DUPONT ELVALOY RESEARCH REPORT STUDY OF BINDER & MIX PROPERTIES OF 5 MIXTURES USING WELD COUNTY, COLORADO AIRPORT AGGREGATE

Transcription

1 This report is a follow-up to work originally reported in 2. A series of Elvaloy modified binders were produced and tested in comparison to an AC-2R Stylink blend. In addition mixes were produced using an aggregate that had been used on the Weld County airport in Weld County, Colorado. The AC-2R binder had been used with that aggregate to pave the airport. The purpose of the original study was to demonstrate that a variety of asphalt cement base materials could be used to produce modified blends with performance properties similar to the AC-2R. In addition the mixes that were produced were tested to demonstrate that the mixture properties of the Elvaloy modified binders were comparable or superior to the AC-2R mixture. The acquisition of a TAInstruments AR-2 Rheometer with special software to perform repeated creep and recovery tests on binders, enabled us to further characterize and compare the binders evaluated in the original study. The repeated creep and recovery test has been proposed as a new protocol 1 to better predict binder performance in mixes with respect to permanent deformation. In addition, using the AR-2, we were able to develop a constant torsional creep stress on slices of each mixture. The failure profile of each specimen is similar to that of simple performance tests proposed by Witczak 2. By allowing the mixture specimens to strain until failure, we were able to compare the relative performance capabilities of each mixture. Furthermore we were able to arrive at a recommendation for a phase angle value that appears to be related to a superior level of mixture performance. 1 Bahia, et. al NCHRP report 459 P. 53 and following, published 21 2 Witczak, M.W.; Bonaquist, R; Von Quintus, H; and Kaloush, K; Specimen Geometry and Aggregate Size Effects in Uniaxial Compression and Constant Height Shear Tests, Association of Asphalt Paving Technolgists, 2, Vol 69, Page 1

2 FIGURE 1 BINDER SAMPLE BEING LOADED INTO RHEOMETER FOR REPEATED CREEP AND RECOVERY TEST TO DETERMINE CUMULATIVE STRAIN OF BINDER. NCHRP report 459 (pp. C.IV.1-C.IV.4) outlines the test method. We used a 25 mm test specimen, 1 mm thickness, 3 Pa of Stress and applied 1 cycles of a 1 second period of stress application followed by a 9 second period of zero stress per cycle. Page 2

3 FIGURE 2 BINDER SAMPLE IN PLACE FOR REPEATED CREEP AND RECOVERY TEST Page 3

4 FIGURE 3 2. KOCH-CONOCO PG 58-28, DENVER, CO, RTFO, 3PA, 64 C, CUM CRT CREEP & RECOVERY CYCLE # CONOCO % strain AC-2R PG global time (s) 1. STRAIN RESULTS OF FIRST CREEP AND RECOVERY CYCLE FOR AC-2R & UNMODIFIED PG The upwards rising portion of the test cycle results from the 1 second stress application. During the 9 seconds of zero stress the binder is allowed to recover some of the strain that was caused by the stress application. The more elastic the binder at the test temperature the more of the strain imparted will be recovered. The PG exhibits very little recovery, whereas the AC-2R recovers from approximately 1% strain at 1 second to approximately 8% strain at 1 seconds. Page 4

5 FIGURE 4 2. KOCH-CONOCO PG 58-28, DENVER, CO, RTFO, 3PA, 64 C, CUM CRT 175. CONOCO % strain AC-2R PG CONOCO MCKEE global time (s) 1. COMPARISON OF THE FIRST CREEP AND RECOVERY CYCLE FOR UNMODIFIED PG 58-28, AC- 2R, A PG MADE FROM CONOCO DENVER ASPHALT AND A PG MADE FROM ULTRAMAR DIAMOND SHAMROCK MCKEE ASPHALT. The Conoco PG and McKee PG were both made using Elvaloy 417 while the AC-2R was made with Stylink SB polymer. Page 5

6 FIGURE DH146A, MCKEE BASE, ELVALOY 417, RTFO, 3PA, 64 C, CUM CRT 4. MCKEE ELVALOY 85.5% STRAIN RECOVERY CYCLE #1 % strain BOTH MATERIALS HAVE NEARLY THE SAME CUMULATIVE STRAIN AT 1 CYCLES THE EXXON SAMPLE HAS A HIGHER STIFFNESS AND THEREFORE HAS LESS CREEP PER CYCLE AND HAS LESS RECOVERY PER CYCLE THE MCKEE HASLOWER STIFFNESS AND THEREFORE HAS MORE CREEP PER CYCLE, BUT HAS MORE ELASTICITY AND THEREFORE MORE RECOVERY PER CYCLE. THE NET RESULT IS BOTH MATERIALS END UP WITH VERY SIMILAR VALUES FOR TOTAL STRAIN EXXON 7-34 SBS MODIFIED 8.% STRAIN RECOVERY global time (s) 1. COMPARISON OF PG MADE WITH MCKEE BINDER USING ELVALOY 417 AND A PG 7-34 MADE WITH A EXXON BILLINGS BINDER USING SBS. The data shown is the creep and recovery results for cycle 1 of the test. Page 6

7 FIGURE 6 2 KOCH-CONOCO PG DENVER, CO, RTFO, 3PA, 64 C, CUM CRT 175 CONOCO CONTROL % strain AC-2R, PG global time (s) 1 COMPARISON OF TOTAL STRAIN AT THE END OF 1 CYCLES FOR THE PG UNMODIFIED BINDER AND THE AC-2R. As on would expect the modified binder has considerably less accumulated strain. Page 7

8 FIGURE DH146A, MCKEE BASE, ELVALOY 417, RTFO, 3PA, 64 C, CUM CRT CONOCO ELVALOY 8. % strain MCKEE ELVALOY SINCLAIR global time (s) 1 COMPARISON OF TOTAL ACCUMULATED STRAIN FROM 3 BINDERS MADE USING ELVALOY 417. Although the Conoco PG and McKee PG both met the same PG grade, the accumulated strain test shows that binders from different crude sources will respond differently to a given polymer. While there appears to be a considerable difference in the total strain of these binders, it must be remembered that the unmodified PG had a total strain of approximately 19,%. The variations shown here may be of little consequence in terms of ultimate mix performance. Page 8

9 FIGURE 8 8. DH146A, MCKEE BASE, ELVALOY 417, RTFO, 3PA, 64 C, CUM CRT AC-2R PG % strain CONOCO ELVALOY MCKEE SINCLAIR global time (s) 1 COMPARISON OF TOTAL ACCUMULATED STRAIN FOR 3 BINDERS MADE WITH ELVALOY 417 AND AC-2R Page 9

10 FIGURE DH146A, MCKEE BASE, ELVALOY 417, RTFO, 3PA, 64 C, CUM CRT CONOCO ELVALOY 8. % strain EXXON 7-34 SBS MODIFIED global time (s) 1 MCKEE SINCLAIR COMPARISON OF TOTAL ACCUMULATED STRAIN AT 1 CYCLES FOR 3 BINDERS (CONOCO PG 64-34, MCKEE PG & SINCLAIR 76-34) MADE WITH ELVALOY 417 AND AN EXXON 7-34 MADE WITH SBS. Page 1

11 FIGURE TYPICAL FLOW TIME FAILURE CURVE TERTIARY FLOW % strain SECONDARY FLOW REGION FAIURE REGION PRIMARY FLOW 2. REGION OF PLASTIC FLOW OF MIX global time (s) 175 TYPICAL RESULTS OF A STATIC CREEP TEST PERFORMED ON A MIXTURE SPECIMEN USING A DYNAMIC SHEAR RHEOMETER. During this test a specimen (see Figure 11) is tested using a constant torsional stress and resulting strain is monitored. As the plot in the figure shows, there is an initial period of rapid strain development (Primary flow) followed by a period of when the strain increases at a linear rate (Secondary flow), and lastly the specimen begins to fail as the rate of change of strain increases quite rapidly (Tertiary flow). See Witczak s paper in footnote 2 for more detailed discussion of this type of mix failure profile. Page 11

12 FIGURE 11 MIX SLICE MOUNTED IN AR-2 RHEOMETER IN PREPARATION FOR STATIC CREEP TESTING. Specimens typically measure 5 mm in length, 12 mm in width and 6.3 mm in thickness. The test consists of a constant torsional stress being applied until the specimen strain reaches 12%. At 12% strain the specimen will have generally reached the tertiary flow region shown on the previous plot. Page 12

13 FIGURE 12 EXAMPLE OF SPECIMENS WHICH HAVE BEEN TESTED TO FAILURE USING A STATIC CREEP TEST AS PERFORMED IN THE AR-2. Page 13

14 FIGURE 13 ANOTHER VIEW OF THE SPECIMENS HAVING BEEN TESTED TO FAILURE DURING THE STATIC CREEP TEST. Page 14

15 FIGURE LAFARGE 58-28, THICK, 5,PA, 64 C 1. MIX ANALYSIS FLOW TIME TO FAILURE UNDER CONSTANT STRESS AT 64 C AND 5, Pa OF APPLIED STRESS 8. CONOCO CONTROL % strain AC-2R PG SB BLEND 2. FLOW TIME FAILURE POINT global time (s) 12. CREEP TEST RESULTS OF PG MIX AND AC-2R MIX. All mixes used the same aggregate blend and % AC. Creep test to failure was conducted at 64 C using a constant stress of 5, Pa or approximately 75 psi. As one would expect for this comparison the PG unmodified binder failed much more rapidly. Page 15

16 FIGURE CONOCO 64-34, LAF-CO, 1-1, THICK, 5,PA, 64 C 6. MIX ANALYSIS FLOW TIME TO FAILURE UNDER CONSTANT STRESS AT 64 C AND 5, Pa OF APPLIED STRESS 5. MCKEE % strain 3. CONOCO global time (s) 14 CREEP TEST TO FAILURE OF MIXES MADE WITH PG USING MCKEE AND CONOCO BINDERS WITH ELVALOY 417. Test conditions were 64 C and 5, Pa of applied stress. Page 16

17 FIGURE LAFARGE 58-28, THICK, 5,PA, 64 C 1. MIX ANALYSIS FLOW TIME TO FAILURE UNDER CONSTANT STRESS AT 64 C AND 5, Pa OF APPLIED STRESS AC-2R, PG % strain MCKEE CONOCO global time (s) 14 COMPARISON OF PG UNMODIFIED, AC-2R (STYLINK) AND MCKEE AND CONOCO BASED MIXES. In this comparison it is easy to observe that the McKee and Conoco mixes exhibited considerably longer times to failure under the same conditions. Page 17

18 FIGURE 17 LAFARGE 58-28, THICK, 5,PA, 64 C THE ADDITIONAL STIFFNESS AND ELASTICITY OF THE PG 76 GRADE SUBSTANTIALLY CHANGES THE RESISTANCE TO MIX FAILURE PG & AC-2R 8. % strain MCKEE & CONOCO PG GRADES SINCLAIR global time (s) 225 COMPARISON OF PG (UNMODIFIED) AC-2R (STYLINK), MCKEE, CONOCO PG (ELVALOY ) AND SINCLAIR PG 76-4 (ELVALOY ). The Sinclair mix sample uses a highly modified binder and as a result at the test temperature of 64 C exhibits a significantly longer time to failure than any of the other mixes. On this scale it is difficult to observe the PG and the Stylink mix results as they are jammed against the left axis. From this comparison it appears as though at a given set of test conditions using a single aggregate blend, the more highly modified the binder used in the mix the more resistant to permanent deformation the mix. Page 18

19 FIGURE 18 % CUMULATIVE STRAIN, 3 Pa, 1 CYCLES, 64 C 1E+5 1E Log1(Y) = X EMS = R 2 =.9 MCKEE ELVALOY PG 63.9 CONOCO ELVALOY PG 68.5 SINCLAIR 76-4 ELVALOY PG 76.3 CORRELATION OF RTFO PHASE ANGLE TO TOTAL CUMULATIVE % STRAIN IN REPEATED CREEP TEST AC-2R STYLINK PG 63.6 CONOCO CONTROL PG 61 LOWER VALUES ARE BETTER LOWER VALUES = LESS CREEP STRAIN PHASE ANGLE OF RTFO 64 C 4/23/1 17:38:5 C:\AR2\RESULTS\DUPONT\colorado project\creep STRAIN VS RTFO PHASE ANGLE CO LAFARGE SAMPLES.spf PLOT OF % TOTAL ACCUMULATED STRAIN OF THE BINDER AS A FUNCTION OF THE BINDER PHASE ANGLE. This plot shows that the phase angle of the binder is very strongly correlated to the binder cumulative strain. This might seem obvious, but when one considers that this data is derived from several different sources of asphalt, using 2 different polymers plus an unmodified sample; the correlation seems significant. Page 19

20 FIGURE 19 CORRELATION OF MIX FLOW TIME TO FAILURE VS. TOTAL % CREEP STRAIN TORSIONAL FLOW TIME, 64 C, 35 KPa STRESS 1E+5 1E SINCLAIR 76-4 MCKEE CONOCO ON THIS GRAPH HIGHER VALUES ARE BETTER THE UPPPER LEFT = LONG TIMES TO FLOW FAILURE WHICH OCCUR AT THE LOWER VALUES OF CREEP STRAIN Log1(Y) = Log1(X) EMS =.3134 R 2 =.985 AC-2R CONOCO E+4 1.E+5 CUMULATIVE STRAIN, 1 CYCLES, 3 Pa, 64 C 4/23/1 17:39:42 C:\AR2\RESULTS\DUPONT\colorado project\co-lafarge FLOW TIME VS CREEP 64 C.spf TIME TO THE ONSET OF TERTIARY FLOW AS A FUNCTION OF BINDER CUMULATIVE STRAIN. The tertiary flow time value is obtained from the mixture creep test performed on the DSR and the cumulative strain is obtained from the repeated creep and recovery test on the binder. The high degree of correlation in these results indicates that mixture creep failure can be controlled to a considerable extent by the binders resistance to strain accumulation as measured by the repeated creep and recovery test. Page 2

21 FIGURE 2 TORSIONAL FLOW TIME TO FAILURE, 64 C, 5 KPa STRESS 1E+5 1E Log1(Y) = X EMS =.1625 R 2 =.892 SINCLAIR 76-4 CONOCO CORRELATION OF FLOW TIME TO FAILURE TO PHASE ANGLE OF RTFO 64 C MCKEE AC-2R (64-34) CONOCO PHASE ANGLE RTFO 64 C 4/23/1 17:4:24 C:\AR2\RESULTS\DUPONT\colorado project\correlate MIX FLOW TIME TO PHASE ANGLE.spf TIME TO ONSET OF TERTIARY FLOW IN THE MIXTURE AS A FUNCTION OF THE BINDER PHASE ANGLE. It would seem logical that sense the binder phase angle and binder cumulative strain are strongly correlated that the phase angle and mixture failure value would be strongly correlated as well. Page 21

22 FIGURE 21 BINDER CUMULATIVE STRAIN AS A NON-LINEAR FUNCTION OF BINDER PHASE ANGLE. The reason for analyzing the data in terms of a non-linear function is to determine a phase angle value that is related to mix performance. See next slide. Page 22

23 FIGURE 22 CUMULATIVE % STRAIN, 1 CYLCES, 3 Pa, 64 C MCKEE RELATIONSHIP BETWEEN PHASE ANGLE & THE POINT WHERE CREEP STRAIN BEGINS TO INCREASE SUBSTANTIALLY NON LINEAR CURVE FIT Y= * EXP(.5612 * X) + (-2498) ON THIS GRAPH HIGHER VALUES MEAN THAT THE BINDER HAS A HIGHER CREEP STRAIN LOWER VALUES ARE BETTER CONOCO SINCLAIR 76-4 CONOCO CONOCO AC-2R INTERSECTION OF THE 2 ASYMTOTES OCCURS AT396% CUMULATIVE STRAIN OF THE BINDER PHASE ANGLE AT 64 C OF RTFO RESIDUE 1/1/1 16:11:43 E:\AR2\RESULTS\DUPONT\colorado project\non LIN REG CREEP STRAIN VS PHASE ANGLE.spf PLOT OF BINDER ACCUMULATED STRAIN AS A FUNCTION OF BINDER PHASE ANGLE WITH TANGENTS DRAWN. By drawing tangents from each leg of the non-linear functional curve and determining the intersection of the tangent lines a cumulative strain should be identified that is indicative of a binder which will be resistant to permanent deformation. The phase angle that corresponds to that strain level is what I am seeking. In the case of this data set a cumulative strain of 396% is indicated. See next slide Page 23

24 FIGURE 23 CUMULATIVE % STRAIN, 1 CYLCES, 3 Pa, 64 C MCKEE RELATIONSHIP BETWEEN PHASE ANGLE & THE POINT WHERE CREEP STRAIN BEGINS TO INCREASE SUBSTANTIALLY NON LINEAR CURVE FIT Y= * EXP(.5612 * X) + (-2498) ON THIS GRAPH HIGHER VALUES MEAN THAT THE BINDER HAS A HIGHER CREEP STRAIN LOWER VALUES ARE BETTER CONOCO ELVALOY SINCLAIR 76-4 AT A % CUMULATIVE STRAIN OF 396% THE PHASE ANGLE IS 65.9 DEGREES CONOCO CONOCO AC-2R INTERSECTION OF THE 2 ASYMTOTES OCCURS AT396% CUMULATIVE STRAIN OF THE BINDER PHASE ANGLE AT 64 C OF RTFO RESIDUE 1/1/1 16:22:36 E:\AR2\RESULTS\DUPONT\colorado project\non LIN REG CREEP STRAIN VS PHASE ANGLE.spf PLOT OF BINDER ACCUMULATED STRAIN AS A FUNCTION OF PHASE ANGLE, CRITICAL PHASE ANGLE SHOWN. At 396% accumulated strain the fitted equation yields a phase angle of 65.9 degrees. My initial reaction to this result was that a 66 degree phase angle was quite low. Consider that we are trying to arrive at a reasonable value for the phase angle that could be used to indicate the potential for high temperature performance of mixes. It might not be too much of a stretch to consider that a phase of about 66 degrees makes sense if one is developing requirements for a PG binder that has been bumped 2 grades (in this case from at least a PG 52 grade to a PG 64 grade). Page 24

25 FIGURE 24 1E+5 FLOW TIME OF MIX VS. PHASE ANGLE OF RTFO RESIDUE OF BINDER TORSIONAL FLOW TIME VALUE OF MIX, SEC 1E+5 9E+4 8E+4 7E+4 6E+4 5E+4 4E+4 3E+4 2E+4 1E+4 E+ SINCLAIR MCKEE CONOCO Y= 1.196e+9 * EXP((-.284) * X) Final Sum of Squares of Residuals: e+9 Coefficient of Determination :.9741 Degrees of Freedom : 3 Fitted Equation: Y= 1.196e+9 * EXP((-.284) * X) AC-2R CONOCO CONTROL PHASE ANGLE OF RTFO RESIDUE 1/1/1 15:58:8 E:\AR2\RESULTS\DUPONT\colorado project\nonlin FIT CO LAFARGE FLOW TIME AS FUNCTION OF PHASE ANGLE.spf PLOT OF MIXTURE TORSIONAL FLOW TIME AS A FUNCTION OF RTFO RESIDUE PHASE ANGLE. There might be another investigative path that can provide support for a critical phase angle of about 66 degrees. In the plot above the mixture flow time has been plotted as a non-linear function of the phase angles of the binders used to make the mixes. It is possible to see that around a phase angle of 65 degrees the fitted line begins to rise at an increasingly rapid rate. Analysis of the first derivative of this function can help to identify the critical value of the phase angle. Page 25

26 FIGURE 25 PLOT OF FIRST DERIVATIVE VS. PHASE ANGLE TO DETERMINE A TARGET PHASE ANGLE THAT CAN BE RELATED TO MIX PERFORMANCE VALUE OF FIRST DERIVATIVE AT PHASE ANGLE E+ -2E+3-4E+3-6E+3-8E+3-1E+4-1E+4-1E+4-2E+4-2E+4-2E+4-2E+4 PHASE ANGLE OF 66.8 DEG IS THE POINT AT WHICH THE 1ST DERIVATIVE LINE BEGINS TO DECREASE 1ST DERIVATIVE = Y=( e+8 * EXP((-.284)*X PLOT OF FIRST DERIVATIVE OF NON LIN FIT OF FLOW TIME VS. PHASE ANGLE Y= 1.196e+9 * EXP((-.284) * X) 1ST DERIVATIVE IS Y=( e+8 * EXP((-.284)*X PHASE ANGLE OF RTFO RESIDUE OF MIX BINDER 1/1/1 15:52:58 E:\AR2\RESULTS\DUPONT\colorado project\1st DERIVATIVE OF FIT OF FLOWTIME VS PHASE ANGLE.spf FIRST DERIVATIVE OF FUNCTIONAL RELATIONSHIP BETWEEN FLOW TIME OF MIX AND PHASE ANGLE. The first derivative of the non-linear curve fit of mix flow time as a function of phase angle yields a plot that rises rapidly and then levels off as it approaches zero. Over the defined data range the fitted equation does not reach a true maximum or true minimum and therefore the first derivative will not reach zero. Extending a tangent from the horizontal leg of the first derivative plot and observing the phase angle where the first derivative plot begins to diverge from the tangent should also give us a prediction of the critical phase angle value. In this instance, the phase angle is 66.8 degrees. Page 26

27 A study of 5 PG binders, four of which were polymer modified, using a single, high quality aggregate was conducted. The aggregate was a 1% crushed granite that was used on a paving project for the Weld County, Colorado airport. The binders used in this study were: 1. AC-2R, which was the binder used on the project. When characterized using SHRP grading procedures this binder actually met a PG grade. 2. A PG from Conoco in Denver to serve as an unmodified control 3. A lab blended PG made using Ultramar Diamond Shamrock base asphalt from McKee, TX and an Elvaloy 417 polymer 4. A lab blended PG made using Conoco Denver base asphalt and an Elvaloy 417 binder. 5. A plant produced PG 76-4 from the Sinclair Refinery in Sinclair, WY. This product was sold as a PG and a PG 7-34 since it met both specifications. The Sinclair product met the requirements for a PG 4 grade when tested using the Direct Tension Test according to the AASHTO MP-1A specification. Tests of the RTFO residues of the binders were conducted using a newly proposed test protocol. This new protocol allows determination of the accumulated strain properties of the RTFO residues of binders. The presence of polymer additives reduces the amount of accumulated strain that a binder will experience. It has been our experience, having performed numerous cumulative strain tests, that every asphalt binder has a different response to a given polymer additive. As a general rule increasing the polymer in a binder will decrease the accumulated strain, but the same amount of the same polymer in 2 different binders can yield significantly different accumulated strain values. In an effort to evaluate the properties of mixes produced from different binders, a creep strain test was developed using a dynamic shear rheometer. Creep strain results expressed in terms of the time to reach tertiary flow (see earlier Witczak reference), enabled us to compare the relative performance of each mixture. Using results from the creep strain test we were able to show that improved performance of mixes produced with different binders was highly correlated to both the binder phase angle and the cumulative strain of the binder. For a given aggregate structure tested at the field service temperature it would appear from these data that, as the binder percent cumulative strain decreases or as the binder phase angle decreases the resistance of the mixture to permanent deformation is improved. Analysis of data relating phase angle to cumulative strain or flow time failure of mix indicates that a binder phase angle of approximately 66 degrees would provide the best resistance to permanent deformation. It should be kept in mind that these results are based on only one aggregate gradation and 4 PMA binders with high temperature PG grades 2 grade levels above the base binder. A binder phase angle of about 66 degrees might be related to the best level of performance for these mixes made with these binders. However, there might well be a higher optimum phase angle if one compared mixes made with PG grades that had only been improved 1 PG grade level. Lastly, this work has shown that PG binders produced with Elvaloy will perform as well as or better than similar a similar PG grade produced with a SB modifier. In addition the Elvaloy modified binders were produced using 3 different asphalt sources and all performed very well in both the binder and mixture tests. Page 27