Click for next page ( 34


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 33
33 help decrease rutting when the HMA mixture is exposed to 50 moisture. The MBV for each mixture is also shown on the fig- y = -1.46x + 69.2 ure. There does not appear to be any pattern to the rutting as 40 R2 = 0.99 a function of the MBV. Indeed the three mixtures showing the Percent Cracking least amount of rutting have MBV ranging from 1.3 to 8.0. 30 20 Fatigue Mixtures These tests were the research team's attempt to produce 10 fatigue cracking in the APT facility and the results were some- what mixed. Three of the HMA mixtures exhibited fatigue 0 25 30 35 40 45 50 cracking; the other three mixtures never developed fatigue FOE21, % cracking due to the inability to control temperature in the APT facility. However, considering the limitations of the data, some Figure 39. Fatigue cracking/flat or general conclusions can be drawn from the fatigue testing por- elongated relationship. tion of the experiment. The percent fatigue cracking (i.e., the percentage of cracked 50 area to total area) as a function of the coarse aggregate UVA and FOE21, shown in Figures 38 and 39, respectively, indi- cates a trend in the data. As UVA or FOE21 increase, so do the 40 number of APT wheel passes required to fatigue HMA mix- tures. Figures 38 and 39 also show best fit lines, equations of Percent Cracking the lines, and R2 values. These are presented for informational 30 purposes only. With three data points an excellent fit can nearly always be obtained. However, the trends appear valid 20 and indicate that an HMA mixture containing coarse aggre- gates with UVA and/or FOE21 values in the 45- to 50-percent range would much better resist fatigue cracking than mix- 10 tures with UVA and/or FOE21 values below 45 percent. Figure 40 is a plot of the percent fatigue cracking as a function of fine aggregate UVA for the three fine-graded 0 40 42 44 46 48 50 UVA, % 50 Figure 40. Fatigue cracking/fine y = -4.62x + 224.7 aggregate UVA relationship. 40 R2 = 0.99 Percent Cracking 30 mixtures. The data are obviously scattered because the FA-3 and FA-4 mixtures never exhibited fatigue cracking 20 because of the inability to control ambient temperature. Both mixtures received 20,000 passes before testing was dis- 10 continued due to rutting. Recent fatigue testing in the APT with temperature control suggests that these mixtures may 0 have sustained additional passes (up to approximately 40 42 44 46 48 50 100,000) before failing in fatigue. From the data available, UVA, % it is not possible to draw conclusions on the trend in the Figure 38. Fatigue cracking/coarse fatigue cracking as a function of the fine aggregate UVA aggregate UVA relationship. relationship.