Comparison of 9.5 mm SuperPave and Marshall Wearing I Mixes in ...

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61CHAPTER 6 DATA ANALYSIS AND RESULTS6.1 INTRODUCTIONOnce data were collected from all mix designs, fine aggregate angularity tests and APA tests itwas compiled into tables presented in the Appendix D. These tables contain the raw data, suchas sample weights, as well as calculated results of corresponding tests. Graphs are presented inthis chapter that show comparisons between rut depths versus various aggregate propertiesand mix design values. These include air voids of APA samples, FAA value, VMA, asphalt contentand percent natural sand in the mix. Results of the APA test were tested statistically forsignificant differences and were compared with those results from the literature. Also, generalobservations, limitations and considerations were discussed with respect to the objectives setforth at the start of the research.6.2 PRELIMINARY DATA ANALYSIS AND GENERAL OBSERVATIONSFine Aggregate Angularity. Preliminary analysis performed on the fine aggregate angularitytests showed that the results calculated from the tests met expectations and past experience.Uncompacted voids percentage increased as the amount of natural sand in the mix decreased.As mentioned before, none of the mixtures met the WVDOH requirement for FAA in SuperpaveHeavy mixtures. If a contractor wanted to use this material for a Superpave Heavy design inWest Virginia this problem could only be overcome by blending another aggregate into the mixthat exhibited an uncompacted void percentage higher than 45%. Also no 100% natural sandcontent mixtures could be designed at the medium traffic volume level since the natural sanditself had a FAA value of 39.4%, just under the WVDOH minimum specification of 40% formedium traffic designs.Superpave Mix Design. Accommodation of direct comparisons between mix designs acrosstraffic level and design method was attempted throughout the mix design process. This meantgetting gradations as close to each other as possible, while still meeting volumetric and strengthrequirements for each mix design method. This was accomplished for the most part by at leastkeeping the gradations of similar design types and levels as close as possible. One place wherethis was not possible was in developing a Superpave Heavy or Medium design with a high levelof natural sand. As mentioned before, the highest natural sand percentage that could beachieved in either mix design type at the heavy and medium level was 13% of the total mixture.Any more than that caused either a problem with volumetric values or with the gradationcrossing through the restricted zone. If a higher sand content design could have beendeveloped at these levels, then a more direct comparison could have been made between themand the Superpave Low 50% NS and 64% NS mix designs.Asphalt Pavement Analyzer Testing. The data collected during this testing did followexpectations of the effects that natural sands would have on the rut depths (i.e. more naturalsand, deeper rutting). However, there were many unexpected results after the data from thistesting was first examined. At first it was expected that all the heavy traffic level mixtures would
62exhibit lower rut depths than any of the other mixes and then the medium mixtures and finallythe low volume mixes, this, however, was not the case. In fact, two Superpave Low mixturesperformed better than three of the four heavy mixes. This was probably due to the fact that thelow volume mixes did not contain any natural sand, while a few of the heavy mixes did. Most allof the pavement designs tested very well, even though the majority of them would have failedthe Georgia DOT criteria for minimum rut depth, especially when compared to APA results ofprevious research involving natural sands and how most pavements in West Virginia fare in APAtests. It should also be mentioned that the equation used to aid in finding the proper weight toachieve 7% air voids in the APA samples worked very well, even though some slight adjustmentsdid need made to the sample weights. This equation brought the estimate to within 20 to 30grams of the correct weight of samples that average 3000 grams.6.3 DATA ANALYSISStudent t-tests were used for the statistical analysis. The two-tailed t-tests were conducted inthe standard method prescribed by statistical data analysis. In all cases, the hypothesis testedwas that the means of the populations are equal, and the null hypothesis is the means are notequal. A critical t-value was determined for each comparison based on the number of degreesof freedom and a confidence level of 95 percent. If the t-statistic value was within the range ofplus or minus of the critical t-value then the null hypothesis of the population means beingunequal was not rejected. An Excel spreadsheet was used to aid in the calculation of the largenumber of t-tests needed for this research.Table 6.1 presents some global comparisons of the data. The comparison of all Marshall mixesversus the Superpave mixes shows the null hypothesis of equal means should be rejected.However, this conclusion is confounded by the fact that there were no Marshall light mixes inexperiment. There was 40 and 64 percent natural sand in two of the Superpave light trafficmixes, with average rutting potential of 15 and 17 mm respectively. These two mixes are thereasons that the average rutting of the Superpave mixes was much greater than the averagerutting of the Marshall mixes. Without these two mixes, the average rutting of the Marshall andSuperpave mixes was fairly close and the t-statistic for comparing the mixes was 0.222,indicating that the null hypothesis should not be rejected. The comparison of the Heavy andMedium traffic mixes showed that the null hypothesis could not be rejected, this is evidencethat the mixes performed equally well. However, there is not enough data to claim that the nullhypothesis should be accepted. The data also suggests that there is not sufficient evidence tosuggest a difference in the performance of the mixes based on the traffic level used in thedesign of Superpave mixes. This result is counter intuitive and should be studied further. It islikely that the forced inclusion of sand in some of the Superpave mixes confounded the resultsof this comparison. Comparison of mixes with limestone only to those with natural sanddemonstrates the null hypothesis should be rejected. From inspection of the data it can beconcluded that on the average mixes with natural sand rutted more than mixes with onlylimestone.
Page 1 and 2:
COMPARISON OF 9.5 MM SUPERPAVE ANDM
Page 3 and 4:
iNOTICEThe contents of this report
Page 5 and 6:
iiiasphalt concrete wearing courses
Page 7 and 8:
vMixing Procedure 78Appendix B Fine
Page 9 and 10:
viiTable C-7 Marshall Medium 13% NS
Page 13 and 14:
4Table 1.1 Mix Design Types in Expe
Page 15 and 16:
6CHAPTER 2 LITERATURE REVIEW2.1 INT
Page 17 and 18:
82. determine aggregate stockpile b
Page 19 and 20: 10SieveAllowable PercentPassing Sie
Page 21 and 22: 12Stability is recorded as the maxi
Page 23 and 24: 14The WVDOH procedure for determini
Page 25 and 26: 16sieve. This is somewhat different
Page 27 and 28: 18G sb = bulk specific gravity of a
Page 29 and 30: 20theoretical gravity at the initia
Page 31 and 32: 22D/B est = adjusted dust to binder
Page 33 and 34: 24P b,est - 0.5%,P b,est ,P b,est +
Page 35 and 36: Percent Passing261009080Superpave U
Page 37 and 38: 28Table 2.6 WVDOH Marshall and Supe
Page 39 and 40: 30Table 2.9 Habib Marshall Analysis
Page 41 and 42: 32theoretically correct in that the
Page 43 and 44: 34the machine. This variability was
Page 45 and 46: 36CHAPTER 3 EQUIPMENT3.1 INTRODUCTI
Page 47 and 48: 38Hose PressureWheel Load100 psi100
Page 49 and 50: 40mouth. This jar rests on a holder
Page 51 and 52: problematic, as the saturated surfa
Page 53 and 54: 44Mechanical Laboratory Sieve. Afte
Page 55 and 56: Percent Passing4610090100% Limeston
Page 57 and 58: 48Maximum specific gravity is a req
Page 59 and 60: 50gradation. This allowed for direc
Page 61 and 62: Percent Passing521009080Light 100%
Page 63 and 64: 54percentage of aggregate from the
Page 65 and 66: 56Table 5.4 Summary of Volumetric a
Page 67 and 68: 58Table 5.5 Calculated and Adjusted
Page 69: 60Table 5.6 Results of APA TestsAir
Page 73 and 74: design had significantly more rutti
Page 75 and 76: 66SP L 100LS SP L 64NS -10.335 2.77
Page 77 and 78: 68percent air voids and percent lim
Page 79 and 80: Air Voids (%)Uncompacted Voids (%)7
Page 81 and 82: 72than the Marshall mixes. Table 6.
Page 83 and 84: Voids in the Mineral Aggregate. As
Page 85 and 86: 76REFERENCESAmerican Association of
Page 87 and 88: 78APPENDIX A BUCKET MIXER INSTRUCTI
Page 89 and 90: 80APPENDIX B FINE AGGREGATE ANGULAR
Page 91 and 92: 82Table B-3 Uncompacted Void Conten
Page 93 and 94: 84AGGREGATE DESIGN DATATable C-1 St
Page 95 and 96: 86Table C-3 Computed Blend Gradatio
Page 97 and 98: 88Table C-7 Marshall Medium 13% NS
Page 99 and 100: 90%G mm%AC VMA VTM VFA @ N ini @N d
Page 101 and 102: 92Table C-14 Superpave Light 64% NS
Page 103: 946 2979.3 1696.7 2988.1 2.307 7.09
Page 106 and 107: 971 2912.7 1620.8 2917.9 2.246 7.65
Page 108 and 109: 992 8.40 10.80 7.402 7.90 9.90 7.80
Page 110 and 111: 1011 9.50 6.90 11.502 9.79 7.15 10.
Page 112 and 113: 1032 8.55 5.20 5.95L R RDate Tested
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Comparison of 9.5 mm SuperPave and Marshall Wearing I Mixes in ...

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