Ontario s Experience with Warm Mix Asphalt

Transcription

1 0 0 Ontario s Experience with Warm Mix Asphalt Seyed Tabib, P.Eng. (Corresponding Author) Senior Bituminous Engineer, Bituminous Section Ministry of Transportation Ontario Wilson Avenue, Room, Building C, Toronto, Ontario Canada MM J Telephone: () - Fax: () - seyed.tabib@ontario.ca Chris Raymond, Ph.D., P.Eng. Acting Head, Bituminous Section Ministry of Transportation Ontario chris.raymond@ontario.ca Loan Le Transportation Technician, Bituminous Section Ministry of Transportation Ontario loan.le@ontario.ca Submitted on: August, 0 Word count: 0

2 Seyed Tabib, Chris Raymond, Loan Le 0 0 ABSTRACT Ministry of Transportation Ontario (MTO) is committed to implementing green technologies such as on provincial highways. Published benefits of include: reduced energy use/fuel consumption, reduced asphalt plant emissions, improved compaction and joint quality, facilitation of late season paving due to increased workability, reduced asphalt binder aging (less potential for cracking), facilitation of longer hauling distances, allowance for earlier opening to traffic after construction, and potential for higher RAP content. To examine the actual benefits of, MTO has built test sections since 00. A comprehensive material sampling and testing program was in place during construction of each test section. Most of the test sections had over,000 tonnes of and included a control section. Contractors were responsible for selecting the technology. All of the selected technologies were chemical additives. For each contract, the following data/samples were collected: supplier s recommendations for producing and placing Stack emissions at the asphalt plant production and paving temperatures Infrared photographs during paving and compaction of and Moisture sensitivity testing (AASHTO T) on the production samples Samples of / for Hamburg wheel track testing at the laboratory Quality Control and Quality Assurance test results on the mix and the PGAC The test sections were all completed successfully and they are currently being monitored for long term performance in comparison with the control section. This paper overviews test sections and provides a summary of the material test results, emissions data, and pavement performance to date. Asphalt plant emissions for were not significantly different than. PGAC test results were in compliance with AASHTO M0 for both and. was paved at temperatures -0 o C lower than without any adverse effect on mix properties or compaction. TSR results for were variable. In general, pavement compaction for was either equal to or better than. Hamburg rut depths were comparable between and.

3 Seyed Tabib, Chris Raymond, Loan Le INTRODUCTION Warm Mix Asphalt () is an innovative green technology that will improve the environmental sustainability of Hot Mix Asphalt (). Ministry of Transportation Ontario (MTO) is committed to implementing green technologies such as on its highways. For this reason, MTO has built test sections since 00. A comprehensive material sampling and testing program was in place during construction of each test section. Most of the test sections had over,000 tonnes of and included a control section. Contractors were responsible for selecting the technology. All the selected technologies were chemical additives namely Evotherm, Hypertherm, and Sasobit. BACKGROUND Warm Mix Asphalt is defined as a group of technologies which allow for a reduction in the temperatures at which asphalt mixtures are produced and placed. This reduction usually varies from 0 to 0 o C while still achieving adequate compaction. can be separated into broad categories (): Chemical Processes Organic Additives Foaming Processes (water-bearing additives or water-based processes) Many studies have shown that lower mixing and placing temperatures lead to (): Reduction in asphalt plant emissions (up to 0%) Fuel savings at asphalt plant Ability to pave/compact in cooler temperatures Longer hauling distances from asphalt plants to job sites Facilitation of higher Recycled Asphalt Pavement (RAP) content Compaction improvement better joints Less thermal segregation and less asphalt aging (i.e., reduced potential for cracking) Earlier opening to traffic MTO S Past Experience With MTO has developed specifications for mandatory as well as permissive use of on contracts. Since 00, MTO has paved about 0,000 tonnes of mostly under trial contracts where is required to be used. The first trial was on Highway (north of Smiths Falls, Ontario), which utilized Evotherm emulsion technology (ET). In 00, was used in two contracts, both initiated by the contractors in a form of change proposals. Hwy 0/Hurontario Street Patrol Yard was paved with 0 tonnes of using Hypertherm technology and Highway 0 west of London was paved with 00 tonnes of Sasobit. In 0, MTO placed in contracts; mandated trials and change proposal. DESCRIPTION OF 0 CONTRACTS In 0, MTO paved,000 tonnes of using Hypertherm, Evotherm and Sasobit technologies on contracts across Ontario (Table ). Eight contracts included a control section in addition to the section. was paved at temperatures of -0 0 C lower than conventional without any adverse effect on mix properties or compaction.

4 Seyed Tabib, Chris Raymond, Loan Le TABLE Description of 0 Contracts Contract #/ Highway # Hwy Hwy Hwy 0 Hwy Hwy Hwy Hwy Hwy / Hwy Hwy Mix Type.FC.FC.FC.FC.....FC.FC PGAC Additive Hypertherm (chemical Hypertherm (chemical Hypertherm (chemical Evotherm G (chemical Evotherm DAT (chemical Evotherm G (chemical Evotherm G (chemical Evotherm G (chemical Evotherm G (chemical Sasobit (organic Asphalt Plant Type/ Burner Type Drum plant - Not open flame burner Drum plant - Induced draft burner Batch plant - counter-flow drum burner Fuel Type Natural Gas Natural Gas Natural Gas Date of Paving September 0 September 0 September 0 Control Section Yes Yes Yes Batch plant Diesel July 0 No Drum plant Batch plant - Forced draft burner Batch plant - Counterflow drum burner No information No information No information Fuel Oil Fuel Oil Natural Gas Natural Gas Natural Gas Natural Gas NOTE FC = coarse aggregates must be supplied from a premium source FC = fine and coarse aggregates must be supplied from a premium source CONSTRUCTION OF TEST SECTIONS November 0 August 0 September 0 July 0 October 0 October 0 padding Specification was specified via a special provision that amended the existing standard specification for. Additional requirements for are described below: Supplier s Recommendations The Contractor was required to submit the technology supplier s established recommendations for usage of their technology. One-point Mix Check Yes Yes Yes Yes Yes

5 Seyed Tabib, Chris Raymond, Loan Le For the chemical and organic technologies, as a minimum, the contractor was required to submit the mix design along with a one-point mix check including the additive. Maximum Paving Temperature A maximum allowable temperature of o C has been specified for 0 contracts. Emissions Measurements The contractor was required to measure stack emissions at the asphalt plant for one day s production of and one day s production of. Stack emissions measurements were required for Contracts to and included carbon monoxide (CO), carbon dioxide (CO ), nitrogen oxides (NO x ), sulphur oxides (SO x ), oxygen (O ), volatile organic compounds (VOC), and total particulate matter (TPM) in accordance to Ontario Source Testing Code (OSTC) and Unites States Environmental Protection Agency (EPA) test methods (). Some additional data such as asphalt production rate, plant fuel usage, stack gas volumetric flow rates, stack gas temperature, and stack gas moisture content were also required. Temperature Measurements The Contractor was required to provide plant production temperatures obtained once per hour during the production of. The temperature of the behind the paver was also required once every 0 lane-metres. MTO staff used an infrared camera to capture thermal images during the paving and compaction of and. The images were analyzed using Smartview software to identify temperature range and thermal evidence of thermal segregation. Identification of Paving Limits The contractor was required to submit an as-built sketch, identifying the stations as well as the GPS coordinates for the paving limits. Moisture Sensitivity Testing on the Production Samples Production samples of were taken and sent to the quality assurance (QA) laboratory for moisture sensitivity testing as per AASHTO T-0. Additional / Samples for Hamburg Wheel Track Testing Samples from the and were taken and delivered to the MTO s Materials Engineering and Research Office (MERO) laboratory for Hamburg Wheel Track Testing. Costs and Challenges In 0, premium costs of were up to % higher than the regular because of the additional testing and emissions measurements required for the trials as well as the cost for the additive. In 0, the additional costs would be reduced to only the additive and limited additional testing. Hence, the cost premium of over is expected to be within %. In addition to costs, created some other challenges during the 0 trials as follows: Lack of knowledge/experience with Lack of an approved list Effectiveness of different technologies not all are the same Ensuring long term performance including moisture susceptibility

6 Seyed Tabib, Chris Raymond, Loan Le 0 Mix design procedure Criteria for PGAC acceptance Recyclability Ensuring adequate drying of aggregates Restrictions/adjustments at the asphalt plant Avoiding pick up vs. achieving compaction; some technologies made the mix stickier and harder to rake MATERIALS TEST RESULTS End Result Specification (ERS) All the contracts followed the ministry s End Result Specification (ERS). The ERS bases the acceptance of the asphalt mix on a lot-by-lot basis. Aggregate gradation of four sieves, asphalt cement (AC) content, air voids, VMA and compaction are accepted based on the percent within limits (PWL) of the lot. Table provides AC content and compaction means for and. Compaction is measured on the pavement cores as a percentage of the maximum relative density. TABLE ERS of 0 MTO Trials Contract Mix Type AC Content (Lot Avg.) Compaction (Lot Avg.) JMF Hwy.FC..... Hwy.FC Hwy 0.FC Hwy Hwy Hwy Hwy Hwy / Hwy Hwy.FC... No control section No control section.. No control section No control section fc fc.....

7 Seyed Tabib, Chris Raymond, Loan Le 0 PGAC Compliance All the PGAC samples, including binders that included the additive, met the requirements of AASHTO M0 for the specified PGAC grade. Moisture Sensitivity Test Currently MTO requires a minimum Tensile Strength Ratio (TSR) of 0% to be conducted during the mix design. There is no TSR requirement for the production mix. The moisture sensitivity testing, specified in the specification, is required for information purpose only. The results are summarized in the Table indicating high variability in TSR values for (ranging from to percent). The main contributing factor to such variable TSR values is the production temperature. It was noted that the contracts with more variable production temperatures resulted in highly variable TSR values which is directly related to the aggregate dryness prior to mixing with the AC. During a separate study, moisture sensitivity of production samples was reviewed. The results were more consistent and, in most cases, the average TSR for production samples was larger than the TSR obtained during the mix design. TABLE TSR Results for Production Samples Contract Mix Type Mix Design TSR Production TSR.FC 0 () Hwy.FC () Hwy.FC () Hwy 0.FC () Hwy. () Hwy. () Hwy. () Hwy. () Hwy /.FC 0 () Hwy NOTE Numbers in parentheses denote mean value Hamburg Wheel Track Testing Hamburg Wheel Track testing was performed on the and samples to evaluating the rutting/stripping potential. MTO follows a modified AASHTO T test method where a pair of treaded pneumatic tires is used for applying the load (Figure ). In this test, asphalt briquettes are submerged in 0 o C water bath and subjected to 0,000 load applications ( hours). Table provides the Hamburg test results on the samples from 0 contracts. MTO has not yet developed pass/fail criteria for the Hamburg results that take into account the mix type as well as PGAC grade. However, based on the recent studies where various mixes were tested, good performing mixes exhibited rut depths within mm. Therefore, samples from Contracts and

8 Seyed Tabib, Chris Raymond, Loan Le seem slightly rut susceptible, although rutted less in Contract and Contract did not include a control section. test sections will be monitored on annual basis for rutting. TABLE Hamburg Wheel Track Testing Results from 0 Trials Contract #/ Mix Type PGAC Technology Max. Rut Depth (mm) Highway #.FC - Hypertherm.. Hwy Hwy Hwy 0 Hwy Hwy Hwy Hwy Hwy / Hwy Hwy.FC -.FC -.FC FC -.FC - Hypertherm Hypertherm Evotherm G Evotherm DAT Evotherm G Evotherm G Evotherm G Evotherm G Sasobit.. N/A MEAN.. FIGURE Hamburg Wheel Tracking Machine Equipped with Pneumatic Tires

9 Seyed Tabib, Chris Raymond, Loan Le THERMAL IMAGES AND TEMPERATURES mixing temperatures, recorded at the asphalt plant, and the paving temperatures, determined using infrared thermometer and thermal camera, are given in Table. Figure compares thermal images between and. Despite a maximum specified paving temperature of o C, many contracts exceeded this requirement and paving temperatures as high as o C were observed. Moreover, relatively variable mixing temperatures were noted for the as compared to conventional. The main reason for such inconsistent production temperature is believed to be inexperience of asphalt plant s operator in maintaining a consistent mixing temperature at target temperature while achieving dry aggregate. TABLE Mixing and Paving Temperature Data for Contract #/ Mixing Temperature Paving Temperature Highway # ( o C) ( o C) Hwy Hwy Hwy 0 Hwy Hwy Hwy Hwy Hwy / Hwy Hwy

10 Seyed Tabib, Chris Raymond, Loan Le FIGURE Thermal imagingg of (left) and (right) during paving. Note the. C drop in average temperature EMISSIONS RESULTS Asphalt plant stack emissions measurements were conducted for Contracts to. Figure shows the typical instruments used for emissions measurementss at the asphalt plant. Emissions measurementss included a single minute particulate testt at the baghouse exhaust stack and triplicate 0 minute emission tests forr combustion gases during the production of and. 0 FIGURE Emissions Measurements Being Taken att the Stack of an Asphalt Plant The carbon dioxide (CO ) emissions are producedd mainly from the combustion of the fuel to heat up the asphalt cement and to heat and dry the aggregates. Because is produced at a lower temperature, it is expected that there will be less fuel consumption and thus lower CO emissions. However, there are other factors influencing g CO emissions that may help to elevate the emissions in the case of (Figure ) ).

11 Seyed Tabib, Chris Raymond, Loan Le 0 Carbon monoxide (CO) is a highly toxic gas that is created during incomplete combustion of fossil fuels. Incomplete combustion can occur if there is a wrong mixture of air and fuel. The correct proportion of air and fuel will depend on the type of burner and the operating temperature and combustion. Figure illustrates CO results for 0 contracts. Nitrogen oxides (NO x ) are normally formed at high temperatures. Theoretically, the NO x emissions should be higher for the. Nitrogen oxides mainly consist of nitrogen oxide (NO) and nitrogen dioxide (NO ). Figure shows the NO x results. Although not being an air pollutant, oxygen was measured for this study as an indicator for complete/incomplete combustion. Incomplete combustion can occur when there is a lack of oxygen. A large amount of oxygen can indicate that complete combustion is occurring. Figure provides the results for Oxygen emissions at the asphalt plants. The major source of sulphur dioxide (SO ) is from the burning process in the dryer. Certain types of fuels have a higher concentration of sulphur than others. The concentrations are particularly high if the fuel source is oil or coal. SO is not a major form of emission in comparison to CO or CO and it is emitted in very minimal amounts (Figure ). Total hydrocarbons or volatile organic compounds (VOCs) include the entire class of organic compounds such as polycyclic aromatic hydrocarbons and chlorinated solvents. The total hydrocarbons measured in this case are converted to methane equivalents. Hydrocarbon emissions are extremely dependent on the fuel type and the types of materials fed through the dryer (Figure ). Stack particulates (or dust) are from the fine minerals that are carried with the aggregates. The majority of the stack particulate emissions are associated with the aggregate drying and heating process. The amount of particulate emission is determined by the raw materials going into the mixer as well as the operating conditions of the plant and the cleanliness of the baghouse (Figure ). CO Emission Comparison Concentration (%) FIGURE Carbon Dioxide Emissions Results

12 Seyed Tabib, Chris Raymond, Loan Le CO Emission Comparison Concentration (ppm) FIGURE Carbon Monoxide Emissions Results NOx Emission Comparison 0 Concentration (ppm) FIGURE Nitrogen Oxides Emissions Results

13 Seyed Tabib, Chris Raymond, Loan Le Oxygen Emission Comparison Concentration (%) 0 0 FIGURE Oxygen Emissions Results SO Emission Comparison 0 Concentration (ppm) FIGURE Sulphur Dioxide Emissions Results

14 Seyed Tabib, Chris Raymond, Loan Le VOC Emission Comparison Concentration (ppm) FIGURE VOCs Emissions Results Particulates Emission Comparison 0 Concentration (mg/m) FIFURE Particulate Emissions Results In Ontario, the Ministry of the Environment (MOE), under Environmental Protection Act (EPA), regulates monitoring and reporting of the airborne contaminant discharge for the manufacturing industry including asphalt plants. Basically, the annual emissions for a given pollutant shall not exceed the annual release threshold specified by the MOE. The EPA has not set any threshold for emissions concentration, though. Use of will allow the asphalt plants to increase their production without exceeding the annual release threshold. Contributing Factors to Elevated Stack Emissions Many factors affect the level of emissions from the asphalt plant. Currently, the flights inside the dryer are adjusted to effectively dry the aggregates at temperature. To maintain the

15 Seyed Tabib, Chris Raymond, Loan Le efficiency at temperature, either the angle of the flight can be changed or the number of flights is reduced. Modifying the flights makes the mixing process much more efficient, thereby reduces the energy needed to dry the aggregate which translates into reduced emissions. Another factor that can affect emission levels is the burner type. A forced draft burner is a type of burner that is more fuel efficient and makes lower emissions than an induced draft burner. Incomplete combustion in the dryer is a consequence of improper use of the burner type and gas introduction. Incomplete combustion can be caused by: improper air and fuel mixtures; inadequate residence time; temperature being too low; and flame quenching. If a burner is operated under 0% of its capacity, emissions will be increased due to lack of air and low velocity. Plant operators are mainly trained to produce. The inexperience of the plant operator in producing can inhibit him from making appropriate adjustments to increase the efficiency. Another factor to consider when examining the emissions data is the amount of temperature reduction occurring in the. The trials did not utilize the full temperature reductions available with technologies and consequently did not yield the full emission benefits. TASK GROUP In 0, MTO formed a Task Group in partnership with Ontario s asphalt industry with several objectives including: compile a state of the practice guide; develop a mix design procedure; develop a usage guideline for contractors; develop educational materials to promote ; and improve MTO s specification. SUMMARY AND CONCLUSIONS In summary, the following conclusions were drawn based upon the review of the 0 contracts: was produced at 0-0 o C lower than. These lower temperatures imply lower fuel consumption and reduced plant emissions was paved at temperatures -0 o C lower than without any adverse effect on mix properties or compaction TSR results for were significantly variable with values ranging from to percent In general, the average ERS compaction results for was either equal to or better than All the PGAC samples were in compliance with AASHTO M0 for both and Hamburg rut depths were generally comparable between and. Asphalt plant emissions were not significantly different, although slightly lower for. The main reasons could be: trials did not maximize temperature reductions, burners were not set for production, burner type/capacity not suitable for temperature, variable moisture content of the aggregate, dryer flights not set for production, inexperience of the plant operator in adjusting the production process for, improper maintenance of the baghouse, fuel type

16 Seyed Tabib, Chris Raymond, Loan Le FUTURE PLANS Past trials in Ontario have been successful and support increased usage. MTO has decided to use in % of the 0 contracts. is to be used in surface and binder course layers. Selection of the contracts will be based on the following criteria: Contracts for which late-season paving is anticipated Multilane highways where operational constraints prevent echelon paving Projects within urban areas where emissions reduction is of the greatest benefit Contracts where long haul distances are expected Asphalt overlay on a pavement with sealed cracks MTO will continue to work with stakeholders through the Task Group. This includes the development of superpave mix design. In the interim, 0 contracts require the following information to be submitted along with the mix design: Flow Number in accordance with AASHTO TP (for information only) Coating test in accordance with AASHTO T (for information only) Compactability test (for information only) Minimum TSR of 0. is required For completed mix designs temperature bracketing is needed to confirm volumetrics. This means that samples are compacted at temperatures - o C above and - o C below the recommended compaction temperature and volumetrics are calculated so as to confirm the appropriate compaction temperature. MTO will continue performing Tensile Strength Ratio on the production samples by the QA laboratory. Furthermore, MTO will develop a comprehensive performance monitoring program for trials. CLOSING REMARKS Warm mix asphalt is an innovative green technology that improves the environmental sustainability of hot mix asphalt. Given the environmental benefits and potential performance improvements, the life cycle cost of is expected to be similar to. MTO will continue to work with Task Group to investigate and refine its specification. By targeting use on % of 0 contracts, the MTO is demonstrating leadership with this technology and providing asphalt industry the opportunity to invest and build confidence in dealing with. REFERENCES. Prowell, B. D., G. C. Hurley, and B. Frank Warm-Mix Asphalt: Best Practices. Quality Improvement Publication, nd Edition. National Asphalt Pavement Association, Lanham, MD, 0.. D Angelo, J., et. al. Warm-Mix Asphalt: European Practice. Publication FHWA-PL FHWA, U.S. Department of Transportation, February 00.. Fore, G., and H. Marks Documenting Emissions and Energy Reductions of and Conventional. National Asphalt Pavement Association, August, 00.