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22 Table 29. Summary of significance of ruggedness test factors on confined tests. Permanent Strain at 500 1000 2000 5000* 8000* Factors cycles cycles cycles cycles cycles Equilibrium Temperature (-1 vs +1 C) 25 25 25 0 0 Transfer time (3 vs 5 min) 0 25 25 0 0 Conditioning Fluid (Water vs Air) 0 0 0 0 0 End Condition (Mill vs Saw) 25 25 25 0 0 Friction Reducer (Teflon vs Latex) 100 100 50 50 50 Axial Stress (± 2 %) 25 25 25 0 0 Confining Stress (135 vs 145 kPa) 25 50 25 0 0 SMA only Data on the repeatability of the flow number test were Project 9-19, these friction reducers should be used in the collected in Phase II of this project (11). The Phase II ex- flow number testing. periment included eight replicates of two mixtures tested by single operators in two laboratories. Laboratory and 2.3.2 Factors Affecting Permanent Strain mixture effects were found to not be significant, therefore, the 32 observations were pooled to obtain estimates of the Figure 13 through Figure 17 show the effects of the signif- repeatability of the flow number. The coefficient of varia- icant ruggedness factors on the permanent strain measured tion for the flow number from the Phase II analysis was after 500, 1,000, 2,000, 5,000, and 8,000 cycles, respectively. found to be 35 percent while the coefficient of variation for The analysis for the permanent strain can only be performed the measured permanent strain was found to be only 14 per- when data are available for all specimens tested in both cent. The high variability of the flow number was attributed labs. The dense graded mixture specimens began to fail after to difficulties detecting the exact point where the perma- 2,000 cycles. The SMA mixture specimens began to fail after nent strain rate begins to increase. Future improvements 8,000 cycles. may be made to the flow point detection algorithm, but it Considering the permanent strain measured in the flow is unlikely that the repeatability of the flow number will be number test has a coefficient of variation of 14 percent, several less than that for the measured permanent strain. Based on observations can be made based on the data shown in Fig- this analysis, the temperature control of ±0.5°C is accept- ure 13 through Figure 17. First, the machine control factors able. However, flexibility can not be permitted in the selec- of temperature, axial stress, contact stress, dwell time, and tion of the end friction reducer. Since the greased latex confining pressure have little effect on the measured perma- membranes provide less friction and were recommended in nent strains over the control range provided by the SPT. Also SMA Confined Confining Stress, +2% Dense Confined Dense Unconfined Dwell, +0.01 sec Contact Stress, +2% Axial Stress, + 2% -Teflon / +Latex - Milled / +Sawed -Water / +Air Time, min Temperature, +0.5 C -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 Change in Flow Number, % Figure 12. Effect of statistically significant ruggedness factors on the flow number.
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23 SMA Confined Confining Stress, +2% Dense Confined Dense Unconfined Dwell, +0.01 sec Contact Stress, +2% Axial Stress, + 2% -Teflon / +Latex - Milled / +Sawed -Water / +Air Time, min Temperature, +0.5 C -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 Change in Permanent Strain, % Figure 13. Effect of statistically significant ruggedness factors on the permanent strain after 500 load cycles. the transfer time has little effect on the measured permanent the confining membrane in-place. Although the ends were strains over the range of 3 to 5 min. However, the three user- uncovered, the path for water infiltration from the ends is selectable factors, conditioning fluid, end condition, and end much longer resulting in less water absorption by the speci- friction reducer, have a major effect on the measured perma- men during conditioning. Clearly, water can not be used as a nent strains. conditioning fluid in the flow number test. In unconfined tests, the permanent strain was much higher The measured permanent strains are higher when greased when water was used as the conditioning fluid. Recall, the latex membranes are used as end friction reducers. Appar- dense-graded mixture that was used had marginal resistance ently this type of end friction reducer is more effective than to moisture damage when tested in accordance with AASHTO TeflonTM resulting in less end friction and greater permanent T283. Apparently water that penetrates the voids in this mix- deformation in the test. Flexibility can not be permitted in ture results in some level of moisture damage during the re- the selection of the end friction reducer. Since the greased peated load test. The conditioning fluid was not significant in latex membranes provide less friction and were specified in the confined tests, probably because less water entered the Project 9-19, these friction reducers should be used in the specimens because these specimens were conditioned with flow number testing. SMA Confined Confining Stress, +2% Dense Confined Dense Unconfined Dwell, +0.01 sec Contact Stress, +2% Axial Stress, + 2% -Teflon / +Latex - Milled / +Sawed -Water / +Air Time, min Temperature, +0.5 C -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 Change in Permanent Strain, % Figure 14. Effect of statistically significant ruggedness factors on the permanent strain after 1,000 load cycles.