lrrb local operational research assistance … lrrb local operational research assistance program...

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LRRB Local Operational Research Assistance Program (OPERA) for

Local Transportation Groups Field Report

Date: May 31, 2011 Project Title: Taconite-enhanced pothole repair using portable microwave technology Project Number: Agency: University of Minnesota Duluth Natural Resources Research Institute (NRRI) 5013 Miller Trunk Highway Duluth, MN 55811 Person Completing Report: Lawrence M. Zanko, University of Minnesota Duluth - NRRI; with David M. Hopstock, PhD., David M. Hopstock and Associates, LLC. Project Leader: Charles Cadenhead, Anoka County; with Jim Foldesi, St. Louis County Phone Number: 218-720-4274 (L. Zanko) Problem: Cold-weather (winter to early spring) pothole repairs that use conventional “cold-patch” or “throw-and-go” mixes and methods can be unreliable and prone to early failure. A more effective and longer-lasting repair option is needed by public works and transportation maintenance departments, especially in the late winter as previous repairs and pavement starts to pop out of the road. The winter of 2010-2011 has again shown that potholes are a serious maintenance and safety issue. Given the budget challenges that county, local, and state governments face, better solutions are needed for longer-lasting repairs. The microwave-based repair tests conducted during this project provide some answers in this regard. Solution: Combine mobile microwave technology with compounds containing recycled/byproduct materials such as recycled asphalt pavement (RAP)/millings, microwave-absorbing taconite materials (Tac), and recycled asphalt shingles (RAS) to repair potholes and damaged pavement. Procedure: Equipment

Mobile microwave equipment having minimum operating power output of 40kW

Portable generator

Air compressor or leaf blower

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Gasoline-powered tamper/compactor

Hopper or truck containing loose but well-blended mixture of repair compound, i.e., recycled asphalt pavement (RAP)/millings, microwave-absorbing taconite materials (Tac), and recycled asphalt shingles (RAS)

Field Tools

Shovels

Stiff broom

Wheel barrow

5-gal buckets

Hand-held infrared thermometer for recording ambient (starting) pavement temperature and final patch temperature

Clean loose debris and/or blow water from pothole. In sub-freezing temperatures, preheat pothole and pavement adjacent to hole with microwave unit to melt or debond any ice or snow in the hole, and to soften the pavement. Remove or blow out loosened/melted ice/snow. Place mixture of recycled asphalt pavement (RAP)/millings, microwave-absorbing taconite materials (Tac), and recycled asphalt shingles (RAS) into the pothole. Overfill the hole by about two inches to allow for final compaction. Heat mixture of RAP, Tac, and RAS until temperature reaches at least 230 F at base of mixture in the hole. Sufficient heating takes place in about 8 to 12 minutes at a 40kW power level. Compact heated mixture with portable gasoline-powered compactor. Results: What worked well

“Clean”, -3/4 inch RAP/millings work best. Therefore, it is important to use RAP/millings that are minimally contaminated with extraneous sand and gravel. RAP derived from more asphalt-rich mill-and-overlay jobs will work better than RAP derived from full-depth reclamation projects.

Taconite materials significantly enhance microwave absorption, especially in RAP/millings where the original aggregate component is granite, quartzite, gneiss, or carbonate rock. RAP that contains basalt/trap rock has better microwave-absorbing characteristics.

Recycled asphalt shingles appear to enhance the binding characteristics of RAP having a relatively low asphalt content.

The microwave does an excellent job of quickly heating and softening the intact asphalt pavement surrounding the pothole. This is critical for providing a good bond and good repair.

System shielding prevented leakage of microwave energy. No leakage was detected during the field tests, showing that the technology can be deployed and used safely.

What did not work well

If base material (sand and gravel) is exposed at the bottom of a pothole, the microwave energy tends to pass into base material and does not heat the bottom of the pothole sufficiently. In these situations, a thin layer (1/2” to 1”) of taconite-enriched RAP should be placed in the bottom of the hole and pre-heated before adding the remaining pothole repair mixture.

Millings/RAP that has incorporated excessive amounts of base material (sand and gravel) makes for a lesser-quality repair. Whenever possible, “clean” millings/RAP should be obtained.

The limited nature and scope of the project meant that, to some degree, a trial-and-error approach was required, especially during field testing. A more

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systematic and quantitative approach would be preferred for better defining the critical operating and repair formulation parameters associated with this repair technology.

Costs and Potential Benefits The single biggest cost factor would be associated with contracting for or acquiring a mobile microwave unit. It is recommended that the microwave technology provider for this project, Microwave Utilities, Inc. of Monticello, MN, be contacted for further details. The investigators also learned that the cost of an insulated vehicle/trailer designed to heat and keep traditional asphalt repair compounds warm or hot for cold temperature pothole/pavement repair situations can approach $80,000. Again, this cost is associated with traditional asphalt-based pothole repair compounds and repair approaches that are too frequently ineffective or short-lived, which in turn can require multiple visits to re-repair the same hole. From a raw materials perspective, the project clearly demonstrated that inexpensive and abundant recycled and byproduct materials (e.g., RAP, taconite, and RAS) can be combined to make a very effective repair compound. This is a big deal, because it demonstrates that “virgin” petroleum-based asphalt compounds (hot mix, cold mix, UPM, etc.) need not be used for all-season pothole repair. In fact, the project showed that the asphalt contained in RAP/millings from old pavements can be easily reheated by microwave energy and re-compacted to form a sound, well-bonded repair. Importantly, this approach reduces the consumption of petroleum-based repair materials. Labor-wise, aside from the mobile microwave equipment operators, a typical maintenance crew is all that is required. Implementation: The technology shows excellent potential for more effective repair of potholes. While it can take several minutes to repair an individual pothole, especially when compared to more conventional (“throw-and-go”) methods, the extra time to achieve a permanent to near-permanent repair in a single attempt must be weighed against the cost of sending out crews to repair the same hole. Fore example, how does the cost of two or three repairs of the same pothole, and the attendant traffic disruptions, compare to a single microwave repair that may take 10 minutes longer to complete? It should also be noted that the microwave equipment used during this testing program was still a prototype. The investigators understand that the next-generation of mobile microwave equipment is under development. It will not only be higher-powered for more rapid heating, it will have additional safety interlocks built in, greater automation/remote controlled operation, and would be designed for easier placement over the pavement repair target. In combination, these modifications/upgrades should speed up the repair process. The objective would be to achieve an effective and permanent repair in about 5 minutes. It is recommended that further field-scale demonstrations and research be conducted, and that implementation of this repair technology be pursued on an expanded basis. This recommendation includes designing a systematic field-scale research program that is coupled with additional mathematical/numerical modeling to better quantify how the microwave energy interacts with various repair compound formulations and under different environmental conditions. The goal would be to develop optimal “designer” formulations from the basic components tested during this OPERA project A cost-benefit analysis that assesses and quantifies equipment, labor, and materials associated

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with microwave-based repair, and weighs them all against conventional repair methods and options, should also be part of a follow-up program. Status: The project has been completed. Please refer to the accompanying technical summary report, in which complete project findings are presented in detail. Included in the technical summary report are: 1) descriptions of changes/modifications that were made as the project proceeded to improve the outcome and efficiency of the test work; and 2) a thorough discussion/presentation of testing procedures, evaluation methods, and results. Total Duration of Project: Because of paperwork complications, a budget was not available until the summer of 2010. Therefore, most project work took place between December of 2010 and early April of 2011. Project End Date: May 31, 2011 Approximate Cost of Entire Project: $20,000 Includes $10,000 OPERA Funds, PLUS: 1) in-kind donation of time and equipment by Microwave Utilities, Inc. totaling $3, 556.65; 2) donation of personnel time and equipment by both St. Louis County and Anoka County for RAP acquisition and traffic control on March 30 and April 8, 2011; 3) Mn/DOT donation of: a) laboratory testing of RAP asphalt content, b) donation and delivery of RAS for tests, and c) personnel time for thermal imaging documentation of March 30 and April 8, 2011 field tests; and 4) in-kind donation of NRRI personnel time. Total OPERA Funds used for project: $10,000 Send and Email a completed report with pictures to: Mindy Carlson, CTS - 200 TSB, 511 Washington Ave. SE, Mpls. MN 55455, email [email protected]. For questions about this report please contact Mindy Carlson at 612-625-1813.

mailto:[email protected]

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TECHNICAL SUMMARY REPORT Taconite-enhanced pothole repair using portable microwave technology

Lawrence M. Zanko (UMD-NRRI)

and David M. Hopstock, PhD. (David M. Hopstock and Associates, LLC)

ABSTRACT Mobile (truck-mounted) microwave technology was field-tested for repairing potholes, using recycled asphalt pavement (RAP) combined with taconite materials (Tac) and recycled asphalt shingles (RAS) as the pothole repair compound. The testing took place at select locations in Anoka and St. Louis counties in 2010 and 2011. A mobile unit, operating at 40kW of power and a microwave frequency of 915 MHz, was used throughout the test period. The testing showed that high-quality repair of potholes can be accomplished safely in all seasons using mobile microwave technology. Importantly, the testing also showed that a combination of -3/4 inch RAP/asphalt millings, -1/4 inch magnetite-containing taconite materials, and recycled asphalt shingles (RAP + Tac + RAS) makes an excellent repair compound. The taconite materials are critical in that they enhance the microwave absorbing properties of the compound, making for a faster and higher-temperature repair. By the project’s last test in Anoka, MN, high-quality microwave-based pothole repairs were being completed in about 10 to 12 minutes. While slower than typical “throw-and-go” methods, the permanence of a microwave-based repair should be considered against the cost of sending crews out to repair the same pothole multiple times and the traffic delays associated with repeat repairs. Faster repairs could be accomplished with higher-powered, e.g., up to 100kW, microwave equipment. From a maintenance department perspective, the RAP/millings that are the basis for the microwave repair compound are cheap and readily available. Taconite byproduct materials are also abundant, and could be made available specifically for such a repair compound. These two ingredients alone are sufficient for making an effective repair blend, assuming the RAP/millings have a high enough asphalt content. RAP that contains at least 5.5 percent asphalt should be used; otherwise recycled asphalt shingles can be added to boost asphalt content. Ideally, “clean” RAP/millings that are largely free of unbound base material (sand and gravel) should be used. Excessive sand and gravel can be incorporated into RAP produced during a full-depth reclamation or full-depth milling jobs. Aside from the microwave unit itself (the services of which could be contracted), simple hand tools and equipment common to most maintenance departments are all that are needed for completing the pothole or pavement repair. A portable generator, a gasoline powered compactor, and a hopper or dump truck that can contain and discharge a pre-blended mixture of -3/4 inch RAP, taconite materials, and (if needed) RAS represent the basic equipment types that would be required for conducting ongoing microwave-based pothole and pavement repairs. It is recommended that further demonstration and implementation of this repair technology be conducted and pursued on an expanded basis.

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Acknowledgements The OPERA program is gratefully acknowledged for supporting this project, a project that represented a truly collaborative effort between the University of Minnesota Duluth Natural Resources Research Institute (NRRI); the Anoka and St. Louis County Highway Departments; Microwave Utilities, Inc. (MUI) of Monticello, MN; and David M. Hopstock, PhD, of David M. Hopstock and Associates, LLC. Special thanks are extended to engineers Charles Cadenhead of Anoka County and Jim Foldesi of St. Louis County for their interest in the project concept and their project support, and for the logistical and field assistance provided by their respective staffs. Messrs. Vern Hegg, Kirk Kjellberg and Lon Ashton of MUI are acknowledged for the enthusiastic professionalism and technical know-how they exhibited throughout the project. Lastly, Mn/DOT’s Office of Materials is thanked for performing RAP asphalt content analyses, providing RAS for the repair compounds, and for offering its thermal imaging services during the 2011 field tests in St. Louis and Anoka counties. Background Research initiated by Dr. David M. Hopstock and carried out at the University of Minnesota Duluth Natural Resources Research Institute (NRRI) by Hopstock and NRRI – beginning in 2003 – suggested that microwave-absorbing taconite aggregate materials, when combined with portable microwave technology, could be an effective solution to cold-weather pothole repair. Subsequent interaction and discussions with representatives of Microwave Utilities, Inc., of Monticello, MN, showed that their company had the technical capability and mobile equipment required to pursue field-testing of the concept of microwave-based pothole repair. Based on these discussions, a preliminary field demonstration was conducted in Anoka County in March of 2009 (Fig. 1).

Pothole repair field trial, March 2009, Anoka

County, using a truck-mounted 30kW unit

Portable unit provided by Vern Hegg, Microwave Utilities, Inc.

Figure 1. Preliminary field demonstration of microwave repair, March 2009.

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As a follow-up, a proposal was submitted to the OPERA program in late 2009 to further investigate field applications of the concept. As conceived, the OPERA project would: 1) conduct laboratory testing on the most promising recycled asphalt pavement (RAP) /taconite combinations; and 2) conduct cold-weather (mid-winter) field testing at NRRI and at select locations in Anoka and St. Louis counties, using a portable microwave unit. The field testing work will be done using mobile microwave equipment provided by Microwave Utilities, Inc. (MUI) of Monticello, MN. An OPERA award was granted in early 2010, but significant delays were encountered in finalizing how the award would be set up and administered within the University system, and an actual budget number was not assigned to NRRI until the summer of 2010. As a result, project work could not officially begin until a budget was available, and no cold-weather field testing was conducted in early 2010, as originally planned. Cold-weather testing was therefore completed during winter-spring of 2011 (February-March-April). Given the lengthy delays and pending field testing, an interim final report was provided to Anoka County, and presented a summary of OPERA project activities through early 2011. To give context to the interim report, findings from previous microwave-related research activities, completed in 2009 and summarized in 2010, were included; they are presented again in this final report as Appendix A (Hopstock, 2010). That earlier work addressed some of the issues that were to be touched on by the current OPERA project, i.e., 1) Repair mix formulation (gradation; asphalt content of RAP; magnetite content of taconite aggregate; RAP/taconite ratio); and 2) Laboratory test data (depth profiles of temperature versus time of laboratory mixes to attain workable/compactable mix). Appendix A is Chapter 6.3 from a much larger study, entitled: “Final Compendium Report to the Economic Development Administration – Research, Development, and Marketing of Minnesota’s Iron Range Aggregate Materials for Midwest and National Transportation Applications”, by Lawrence M. Zanko, Donald F. Fosnacht, and Steven A. Hauck, November, 2010, Technical Report, NRRI/TSR-2010-01 (Zanko et al., 2010) http://www.nrri.umn.edu/egg/REPORTS/TSR201001/TSR201001.html Overview of Project Work June 24, 2010 Even though an official budget number was still not available, a preliminary test of the concept was conducted near NRRI on June 24, 2010, to take advantage of an opportunity provided by another event. Microwave Utilities, Inc. (MUI) had traveled to Duluth to demonstrate their microwave ground-thawing technology to Minnesota Power, using an upgraded 50kW mobile unit equipped with an articulated wave-guide (Figs. 2 and 3). MUI’s equipment operates at a frequency of 915 MHz, which allows for deeper ground penetration needed for its ground thawing applications. Conventional microwave ovens like the kind most people have in their homes operate at a frequency of 2450 MHz and at much lower power levels (1 to 2 kW).

http://www.nrri.umn.edu/egg/REPORTS/TSR201001/TSR201001.html

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Figure 2. Microwave Utilities, Inc. mobile equipment in Duluth, June 24, 2010.

Figure 3. Articulated wave guide on MUI equipment.

While in Duluth, Messrs. Vern Hegg and Kirk Kjellberg of MUI agreed to bring their equipment to NRRI and conduct a preliminary pothole repair test. A pothole located in a nearby parking lot was chosen, and granular RAP left over from testing conducted in 2009 (see Appendix A) was used.

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The hole was prepared by first removing loose material with a stiff shop broom and a shovel. The applicator (horn) was positioned over the hole and lowered to the pavement. A bladder that surrounds the perimeter of the horn was filled with water (in the wintertime, anti-freeze would be added) to seal off and absorb any potential microwave leakage (Fig. 4).

Figure 4. Positioning equipment and microwave-absorbing bladder. Vern Hegg of MUI on the left; Paul Kimpling of NRRI on the right.

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NOTE: A microwave leakage detector was used to monitor for leakage throughout the test. No leakage was detected. Before adding the RAP mixture, the hole was pre-heated for 2 minutes at a power level of 40kW. Following heating, the horn was lifted, and the condition of the pothole was observed. A temperature of about 180° F was indicated with a hand-held infrared thermometer. The bottom of the hole was stirred, and it was evident that loose asphalt at the base of the hole had softened; note the black color (Fig. 5). In cold-weather applications, the pre-heating step should provide for better bonding conditions for the final RAP repair compound.

Figure 5. Pre-heated pothole; note dark softened asphalt in base of hole.

Following pre-heating, a granular RAP mixture (-3/8”) was poured into the hole (Fig. 6).

Figure 6. Loose granular RAP placed in pothole.

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The horn was again lowered, and the mixture was heated with the microwave. During this step, an equipment cooling issue arose, and the microwave was powered down before a full 2 minutes was reached. Still, the mixture had been heated sufficiently to allow for tamping and compaction with a shovel. In a real highway repair application, a gasoline-powered portable compactor would be recommended. The finished repair is shown in Figure 7.

Figure 7. Completed repair.

Figure 8 shows the condition of the same hole as of May 19, 2011. The top ½” of the repair has worn away, which is not unexpected given the limited compaction (accomplished with only a shovel). However, the bulk of repair is intact and sound, suggesting that sufficient heating was achieved to establish a good bond with depth.

Figure 8. Photograph of June 24, 2010, test repair (photo taken May 19, 2011).

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The June 24, 2010, test was also instructive in that it gave the investigators a sense of time, materials, and equipment that would be required for the full-scale field trials to be performed during the winter of 2010-2011.

Winter/Spring 2010-2011 Activities Because the all-season utility of this repair concept would be best demonstrated under cold temperature and/or spring break-up conditions, the remaining project field work took place between February and April of 2011. In November of 2010, arrangements were made through Jim Foldesi of St. Louis County to provide the project with about 3 tons of RAP. Pat McCarthy of St. Louis County’s Pike Lake facility instructed county personnel to load a dump truck with RAP from a local stockpile. On December 3, 2010, NRRI brought a trailer and three super sacks to Pike Lake, county personnel removed the granular (-3/4”) RAP from the back of a dump truck with a loader, and carefully loaded three 3,000 lb capacity super sacks, the loops of which were strung between the forks of a forklift. The filled sacks were placed in the NRRI trailer, and the sacks were brought back to NRRI. A sieve analysis was performed by Will DeRocher of NRRI to confirm the gradation of the granular RAP (Fig. 9), showing it to be essentially 100% passing ¾”. A sub-sample, screened to pass ½”, was prepared by NRRI personnel in early January to allow for comparative testing with the “as-is” RAP, as needed.

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Figure 9. Gradation of RAP acquired from St. Louis County on December 3, 2010.

Following acquisition of the RAP material, plans were put in place to conduct field tests on January 19, 2011, with St. Louis County providing traffic control assistance. Unfortunately, a County labor contract issue arose prior to the 19th. When this situation was coupled with ongoing snow removal needs, a decision was made to postpone the field testing until a later date. Arrangements were then made with Anoka County to conduct a test in early February. February 9, 2011 Anoka County Field Test The first true cold-weather field test was conducted on February 9, on an access road near the Anoka County Highway Department’s fueling station (Fig. 10). Several 5-gal

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buckets of -3/4” and -1/2” RAP were prepared for the test by NRRI personnel. Two buckets of -1/2” taconite waste rock crusher fines were also prepared for the test.

Figure 10. Anoka County Highway Department location, February 9, 2011; Microwave Utilities, Inc. equipment. Conditions:

Sunny and breezy

Air temperature 6° F (-14.4° C)

Pavement temperature 12° F (-11.1° C) Personnel Present:

Vern Hegg and Lon Ashton, Microwave Utilities, Inc.

David Hopstock, David M. Hopstock & Associates, LLC

Charles Cadenhead, Jim Christenson, and Phil Faulhaber, Anoka County Two potholes were targeted for repair. The first hole was filled with RAP screened to pass -1/2”; the second hole (at the yard entrance gate) was filled using as-is (unscreened, -3/4”) RAP augmented with crushed -1/2” taconite waste rock. The condition of both holes and the surrounding asphalt pavement was poor (cracked/alligatored). Underlying road base material (sand) was exposed at the bottom of the first hole (Fig. 11). For both tests, the microwave unit was operated at 2/3 of full power, i.e., at 33kW.

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Figure 11. Photograph showing pre-treatment condition of pothole for February 9, 2011, tests. Test #1: Screened millings (-1/2”); no taconite addition

3 minute pre-heat: Temperature raised to ~80° F (27° C), but with localized hot spots

3 minute additional heat: Localized temperatures of 150° F to 180° F (65° C to 82° C), but one-half of hole remained cool. Repositioned unit approximately 4 to 6 inches to improve the heating of cool areas.

3 minute additional heat: Steam was generated (Fig.12) accompanied by asphalt odor, indicating that good heating was being achieved.

Total pre-heat time of 9 minutes at 33kW. Following the pre-heat, the hole was overfilled with the -1/2” screened RAP to about 110% to 120% of volume

The hole was heated for 2 more minutes, the equipment repositioned, and heated for an additional 2 minutes.

Total patch heating time of 4 minutes at 33kW. The heated patch was compacted with a shovel and by driving over it with a pickup truck. NOTE: The substrate (below the pavement) was sandy, which likely meant microwave energy was being lost (not absorbed) through the bottom of the pothole and into the subsurface.

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Figure 12. Steam generated by heating of pothole: February 9. 2011. Test #2: As-is (-3/4”) millings, blended with an estimated 10% crushed taconite waste rock crusher fines

Instead of pre-heating the hole, a shovel-full of taconite waste rock crusher fines was placed at the base of the hole, with the idea that the taconite rock would absorb the microwave energy and prevent it from passing into the sandy substrate.

The RAP/taconite mixture was placed in the hole (overfilled as in Test #1) and subjected to four 4-minute heating treatments, and a final 2-minute heat.

Total heating time of 18 minutes at 33kW. Once again, localized (non-uniform/hot-spot) heating of the pavement and patch occurred. However, the unscreened RAP/taconite blend seemed to perform nominally better than the first, probably because the second pothole’s base was somewhat more solid, and the taconite added to the base of the hole and to the RAP mix provided better microwave energy absorption overall. For example, softened asphalt “erupted” to the surface of the patch following the heating steps. The patch was compacted with a shovel and by driving over it with a pickup truck. Synopsis of February 9, 2011 testing: Lessons Learned Following Test #2, the testing was stopped, as it was obvious to the investigators that the two test repairs would likely be unsatisfactory, due to: 1) the poor condition of the holes and the surrounding pavement; 2) microwave energy lost through the sandy substrate (especially through the base of the first pothole) and being expended on vaporizing the water in the wet sand underneath; and 3) non-uniform (hot-spot) microwave heating of the pavement and patch material, which contributed to inadequate patch binding and compaction. The investigators agreed that before the next field trials took place, the following steps needed to be taken:

Modify the microwave equipment to allow for more uniform distribution of microwave energy. The non-uniform/hot-spot heating not only lengthened the

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time needed to heat the mix adequately, it resulted in variability of the mix’s physical/thermal properties, which made it difficult to assure good compaction and repair performance.

Determine what percentage of recycled asphalt shingles (RAS) would be needed to enhance the repair’s performance.

Augment the repair compound with taconite materials having a greater (and predictable) magnetite content. In fact, it was later recognized that the magnetic iron content of the crushed taconite waste rock was quite low, which did little to enhance microwave energy absorption during the February 9, 2011, test.

The investigators felt that a better repair could be achieved if these modifications and steps were taken. The final section of this report summarizes the subsequent laboratory tests and field trials that were conducted to achieve that end. Follow-up Laboratory Work and Equipment Modification On February 10, samples of the unscreened (-3/4”) and screened (-1/2”) RAP were brought to Mn/DOT’s Office of Materials in Maplewood for determination of asphalt content (AC). Results were provided to NRRI the following week, as arranged by Ed Johnson, Mn/DOT, and are presented in Figures 13 and 14, respectively. The aggregate components of both samples were also retained following the AC content extractions, and a screen analysis performed. The results showed the AC content of the unscreened RAP to be 5.3%, while the screened RAP returned an AC content of 8.8%. An inspection of the retained aggregate particles showed them to be predominantly basaltic (1.1 billion year old Northshore Volcanics) recovered from local glacial sand and gravel deposits near Duluth. Previous work by Hopstock and Zanko (2004) showed basalt to be a better microwave absorbing material than other conventional aggregate types like granite and limestone.

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Figure 13. Asphalt content of unscreened St. Louis County RAP, and sieve analysis (courtesy Mn/DOT Office of Materials).

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Figure 14. Asphalt content of screened (-1/2”) St. Louis County RAP, and sieve analysis (courtesy Mn/DOT Office of Materials). Based on these results, the investigators agreed that the as-is unscreened RAP should be used for a follow-up field test in St. Louis County, even though its asphalt content was lower than the screened RAP. This decision was based, in part, on using a material (unscreened RAP) that required little or no post-processing prior to use in a repair

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mixture. It was also decided that incorporating granular recycled asphalt shingles (RAS) to increase a repair mixture’s asphalt (binder) content was in keeping with the goal of using 100% recycled materials and taconite mining byproducts and co-products. Therefore, two 5-gallon buckets of granular RAS were provided to NRRI by Mn/DOT’s Office of Materials. Final mix formulations for spring 2011 laboratory and field tests Following a review of the project’s findings and experiences to date, and referring to Hopstock and Zanko’s (2004) earlier work, a decision was made to develop blends that had quantifiable magnetite and asphalt contents. Satmagan analyses (which measure magnetic iron content of taconite materials in weight percent) were used for estimating the magnetite content of coarse taconite tailings and taconite concentrate available to the investigators. From these values, a combination of tailings and concentrate was prepared that resulted in a 24.5% magnetite equivalent taconite portion. This taconite portion comprised 10% by weight of the final RAP mixture formulation. Similarly, RAS estimated to have an asphalt content of 25% by weight (E. Johnson, pers. comm.) was added to the RAP and taconite mixture to provide a final mix asphalt content of 6.5%. Table 1 shows the relative proportions of each component. Table 1. Mix formulations for spring 2011 tests.

Taconite Taconite Recycled

Formulation per 50 lbs Coarse Magnetite Asphalt

of unscreened RAP Tailings Concentrate Shingles†

Final Mix Final Mix

(lbs) (lbs) (lbs) lbs Total % AC

1) Straight RAP (5.3% AC) 0.0 0.0 0.0 50.0 5.3

2) RAP w/10% taconite* (4.8% AC) 4.3 1.3 0.0 55.6 4.8

3) RAP w/10% taconite* and RAS (6.5% AC) 4.7 1.4 5.4 61.6 6.5

*NOTE: Taconite portion at 24.5% magnetite equivalent (blend of coarse tailings and concentrate)†NOTE: RAS assumed to have 25% asphalt content by weight

March 27 Lab Testing: RAP alone, RAP mixed with taconite (RAP + Tac), and RAP mixed with taconite and recycled asphalt shingles (RAP + Tac + RAS) In preparation for the field tests and as a check of the impact of magnetite content and the use of recycled asphalt shingles (RAS), three bench scale comparisons were conducted using NRRI’s 1.5kW SHARP bench top microwave (2450 MHz frequency). Three 3-inch inside diameter and 3-inch tall PVC rings were filled to a depth of about 2.75", first with as-is RAP, then with RAP mixed with a 10% by weight blend of coarse taconite tailings and taconite concentrate (RAP + Tac) to achieve a magnetite concentration of 24.5% Fe3O4 in the taconite component, and finally with a mixture of RAP mixed with taconite and recycled asphalt shingles (RAP + Tac + RAS). The tests used equivalent mix weights of about 505 g. The tests were run in successive 10 second increments, and the temperature measured with a metallic thermocouple probe at depths of about 0.5", 1.25", 1.50”, 2.00", 2.50”, and 2.75" (measured downward from the PVC ring lip) following each 10 second treatment (Fig. 15). Based on these tests, it appeared that the magnetite was initially absorbing the energy closer to the specimen surface, but eventually heated the mix to a somewhat higher temperature with depth over time.

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RAP+Tac+RAS2.50"

RAP+Tac+RAS

Figure 15. Bench top microwave heating tests of RAP, RAP and taconite (RAP + Tac), and RAP, taconite, and recycled asphalt shingle (RAP+Tac+RAS) mixes at various depths. Overall, the mixes containing 10% taconite materials by weight (heavy lines and stippled lines) enhanced the microwave absorbing characteristics of the as-is RAP (dashed lines). Following heating, the three mixes were manually compacted in their PVC ring holders, allowed to cool, and then removed from the holders. Based on the heating rates shown in Figure 15 and the relative integrity of the mixes after cooling, it was determined that the optimal mix was comprised of RAP + Tac + RAS. With the lower frequency (915 MHz) microwaves produced by MUI’s generators, the penetration depth, at least in theory, will be 2.5-3 times greater than the conventional microwave frequency. Therefore the surface heating effect should not be as pronounced. In the previous pothole tests the coldest material seemed to be at the top, with hot tar bubbling up through it. The top layer loses heat by convection to the surroundings, which was even demonstrated in the indoor lab tests at an ambient temperature 70° F (21° C). The thermocouple readings also showed that the temperature of specimens was warmest at the center of the ring and cooled progressively toward the ring edge. In field applications, when the ambient air temperature and the temperature of the surrounding pavement are in the 0° to 32° F range (-18° to 0° C), heat loss at the surface and edges of the repair is expected to be more significant. Therefore, pre-heating the hole (and adjacent pavement) before placing, heating, and compacting the repair compound would likely be beneficial. Modification of Microwave Utilities, Inc. (MUI) equipment Following the February 9 Anoka County test, MUI modified its equipment so that microwave energy would be more uniformly distributed to the pothole repair area. When MUI completed this work in March, arrangements were made with both St. Louis and Anoka Counties to conduct final field tests.

21

Final Field Tests: March 30 and April 8, 2011 Final full-scale field tests were arranged through Jim Foldesi of St. Louis County and Charles Cadenhead of Anoka County. Test locations were recommended, and field assistance/traffic control personnel were provided by both counties. News media coverage (print and television) for both tests was arranged by June Kallestad, NRRI’s Public Relations Manager. Nicole Flint of Mn/DOT’s Office of Materials also conducted thermal imagining documentation during both tests. Her thermal image reports for the St. Louis and Anoka County tests are included as Appendix B and Appendix C, respectively. Principle project personnel present for both tests included:

Vern Hegg, MUI

Kirk Kjellberg, MUI

Lon Ashton, MUI

David Hopstock, David M. Hopstock and Associates, LLC

Larry Zanko, NRRI March 30, 2011 Test: St. Louis County, Tuhkanen Drive St. Louis County recommended that Tuhkanen Drive be used for the pothole repair test. Tuhkanen Drive is located north of NRRI and south of Twig, MN, parallel to and just south and west of U.S. Hwy 53 (Fig. 16). The overall condition of the existing pavement was fair to poor (alligatored). Approximate UTM Zone 15, NAD 83 location: Easting: 549,500m Northing: 5,192,035m

Tuhkan

enD

rive

Potholes

Mu

ng

er

Sh

aw

Rd

Hw

y 53

Figure 16. March 30, 2011, pothole repair test location, St. Louis County.

22

As per the formulations developed and described previously (refer to Table 1), batches of RAP, RAP+Tac, and RAP+Tac+RAS were prepared and blended at NRRI. Five-gallon buckets were filled with each mixture and brought to the Tuhkanen Drive site. The microwave power level used throughout the test was 40kW. Conditions for the test were good (dry and sunny). The air temperature at the start of the test was 35° F (2° C). Five potholes (six unique portions) were repaired using the following mix combinations:

Hole 1: RAP only

Hole 2: RAP+Tac+RAS

Hole 3a: RAP+Tac

Hole 3b: RAP+Tac+RAS

Hole 4: RAP+Tac+RAS

Hole 5: RAP+Tac+RAS Their approximate pothole locations are depicted schematically in Figure 17.

Tuhkanen

Driv

e

100 feet

NUS 53

Potholes

2

13ab

4

5

Approximate UTM Zone 15, NAD 83 location:

Easting: 549,500 m Northing: 5,192,035 m

Figure 17. Approximate location of Tuhkanen Drive potholes, St. Louis County. The repairs allowed for several approaches to be taken and tested, to help determine what combination(s) appeared to work best, i.e., using different mixes, varying pre-heat duration, etc. A hand-held infrared thermometer was used to record surface temperatures pre- and post-microwave treatment, and a metallic thermocouple probe was used to measure the internal temperature of the patch and adjacent pavement (Fig. 18). Field notes were taken and later transcribed, as summarized in Tables 2 and 3.

23

Figure 18. Taking temperature of repair. Table 2. St. Louis County field test data for holes 1, 2, and 3a.

Hole 1 RAP only Patch Adjacent

Heating Heating Temperature Temperature Asphalt

Start Time End Time Surface Internal Temperature

Treatment (minutes) (minutes) (degrees F) (degrees F) (degrees F)

Pre-heat 0 10 250 n/a 475

Pre-heat 10 14 210 n/a n/a

Add mix & heat 14 18 250 n/a n/a

Compacted

NOTES: 10 minute pre-heat too long

Adjacent asphalt reached 475 F.

29-Apr FOLLOW-UP: Good patch; minimal attrition

Hole 2 RAP+Tac+RAS Patch Adjacent







Add mix & heat 8 12 290 215 n/a

Compacted

NOTES: Pre-treated base of hole with magnetite concentrate,

then pre-heated hole for 4 minutes

Steam generated at 3 minutes and 30 seconds.

29-Apr FOLLOW-UP: Good, but some loss of patch material on north edge.

Hole 3a RAP+Tac Patch Adjacent




Pre-heat 0 4 185 n/a 230

Add mix & heat 4 11 300 230 n/a

Compacted

NOTES: No magnetite concentrate pre-treatment

Wetted mixture before heating

29-Apr FOLLOW-UP: Good; a tighter patch than 3b, but being adjacent to 3b,

probably benefitted from additional heating

24

Table 3. St. Louis County field test data for holes 3a, 4, and 5.

Hole 3b RAP+Tac+RAS Patch Adjacent





Add mix & heat 4 12 300 250 n/a

Compacted

NOTES: Pre-treated base of hole with RAS

Final internal temperature of patch ranged from 220 to 280 F.

29-Apr FOLLOW-UP: Patch showing some attrition at surface.





Pre-heat 0 8 300 to 500 n/a n/a

Add mix & heat 8 18 300 240 400 to 600

Compacted

NOTES: Asphalt softened following preheat; strong asphalt smell

Very high temperatures on adjacent asphalt.

29-Apr FOLLOW-UP: Good patch.




(minutes) (minutes) (degrees F) (degrees F) (degrees F)

Pre-heat 0 6 190 n/a 300

Add mix & heat 6 16 220 250 n/a

Compacted

NOTES: Patch near edge of road/shoulder

1/2 of patch over intact old blacktop

1/2 of patch over gravel base

29-Apr FOLLOW-UP: Patch over asphalt portion has good bond

Patch over gravel is weak along its edges; spalling

In addition to providing traffic control, preparing the potholes for microwave repair by removing loose debris (Fig. 19), and compacting the repairs after heating (Fig. 20), the St. Louis County personnel were also there to observe and offer feedback. Personnel from the City of Duluth Public Works were also present to observe the repair procedure. Both groups commented on the mediocre quality of the RAP, and explained that better material having little or no sand and gravel contamination could be obtained. The investigators agreed.

25

Figure 19. Pothole preparation, Tuhkanen Drive, by St. Louis County personnel (right); David Hopstock to the left.

Figure 20. St. Louis County personnel compacting repair after microwave heating. Nicole Flint of Mn/DOT conducted thermal imaging of the test. An example of her imaging work is presented in Figure 21. The temperature profile across the repair clearly shows the degree and distribution of heating achieved. Ms. Flint’s summary report is included as Appendix B.

26

Thermal imaging courtesy

of Nicole Flint, Mn/DOT Figure 21. Microwave repair and thermal imaging. Local news media (Duluth News Tribune) and KBJR television covered the March 30 field test. The story spread rapidly via the Associated Press, and received nationwide attention (Fig. 22).

Published March 31, 2011, 12:00 AM

http://www.duluthnewstribune.com/event/article/id/195271/

There's a new answer for Minnesota's

potholes

How do you mix taconite tailings and old shingles into an effective pothole patch? Put

them in a microwave.

By: John Lundy, Duluth News Tribune

Figure 22. Examples of media coverage of March 30 microwave repair test.

27

The NRRI investigator revisited the Tuhkanen Drive test location on April 29, 2011, to observe the condition of the March 30 test repairs (see related comments in Tables 2 and 3). The follow-up visit suggested that the condition of the repairs could be related to the level of pre-heating achieved prior to installation of the patch compound, and to the internal temperature of the patch compound following microwave heating. Achieving an in-hole pre-heat temperature approaching 200° F (93° C) or greater, heating the adjacent pavement to an even higher temperature (200° to 300° F; or 93° to 149° C), and reaching an internal patch compound temperature greater than 225° F (107° C) seemed to result in a better repair. Finally, Hole 5 was very instructive in that it confirmed what we had experienced during the February 9 test at the Anoka County Highway Department. This hole (and repair) straddled a portion of road that was half underlain by old blacktop, and half underlain by sand and gravel base material. The April 29 follow-up inspection revealed that the portion of the repair over the old blacktop was solid and had a good bond, whereas the portion overlying the sand and gravel base was weak along its edges (spalling patch material). Again, potholes that completely penetrate the pavement are more difficult to repair because the microwave energy will tend to pass through the unbound sand and gravel at the pothole’s bottom and continue into the base material. This situation tends to be more common on rural or secondary roads having thinner or more degraded asphalt, rather than on major roads or highways where potholes seem to form when the wear-course delaminates from the underlying asphalt layer.

28

April 8, 2011 Test: Anoka, Anoka County Anoka County recommended that the pothole repair test be conducted in the city of Anoka, on 4th Avenue between Polk and Harrison Streets (Fig. 23). This test site receives steady traffic, and should be excellent location for tracking the repair performance over time. The condition of the pavement was generally fair to good, except for several small but deep potholes that were targeted for the test. Approximate UTM Zone 15, NAD 83 location: Easting: 469,733 m Northing: 5,005,525 m

Anoka

4th

Ave

.

Harrison St.

Polk St.

Potholes

US Hwy 10

US

Hw

y 1

69

Mississ

ippi R

iver

Main St.

N

Figure 23. April 8, 2011, pothole repair test location, Anoka County.

Prior to the test, the investigators were directed to an asphalt millings (RAP) pile located at the Anoka County Highway Department (Fig. 24). Much of the Anoka RAP was oversized, and had to be broken and screened to pass ¾” on site. The aggregate component of the RAP was determined to be a combination of carbonate rock (limestone and/or dolomite) and granite.

29

Figure 24. RAP pile used for Anoka test. Following screening, several 5-gallon buckets containing 50 lbs. of Anoka RAP were assembled, and combined with pre-weighed portions of coarse taconite tailings, taconite concentrate, and RAS. The intent was to make a repair mix having the same proportion of components (RAP+Tac+RAS) used in the March 30 St. Louis County test. Six potholes were repaired on April 9, using the following mix composition: Hole 1: Anoka RAP+Tac+RAS Hole 2: Anoka RAP+Tac+RAS Hole 3: Anoka RAP+Tac+RAS Hole 4: Anoka RAP+Tac+RAS Hole 5: St. Louis RAP+Tac+RAS (basaltic RAP aggregate) Hole 6: Anoka RAP+Tac+RAS The approximate pothole locations are depicted schematically in Figure 25.

30

200 feet

Potholes

Approximate UTM Zone 15, NAD 83 location:

Easting: 469,733 m Northing: 5,005,525 m

1

2

3

4

5,64

thA

ve

.

Polk St.

N

N 5

thA

ve

.

Figure 25. Approximate location of 4

th Ave. potholes in Anoka, Anoka County.

Traffic control was very important at this location, and was well-handled by the Anoka County personnel. In addition to providing traffic control, they prepared the potholes for microwave repair by blowing out loose debris with a leaf blower, and compacted the repairs after heating with a gasoline-powered compactor/tamper. Several people from the City of Anoka were also on hand to observe the repairs. Local media (ABC Newspapers of Coon Rapids, MN) covered the test. As before, a hand-held infrared thermometer was used to record surface temperatures pre- and post-microwave treatment, and a metallic thermocouple probe connected to a digital readout was used to measure the internal temperature of the patch and adjacent pavement. Field notes were taken and later transcribed, as summarized in Table 4 and Table 5. Four things made this final test different from the previous tests:

1. The starting conditions were considerably warmer. The air temperature at the start of the early afternoon testing was 63° F (17° C), and the sunshine warmed the pavement’s surface temperature above 90° F (32° C).

2. The potholes bottomed out in intact asphalt pavement, not gravel. This situation is optimal for creating a quality bond, or “weld”, between the pothole repair compound the surrounding/underlying asphalt pavement.

3. Only two holes (1 and 2) were pre-heated; the remaining holes were only heated after the repair compound was placed in the hole.

4. A microwave shielding fabric was used instead of the liquid fillable bladder to prevent microwave leakage. The fabric can be seen surrounding the applicator box in Figure 26. Readings taken during the test confirmed that the fabric prevented leakage.

31

Table 4. Anoka field test data for holes 1, 2, and 3.

Anoka





Pre-heat 0 4 160 to 200 n/a 300 to 350

Add mix & heat 4 10 200 to 230 210 n/a

Compacted

NOTES:

27-Apr FOLLOW-UP: Good patch

Anoka





Pre-heat 0 3 115 to 120 n/a 170 to 180

Add mix & heat 3 11 170 to 200 260 to 280 n/a

Compacted

NOTES: Highest temp at bottom of hole/base of patch (3" to 3.5" deep)

Ambient pavement temperature 92 F (solar heating)


Anoka





Add mix & heat 0 6 170 210 to 215 n/a

Add mix & heat 6 9 180 to 190 230 to 240 n/a

Compacted

NOTES: No pre-heat of this hole.

Patch material temperature ~ 50 F.


32

Table 5. Anoka field test data for holes 4, 5, and 6.

Anoka





Add mix & heat 0 10 180 to 190 230 n/a

Compacted


Final internal temperature of patch ranged from 220 to 280 F.

27-Apr FOLLOW-UP: Very good patch

St. Louis





Add mix & heat 0 12 240 270 n/a

Compacted


27-Apr FOLLOW-UP: Good patch.

Anoka




(minutes) (minutes) (degrees F) (degrees F) (degrees F)

Add mix & heat 0 12 210 300 n/a

Compacted


27-Apr FOLLOW-UP: Good patch; minor attrition

33

Figure 26. Microwave repair of Hole 5 on 4th Ave., Anoka, showing microwave equipment, fabric shielding around base of applicator box, and pothole compactor. Pictured (from left to right) are David Hopstock, Lon Ashton (MUI), and Nicole Flint (Mn/DOT). Holes 5 and 6 presented an opportunity to conduct a side-by-side comparison of repair compounds made with RAP from St. Louis County (Hole 5) and RAP from Anoka County (Hole 6). Both contained the same proportion of taconite materials and RAS. The RAP used in the Hole 5 repair contained basaltic aggregate, and had a much more uniform temperature profile, top to bottom, than the repair for Hole 6 (Table 5). This difference can be explained by the aggregate component of the Hole 6 RAP being comprised of low- or non-microwave absorbing carbonate rock and granite. It also explains why the repair stayed relatively cool at the surface (210° F versus 240° F; or 99° C versus 116° C) over the same duration of microwave heating. The temperature differences between the Hole 5 and Hole 6 repairs show how aggregate type (and mineralogy) can influence the degree and rate of microwave energy absorption. Once again, Nicole Flint of Mn/DOT traveled to the test location and conducted thermal imaging of the repairs. An example of the imaging work is presented in Figure 27, which shows a line of completed holes looking north to south along 4th Ave. (Hole 1 is in the foreground, and Hole 5 is in the background). The image shows progressive cooling of the holes from last (5) to first (1). Ms. Flint’s summary report is included as Appendix C.

34

Figure 27. Thermal image of Anoka repairs. The NRRI investigator revisited the 4th Avenue test location on April 27, 2011, to assess and photograph the condition of the April 8 test repairs (see related comments in Tables 4 and 5). All six of the repairs appeared intact and strong (Fig. 28). As before, heating the adjacent pavement to temperatures of 200° to 300° F (93° to 149° C), and reaching an internal patch compound temperature greater than 225° F (107° C) results in a better repair. The fact that each hole was underlain by asphalt pavement likely contributed to a more resilient repair. Periodic assessment of these holes is recommended.

35

3

4

1

2

56

Figure 28. Anoka repairs as of April 27, 2011. Conclusions This project showed that high-quality repair of potholes can be accomplished safely in all seasons using mobile microwave technology. Importantly, the testing also showed that a combination of -3/4 inch RAP/asphalt millings, -1/4 inch magnetite-containing taconite materials, and recycled asphalt shingles (RAP + Tac + RAS) makes an excellent repair compound. This finding is significant, because it demonstrates that “virgin” petroleum-based asphalt compounds (hot mix, cold mix, UPM, etc.) need not be used for all-season pothole repair. In fact, the project showed that the asphalt contained in RAP/millings from old pavements can be easily reheated by microwave energy and re-compacted to form a sound, well-bonded repair. Importantly, this approach reduces the consumption of petroleum-based repair materials. Not only are the taconite materials critical because they enhance the microwave absorbing properties of the compound, making for a faster and higher-temperature repair, the use of magnetite-bearing taconite is particularly critical when using industrial-scale 915 MHz microwave equipment. At this frequency the penetration depth of the microwaves is 2.5-3 times greater than at the more conventional microwave oven frequency of 2450 MHz. If the penetration depth is too great, the microwave energy will be used inefficiently, with a large portion of it being absorbed not in the patching material, but in the substrate underneath. This is especially true at low ambient temperatures. If the penetration depth is too great, when the patch material at depth reaches the required temperature of 225° to 250° F (107° to 121° C), the material at the surface will still be relatively cool and will not soften, compact, and bond properly. By adding magnetite-bearing taconite to the mix, we decrease the penetration depth to optimize patching efficiency by making the temperature at the surface similar to the temperature at several inches depth. The required proportion of taconite required

36

depends upon the composition of the aggregate in the RAP. More taconite is required when the aggregate is carbonate rock (limestone and/or dolomite) or granite than when the aggregate is of basaltic or trap rock composition, which has more significant microwave-absorption properties Overall, the technology shows excellent potential for more effective repair of potholes. While it can take several minutes to repair an individual pothole, especially when compared to more conventional (“throw-and-go”) methods, the extra time to achieve a permanent to near-permanent repair in a single attempt must be weighed against the cost of sending out crews to repair the same multiple times. Equipment modifications/upgrades should speed up the repair process. The objective would be to achieve an effective and permanent repair in about 5 minutes. It is recommended that further field-scale demonstrations and research be conducted, and that implementation of this repair technology be pursued on an expanded basis. This recommendation includes designing a systematic field-scale research program that is coupled with additional mathematical/numerical modeling to better quantify how the microwave energy interacts with various repair compound formulations and under different environmental conditions. The goal would be to develop optimal “designer” formulations from the basic components tested during this OPERA project A cost-benefit analysis that assesses and quantifies equipment, labor, and materials associated with microwave-based repair, and weighs them all against conventional repair methods and options, should also be part of a follow-up program. References Hopstock, D.M., and Zanko, L.M., 2004, Minnesota taconite as a microwave-absorbing road aggregate material for de-icing and pothole patching applications, University of Minnesota Duluth, Natural Resources Research Institute, Technical Report NRRI/TR-2004/19, 18 p.; and University of Minnesota Center for Transportation Studies, Report no. CTS 05-10, 2005. Hopstock, D.M., 2010, Laboratory Experiments on Pothole Repair With Microwave Energy, in Final Compendium Report to the Economic Development Administration – Research, Development, and Marketing of Minnesota’s Iron Range Aggregate Materials for Midwest and National Transportation Applications, Natural Resources Research Institute, University of Minnesota, Duluth, MN, Technical Summary Report NRRI/TSR 2010/01, p. 996-1008. Zanko, L.M., Fosnacht, D.R., and Hauck, S.A., 2010, Final Compendium Report to the Economic Development Administration – Research, Development, and Marketing of Minnesota’s Iron Range Aggregate Materials for Midwest and National Transportation Applications, Natural Resources Research Institute, University of Minnesota, Duluth, MN, Technical Summary Report NRRI/TSR 2010/01, 1295 pp.

APPENDIX A

Laboratory Experiments on Pothole Repair with Microwave Energy by

David M. Hopstock

996

CHAPTER 6.3: Laboratory Experiments on Pothole Repair With Microwave Energy By David M. Hopstock Tests conducted in September, 2009 Abstract and Conclusions. In a series of laboratory experiments we generated data which makes it possible to draw several conclusions about the feasibility of all‐season repair of potholes and other road defects by means of microwave energy. The patching compound is similar to conventional hot‐max asphalt in granulated form. Reclaimed asphalt pavement (RAP) is quite suitable as a base material for this application. On the basis of these experiments we can project that, if a truck‐mounted 100‐kW generator is available, a 10‐cm layer of patching compound can be heated to the temperature required for compaction in about one minute. When allowance is made for the time required for cleaning and preheating the hole, raising and lowering the antenna, compacting the compound, etc., total time for permanently repairing a 30‐cm‐deep pothole should be no more than ten minutes. If only a 50‐kW generator is available, the time estimate is raised to no more than fifteen minutes. All other factors being equal, for pothole repair microwave power at 2.45 GHz is preferable to power at 915 MHz. However, lower frequency equipment can be used if the penetration depth of the microwaves is reduced by the addition of a good microwave absorber, such as taconite rock, to the mix. At the higher frequency it may not be necessary to add a microwave absorber if the aggregate is already a fairly good microwave absorber, such as traprock. With aggregate that is a poor absorber of microwave energy, such as granite or quartzite, addition of taconite to improve microwave absorption is expected to be beneficial in reducing the microwave penetration depth to the most effective level. Introduction. A series of experiments was undertaken to determine the feasibility of making pothole repairs by heating in‐situ a granulated aggregate‐asphalt compound by means of microwave energy. Once the compound has reached its softening temperature, it is compacted to produce a permanent repair. When used under cold‐weather conditions when conventional hot‐mix asphalt is not available, this method would represent a significant improvement in performance and reduction in cost over the conventional method of temporary repair with cold‐mix, followed by having to redo the repair once hot mix becomes available. Materials. We are particularly interested in using reclaimed (or recycled) asphalt pavement (RAP) as the primary component of the pothole repair mix. RAP is produced when existing asphalt concrete pavement is removed, either with a milling machine or by full‐depth removal by such methods as bulldozers and pneumatic pavement breakers. Contamination with extraneous material, such as soil or sub‐base material, should be minimized. The broken pavement is then crushed and screened into a desirable size range for reuse. Reuse of RAP to make new pavement is desirable both from an economic and from an environmental viewpoint. When recycled into hot‐mix Superpave formulations in quantities up to 20 percent, RAP can be accounted for solely as a component of the aggregate (McDaniel & Anderson, 2001). For recycling at higher quantities (typically up to 50 percent) the qualities of the recycled binder must be taken into account. As a result of aging, primarily through the process of oxidation, the long‐chain aliphatic oils in the original asphalt or bitumen tend to convert into aromatic resins, and the resins in turn into high‐molecular‐weight polyaromatic asphaltenes. As a result the stiffness and viscosity of the binder increase. (Papagiannakis & Masad, 2008, pp. 108–111). This can be compensated for in a mix design by addition of a lower viscosity asphalt.

997

We obtained a sample of minimally contaminated RAP from a recently generated stockpile from the Rice Lake Road project in St. Louis County, Minnesota. As received, the material had a wide range in fragment size, up to several inches, which was too large for the pothole patching application. We found that it was difficult to reduce the fragment size at normal laboratory temperatures with typical laboratory equipment, such as jaw mills and roll crushers. Because of the plasticity of the material, the larger pieces tended to deform, rather than to break. Therefore we chose to screen the material at 3/8 inch (9.5 mm) and to use the sub‐9.5‐mm fraction for testing. This procedure may have increased the net asphalt content of the RAP used to a small extent. In large‐scale practice all of the RAP would be reduced to the desired size by use of the use of high‐impact crushers, such as hammer mills, possibly combined with reducing the temperature of the material to decrease plasticity (Wills, 1988, p. 242). The moisture content of the screened material was 3.1 percent. A representative sample of the RAP was sent to the Maplewood, MN, laboratory of the Office of Materials and Road Research of the Minnesota Department of Transportation for analysis. The size distribution is given in Table 6.3‐1. The asphalt content of the RAP, determined by extraction with solvent followed by high‐speed centrifuge, was 5.34 percent. The moisture content, asphalt content, and size distribution (other than the restriction on top size) were all typical of RAP normally encountered. The cleaned aggregate remaining after asphalt extraction was examined under the microscope. The particles were rounded, typical of a river gravel. As is typical of northeastern Minnesota, the gravel was predominantly derived from rocks of basaltic composition. In addition to the typical dark gray color of basalt, particles of basaltic composition also occur in the colors red and green. The red color results from partial oxidation of minerals containing ferrous iron, such as olivine and magnetite, to hematite. The green color results from metamorphic transformation into greenstone, with the green color largely a result of formation of chlorite (Pirsson & Knopf, 1947, pp. 212‐13). In this set of experiments we tested the effect of adding taconite rock to the RAP to enhance microwave absorption. The taconite was waste rock crusher fines from the ArcelorMittal Minorca taconite open pit mine near Virginia, Minnesota. As in the case of the RAP, it was screened to pass 3/8 inch (9.5 mm), with the finer material used for further testing. The minus‐9.5‐mm material was found to contain 3.0 percent moisture. A sample of the screened material was analyzed by the Satmagan magnetic balance and found to contain xxx percent magnetite by weight. For testing this material was blended with RAP in 10 and 20 percent proportions by weight. Ideally in the case of 100‐percent RAP a small amount of low‐viscosity asphalt or other additive would be blended into the mix to compensate for aging of the original asphalt and to improve binding properties. However, we have found in previous field testing that serviceable pothole patches can be made by application of microwaves to unmodified RAP. Therefore we did not attempt to modify the RAP. When magnetite is added to the mix, if no additional asphalt is added, the mix will be starved for available binder and will not achieve optimal physical properties. But since in these experiments we were primarily interested in thermal properties, and because compaction of the mix into a cohesive solid was not planned, simple mixtures of RAP and taconite were used. In future work we plan to work with more complicated mixtures in which the asphalt content is optimized by the addition of recycled asphalt shingles to the mix (California Integrated Waste Management Board, 2009). Apparatus. A box made of wood, lined with plasterboard, was constructed to hold the RAP or RAP/taconite mixture to be tested. The sides of the box fit into slots, facilitating rapid assembly and disassembly. The interior dimensions of the sample space were 28.7 cm by 31.3 cm. The maximum

998

depth of the sample was 30.5 cm. Along the centerline of the 31.3‐cm side of the box perpendicular holes were drilled at 2.54‐cm intervals, to allow insertion of thermocouples. Microwave power at 2.45 GHz was supplied by a nominal 15‐kW power supply manufactured by Microdry and carried by a rectangular waveguide of 8.64 by 4.32 cm internal dimensions into a screened and grounded Faraday cage enclosure in which testing was conducted. In the experiments to be described the sample holder was filled to the maximum depth of 30.5 cm, and microwave energy was applied to the top of the sample at the centerpoint from the end of a 30.5‐cm section of waveguide positioned at a distance of 7.6 cm above the bed. Previous experimentation had shown that at this distance the microwave energy impinged on the top of the sample in a single slightly elliptical area of about 8 cm equivalent circular diameter. The sample box was placed over a plastic pan containing about a 4 cm depth of water, which acted to absorb the microwaves penetrating completely through the sample, minimizing reflection of microwaves back into the sample from underneath. The experimental setup is illustrated in Figure 6.3‐1. Procedure. The RAP or RAP/taconite mixture was layered into the sample box. As a given measurement depth was reached, a stainless‐steel‐sheathed type T copper‐Constantan thermocouple assembly was inserted such that the thermocouple junction was in the center of the assembly. Measurement depths corresponding to the six thermocouples used are given in Table 6.3‐2. After the screened measurement enclosure was vacated and the conducting door sealed, microwave energy was applied at the 4.0 kW level. The thermocouples were connected to a data acquisition board, which in turn was connected to a personal computer which converted the thermocouple voltages into temperatures and automatically recorded them in a data file. The interval between temperature measurements was user‐selectable; in this case it was either 5 or 3 seconds. The test was continued until the highest recorded temperature exceeded about 210°C, at which scorching of the asphalt would begin to occur. Observations. The heating curves for RAP with 0, 10, and 20 percent taconite are shown in Figures 6.3‐2, 6.3‐3, and 6.3‐4, respectively. In all cases the temperature reaches a plateau at just over 100°C for thermocouples T1 and T2. This can be attributed to the moisture in the sample being converted to steam and driven out at this temperature. The curve for T2 shows an upward inflection occurring a short time after T1 leaves the plateau region and reassumes its upward climb, indicating that all the moisture down to the T1 level have been driven out. A likely explanation for the upward jog in T2 is that superheated steam from higher regions penetrates down to that level, producing a rapid rise in temperature to just above 100°C. To facilitate comparison of the effect of the taconite addition, curves for thermocouple T1 have been superimposed in Figure 6.3‐5 and for T3 in Figure 6.3‐6. Figure 6.3‐5 shows that at the 2.5 cm depth the addition of taconite significantly increased the rate of heating. The faster heating observed with 10 percent taconite than with 20 percent is an anomalous result that probably resulted from not precisely replicating the experimental conditions. Note that after the plateau region just above 100°C is passed, the temperature begins to increase again, but at a slower rate than before the plateau was reached, suggesting that the moisture content was a significant factor contributing to microwave absorption at the lower temperatures. At the higher temperatures the rate of temperature increase is significantly greater for the samples containing taconite, indicating that moisture content was a more significant contribution to microwave absorption when no taconite was present. Figure 6.3‐6 shows that at the greater depth of 12.7 cm the heating rates for 0 and 10 percent taconite were essentially identical. The result with 20 percent taconite again appears to be an anomalous result of experimental variation. Factors that could vary from test to test include precise height of the bed, density of packing, positioning of the thermocouples, and exact vertical and lateral positioning of the end of the waveguide with respect to the sample.

999

Theory. For microwave energy penetrating through an absorptive bed, the energy absorbed per unit volume per unit time at depth z is equal to 2αP(z), where α is the microwave absorption coefficient (also known as the attenuation constant) of the material (m‐1) and P(z) is the areal power density of the microwave energy (W/m2) at depth z. The reciprocal of the absorption coefficient 1/α is known as the penetration depth or attenuation distance. Within the penetration depth 86.5 percent of the incident energy is absorbed. The factor of 2 enters because the absorption coefficient α is generally defined in terms of the amplitude of the TEM wave, while the power density carried by the wave depends upon the square of the amplitude. (This discussion follows the notation given by Von Hippel [1954a, p. 28]. Some writers, such as Lindroth et al. [1995], use the notation “α” for what we label “2α”. Their definition of penetration depth is one‐half of our definition. The governing equation for microwave energy passing through the bed can then be written

( ) ( )zPzzP α2−=

∂∂

(1)

If α is assumed to be constant, this equation is readily solved to give

( ) zePzP α20

−= (2)

where P0 is the areal density of power entering the top of the bed (Thuéry, 1992, p. 47). If we can neglect the diffusion of heat from the site, the microwave energy absorbed per unit volume per unit time can be related to the heat capacity of the bed by

( )tTCzP p ∂∂

= ρα2 (3)

where ρ is the density of the material (kg/m3), Cp is its heat capacity on a mass basis (J/kg/°C), T is temperature (°C), and t is time (s). (For an inhomogeneous material like a bed of RAP, ρ and Cp are appropriate average values.) Equations (2) and (3) can then be solved for the rate of increase in temperature to give

z

p

eCP

tT α

ρα 202 −=

∂∂

(4)

Taking the natural logarithm of both sides gives

zCP

tT

p

αρα 22lnln 0 −⎟

⎟⎠

⎞⎜⎜⎝

⎛=⎟

⎠⎞

⎜⎝⎛∂∂

(5)

Thus if we can assume constant power entering the bed P0 and minimal dependence of α and Cp on temperature, then the first term on the right side of equation (5) is a constant, and a plot of the logarithm of the rate of temperature increase against depth in the bed z should give a straight line with slope ‐2α. Determining the slope will allow us to determine the penetration depth of the microwaves. Results. It can be seen in Figures 6.3‐2, 6.3‐3, and 6.3‐4 that the rate of temperature increase is fairly constant at depths of 12.7 cm and greater. On the other hand, large departures from linearity were

1000

apparent at shallower depths corresponding to thermocouples T1 and T2. As previously discussed, much of the nonlinearity is related to the conversion of water into steam at just over 100°C. For purposes of applying equation (5) to determine the penetration depth, it is most appropriate to use the initial heating rate, in the fraction of a minute when the microwave energy is first applied. At this time the temperature is not far above room temperature, the assumption of negligible diffusion of thermal energy is most appropriate, and the conversion of water into steam is not a consideration. To determine initial heating rates at least fifteen temperature data points beginning at time zero were fit by standard least‐squares techniques. Generally a good fit was obtained to a straight line, but in some cases a parabolic curve was used if it gave a significantly better fit. The slope of the straight line, or the linear term for a parabolic fit, gave the initial rate of temperature increase. The results of the calculations are given in Table 6.3‐3. According to equation (5), if the initial rate of temperature increase is plotted on a logarithmic scale against bed depth, the data points should follow a straight line relationship with a slope of ‐2α. Figure 6.3‐7 shows that the data are in accord with this expectation. The lines shown were fit by the least‐squares technique. The slopes and calculated penetration depths are given in Table 6.3‐4. Discussion. The penetration depths with 10 and 20 percent taconite addition were statistically indistinguishable, but were significantly about 17 percent less than that with no taconite addition, corresponding to about a 20 percent greater efficiency of microwave absorption. The taconite addition did not have as large an effect on absorption efficiency as expected because the absorption by the as‐received RAP was much more effective than expected. One reason for this was the 3.1 percent moisture content. From data given by Von Hippel (1954b, p. 314) it can be calculated that the penetration depth was decreased from 3.9 m in dry sandy soil to 0.82 m in the same soil containing 2.2 percent moisture. Similarly a dry loamy soil gave a penetration depth of 23 m, which was decreased to 0.52 m by the addition of only 2.2 percent moisture. A second factor accounting for the relatively high microwave absorption by the RAP was the mineralogical composition of the aggregate in the RAP. As noted above, it consisted largely of basalt, often referred to commercially as traprock. Figure 6.3‐7 shows results for heating in a microwave oven of specimens containing the same weight percent of various aggregate materials in a matrix of plaster‐of‐Paris. The four samples with the highest heating rates were taconite waste rock materials, with LC‐5 containing the highest percentage of magnetite and LS‐2 the lowest. The quartzite and granite aggregate materials heated only marginally faster than control specimen consisting only of plaster‐of‐Paris, indicating very low microwave absorption by those materials. The remaining two aggregate materials, limestone and traprock, showed significant microwave absorption. Traprock was the best absorber, almost approaching the behavior of taconite sample LS‐2. The high microwave absorption of the traprock is most likely predominately a result of the presence of finely disseminated magnetite and ilmenite. The microwave penetration depth should fall into a limited range for optimum performance in pothole patching. If the penetration depth is too great, only a small fraction of the applied microwave energy will be absorbed into the patching compound with most of the energy passing into the ground underneath. If the penetration depth is too shallow, all of the microwave energy will be absorbed, but in a very thin top layer, producing scorching of the asphalt at the surface but cold compound a few centimeters underneath.

1001

Although accurate determination of the optimum penetration depth can only be determined with field studies and mathematical modeling, we can begin to make reasonable estimates. The maximum temperature at which a hot‐mix asphalt should be held for very long is about 165–170°C. Above this temperature age‐hardening can occur as the more volatile components are evaporated or burned off (Mansell, 2009), and noxious fumes can become quite significant. Hot mix is typically laid down at a temperature of about 135–140°C. The optimum temperature for compaction is typically between 105 and 120°C (Chadbourn et al., 1998). Although potholes can be 30 cm deep or greater, it is probably only practical to compact about 10 cm of patching compound at one time. In other words, a 30‐cm‐deep hole would be patched in three stages. Allowing for some surface cooling, let us take the desired surface temperature of the mix to be 190°C and the desired temperature at a depth of 10 cm as 110°C. Assume the mix is at an initial temperature of 10°C. If we assume the increase in temperature of the mix is directly proportional to the microwave power, then the power at a depth of 10 cm should be related to the power at surface in the ratio 100:180 or 0.556. Solving equation (2) for α gives a value of 0.0278, corresponding to a penetration depth of 36 cm. Our observed penetration depths in the 17–22 cm are of the right order of magnitude for the pothole patching application, but less than optimal from the standpoint of uniformity of heating over 10 cm. On the other hand, the shorter penetration depth is more energy efficient. A penetration depth of 36 cm corresponds to absorption of 43 percent of the incident microwave energy; at 22 cm 60 percent would be absorbed, and at 17 cm, nearly 70 percent. Consideration of the actual heating curves in Figures 6.3‐6.3‐2, 6.3‐3, and 6.3‐4, suggests that the more uniform heating shown in Figure 6.3‐2 is most desirable. Thus the use of this particular type of RAP without any added taconite would be recommended. There are a number of situations when addition of magnetite‐containing taconite to the RAP would be recommended. If the aggregate in the RAP had been predominately granite or quartzite, rather than traprock, addition of taconite would have been required to develop adequate absorption of microwaves, especially after all the moisture had been driven out. Although these experiments were run at 2450 MHz, much industrial‐scale microwave equipment runs at the lower frequency of 915 MHz. If the frequency‐dependence of the dielectric properties can be neglected, the penetration depth is directly proportional to the wavelength of the microwaves, or inversely proportional to the frequency (Von Hippel, 1954a, p. 28). Thus at 915 MHz, as a first‐order approximation, the penetration depth will be greater by a factor of 2.7 than at 2450 MHz. Thus, if the lower‐frequency equipment is used, addition of magnetite‐bearing taconite to the patching compound is highly desirable as a means of reducing the penetration depth to the most effective level. Time requirement. In these laboratory experiments the patching compound was sufficiently heated for compaction in four or five minutes. In the field it would desirable to keep the time requirement to five minutes at most. Because of spreading of the microwave beam and lateral conduction of heat, the area over which the four kilowatts of microwave power were applied is not well‐defined. However, it is possible to obtain a reasonable estimate of the area. After the conclusion of the test with 10 percent taconite added to the RAP, thermocouples T1, T2, and T3 were gradually drawn out of the bed and the temperatures recorded at 2.5 cm intervals. The results, shown in Figure 6.3‐9, indicate that the temperature dispersion increases as the depth increases. If we take the lateral distance at which the temperature has been reduced halfway to the ambient temperature of 20°C as the effective radius of the beam, the beam radius is about 7 cm at T1, about 10 cm at T2, and over 13 cm at T3. Taking 8 cm at a representative radius gives an area of about 200 cm2, corresponding to an areal power density of 200 kW/m2. In the field an antenna irradiating an area with an effective diameter of 40 cm (15.7 inches) would be of adequate size for most pothole repairs. This corresponds to an effective area

1002

of about 0.125 m2. To obtain 200 kW/m2 would require a power supply producing 25 kW. Since 25‐kW power supplies are readily available, there would be no problem in heating at 10‐cm thickness of patching compound in 4–5 minutes. If a 100‐kW power supply were available, the time requirement would be reduced to about one minute for each 10‐cm layer. Acknowledgments. This work could not have been completed without the combined efforts of a dedicated team of experts in their fields. The project leader was Lawrence M. Zanko, who provided essential coordination of all aspects of the project. David P. Lindroth provided critical assistance in setting up the microwave equipment and the thermocouples, developing operating procedures, and guaranteeing safe operation of the equipment. James Harrison developed the computer‐based data acquisition system. Paul Kimpling and Michael Cable collaborated on design and construction of the sample box. Paul also obtained and screened the RAP sample used, screened the taconite, and prepared the blends.

References California Integrated Waste Management Board (2009), Asphalt Roofing Shingles Recycling, http://www.ciwmb.ca.gov/condemo/Shingles/default.htm, accessed on 11/16/09. Chadbourn, B.A., D.E. Newcomb, V. R. Voller, R.A. DeSombre, J.A. Luoma, and D.H. Timm (1998). An Asphalt Paving Tool For Adverse Conditions, Report MN/RC‐1998‐18, Minn. Dept. of Transportation, St. Paul, Minn. Accessed on 11/22/09 at http://www.dot.state.mn.us/app/pavecool/docs/199818.pdf . Lindroth, D.P., W.R. Berglund, and C.F. Wingquist (1995). “Microwave thawing of frozen soils and gravels,” J. Cold Regions Engineering, 9(2), pp. 53–63. McDaniel, R., and R. M. Anderson (2001). Reclaimed Asphalt Pavement in the Superpave Mix Design Method: Technician's Manual, National Cooperative Highway Research Program Report 452, National Academy Press, Washington, DC. Accessed on 11/15/09 at http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_452.pdf. Mansell, T. (2009). Raveling in Hot Mix Asphalt Pavements, Graniterock Research and Technical Services, http://www.graniterock.com/technical_notes/raveling_in_hot_mix_asphalt_pavements.html, accessed 11/22/09. Papagiannakis, A.T., and E. A. Masad (2008). Pavement Design and Materials, John Wiley & Sons, New York. Pirsson, L.V., and A. Knopf (1947). Rocks and Rock Minerals, 3rd edition, John Wiley & Sons, New York. Thuéry, J. (1992). Microwaves: Industrial, Scientific, and Medical Applications. Artech House, Boston, Mass. Von Hippel, A.R. (1954a). Dielectrics and Waves, M.I.T. Press, Cambridge, Mass. Von Hippel, A.R. (1954b). Dielectric Materials and Applications, M.I.T. Press, Cambridge, Mass. Wills, B.A. (1988). Mineral Processing Technology, 4th edition, Pergamon Press, Oxford, England.

1003

Table 6.3‐1. Size Distribution of RAP Material Tested

ASTM Sieve Particle Size (mm) Percent Passing 3/8 inch 9.5 100

#4 4.75 85 #8 2.36 69

#10 2.00 66 #16 1.18 56 #30 0.60 43 #40 0.42 36 #50 0.30 29 #100 0.15 17 #200 0.075 11

Table 6.3‐2. Depths Corresponding to Thermocouple Locations

Thermocouple Depth (cm) T1 2.5 T2 7.6 T3 12.7 T4 17.8 T5 22.9 T6 27.9

Table 6.3‐3. Calculated Initial Rates of Temperature Increase (°C/sec)

Depth (cm) 0% taconite 10% taconite 20% taconite 2.5 0.412 0.659 0.775 7.6 0.381 0.470 0.319

12.7 0.1715 0.1669 0.1405 17.8 0.0931 0.0979 0.1055 22.9 0.0676 0.0648 0.0691 27.9 0.0464 0.0439 0.0361

Table 6.3‐4. Penetration Depth Versus Taconite Content

Taconite Content (%) Slope 2α (cm-1) Penetration Depth (cm) 0 0.094 21.3 10 0.113 17.8 20 0.114 17.6

1004

Figure 6.3‐1. Experimental test assembly.

20

40

60

80

100

120

140

160

180

200

220

0 60 120 180 240 300 360

Time (sec)

Tem

pera

ture

(C)

T1

T2

T3

T4

T5

T6

Figure 6.3‐2. Heating curves for 100% RAP/0% taconite.

1005

20

40

60

80

100

120

140

160

180

200

220

240

0 30 60 90 120 150 180 210 240 270

Time (sec)

Tem

pera

ture

(C)

T1

T2

T3

T4

T5

T6

Figure 6.3‐3. Heating curves for 90% RAP/10% taconite mixture.

20

40

60

80

100

120

140

160

180

200

220

0 30 60 90 120 150 180 210 240 270

Time (sec)

Tem

pera

ture

(C)

T1

T2

T3

T4

T5

T6

Figure 6.3‐4. Heating curves for 80% RAP/20% taconite mixture.

1006

20

40

60

80

100

120

140

160

180

200

220

240

0 60 120 180 240 300 360

Time (sec)

Tem

pera

ture

(C)

0% taconite

10% taconite

20% taconite

Figure 6.3‐5. Effect of taconite addition on heating at a depth of 2.5 cm.

20

30

40

50

60

70

0 60 120 180 240 300 360

Time (sec)

Tem

pera

ture

(C)

0% taconite

10% taconite

20% taconite

Figure 6.3‐6. Effect of taconite addition on heating at a depth of 12.7 cm.

1007

0.01

0.1

10 5 10 15 20 25 30

Depth (cm)

Rat

e of

Tem

pera

ture

Incr

ease

(C/s

)

0% taconite

10% taconite

20% taconite

0% fit

10% fit

20% fit

Figure 6.3‐7. Effect of depth in the bed on initial rate of temperature increase.

Figure 6.3‐8. Results of microwave heating of specimens containing the same weight percentage of various aggregate materials in a plaster‐of‐Paris matrix.

0

20

40

60

80

100

120

140

0 20 40 60 80 100 120

Time (sec)

Tem

pera

ture

(C)

BlankQuartziteGraniteLimestoneTraprockLS-2LUCLC-8LC-5

1008

20

40

60

80

100

120

140

160

180

200

220

240

0 2 4 6 8 10 12 14

Lateral Distance (cm)

Tem

pera

ture

(C)

T1

T2

T3

Figure 6.3‐9. Lateral temperature profile after completion of test with 90% RAP/10% taconite mixture.

APPENDIX B

Pothole Patching Demonstration Tuhkanen Drive

Twig, MN St. Louis County / NRRI

Nicole Flint, MnDOT

Date: 4/5/2011

FLIR Systems AB 4/5/2011

TwigMicrowaveReport.REP Page 1

Pothole Patching DemonstrationTuhkanen Drive

Twig, MN

St. Louis County/NRRI

Nicole Flint, MnDOT

Date:

4/5/2011



3.8°C

31.1°C

5

10

15

20

25

30

SP01

File name Time Date

B0330-15.img

10:17:17 AM

3/30/2011

Pothole Patching - Hole #2

Machine down on pavement

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C

Reference temperature

*

Label

Value IR : max

41.6°C

IR : min

-6.6°C

SP01

12.6°C



3.8°C

31.1°C

5

10

15

20

25

30

SP01

LI01

0

10

20

30

40

50

60

70

Line Min Max Cursorli01 8.9°C 66.9°C -

°C IR01

File name Time Date

B0330-16.img

10:21:39 AM

3/30/2011


After 4 min initial heating

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

110.1°C

IR : min

3.0°C

SP01

35.0°C

LI01 : max

66.9°C

LI01 : min

8.9°C

LI01 : max-min

58.1°C



3.8°C

99.2°C

10

20

30

40

50

60

70

80

90

SP01

LI01

0

20

40

60

80

100

120


°C IR01

File name Time Date

B0330-17.img

10:25:19 AM

3/30/2011


After another 4 min initial heating

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

142.1°C

IR : min

1.0°C

SP01

67.8°C

LI01 : max

128.9°C

LI01 : min

6.7°C

LI01 : max-min

122.2°C



3.8°C

99.2°C

10

20

30

40

50

60

70

80

90

SP01

LI01

0

20

40

60

80

100


°C IR01

File name Time Date

B0330-18.img

10:25:45 AM

3/30/2011


After initial heat (with Hole #1 in the foreground)

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

121.8°C

IR : min

3.9°C

SP01

66.8°C

LI01 : max

104.5°C

LI01 : min

6.6°C

LI01 : max-min

97.9°C



3.8°C

99.2°C

10

20

30

40

50

60

70

80

90

SP01

LI01

0

20

40

60

80

100

120


°C IR01

File name Time Date

B0330-19.img

10:27:52 AM

3/30/2011


Cold asphalt added to hole

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

124.1°C

IR : min

1.5°C

SP01

13.3°C

LI01 : max

109.9°C

LI01 : min

6.1°C

LI01 : max-min

103.8°C



3.8°C

99.2°C

10

20

30

40

50

60

70

80

90

SP01

LI01

0

20

40

60

80

100


°C IR01

File name Time Date

B0330-20.img

10:29:15 AM

3/30/2011


All asphalt added to hole

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

92.1°C

IR : min

0.5°C

SP01

15.0°C

LI01 : max

91.2°C

LI01 : min

7.2°C

LI01 : max-min

84.0°C



5.1°C

130.8°C

20

40

60

80

100

120

SP01

LI01

0

20

40

60

80

100

120


°C IR01

File name Time Date

B0330-21.img

10:34:47 AM

3/30/2011


After 2 min asphalt heat

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

132.4°C

IR : min

2.2°C

SP01

76.5°C

LI01 : max

115.6°C

LI01 : min

9.8°C

LI01 : max-min

105.7°C



5.1°C

130.8°C

20

40

60

80

100

120

SP01

LI01

0

20

40

60

80

100

120


°C IR01

File name Time Date

B0330-22.img

10:41:33 AM

3/30/2011


After another 2 min asphalt heat

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

139.2°C

IR : min

5.2°C

SP01

100.6°C

LI01 : max

125.3°C

LI01 : min

11.2°C

LI01 : max-min

114.2°C



5.1°C

130.8°C

20

40

60

80

100

120

SP01

LI01

0

20

40

60

80

100

120

140

160


°C IR01

File name Time Date

B0330-23.img

10:42:43 AM

3/30/2011


After asphalt heating

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

158.0°C

IR : min

9.4°C

SP01

94.2°C

LI01 : max

156.7°C

LI01 : min

12.0°C

LI01 : max-min

144.7°C



5.1°C

130.8°C

20

40

60

80

100

120

SP01

LI01

0

20

40

60

80

100

120

140


°C IR01


After asphalt heating

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

148.6°C

IR : min

4.7°C

SP01

96.5°C

LI01 : max

135.6°C

LI01 : min

8.3°C

LI01 : max-min

127.3°C

File name Time Date

B0330-24.img

10:45:23 AM

3/30/2011

APPENDIX C

Pothole Patching Demonstration 4th Avenue Anoka, MN

Anoka County / NRRI

Nicole Flint, MnDOT Date:

April 8, 2011


AndoverPotholePatching.REP Page 1

Pothole Patching Demonstration4th AvenueAndover, MN

Anoka County / NRRI

Nicole Flint, MnDOT

Date:

April 8, 2011



-17.8°C

38.0°C

-10

0

10

20

30

SP01

LI01

0

20

40

60

80

100


°C IR01

File name Time Date

B0408-01.img

1:10:06 PM

4/8/2011

Hole 2

Preheated, cold asphalt added

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

104.1°C

IR : min

-5.8°C

SP01

17.9°C

LI01 : max

87.3°C

LI01 : min

18.0°C

LI01 : max-min

69.3°C



3.6°C

149.3°C

20

40

60

80

100

120

140

SP01

LI01

20

40

60

80

100

120

140


°C IR01

File name Time Date

B0408-02.img

1:20:10 PM

4/8/2011

Hole 2

Heated with asphalt

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

171.2°C

IR : min

-6.2°C

SP01

83.4°C

LI01 : max

132.2°C

LI01 : min

23.8°C

LI01 : max-min

108.4°C



23.1°C

165.6°C

40

60

80

100

120

140

160

SP01

LI01

40

60

80

100

120

140

160


°C IR01

File name Time Date

B0408-03.img

1:22:09 PM

4/8/2011

Hole 2

Heated with asphalt

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

166.6°C

IR : min

21.7°C

SP01

91.4°C

LI01 : max

129.4°C

LI01 : min

24.2°C

LI01 : max-min

105.2°C



14.1°C

22.4°C

15

16

17

18

19

20

21

22

SP01

LI01

16

18

20

22


°C IR01

File name Time Date

B0408-04.img

1:26:52 PM

4/8/2011

Hole 3

Cold hole with ashalt added

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

22.9°C

IR : min

12.2°C

SP01

14.9°C

LI01 : max

19.9°C

LI01 : min

13.8°C

LI01 : max-min

6.0°C



21.7°C

129.2°C

40

60

80

100

120

SP01

LI01

40

60

80

100

120


°C IR01

File name Time Date

B0408-05.img

1:38:01 PM

4/8/2011

Hole 3

Hole with ashalt after initial heating (Hole 2 in foreground)

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

124.4°C

IR : min

19.8°C

SP01

91.5°C

LI01 : max

111.5°C

LI01 : min

23.3°C

LI01 : max-min

88.3°C



6.0°C

126.6°C

20

40

60

80

100

120

SP01

LI01

20

40

60

80

100

120


°C IR01

File name Time Date

B0408-06.img

1:39:10 PM

4/8/2011

Hole 3

Hole with ashalt after initial heating (Hole 2 in foreground)

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

122.9°C

IR : min

*-47.2°C

SP01

70.9°C

LI01 : max

103.5°C

LI01 : min

21.7°C

LI01 : max-min

81.8°C



-9.1°C

139.2°C

0

20

40

60

80

100

120

SP01

LI01

0

20

40

60

80

100

120


°C IR01

File name Time Date

B0408-07.img

1:43:47 PM

4/8/2011

Hole 3

Hole with ashalt after second heating (Hole 2 in foreground)

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

131.8°C

IR : min

-17.0°C

SP01

89.3°C

LI01 : max

123.4°C

LI01 : min

25.6°C

LI01 : max-min

97.8°C



13.5°C

26.5°C

14

16

18

20

22

24

26

SP01

LI01

14

16

18

20

22

24

26


°C IR01

File name Time Date

B0408-08.img

1:49:30 PM

4/8/2011

Hole 4

Cold hole with ashalt added

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

23.2°C

IR : min

12.3°C

SP01

15.2°C

LI01 : max

19.0°C

LI01 : min

13.9°C

LI01 : max-min

5.1°C



-28.5°C

157.3°C

-20

0

20

40

60

80

100

120

140

SP01

LI01

0

50

100

150


°C IR01

File name Time Date

B0408-09.img

2:02:57 PM

4/8/2011

Hole 4

Hole with ashalt after initial heating

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

158.1°C

IR : min

-36.3°C

SP01

85.1°C

LI01 : max

148.3°C

LI01 : min

24.1°C

LI01 : max-min

124.2°C



17.6°C

158.2°C

20

40

60

80

100

120

140

SP01

LI01

20

40

60

80

100

120

140


°C IR01

File name Time Date

B0408-10.img

2:03:45 PM

4/8/2011

Hole 4


Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

162.6°C

IR : min

15.4°C

SP01

108.7°C

LI01 : max

152.3°C

LI01 : min

23.7°C

LI01 : max-min

128.6°C



21.5°C

168.8°C

40

60

80

100

120

140

160

SP01

LI01

40

60

80

100

120

140

160


°C IR01

File name Time Date

B0408-12.img

2:23:04 PM

4/8/2011

Hole 5


Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

158.1°C

IR : min

17.4°C

SP01

137.3°C

LI01 : max

139.4°C

LI01 : min

24.6°C

LI01 : max-min

114.8°C



20.6°C

160.7°C

40

60

80

100

120

140

160

SP01

LI01

40

60

80

100

120

140

160


°C IR01

File name Time Date

B0408-13.img

2:24:56 PM

4/8/2011

Hole 5


Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

150.6°C

IR : min

17.0°C

SP01

110.3°C

LI01 : max

128.3°C

LI01 : min

23.5°C

LI01 : max-min

104.8°C



17.8°C

90.5°C

20

30

40

50

60

70

80

90

SP01

LI01

20

40

60

80

100

120


°C IR01

File name Time Date

B0408-14.img

2:27:54 PM

4/8/2011

Holes 1-5

Hole 1 (front) to Hole 5 (back)

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

115.4°C

IR : min

15.9°C

SP01

49.1°C

LI01 : max

115.4°C

LI01 : min

18.5°C

LI01 : max-min

96.9°C



17.8°C

90.5°C

20

30

40

50

60

70

80

90

SP01

LI01

20

40

60

80

100

120


°C IR01

File name Time Date

B0408-15.img

2:28:05 PM

4/8/2011

Holes 1-5

Hole 1 (front) to Hole 5 (back)

Object parameter

Value Emissivity

0.95

Object distance

2.4 m

Ambient temperature

23.9°C


*

Label

Value IR : max

115.7°C

IR : min

15.9°C

SP01

74.9°C

LI01 : max

106.6°C

LI01 : min

18.4°C

LI01 : max-min

88.2°C

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