Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 10
10 binders. The study showed that mixing and compaction Survey of Current Practices for Determining temperatures for polymer modified mixes were higher than Mixing and Compaction Temperatures for conventional unmodified binders. Mixing temperature ranged from 160°C to 177°C (320°F to 351°F). They noted A survey was conducted to examine procedures used by that the linear temperature-viscosity relationship assumed highway agencies to determine mixing and compacting tem- for unmodified binders may not be valid for modified asphalt peratures for mix design and construction operations. Survey binders. results were obtained from 65 agencies including the highway agencies for all 50 states and the U.S. Army Corps of Engi- Recognizing the potential problems with using the equiv- neers. Survey responses also were received from highway iscous method with modified asphalts, a note was added to agencies in Canada, Australia, China, Denmark, India, Japan, AASHTO T 312 in the section on preparation of specimens: and Malaysia. A table listing each agency's responses is in- Note 4 Modified asphalts may not adhere to the equiviscosity cluded in Appendix A. requirements notes, and the manufacturer's recommendation In the survey summary, the survey responses add up to more should be used to determine mixing and compaction temperatures. than 100% for each of the questions because some agencies used more than one method for determining mixing and In 2000, the Asphalt Pavement Environmental Council pub- compaction temperatures. For example, an agency may gen- lished an industry guidance document titled Best Management erally follow AASHTO T 245 and T 312 to determine mixing Practices to Minimize Emissions During Construction also known and compaction temperatures, but if the temperatures exceed as EC 101 (38). This document includes several important rec- a certain value then the supplier's recommendation would be ommendations regarding mixing and compaction tempera- used. Likewise, for setting production and placement temper- tures. It states that the equiviscous method is meant to be used atures, some agencies may follow AASHTO T 245 and T 312, only for laboratory purposes and should not be used as a start- but allow the contractor some flexibility to change those tem- ing point for plant mixing and field compaction temperatures. peratures depending on ambient temperature, haul distance, For modified binders, it is advised to use the binder supplier's and layer thickness. recommendation for proper laboratory and plant mix produc- The survey questions, along with a summary of responses, tion and field compaction temperatures. are as follows: Table 1, reproduced from this publication, serves as a guide for the industry on suitable temperatures for field operations. 1. What procedure does your agency/organization currently use to determine mixing and compaction temperature for These recommended HMA plant temperature ranges were asphalt binders used in unmodified hot-mix asphalt? considered as practical guidelines for mixing temperatures in As shown in Figure 1, the largest response (46%) indi- this study. cated that the guidelines in AASHTO T 245 and T 312 were used to determine mixing and compaction tempera- Table 1. Recommended plant temperatures tures for unmodified asphalt. Several agencies reported for different binder grades (38). using the AASHTO procedures unless the temperature ex- ceeded a certain limit, such as 166°C (325°F), and if that Asphalt Pavement Environmental Council Best Practices limit were exceeded, they would use the binder supplier's Typical Asphalt Binder Temperatures HMA Plant Asphalt Tank HMA Plant Mixing recommendation. A few agencies reported that they avoided Binder Grade Storage Temperature (ºF) Temperature (ºF) the mixing and compaction temperature issue altogether Range Midpoint Range Midpoint PG 46-28 260 290 275 240 295 264 PG 46-34 260 290 275 240 295 264 PG 46-40 260 290 275 240 295 264 PG 52-28 260 295 278 240 300 270 Question 1 Response PG 52-34 260 295 278 240 300 270 10% 1% PG 52-40 260 295 278 240 300 270 PG 52-46 260 295 278 240 300 270 PG 58-22 280 305 292 260 310 285 13% PG 58-28 280 305 292 260 310 285 T245/T312 PG 58-34 280 - 305 292 260 310 285 46% PG 64-22 285 315 300 265 320 292 Supplier PG 64-28 285 315 300 265 320 292 PG 64-34 285 - 315 300 265 320 292 Own PG 67-22 295 320 320 275 325 300 Other PG 70-22 300 325 312 280 330 305 PG 70-28 295 320 308 275 325 300 N/A PG 76-22 315 330 322 285 335 310 PG 76-28 310 325 318 280 330 305 30% PG 82-22 315 335 325 290 340 315 Figure 1. Survey responses to Question 1.
OCR for page 11
11 by using the supplier's recommendation for all binders. A received to the surveys. However, Gaylon Baumgardner of few agencies also reported that they have established a Paragon Technical Services, Inc., (a division of Ergon) and standard mixing and compacting temperature based on Frank Fee of NuStar Energy, L.P., were very helpful in pro- their own experience and use those temperatures for all viding information by telephone and e-mail in regard to unmodified binders. Nevada indicated that they no longer industry procedures. use unmodified asphalt binders. Suppliers most often use temperature-viscosity charts Of those using other methods, ASTM D2493 was the pro- based on AASHTO T 245 and T 312 for determining cedure most often used. The ASTM procedure is a method mixing and compacting temperatures for unmodified for determining the standard viscosity-temperature chart asphalt. Some suppliers of modified asphalt use a rough but does not specify mixing and compacting temperatures. adjustment of 10°F for each grade increase with polymer The Japan Road Association uses a procedure that is modification. Other suppliers set mixing and compaction similar to AASHTO T 245 and T 312, but allows a slightly temperatures solely based on experience with the partic- higher temperature. The mixing temperature range is that ular binder and modification system. It was stated that which gives a viscosity of 180 ±20 mm2/s, and the com- prior experience has shown that a mixing temperature paction temperature range is that which gives a viscosity in the range of 160°C to 171°C (320°F to 340°F) and a of 300 ± 30 mm2/s. compaction temperature in the range of 143°C to 155°C 2. What procedure does your agency/organization currently (290°F to 310°F) are adequate for most mixes with polymer- use to determine mixing and compaction temperatures for modified binders. Suppliers also may allow some flexibil- asphalt binders used in polymer-modified hot-mix asphalt? ity in adjusting those temperatures depending on project The overwhelming response to Question 2 (Figure 2) was conditions such as ambient temperature, haul distance, that binder supplier recommendations are used for deter- layer thickness, etc. For highly modified binders such as mining mixing and compacting temperatures for polymer- PG 82-22, the temperatures may need to be increased modified asphalt mixtures. Fifty-six percent of the agencies slightly. However, suppliers generally recommend that responding stated they use supplier recommendations. A few of those indicated they use AASHTO T 245 and mixing temperatures never exceed 190°C (375°F), which T 312 unless unusually high temperatures are needed, and is consistent with EC 101. in that case, they would use supplier recommendations. 3. What procedure does your agency/organization currently Even though supplier recommendations were used most use to determine mixing and compaction temperatures often, some agencies also established a maximum mix- for asphalt binders used in crumb rubber-modified hot- ing and compaction temperature. Four agencies (British mix asphalt? Columbia, Canada; Hawaii; New York State Thruway Sixty-four percent of agencies responded that they do not Authority; and Puerto Rico) reported that they do not cur- use crumb rubber modifiers (Figure 3). Of those that use rently use polymer-modified asphalt. crumb rubber, most rely on supplier recommendations that Since supplier recommendations are typically used for are generally based on experience. Some states supplement polymer-modified asphalts, an obvious question is, "What the supplier recommendations with a maximum mixing procedures do suppliers use?" For answers to this ques- temperature of their own. From the responses, the highest tion, 17 surveys were sent to representatives of the modi- mixing temperature allowed in the United States and Canada fied asphalt industry. Unfortunately, no responses were is 176°C (350°F). Asian countries generally allow slightly Question 3 Response Question 2 Response 64% 18% T245/T312 T245/T312 Supplier 5% Supplier Own Own Other 56% Other 3% 5% N/A N/A 9% 9% 16% 15% Figure 2. Survey responses to Question 2. Figure 3. Survey responses to Question 3.
OCR for page 12
12 higher temperatures. For example, India uses a mixing Question 5 Response temperature range of 165°C to 185°C (330°F to 365°F) and Japan has a maximum mixing temperature of 185°C 61% (365°F) for all types of modified asphalts. 3% Yes 4. Does your agency/organization have experience with air- Own blown or chemically modified asphalt? If so, what proce- Supplier dure is currently used to determine mixing and compaction temperatures for asphalt binders used in hot-mix asphalt 14% Contractor modified in this manner? Other Fifty-nine percent of the agencies responded that they 11% do not have experience with or do not allow air-blown or 11% chemically modified asphalt (Figure 4). Most of the agen- Figure 5. Survey responses to Question 5. cies that allow these modifiers use supplier recommen- dations or a combination of AASHTO T 245 and T 312 and supplier recommendations. The Quebec Ministry of the maximum mixing temperature is exceeded, the con- Transportation uses a combination of AASHTO T 245 tractor is required to provide special safety precautions and T 312 and specification limits. If the temperature that (such as "space suits") for workers. In order to keep from corresponds to 0.17 Pa s exceeds 170°C (338°F), then being associated with hazardous materials, contractors avoid 170°C (338°F) becomes the maximum temperature and a going over the maximum limit. For unmodified asphalt, the mixing temperature range of 156°C to 170°C (313°F to maximum mixing temperature is 180°C (355°F). 338°F) is used. Where polymer-modified asphalt is used in China, the 5. Are the same procedures used to determine plant produc- agency has set temperatures for heating the aggregate and tion and laydown temperatures? the modified binder, and if the combined mixture exceeds Most agencies (61%) responded that they use the same 195°C (383°F), the mixture is discarded. A minimum com- procedures for establishing mixing and compaction tem- paction temperature is also established depending on sur- peratures in the field as they do for laboratory work (Fig- face temperature and layer thickness as indicated in Table 2. ure 5). Fifteen percent of the responding agencies allow the The Japanese method for determining mixing and com- contractor flexibility to set the temperatures for construc- paction temperatures for mixes with polymer-modified tion (or to adjust temperatures to account for ambient binders is interesting and rather straightforward. A 13-mm temperature, haul distance, layer thickness, etc.) so long as maximum aggregate size mix using the same aggregates as a maximum temperature such as 177°C (350°F) is not ex- will be used in the project is mixed with straight-run un- ceeded. Four agencies vary production temperature based modified asphalt and compacted using their standard on PG grade, and two others vary production temperatures temperature-viscosity curves. The density of the samples depending on whether the binder is virgin or modified. are determined and used as the standard density. Using the In Denmark, the maximum mixing temperature is reg- same mix with the modified asphalt specified for the proj- ulated by legislation with the Danish Working Environment ect, mixture is compacted at three to five incremental tem- Authority. Based on those guidelines, contractors must not perature levels up to a compaction temperature of 185°C exceed 190°C (375°F) for polymer-modified mixtures. If (365°F). The density of each set of samples is determined Question 4 Response Table 2. Minimum compaction temperatures 59% of HMA in China. Surface Minimum Compaction Temperature Related to T245/T312 Temperature of the Following Thickness (°C) Existing Layer Unmodified Modified or SMA Supplier (°C) 80mm 80mm Own <5 NA NA 140 NA NA NA Other 5 - 10 NA 140 135 NA NA NA 4% N/A 10 - 15 145 138 132 165 155 150 6% 15 - 20 140 135 130 158 150 145 12% 20 - 25 138 132 128 153 147 143 19% 25 - 30 132 130 126 147 145 141 >30 130 125 124 145 140 139 Figure 4. Survey responses to Question 4.