difficult to obtain joint density (Table 72). Additional respondent comments about the flow of the mixture out of the haul truck included: • Flows out of the truck in portions instead of being continuous. TABLE 71 RECYCLED MATERIAL HANDLING AND PROCESSING ADJUSTMENTS AT THE ASPHALT PLANT Survey Question: Indicate if any of the following are seen or adjustments are needed when using higher than typical RAP% mixtures, RAS mixtures, or a combination of RAP/RAS mixtures on asphalt plant operations. (Check all that apply.) Statement >25% RAP% Shingles (RAS) Combination of RAP/RAS No Difference from Conventional Mixtures % n % n % n % n Handling Recycled Materials Recycled material stockpile crusting, clumping, and bridging of materials influence handling and feeding into plant 24 5 29 6 24 5 29 6 Difficult to obtain uniform feed of recycled materials 14 3 29 6 19 4 33 7 Feeding Recycled Materials into Plant Additional cold feed bins are used to meet the required recycled material gradation 24 5 19 4 29 6 29 6 Recycled material screened and sized as it is fed into asphalt plant 29 6 19 4 14 3 38 8 In-line crushing and sizing is used (i.e., recycled material is processed as it is added to the plant) 29 6 5 1 5 1 43 9 Point of introduction of the recycled material into the plant needs to be changed (e.g., RAP collar relocated closer to the drum discharge point or the recycled material fed directly into pugmill at batch plant) 10 2 5 1 5 1 38 8 Separate dryer drum used to dry recycled materials 0 0 0 0 0 0 48 10 Adjustments of either metering methods or sensors are needed to properly measure small percentages of recycled materials 0 0 19 4 10 2 29 6 Plant Operations Production rates need to be slowed (e.g., extra drying time needed) 29 6 14 3 19 4 33 7 Plant temperatures need to be lowered when using recycled materials 5 1 5 1 5 1 38 8 Plant temperatures need to be raised when using recycled materials 35 7 35 4 35 4 35 6 Minimum silo storage times are needed 0 0 0 1 0 0 0 9 Maximum silo storage times are needed 16 3 16 2 16 3 16 6 Mixture Characteristics Difficult to obtain mixture uniformity 38 8 19 4 24 5 38 8 Mixtures with recycled material content tend to segregate more frequently during load out 10 2 5 1 5 1 52 11 Not all survey respondents answered all questions. n = 21.

73 • Less fluid and moves in a stiff, harsh mass that is very temperature sensitive. • Stiff and crusty. Additional respondent comments about windrow crusting included: • Drag marks are seen when clumps get in front of the screed. • Visible temperature segregation. • Small chunks of the mixture can be seen in the mat surface. This is more of an issue with an equipment breakdown than with the high RAP content. RAS mixtures tend to flow differently from the haul truck into the paver and sometimes crust over in the windrow or in the paver wings (Table 73). Other difficulties associated with placing stiffer mixtures are also sometimes seen, such as visible lines in the mat behind the paver, difficulty in achieving joint density, and being more difficult to work by hand (e.g., luting). Similar responses were provided that used a combination of RAP and RAS in the mixtures (Table 74). Asphalt Mixture Production and Placement— Section Summary Handling and Processing Recycled Material Mixtures • Recycled materials can be more difficult to feed into the asphalt plant because of crusting on the stockpile surface, clumping, and bridging of recycled materials over weigh belt scales. • Recycled materials are routinely fed into the plant using in-line crushing and screening, screening and crushing as material is fed into the plant, and by using additional cold feed bins. • Additional cold feed bins appear to be a preferred method. TABLE 72 OBSERVED MIXTURE BEHAVIOR FOR MIXTURES WITH MORE THAN 25% RAP Not all survey respondents answered all questions. Responses for “Don’t Know” choice not shown. n = 20. Survey Question: When placing asphalt mixtures with more than 25% RAP, how frequently each of the following is observed. Statement Always Often Sometimes Rarely Never % n % n % n % n % n Stiffer mixtures flow differently from end dump haul truck to paver hopper 20 4 5 1 15 3 15 3 10 2 Crusting of mixtures when deposited in windrows can be a problem (e.g., clumps deposited into hopper) 0 0 5 1 25 5 5 1 10 2 Mixture in paver wings more likely to build up and form crust on top 10 2 0 0 30 6 15 3 15 3 Visible “lines” in the direction of paving more noticeable between screed and extension 10 2 5 1 25 5 10 2 15 3 Uniformity and density at the joint is more difficult to obtain 5 1 5 1 45 9 5 1 10 2 Hand work is more difficult 15 3 5 1 15 3 25 5 5 1 Mixtures are more likely to segregate 5 1 0 0 45 9 5 1 15 3 Not all survey respondents answered all questions. Responses for “Don’t Know” choice not shown n = 18. Survey Question: When placing asphalt mixtures with shingles (RAS), how frequently each of the following is observed. Statement Always Often Sometimes Rarely Never % n % n % n % n % n Stiffer mixtures flow differently from end dump haul truck to paver hopper 17 3 6 1 11 2 6 1 6 1 Crusting of mixtures when deposited in windrows can be a problem (e.g., clumps deposited into hopper) 0 0 0 0 22 4 0 0 0 0 Mixture in paver wings more likely to build up and form crust on top 11 2 6 1 28 5 0 0 6 1 Visible “lines” in the direction of paving more noticeable between screed and extension 6 1 0 0 22 4 6 1 6 1 Uniformity and density at the joint is more difficult to obtain 6 1 0 0 28 5 11 2 0 0 Hand work more difficult 17 3 6 1 17 3 6 1 0 0 Mixtures are more likely to segregate 6 1 0 0 22 4 22 4 0 0 TABLE 73 OBSERVED MIXTURE BEHAVIOR FOR MIXTURES WITH RAS

74 Survey Question: When placing asphalt mixtures with a combination of RAP and shingles (RAS), how frequently each of the following is observed. Statement Always Often Sometimes Rarely Never % n % n % n % n % n Stiffer mixtures flow differently from end dump haul truck to paver hopper 17 3 6 1 11 2 11 2 6 1 Crusting of mixtures when deposited in windrows can be a problem (e.g., clumps deposited into hopper) 0 0 0 0 22 4 0 0 6 1 Mixture in paver wings more likely to build up and form crust on top 6 1 11 2 17 3 11 2 6 1 Visible “lines” in the direction of paving more noticeable between screed and extension 6 1 11 2 17 3 6 1 6 1 Uniformity and density at the joint is more difficult to obtain 6 1 0 0 28 5 11 2 0 0 Hand work more difficult 11 2 11 2 17 3 11 2 0 0 Mixtures are more likely to segregate 6 1 0 0 28 5 17 3 0 0 Not all survey respondents answered all questions. n = 18. TABLE 74 OBSERVED MIXTURE BEHAVIOR FOR MIXTURES WITH A COMBINATION OF RAP AND RAS Survey Question: Do any of the recycled materials seem to influence the nondestructive test results? Answer % n Yes 0 0 No 65 13 Maybe 35 7 Not all survey respondents answered all questions. n = 20. TABLE 76 IMPACT OF RECYCLED MATERIALS ON IN-PLACE DENSITY MEASUREMENTS Survey Question: Indicate the method used to determine the density testing of the finished mat. Method % n Nuclear density gauge 24 5 Nonnuclear gauge 0 0 Cores 76 16 Not all survey respondents answered all questions. n = 21. TABLE 75 METHODS USED FOR DETERMINING THE IN-PLACE MAT DENSITY • Production rates may need to be slowed down for dry- ing the recycled materials, obtaining the desired mix- ture temperature, and to provide adequate mixing times. • Maximum silo storage times may be required to keep the mixture from getting too stiff. • Stiffer mixtures can be more difficult to place without screed lines, drag lines from clumps of material in front of, or under, the screed, and to work by hand. • Blend RAS with sand to help prevent clumping. – Update or upgrade existing plant equipment. n Add more cold feed bins, and n Change drum flighting. – Provide separate weigh systems for different types of recycled materials. • Transport and placement: – Use proper paver operations to keep mixture from crusting in the windrow or in the paver wings. VOLUMETRIC QUALITY CONTROL TESTING QC and QA density testing once the mixture is placed can be accomplished using nuclear gauges, nonnuclear gauges, or by taking and testing cores. The majority of respondents take cores for laboratory testing (Table 75). Although some agencies use nuclear density gauges, none of the respon- dents mentioned that they use nonnuclear density gauges. Most respondents do not believe that the recycled materials influence nondestructive test method density results; how- ever, seven agencies were not sure if the recycled material influences any of the nondestructive density test measure- ments (Table 76). Agencies may obtain mixture from either the haul truck or from behind the paver so that samples are compacted in the laboratory for density testing. Some respondents indi- cated that they use a QC compaction level (i.e., number of gyrations) based on traffic levels and mixture types per AASHTO M323 for compacting the samples, whereas others use agency-defined levels of gyrations (Table 77). Respondents were asked to indicate if it is more difficult to obtain required volumetrics with recycled material asphalt mixtures compared with conventional mixtures. Most of the respondents that answered this question (eight agencies) believe it is more difficult to meet air voids and VMA require- ments, and some agencies believe it is also more difficult to meet the VFA requirements (Table 78). KEY POINTS FOR FIELD INSPECTORS A survey question was included to collect information about what field inspectors need to be aware of when working with high percentage RAP, RAS, or RAP and RAS combination

75 mixtures. The comments received for this question are sepa- rated into those generally related to all recycled materials, specifically for RAP, and specifically for RAS. General comments: • Ensure mixture characteristics are being controlled by the contractor. • Check for consistency in recycled products. Comments for high RAP mixtures: • Start milling with a clean road free of debris, etc. • Important to monitor the quality of stockpiles and watch milling operations. • We have found that the mixtures are “cleaner” in the field with the higher RAP percentages, but we believe the preprocessing used for these mixtures is the major factor for this. • Temperature segregation, clumping, or overheated mix- tures can be a problem when placing high RAP mixtures. Check mixture temperatures and follow good paving practices. • Streaking, pulling, tearing, segregation, and foreign material from the RAP stockpile can be seen in the fin- ished mat. Check for texturing and uniformity of the mat. • On high RAP projects stay on top of segregation and joint density checks. • Generally, inspection is the same, except constituent percentages may have to be verified if various RAP sources are used. This is because incentive payments offered to contractors are dependent on who owns the RAP being used. Comments for RAS mixtures: • Ensure that the proper amount of RAS is going into the mixture. • Watch for foreign materials, visible RAS, and dry- looking mixtures. • Check for clumping and dust balls in the mat when using RAS. These balls may form in the drum. • Look for dry, bony mixture with uncoated aggregate that can lead to segregation and premature raveling. Survey Question: Indicate the number of gyrations used to prepare samples for lab density testing. Information NDesign NMax Based on Traffic Level (ESALs) AASHTO M323 Mixture Type 40* 50** 65** 75 80 95 100 115 160 AASHTO M323 ESALs for Given NDesign <0.3 0.3 to <3 3 to 30 Number of Agencies Using a Given Compaction Level 1 4 3 4 1 1 2 1 1 5 4 *Shoulder mixtures. **Low traffic volume roadways. Not all survey respondents answered all questions. n = 20. TABLE 77 COMPACTION LEVEL USED FOR PREPARING SAMPLES FOR DENSITY TESTING Survey Question: Check the box if it is more difficult to obtain acceptable properties (within specification limits) when compared to similar mixtures without any recycled material content. Properties 25% or More RAP Shingles (RAS) RAP and RAS Combination Mixtures % n % n % n Air Voids, % 88 7 75 6 75 6 VMA, % 88 7 50 4 38 3 VFA, % 63 5 50 4 50 4 Not all survey respondents answered all questions. n = 8. TABLE 78 IMPACT OF RECYCLED MATERIALS ON MIX DESIGN VOLUMETRICS

Next: Chapter Five - Case Examples »
Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 495: Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures summarizes current practices for the use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in the design, production, and construction of asphalt mixtures. It focuses on collecting information about the use, rather than just what is allowed, of high RAP, RAS, and/or a combination of RAP and RAS.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!