The National Academies Press

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From page 8... ... should be avoided in wearing and intermediate course mixtures because low design air void contents should be expected to promote low in-place air voids and increase the possibility of constructing a pavement with poor rut resistance. Therefore, it appears reasonable to use a range for design air voids of from 3% to 5%. Read the entire page →
From page 9... ... Most commonly, the design air voids content is expanded to a range of 3% to 5% and a maximum VMA is established at 1.5% to 2% above the established minimum values. A number of states have also slightly increased minimum VMA values, providing for somewhat richer mixtures than produced by the current version of Superpave. Read the entire page →
From page 10... ... . Although these data were gathered using flexural fatigue tests, continuum damage theory predicts that the damage in the extreme fiber at the test conclusion for this procedure should be constant and can thus be related to the results of uniaxial tests. Read the entire page →
From page 11... ... In analyzing a wide range of aggregate gradation data, it was found that for routine purposes the aggregate speciﬁc surface can be accurately estimated by summing the percent passing the 75-, 150-, and 300-μm sieves and dividing the total by 5. The sum of the percent passing the 75-, 150-, and 300-μm sieves is called the ﬁneness modulus,300-μm basis, abbreviated as FM300.The relationship between this parameter and aggregate speciﬁc surface was evaluated using data from eight projects, as shown in Figure 1; the data used in this analysis was as reported for NCHRP Project 9-9, the NCAT Test Track, Pooled Fund Study 176, the Florida permeability study, MnRoad, FHWA's Accelerated Loading Facility (ALF) Read the entire page →
From page 12... ... The r2 value for this model was 89%, which is very good considering that this model includes data from three widely different climates and uses only laboratory mix data and in-place air voids to predict the rutting rate. The 90% prediction limits shown in Figure 4 correspond closely to plus or minus a factor of 2.0 in the estimated rut depth. Read the entire page →
From page 13... ... It should also be noted that using as-designed data when applying Equation 2 to ﬁeld data will often result in poor predictions of rutting rate because HMA mixes as-placed often vary substantially from their as-designed characteristics. If an estimate is needed of the effect of deviations during production from as-designed characteristics, rutting should be calculated 13 Section Mix Design Method Ndesign or Blows Aggregate Type Aggregate NMAS mm Aggregate Gradation Binder Grade Modifier Type NCAT Test Track Mixtures N1 Superpave 100 Slag/Limestone 12.5 ARZ PG 76-22 SBS N2 Superpave 100 Slag/Limestone 12.5 ARZ PG 76-22 SBS N3 Superpave 100 Slag/Limestone 12.5 ARZ PG 67-22 N/A N4 Superpave 100 Slag/Limestone 12.5 ARZ PG 67-22 N/A N5 Superpave 100 Slag/Limestone 12.5 BRZ PG 67-22 N/A N6 Superpave 100 Slag/Limestone 12.5 BRZ PG 67-22 N/A N7 Superpave 100 Slag/Limestone 12.5 BRZ PG 76-22 SBR N8 Superpave 100 Slag/Limestone 12.5 BRZ PG 76-22 SBR N9 Superpave 100 Slag/Limestone 12.5 BRZ PG 76-22 SBS N10 Superpave 100 Slag/Limestone 12.5 BRZ PG 76-22 SBS N11 Superpave 100 Granite 12.5 TRZ PG 76-22 SBS N12 SMA 50 Granite 12.5 SMA PG 76-22 SBS N13 SMA 50 Gravel 12.5 SMA PG 76-22 SBS S1 Superpave 100 Granite 12.5 BRZ PG 76-22 SBS S2 Superpave 100 Gravel 9.5 BRZ PG 76-22 SBS S3 Superpave 100 Limestone/Gravel 9.5 BRZ PG 76-22 SBS S4 Superpave 100 Limestone 12.5 ARZ PG 76-22 SBS S5 Superpave 100 Gravel 12.5 TRZ PG 76-22 SBS S6 Superpave 100 Limestone/RAP 12.5 ARZ PG 67-22 N/A S7 Superpave 100 Limestone/RAP 12.5 BRZ PG 67-22 N/A S8 Superpave 100 Marble/Schist 12.5 BRZ PG 67-22 N/A S9 Superpave 100 Granite 12.5 BRZ PG 76-22 SBS S10 Superpave 100 Granite 9.5 ARZ PG 67-22 N/A S11 Superpave 100 Marble/Schist 12.5 BRZ PG 76-22 SBS S13 Superpave 100 Granite 12.5 ARZ PG 76-22 SB MnRoad Mixtures 1 Marshall 75 Gravel/Granite 12.5 ARZ PG 58-28 N/A 2 Marshall 35 Gravel/Granite 12.5 ARZ PG 58-28 N/A 3 Marshall 50 Gravel/Granite 12.5 ARZ PG 58-28 N/A 4 Superpave 100 Gravel/Granite 12.5 ARZ PG 64-22 N/A 14 Marshall 75 Gravel/Granite 12.5 ARZ PG 58-28 N/A 15 Marshall 75 Gravel/Granite 12.5 ARZ PG 58-28 N/A 16 Superpave 100 Gravel/Granite 12.5 ARZ PG 64-22 N/A 17 Marshall 75 Gravel/Granite 12.5 ARZ PG 58-28 N/A 18 Marshall 50 Gravel/Granite 12.5 ARZ PG 58-28 N/A 19 Marshall 35 Gravel/Granite 12.5 ARZ PG 58-28 N/A 20 Marshall 35 Gravel/Granite 12.5 ARZ PG 58-28 N/A 21 Marshall 50 Gravel/Granite 12.5 ARZ PG 58-28 N/A 22 Marshall 75 Gravel/Granite 12.5 ARZ PG 58-28 N/A 23 Marshall 50 Gravel/Granite 12.5 ARZ PG 58-28 N/A WesTrack Mixtures 35 Superpave 96 Andesite 19.0 BRZ PG 64-22 N/A 38 Superpave 96 Andesite 19.0 BRZ PG 64-22 N/A 39 Superpave 96 Andesite 19.0 BRZ PG 64-22 N/A 54 Superpave 96 Andesite 19.0 BRZ PG 64-22 N/A Notes: SMA = stone matrix asphalt; RAP = recycled asphalt pavement; ARZ = above restricted zone; BRZ = below restricted zone; TRZ = through restricted zone; SBS = styrene-butadiene-styrene rubber; SBR = styrene-butadiene rubber; SB = styrene-butadiene Table 1. Read the entire page →
From page 14... ... as a function of design VMA and design air void content for a constant in-place air void content of 7%.As VMA increases, rut resistance decreases; the estimated rutting rate decreases by about 20% for each 1% decrease in VMA. Each 1% increase in design air voids decreases rutting rate by 18%. Read the entire page →
From page 15... ... Effect of VMA and In-Place Air Voids on Rut Resistance of Superpave Mixtures at a Constant Design Air Void Content of 4%. 0.0 0.5 1.0 1.5 25 50 75 100 125 150 Ndesign R u t R at e, m m /m /E SA Ls (1/ 3) Read the entire page →
From page 16... ... It is well known that at in-place air void contents below about 2% to 3%, many HMA pavements will exhibit a sudden and dramatic decrease in rut resistance. This is attributable to excessive asphalt binder content, which prevents aggregate particles from developing the internal friction needed for good rut resistance. Read the entire page →
From page 17... ... Another important ﬁnding in analyzing the NCHRP Projects 9-25 and 9-31 fatigue data was that the complex modulus in tension/compression, as determined at the start of the uniaxial fatigue tests, was signiﬁcantly lower than that measured in dynamic compression. Based upon comparing the measurements made during these fatigue tests and dynamic compression values predicted using the Hirsch equation, the following empirical equation was developed for estimating tension/compression modulus values (\|E* Read the entire page →
From page 18... ... Properties of this data set are summarized in Table 3. Application of continuum damage theory to ﬂexural fatigue data in part is dependent upon the ﬁnding that at completion of a ﬂexural fatigue test, when the ﬂexural stiffness has decreased by 50%, the extreme ﬁber damage will be constant at about 86.4%, corresponding to a damage ratio of 0.136. Read the entire page →
From page 19... ... Effect of Mixture Composition on In Situ Fatigue Resistance Some discussion of the relationships among fatigue resistance and binder content, design compaction level, and ﬁeld compaction is useful at this point to illustrate the practical implications of Equation 9. Many pavement engineers and technicians assume that lower values of Ndesign automatically result in higher binder contents, so lowering Ndesign will improve fatigue resistance because increased binder content will improve fatigue life. Read the entire page →
From page 20... ... If an agency feels that higher binder contents and lower in-place air voids are needed to improve fatigue resistance, higher minimum binder contents (higher minimum VMA at a given design air void level) and improved ﬁeld compaction requirements should be speciﬁed, perhaps in combination with lower Ndesign values if it is felt that this latter change will help materials suppliers and contractors deal with the ﬁrst two changes. Read the entire page →
From page 21... ... Alternately, asphalt binder content by weight can be specified as a function of aggregate specific gravity, but this is a somewhat more cumbersome approach. Furthermore, it is clear that if in-place air voids are allowed to vary with design air voids, there is little net affect on fatigue resistance. Read the entire page →
From page 22... ... • At a given design values for VBE, design air voids, and inplace air voids, fatigue resistance will increase with increasing values of Ndesign. • At given design values for VBE, air void content, and Ndesign, fatigue resistance will increase with decreasing in-place air void content. Read the entire page →
From page 23... ... . Property Average Value Minimum Maximum Total number of tests 113 Total number of field projects 7 Total number of mixtures 13 Aggregate types Alabama limestone, Florida limestone, Georgia granite, RAP Aggregate NMAS and gradation 12.5-mm and 19-mm, all BRZ Binder grade, type PG 67-22, unmodified Estimated aggregate specific surface, m2/kg 4.47 3.57 5.34 Air void content, Vol. Read the entire page →
From page 24... ... ; Xi5 = indicator variable for aggregate/binder "5" and = 1 for aggregate/binder "5" and 0 otherwise; β6 = average effect for aggregate binder "6" (California granite and PG 58-28) ; Xi6 = indicator variable for aggregate/binder "6" and = 1 for aggregate/binder "6" and 0 otherwise; β7 = coefﬁcient for effect of air void content (VTMi) Read the entire page →
From page 25... ... For these reasons, a modiﬁcation of Mirza and Witczak's global aging system was developed, which provides results very similar with the original system but makes use of rational rheological measurements and binder master curve parameters. The modified global aging system was used to analyze several hypothetical situations to evaluate the effect of air voids and aggregate specific surface on age hardening. Read the entire page →
From page 26... ... Resistivity is proportional to the square of aggregate speciﬁc surface and is inversely proportional to the cube of VMA, and because most Superpave mixes are designed at or very close to 4.0% air voids, there is a direct relationship between VMA and effective binder content. Therefore, there should be a very good relationship between AFT and resistivity and between AFT and rut resistance. Read the entire page →
From page 27... ... • Rut resistance as indicated by laboratory tests and as measured in a wide range of field test tracks/test roads was predicted to within about a factor of 2 using a model incorporating mixture resistivity, design compaction, and relative field compaction. • The rutting/resistivity model suggests that each 1% decrease in VMA, 1% increase in design air voids, and/or 1% decrease in field air voids increases rut resistance by about 20%,as indicated by rutting rate in mm/m/ESALs1/3. Read the entire page →
From page 28... ... decreases fatigue resistance by about 20%. • Permeability of HMA increases with increasing air voids and decreasing aggregate specific surface. Read the entire page →

From page 8...

... should be avoided in wearing and intermediate course mixtures because low design air void contents should be expected to promote low in-place air voids and increase the possibility of constructing a pavement with poor rut resistance. Therefore, it appears reasonable to use a range for design air voids of from 3% to 5%.