Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 23


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 22
22 that for the mixtures that contained in excess of 30% parti- and 30% of particles exceeding the 31 ratio increased the cles exceeding the 31 ratio, the percent F&E decreased mixture VMA by 1% to 1.5%. from the quarry to the plant stockpile, from the plant stock- pile to the plant mix, and from the plant mix to the sample taken behind the paver. None of the five projects indicated a 2.3.3 Precision of F&E Tests significant difference between the percent of F&E measured on samples recovered behind the paver to samples recovered ASTM D4791 does not contain a precision statement. after compaction (39). Prowell and Weingart (41) conducted a study to determine a Comparisons were made between the amount of breakdown precision statement for ASTM D4791. A total of five aggre- that occurred during construction and the amount of break- gates were tested in the study, but only three were used for down that occurred during gyratory compaction. The data determining a precision statement for ASTM D4791. The indicated practically no difference between the amount of aggregates were igneous granite, diabase, and dolomitic breakdown that occurred for samples compacted to 4% or limestone with percentages of particles exceeding the 31 7% air voids. The authors concluded that the amount of ratio ranging from 8.2 to 45.8 and percentages of particles breakdown that occurs during gyratory compaction generally exceeding the 51 ratio ranging from 0.2% to 12.7%. Fifteen exceeds that which occurs during normal construction (39). labs participated in the study. Each laboratory tested two Ongoing research as part of NCHRP Project 4-19(2) has replicates (100 particles each) of each of three particle sizes: examined the effect of F&E on volumetric properties and -3/4 in. to +1/2 in., -1/2 in. to +3/8 in., and -3/8 in. to +No. 4. permanent deformation during accelerated loading. Signifi- Figure 3 shows the pooled within lab (W/L) and between cant relationships were observed between the percent of flat lab (B/L) standard deviations versus the average percent for or elongated or the percent F&E and both LA abrasion loss the 51 particles. From Figure 4, there appears to be a linear and uncompacted voids in coarse aggregate, as shown in relationship between the standard deviation and average Table 5. Based on the six aggregates tested in this study, level of the test. A similar trend was observed for the 31 there was no correlation between F&E and VMA; however, samples. In cases in which a linear relationship exists the gradations differ slightly between the mixes. A strong pos- between the standard deviation and the mean of the test val- itive correlation (R = 0.993, p-value = 0.0007) was observed ues, ASTM C802 recommends that one use the coefficient of between percent flat or elongated particles at the 21 ratio variation. Figure 3 shows the coefficient of variation versus and total binder content. No significant relationships were the average percent particles exceeding the 51 ratio. The observed between F&E and the rutting performance of the coefficient of variation sharply decreased with increasing mixes (23). It should be noted that the percent of F&E only mean test values for the 51 ratio until it reaches an asymp- ranged from 11.6% to 28.0% for the 31 ratio and 1.8% to totic level. This indicates that the test method (51 ratio) is 8.1% for the 51 ratio. subject to erratic variations. The test is variable, even at low levels of F&E. The coefficient of variation is inflated by Additional research on F&E is ongoing at the International dividing the standard deviation by the low (close to zero) Center for Aggregates Research. The study is examining the mean levels of 51 F&E; however, the coefficient of variation change in the percentage of F&E during laboratory mixing for the 31 ratio was relatively constant. and compaction, aggregate breakdown during mixing and The precision statement for ASTM D4791 was written compaction, volumetric properties, tensile strength, and resis- according to ASTM C670 (42). The single-operator coeffi- tance to rutting (40). In addition to the proportional caliper cient of variation for the 31 ratio was found to be 26.1% typically used for ASTM D4791, the study examined the use (41). The difference between two individual test results with of the multiple ratio shape analysis device. Using similar gra- a 95% confidence interval is determined by multiplying the dations, increasing F&E on the 31 ratio from cubical to 20% standard deviation by 2 2; therefore, results of two properly TABLE 5 Significant correlations between different coarse aggregate tests in NCHRP Project 4-19(2) (23) Tests Correlation Coefficient, p-value Flat or Elongated Particles 2:1 and Uncompacted Voids 0.786, 0.0641 Method A Micro-Deval and Magnesium Sulfate Soundness 0.863, 0.027 Flat or Elongated Particles 5:1 and LA Abrasion 0.832, 0.040 Flat and Elongated Particles 5:1 and LA Abrasion 0.844, 0.035 Micro-Deval and Bulk Specific Gravity 0.877, 0.022 LA Abrasion and Bulk Specific Gravity 0.812, 0.049 Micro-Deval and Water Absorption 0.961, 0.002 Magnesium Sulfate Soundness and Water Absorption 0.894, 0.016 1 Not significant at the 5% level, significant at the 10% level.