Evaluation of Fine Graded Polymer Asphalt Mixture Produced Using Foamed Warm Mix Asphalt Technology

Transcription

1 Evaluation of Fine Graded Polymer Asphalt Mixture Produced Using Foamed Warm Mix Asphalt Technology Munir D. Nazzal, PhD., P.E. (Corresponding Author) Assistant Professor, Civil Engineering Department, Ohio University, Athens, OH 1 Shad Sargand, Ph.D. Russ Professor, Civil Engineering Department, Ohio University, Athens, OH 1 David Powers, P.E. Asphalt Materials Engineer Ohio Department of Transportation Columbus, OH Edward P. Morrison Quality Control Manager Shelly & Sands, Inc. / Mar-Zane Materials Inc. & Abdalla Al-Rawashdeh Graduate Research Assistant, Civil Engineering Department, Ohio University, Athens, OH 1 Submitted to: nd International Warm-Mix Conference October -1, St. Louis, Missouri No. of text words = No. of Figures= No. of Tables=

2 Evaluation of Fine Graded Polymer Asphalt Mixture Produced Using Foamed Warm Mix Asphalt Technology Abstract Fine graded polymer asphalt mixture has been used in the past few years in the construction of the thin overlays in Ohio. This mixture is produced at temperatures that are higher than those typically used for other types of Hot Mix Asphalt (HMA). This paper presents the results of a field demonstration project in Ohio in which a fine graded polymer asphalt mixture was produced using foamed Warm Mix Asphalt (WMA) technology. Laboratory and field testing programs were conducted to evaluate the produced mixture. The laboratory testing program included performing modified Lottman, flow number, Asphalt Pavement Analyzer (APA), and dynamic modulus tests on plant mixed laboratory compacted samples to evaluate the performance properties of the produced WMA mixture. In addition, the field testing program included measuring the initial surface roughness as well as conducting Light Falling Weight Deflectometer (LFWD) and Portable Seismic Pavement Analyzer (PSPA) tests to evaluate the in-situ stiffness properties of the constructed mixtures. The results of this project showed that the fine graded polymer asphalt mixture could be produced and compacted using the foamed WMA technology at a lower temperature than that typically used for a similar HMA mix. In addition, the laboratory test results indicated that the considered WMA mixture had acceptable resistance to moisture induced damage but did not have a good rutting performance. Finally, the field test results showed that the considered WMA mixture had good initial field performance. Keywords: Thin Overlay, Foamed WMA, Field Trials, PSPA

3 Introduction Thin overlays with thickness of 1½ inch or less are gaining considerable attention as one of the most effective preventative maintenance techniques performed to extend the service life of the existing pavements. Those overlays have several benefits that include protecting the pavement structure, reducing the rate of pavement deterioration, correcting surface deficiencies, reducing permeability and improving the ride quality of the pavement, particularly when accompanied by surface milling (1). In Ohio, fine graded polymer asphalt mixture has been used in the construction of the thin overlays. This mixture consists of fine aggregates with a maximum nominal size of. mm and a relatively high content of -m polymer modified asphalt binder. It is produced at temperatures that are relatively higher (- F) than those typically used for other types of Hot Mix Asphalt (HMA). Recently, the foaming WMA technologies produced via a foaming nozzle have been gaining popularity among asphalt mix producers. The main advantage of those systems is that they allow the production of WMA with a standard grade asphalt binder through a one-time mechanical plant modification minimizing the impact of increased material costs identified with other WMA technologies. The use of foamed WMA to produce fine graded polymer asphalt mixture can result in several benefits by allowing the asphalt mixture to be produced and compacted at lower temperatures. Utilizing Reclaimed Asphalt Pavement (RAP) in that mixture can add further benefits by reducing their cost and enhancing their rut performance. Despite the advantages of producing fine graded polymer asphalt mixture with foaming WMA technology, there are some concerns regarding its performance and durability. This paper presents the results of a field project in Ohio where a fine graded polymer asphalt mixture containing RAP and produced with the foamed WMA technology was used in construction of a thin overlay. Laboratory and field testing programs were conducted to evaluate the WMA mixture. The field testing program included measuring the initial surface roughness as well as conducting Light Falling Weight Deflectometer (LFWD) and Portable Seismic Pavement Analyzer (PSPA) in-situ tests. In addition, modified Lottman, flow number, Asphalt Pavement Analyzer (APA), and dynamic modulus tests were conducted on plant mixed laboratory compacted samples to evaluate the performance properties of the considered WMA mixture. TESTING PROGRAM Description of Field Project and Evaluated Mixture The field test section was part of a rehabilitation project on State Route 1 (SR 1) near Zanesville and Chandlersville Counties. The rehabilitation project in this study consisted of the placement of a thin overlay layer with thickness of 1 inch. The overlay placed on SR 1 consisted of a fine graded polymer asphalt mixture with a / inch nominal maximum aggregate size (NMAS) designed to meet ODOT specification for Item B for medium traffic roads. The mixture included percent RAP. The optimum asphalt binder content for this mixture was. percent (. percent virgin binder and. percent from the RAP). The asphalt binder used was an SBS elastomeric polymer-modified PG -M binder. This mixture was produced using the foamed WMA technology. Table 1 presents the Job Mix Formula of the considered mixture. The average mixing temperature that was recorded in the asphalt plant was also included in this

4 table. It is worth noting that this temperature is about F less than the average temperature typically used for this mixture when produced as a HMA. TABLE 1 Job Mix Formula for Considered Mixtures Mixture Designation B % No. Gravel, 1% No. Gravel, Aggregate blend % Limestone,% Natural Sand, 1% Bag House Fines, % RAP Binder type PG-M Binder content, %. (. Virgin binder) Mixing Temperature ( F) Sieve Size Gradation (% passing) 1/" /" # # #1 # # # #. Description of Laboratory Testing Program Sufficient loose mixture was secured within the paver extensions and at the plant and sent to the laboratory. The foamed WMA mixture samples were prepared in this study in accordance with the AASHTO T 1- procedure. Samples were compacted using the Superpave Gyratory Compactor (SGC) to an air void of %. Various laboratory tests were performed to examine the mechanical properties of the mixture that was used in the construction of the field test section. Triplicate samples were tested. Table presents a list of the mixture performance tests that were conducted in this study. Moisture susceptibility was evaluated using the modified Lottman test. In addition, flow number and Asphalt Pavement Analyzer (APA) tests were used to assess high temperature permanent deformation resistance. Finally, the dynamic modulus test was used to characterize the visco-elastic behavior of the asphalt mixture at different temperatures and loading frequencies. TABLE Asphalt Treated Mixture Performance Test Conditions Laboratory Test Performance Indication Test Temperature Test Protocol Modified Lottman moisture susceptibility º F AASHTO Asphalt Pavement Resistance to Analyzer (APA) permanent deformation 1 º F ODOT Specification () Flow Number Resistance to permanent deformation 1 º F NCHRP 1 () Dynamic Modulus Visco-elastic properties Various AASHTO TP - ()

5 Description of Field Testing Program The field testing program in this study included taking roughness measurements of the test section immediately after construction as well as conducting Light Falling Weight Deflectometer (LFWD) and Portable Seismic Pavement Analyzer (PSPA) tests at the thirty points along the test section to characterize the in-situ properties of fine mixtures. The LFWD is a portable device that is designed for estimating the elastic modulus of pavement materials. The Prima LFWD was used in this study. This device consists of a lbs drop weight that falls freely onto a loading plate that has a. in diameter, producing a load pulse. During any test operation, the Prima device measures both the applied force and center deflection, utilizing a velocity transducer. The measured load and deflection are used to compute the LFWD elastic modulus. The PSPA is a device designed to determine the average modulus of the top layer of pavements. It consists of two receivers (accelerometers) and a source packaged into a hand-portable system, which can perform high frequency seismic tests. The operating principle of the PSPA is based on generating and detecting stress waves in a medium. The Ultrasonic Surface Wave (USW) method, which is an offshoot of the Spectral Analysis of Surface Wave (SASW) method (), is used to determine the modulus of the material. It is noted that the loading frequency of this device is approximately, Hz. RESULTS AND ANALYSIS Compaction and Field Density Results The overlay layer in the test section was compacted using the same rolling pattern typically used for HMA mixtures with similar gradation. In general, the selected pattern included first performing four compaction passes using a vibratory breakdown roller; followed by four compaction passes of an oscillatory finish roller. The average maximum compaction temperature was F. In addition, the average relative density obtained for the cores obtained from the test section was.%. This indicates that although the WMA mixture was produced and compacted at a temperature lower than that typically used for similar HMA mixtures, it achieved the density that is required in the Ohio Department of Transportation (ODOT) specifications. Results of Laboratory Tests Modified Lottman Test Results This test was used to quantify the asphalt treated mixtures sensitivity to moisture damage, which is necessary to assure its durability. Moisture sensitivity is measured by the percentage of retained tensile strength ratio (TSR) of the conditioned samples compared to the control samples. The conditioned samples are samples that have been subjected to the required freeze/thaw cycle. In this study, triplicate samples were tested for foamed WMA fine polymer asphalt mixture produced during the six days of construction. Figure 1 presents the average TSR values for the samples prepared in the second, third, and sixth day of construction. It is noted that the average TSR values were greater than.; thus the mixture met the minimum TSR requirement specified by ODOT for medium traffic mixtures. Furthermore, the average TSR value of samples obtained from the different days construction were similar. This indicates that there was no variation in the produced WMA mixture.

6 Asphalt Pavement Analyzer (APA)Test Results This test was conducted according to the ODOT standard test procedure to determine the rutting characteristics of the mixture. Superpave Gyratory compacted cylindrical samples inch in diameter were prepared at an air void content of % and used in the APA tests. As per ODOT Supplement, the APA samples were preheated to the test temperature of 1 F for a minimum of 1 hours prior to testing. Upon testing, the APA samples were subjected to repeated wheel loading of lbf using a hose pressure of psi. Rut depth measurements were recorded at,,, and cycles. For each APA sample, a total of four rut depth readings were used to calculate the average rut depth value within the specimen. The total rutting within the sample was calculated as the difference between the rut depth readings at the th cycle and the th cycle. Based on the APA test results, the average total rut depth for the tested samples was. in. This value is greater than the maximum acceptable rut depth of. in that ODOT specifies for heavy traffic mixtures. The relatively lower rutting resistance is mainly attributed to the substantial amount of natural sand in the mixture. The use of foamed WMA technology could also be a contributing factor since it reduces binder aging during the mixing. TSR Day- Day- Day- FIGURE 1 Modified Lottman test results Flow Number Test Results The flow number test is a laboratory approach to determine the permanent deformation characteristic of paving materials by applying a repeated dynamic load for, repetitions on a cylindrical asphalt sample. This test was conducted according to the Annex B of the NCHRP Report 1. The average flow number value for the considered foamed WMA mixture used to construct the field section was less than cycles. This low flow number value is consistent with APA test results, which suggests that the mixture does not have a high rutting resistance. Dynamic Modulus (E*) Test Results The E* test was used to characterizes the viscoelastic properties of the asphalt mixtures at different loading times and temperatures. This test was conducted on unconfined cylindrical samples in accordance with AASHTO Standard TP -. Figures a-c show the dynamic modulus isotherms for considered foamed WMA mixture at different temperatures and frequencies. The dynamic modulus isotherms for Evotherm WMA and HMA mixtures used in an overlay layer in another pavement section on State Route 1 (SR 1) near Guernsey and Coshocton Counties were also presented for comparison. The E* values for all mixtures increased with an increase in frequency and a decrease in temperature. At low temperatures ( F), the E* isotherms maintained the pattern of an inclined straight-line, which indicated that

7 1 1 the mixture behavior was in the linear viscoelastic region at those temperatures. However, at intermediate and high temperatures ( F and 1 F), the E* isotherms gained a concave shape (Figure b,c) which represents the non-linear behavior of the mixtures under compression. The B mixture consistently had the lowest E* values at the F and C temperatures. However, it had similar E* values to the HMA control mix at the 1 F. This is also demonstrated in Figure, which presents the master curve for each of the considered mixtures. It is worth noting that the mixture in SR 1 had coarser aggregate gradation than that of the mixture evaluated in the study, which might explain the differences obtained in the E* values. E* (ksi) a. HMA-SR1 Foamed WMA Evotherm-SR Frequency (Hz) FIGURE E* Test results: (a) E* isotherms at F (b) E* isotherms at F (c) E* isotherms at 1 F. log E (psi) E* (ksi) 1 1 c. E* (ksi) Control HMA-SR1 Foamed WMA log fr (1/sec) FIGURE Master curve.1 1 Frequency (Hz) Reference Temperature= F b. Foamed WMA HMA-SR1 Evotherm-SR Frequency (Hz) HMA (SR 1) Foamed WMA Evotherm WMA (SR 1)

8 Results of In-Situ Tests The mechanistic properties from field tests included the LFWD and PSPA moduli. It is noted that the field test results were corrected to C using the following equation (): ET E 1..1 T (1) where, E : modulus at C, ksi E T : modulus at test temperature T, ksi T : pavement mid depth temperature, C The pavement mid depth temperature was obtained using BELLS model () as shown in the following equation: T =. +. IR + {log (d) 1.}{-. IR +.1 (1-day)+ 1. sin (hr1 1.)} +. IR sin (hr1-1.) () where, T : Pavement temperature at depth d, C IR : Infrared surface temperature, C Log : Base logarithm d : Depth at which mat temperature is to be predicted, mm 1-day : Average air temperature the day before testing, C sin : Sine function on an 1-hr clock system, with π radians equal to one 1-hr cycle hr1 : Time of day, in -hr clock system, but calculated using an 1-hr asphalt concrete PSPA Test Results Figure presents the variation of the PSPA moduli along the test section. The moduli in this figure were corrected to a temperature of C using Equations 1 and. The PSPA modulus varied between 1 and 1 ksi with a mean value of 1 ksi and coefficient of variation of 1.%. The mean PSPA modulus value is similar to those reported for a well a performing HMA mixture ((),()). Furthermore, the percent coefficient of variation of the PSPA modulus is lower than those observed when testing HMA sections (). It is worth noting that the PSPA modulus is higher than that obtained in the laboratory or other in-situ tests as the test is conducted at a very high frequency of, Hz. LFWD Test Results Figure shows the variation of the corrected LFWD modulus along the test section. It is noted that LFWD modulus values varied widely, as it may be affected by the underlying pavement structure. The mean value of LFWD modulus was. ksi, which is similar to those of good performing HMA mixtures that were reported in previous studies ((),() ). The coefficient of variation of the LFWD modulus was 1.%, which is higher than that of PSPA. This indicates the LFWD test had more variability than the PSPA test. Results of Roughness Measurements Roughness measurements of the SR 1 section were conducted after the placement of the overlay. The results of the roughness measurement were expressed as International Roughness

9 Index (IRI) for every.1 mile segment. IRI simulates a standard vehicle traveling down the roadway and is equal to the total anticipated vertical movement of this vehicle accumulated over the length of the section. The average initial IRI value was. in/mile with a coefficient of variation of %. It is worth noting that according to FHWA standards, pavements with IRI less than in/mile are classified to have very good riding quality. PSPA Modulus (ksi) E LFWD (ksi) Test points FIGURE PSPA test results Test points FIGURE LFWD test results CONCLUSIONS: This paper presented the results of a field and laboratory testing programs that were conducted to evaluate a fine graded polymer asphalt mixture produced using foamed WMA technology. Based on the results of this paper, the following conclusions can be drawn: Although the WMA mixture was produced and compacted at lower temperature than that typically used for similar HMA mixture, it achieved the required in-place density. The foamed WMA mixture showed acceptable resistance to moisture induced damage as indicated by the modified Lotmman test. The evaluated mixture did not exhibit good rutting performance in the APA and flow number tests.

10 The foamed WMA mixture had similar LFWD and PSPA moduli as those of good performing HMA mixtures. The PSPA test exhibited better repeatability and lower variability compared to the LFWD test. The foamed WMA test section showed very good riding quality as indicated by the IRI values that were obtained directly after the placement of thin overlay. ACKNOWLEDGEMENT The authors would like to express thanks to ODOT personnel that helped in this research study, particularly Roger Green. We thank Dan Radanovish of ODOT for taking the IRI measurements. REFERENCES 1- K.T. Hall, C.E. Correa, and A.L. Simpson, Performance Of Flexible Pavement Maintenance Treatments In The Long-Term Pavement Performance SPS- Experiment, Transportation Research Record,. - Ohio Department of Transportation, Construction And Material Specifications, Ohio Department Of Transportation, Columbus, Ohio,. - R. Bonaquist, NCHRP Report 1: Simple Performance Tester for Superpave Mix Design: First-Article Development and Evaluation, National Cooperative Highway Research Program (NCHRP),. - AASHTO TP-, Determining the Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures,. - S. Nazarian, D. Yuan, and V. Tandon, Structural Field Testing of Flexible Pavement Layers with Seismic Methods for Quality Control., Transportation Research Record, vol. 1, 1, pp T.G. Ray and S.C. Shah, with J. B. Metcalf, Evaluation of Louisiana s Statistically Based Quality Control and Acceptance Specifications for Asphaltic Concrete, Louisiana Department of Transportation and Development, Louisiana Transportation Research Center, Baton Rouge, LA, 1. - E. Lukanen and R. Stubstad, Temperature Predictions and Adjustment Factors for Asphalt Pavement, FHWA-RD--, FHWA,. - L. Mohammad and S. Saadeh, Comparative Study of the Mechanical Properties of HMA Mixture: Field Vs Laboratory, Transportation Research Record,. - C. Zhang, Comparative Study of the Physical and Mechanistic Properties of HMA Mixture: Field Vs Laboratory, Civil and Environmental Engineering, Louisiana State University,.

11