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36 decreases. The trend, if it does exist would seem logical. How- aggregate MGSO4 was 4.2. Coarse aggregate MDEV has little ever, with the limited data obtained in the research (three data correlation to mixture rutting performance. The fine aggre- points) and given that two of the mixtures never exhibited gate MDEV and MGSO4 have fair correlations with mixture fatigue cracking, the fine aggregate UVA cannot be recom- rutting performance. If only data at 20,000 APT wheel passes mended as an aggregate test related to fatigue performance. A is considered, the correlation between rutting performance relationship may exist, but additional testing is needed before and the fine aggregate MDEV and MGSO4 are excellent. The a conclusive recommendation can be made. amount of rutting at 20,000 APT passes increases as the fine aggregate MDEV and/or MGSO4 values increase. However, the opposite trend exists at 1,000 passes. Nonetheless, there Methylene Blue Test does appear to be a good enough correlation between fine Based on the AASHTO T 283 tests of cores taken from the aggregate MDEV and MGSO4 to recommend their use to APT test lanes, the MBV appears to be somewhat related to the specify aggregates used in HMA mixtures. A maximum value TSR values. The higher the MBV, the lower the TSR value or of 15 and 20 percent for MDEV and MGSO4, respectively, the more susceptible the HMA mixtures are to moisture. How- would limit rutting at 20,000 wheel passes to 12.5 mm. ever, the relationship does not seem strong and appears to be affected by the amount of p0.075 material in the mixture. For Summary example, mixture FAM1 had a high MBV, but low p0.075 con- tent. Despite the high MBV, the mixture had a high retained The research has shown that for coarse aggregates, both UVA tensile strength after being subjected to one freeze-thaw cycle. (UVB) and FOE21 are good predictors of HMA mixture per- Furthermore, research covered in the literature review indi- formance. It is recommended the tests be used in all climates cates a high MBV does not always indicate the presence of and for all materials. For traffic above 100,000 ESAL, a coarse harmful material in the aggregate blend. aggregate UVA of 45 percent or greater is recommended. A Research results suggest the MBV test is not a good predic- minimum UVA of 40 percent is recommended for traffic below tor of HMA performance and should therefore not be used to this level. The FOE21 value should be a maximum of 50 per- specify HMA mixture fine aggregates. cent for all traffic levels. For fine aggregates, UVA, UVB, or VTM5 tests can be used to control HMA rutting performance. The MDEV and Particle Size Analysis MGSO4 tests on fine aggregates can also be used to control The effect of the p0.075 fraction on fine-graded mixtures HMA mixture rutting performance. The UVA (UVB, VTM5) was investigated using the APT. Overall, the D60 and D30 val- should be used in all climates and for all materials. For expected ues show a fair correlation with rutting performance. HMA traffic of less than 500,000 ESAL, the minimum recommended mixture total rut depth increases as the amount of D60 or UVA (UVB, VTM5) value is 40 percent; a minimum UVA D30 material increases. When used in conjunction with the (UVB,VTM5) of 45 percent is recommended for expected traf- fine aggregate UVA, neither the D60 nor D30 parameters fic greater than 500,000 ESAL. improve the fine aggregate UVA prediction of HMA mixture The MDEV and MGSO4 tests should be used in all climates rutting. The D10 parameter does not appear to correlate at all and for all materials. These tests may be important in high with HMA mixture rutting performance. Considering the moisture climates. A maximum value of 15 and 20 percent for effort that goes into completing the particle size analysis of MDEV and MGSO4, respectively, are recommended for all the p0.075 fraction and its fair ability to predict mixture per- traffic levels. formance, particle size analysis of the p0.075 fraction is not recommended for routine aggregate specification testing. Recommended Research Problems were encountered in the fatigue testing portion Micro-Deval and Magnesium of the experiment because of the lack of temperature control. Sulfate Soundness Also, only limited fatigue tests could be incorporated in the Kandhal and Parker (1) recommended MDEV and MGSO4 study because of budget and time constraints. As a result, per- tests to address aggregate durability and toughness when used formance relations in the study are not as strong as they need in HMA mixtures. The MDEV for both coarse and fine aggre- to be. Although it is true that fatigue performance depends on gates and the MGSO4 for fine aggregates were determined and coarse and fine aggregates, other factors contribute to the per- correlations were made with rutting performance. The MDEV formance, including gradation, binder type and volume, tem- descriptive rankings for coarse and fine aggregates were perature, initial mixture density, pavement thickness, applied 2.7 and 5, respectively. The descriptive ranking for the fine loads, tire pressures, and traffic speed and volume. Gradation,
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37 binder volume, and binder grade and type are likely the most positive results. It is recommended that a laboratory fatigue significant factors related to fatigue performance. The other study be conducted with a goal of screening aggregate charac- items are of only slightly less importance. teristics and tests affecting HMA fatigue performance. Nor- A comprehensive laboratory study was undertaken in mally, the difference between laboratory and in-service fatigue NCHRP Project 4-19 to screen aggregate properties and tests performance is a matter of using a scaling factor. For this rea- related to HMA mixture rutting and moisture effects. The cur- son, the research team believes that adequate information can rent study built on the experience of that research to produce be collected without the need for further full-scale testing.