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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
×
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Suggested Citation:"Chapter 2 - Findings." National Academies of Sciences, Engineering, and Medicine. 2006. Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements. Washington, DC: The National Academies Press. doi: 10.17226/13977.
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8State-of-the-Art Summary The summary focuses on literature published after NCHRP Report 405. Multiple databases were used; 46 papers were reviewed. This summary provides a synopsis of the lit- erature in terms of the reported effects of aggregate proper- ties on rutting, fatigue life, and durability of HMA pavements and organized by effect of gradation and nominal maximum size; particle shape, angularity, and surface texture; and prop- erties of p0.075 materials. Effects of Aggregate Gradation and Size Selection of aggregate gradation for use in HMA pavement is important to pavement performance. Recent guidance for HMA gradation has been defined in terms of the Superpave restricted zone. This zone is located along the maximum den- sity line between the 0.300-mm and 4.75- or 2.36-mm particle sizes (depending on the maximum nominal size of the aggre- gate). Avoiding this zone was intended to limit the amount of rounded natural sand that can contribute to mixture instabil- ity. Some research suggests that aggregate gradations plotting below this zone produce more rut-resistant mixtures. How- ever, other studies have shown that gradations plotting above the restricted zone provide equal or even more rut-resistant mixtures (2). Comparing HMA pavement performance based only on different aggregate gradations is not a simple matter. The interrelationships among aggregate gradation, aggregate characteristics, and HMA volumetric properties are complex. In general, dense-graded HMA mixtures with adequate Voids in the Mineral Aggregate (VMA) provide improved resistance to degradation and improved resistance against fatigue crack- ing when used in thick pavements (1). In a recent study, coarse-graded HMA mixtures were found to be more sensi- tive to variations in asphalt binder content and p0.075 mate- rial than were fine-graded mixtures (3). The following observations concerning the effects of aggre- gate gradation and size on HMA mixture properties and per- formances were reported in the literature: • HMA mixtures with gradations passing through the restricted zone exhibit higher bulk density and lower air voids than mixtures with gradation plotting below and above the zone (4); • Fine-graded HMA mixtures have better fatigue perfor- mance than do more coarsely graded mixtures (5); • HMA specifications that allow gradations to pass through the restricted zone produce the best performing pavements in Georgia (6); • In accelerated loading tests, HMA mixtures with grada- tions above the restricted zone generally exhibit less rutting than those with gradations below and through the restricted zone (7, 8); • Triaxial test results indicate that fine-graded HMA mix- tures have greater shear strength than those with coarser gradations (2); and • The SST indicated that an aggregate gradation passing through the restricted zone had no significant effect on HMA mixture performance (4). HMA performance is also influenced by the maximum aggregate size. HMA mixtures with larger maximum aggre- gate sizes were reported to exhibit better rutting performance than those with smaller maximum aggregate sizes (9, 10). Khedaywi and Tons (11) also found that smaller coarse aggre- gate particles provided more aggregate interlocking and resulted in increased HMA shear strength. Accelerated pavement testing seems to delineate the effect of maximum aggregate size on HMA performance much more effectively than do the laboratory methods. It was reported that differences between mixtures with different nominal maximum aggregate sizes (NMAS) that had shown significant performance differences when tested in the FHWA C H A P T E R 2 Findings

Accelerated Loading Facility (ALF) could not be detected by laboratory methods (9). The following observations regard- ing aggregate size effects were reported in the literature: • Increasing the maximum aggregate size in a gradation will improve the mixture quality with respect to creep per- formance, resilient modulus, and tensile strength, but will decrease the Marshall stability and flow (10); • Pavement sections tested with the FHWA ALF indicated that mixtures with an NMAS of 37.5 mm perform better than those with a 19.0 mm NMAS (9); and • A national pooled-fund study found that mixtures with a NMAS of 9.5 mm and 19.0 mm performed similarly when tested with the Purdue APT and the Purdue laboratory wheel tracking device (PurWheel) (7). Particle Shape, Angularity, and Surface Texture Generally, aggregate shape, angularity, and surface texture characteristics influence HMA performance; however, some state agencies and aggregate producers have expressed concerns with the validity and practicality of the specifica- tions and methods used to determine these characteristics— generalizing these specifications to all types of aggregates may be inappropriate. For instance, HMA performance problems associated with some aggregate types (e.g., igneous aggregate) are usually not related to particle shape (12). Numerous studies have been conducted on the effects of particle shape, angularity, and surface texture on HMA per- formance. Results of a study indicated uncompacted voids content of the coarse aggregate, often referred to as the coarse aggregate angularity (CAA), did not correlate with the actual observed performance of either the fine- or coarse-graded mixtures (8, 13). An accelerated pavement testing study revealed that the amount of crushed gravel in HMA mixtures affected rutting performance. Tests on two mixtures made with gravel aggregate showed a mixture with 40-percent crushed gravel was more sensitive to rutting than a mixture with 70-percent crushed gravel (14). Also, increasing the per- centage of crushed particles in HMA mixtures increased the Marshall stability (14). The particle shapes of coarse aggregates used in HMA mixtures have been found to affect both performance and workability of the mixtures. A study conducted using the Superpave Gyratory Compactor (SGC) showed that increasing the amount of flat and elongated particles increased the required compaction energy (15), indicating that HMA mixtures with high percentages of flat and elon- gated particles are less workable. In addition, increased amounts of flat and elongated particles in HMA mixtures result in more aggregate breakdown, thus exposing the aggregate surface and creating a potential durability prob- lem. The VMA was also found to increase slightly with an increasing percentage of flat and elongated coarse aggregate particles. The uncompacted voids content of fine aggregate or fine aggregate angularity (FAA), as affected by particle shape, angularity, and surface texture, is determined in accordance with ASTM C 1252 by measuring the voids ratio of loosely placed fine aggregate in a standard cylinder. In general, fine aggregates with high FAA values result in higher internal fric- tion and stronger bonds with asphalt binder that leads to bet- ter stability and rut resistance of HMA mixtures. Kandhal and Parker (1) indicated that FAA value is an important factor in HMA mixtures performance with aggre- gate gradations above the restricted zone. They concluded that the higher the FAA, the greater the resistance of HMA to permanent deformation. For coarse-graded mixtures, a study showed that FAA did not impact the HMA perform- ance as measured by the Asphalt Pavement Analyzer (APA), Couch Wheel Tracker, and SST (16). However, studies con- ducted using the APT, PurWheel, and triaxial tests found that FAA of coarse-graded mixtures correlated well with HMA rutting performance. These results also indicated that very high FAA values do not necessarily provide better perform- ance than do sands with more typical FAA values in the range of 40 to 45 (7, 17). Stiady (7) reported that design asphalt binder content is affected by FAA; higher FAA is associated with increased resistance to compaction, higher VMA, and higher asphalt binder content. Higher asphalt binder content results from the fixed 4-percent air voids criteria. Very high FAA values also tend to indicate slivered particle shape and/or extremely rough texture. During mixture design compaction, slivered particles orient themselves randomly resulting in high VMA and asphalt binder content. When such a mixture is put into service, traffic breaks or turns the slivered particles flat and the original binder content becomes excessive. Rough aggre- gate such as slag resists both laboratory compaction and in- service traffic densification and thus maintains a higher VMA. This high VMA accommodates high design binder content. Brown and Cross (18) conducted field studies of rutted HMA pavements in several states. They concluded that the initial air voids of HMA mixtures have a strong correlation with rutting. They also concluded that aggregate proper- ties have little effect on the rutting rate for HMA mixtures with in-place voids below 2.5 percent. Sousa and Weisman (19) reported that, for HMA mixtures with air voids con- tent below 2 to 3 percent, the binder acts as a lubricant between the aggregates and reduces point-to-point contact pressure. 9

Properties of Material Passing the 0.075-mm Sieve Addition of mineral filler, material passing the 0.075-mm sieve, affects HMA mixture performance. Depending on the particle size, mineral filler can act as filler or as an extender of the binder. When the mineral filler functions as a binder extender, over-rich HMA mixtures can result and lead to flushing and/or rutting. Some p0.075 materials cause stiffen- ing of the binder and/or HMA mixtures and thus increase fatigue cracking. The amount and characteristics of the p0.075 material can also contribute to HMA mixtures that become susceptible to moisture damage. This can lead to a loss of mixture integrity, lower shear strength, cracking, and increased rutting. Kandhal and Parker (1) investigated the effect of mineral filler by examining filler-binder mortar stiffness of mortars with filler-binder ratios of 0.8 and 1.5 by weight. They found that the MBV of the p0.075 material was related to the filler- binder mortar stiffness. The higher the MBV value, the stiffer was the filler-binder mortar. They also found a strong rela- tionship between the MBV of the p0.075 material and the stiffness parameters |G*| /sinδ and |G*| ×sinδ, obtained from the SST tests. The G* parameter is the complex modulus and δ is the phase angle of material tested under dynamic loading. The |G*| /sinδ parameter is a measure of HMA stiffness at high temperatures or slow loading rates. High |G*| /sinδ values indicate high stiffness HMA mixtures and high resistance against rutting at high temperature. The product |G*| ×sinδ is a measure of HMA stiffness at inter- mediate temperatures or high loading rates. High |G*| ×sinδ indicates high HMA mixture stiffness and thus low resistance to fatigue cracking. Khedaywi and Tons (11) suggested introduction of a spe- cific size of fine particles into the HMA mixtures could increase mixture shear strength. The surface characteristics of the coarse aggregate (rugosity) determines the size of fine particles that contribute the most to the interlocking mecha- nism between the coarse aggregate particles in an HMA mix- ture. It was suggested that, depending on the relative size of the fine particles and the size of coarse particle surface voids, the fine particles can be completely or partially lost in the sur- face voids of the larger particles. When completely lost inside the surface rugosities, fine particles do not participate in HMA shear resistance. When partially lost by rugosity, fine particles can either improve or reduce the interlock between the coarse aggregate particles. Increased interlock occurs when parts of the fine particles are embedded in surface voids of adjoining coarse particles. Reduction of interlock occurs when the average size of the fine particles is larger than the average size of the coarse aggregate surface voids. In this case, the fine particles act like roller bearings between the coarse aggregate particles. It was found that the higher the rugosity of the coarse aggregate, the larger the size of fine particles that result in higher HMA mixture shear strength. The amount of mineral filler used in HMA mixtures does not seem to affect rutting performance adversely as measured by the Repeated Shear at Constant Height (RSCH) test. The RSCH test is performed by applying shear load pulses to a cylindrical HMA specimen and keeping the specimen height constant (AASHTO TP 7). Although increasing the amount of filler does not affect the test result, increasing the mineral filler content does lead to decreased optimum binder content. Ultimately, this can lead to durability and fatigue problems (20). Also, coarse-graded mixtures that have gradations plot- ting below the MDL have been found to be sensitive to the amount of p0.075 material (3). Kandhal and Parker (1) indicated that decreasing the size of D60 (particle size at which 60 percent of the material passes) of the p0.075 increases the HMA mixture’s stiffness and resistance to rutting. Logically, this increase in mixture stiffness would also reduce the mixture’s resistance to fatigue cracking. The HMA mixtures tested consisted of coarse and fine limestone aggregates of sizes larger than the 0.075-mm sieve. Different types of p0.075 material were incorporated with the coarse and fine limestone to study the effects on rut- ting, fatigue, and stripping performance. In addition to D60 (particle size at which 60 percent is smaller) of the p0.075 material, the MBV and D10 (particle size at which 10 percent is smaller) of the p0.075 material were also related to HMA mixture rutting performance. The higher the MBV, the stiffer was the HMA mixture. Increasing the D10 particle size was found to reduce the tensile strength ratio of HMA mixtures (1). These findings were based on the AASHTO T 283 test, the SST Frequency Sweep at Constant Height (FSCH), and Simple Shear at Constant Height (SSCH) tests (AASHTO TP 7). AASHTO T 283 determines the ratio between the tensile strength of unconditioned and moisture-conditioned specimens subjected to a freeze-thaw cycle. In the FSCH test, an HMA specimen is subjected to a sinusoidal shear strain applied at different frequencies while a vertical load is also applied to keep the specimen height con- stant. In this test, the stiffness of the specimen is determined as a function of frequency. In the SSCH test, a constant shear load is applied to an HMA specimen while keeping the spec- imen height constant. Aggregate Test Results Coarse Aggregate Table 6 lists the type, source location, and properties of the coarse aggregates used in the study. Two traprock sources were evaluated, but only Traprock #88 was used in the performance 10

tests. The research team was unable to produce an acceptable mixture design with the coarser traprock (#78). Laboratory Sample Results Before completing mixture designs, samples of each coarse aggregate were received in the laboratory from the aggregate manufacturers. These samples were tested for the various properties shown in Table 6. Flat or elongated particle percentages were separately determined on two size fractions, 12.5 mm to 9.5 mm and 9.5 mm to 4.75 mm. The weighted averages reported were com- puted based on the amount of each size fraction in the actual coarse aggregate gradation. Determining the percentage of flat or elongated and flat and elongated particles at the 3:1 ratio was added during the course of the research. The uncompacted voids of Method A (UVA) were meas- ured on a standard coarse aggregate specimen consisting of 1,970 g of 12.5-mm to 9.5-mm and 3,030 g of 9.5-mm to 4.75-mm aggregate sizes. Uncompacted voids of Method B (UVB) were measured on two size fractions, 12.5 mm to 9.5 mm and 9.5 mm to 4.75 mm, separately. The void measure- ments on the two fractions were averaged and are reported as Method B values. The Micro-Deval (AASHTO TP 58) tests were performed on a standard specimen consisting of 750 g of 12.5-mm 11 Aggregate Type Dolomite Lime- stone Uncrushed Gravel Granite Trap- rock #78 Designation CA-1 CA-2 CA-3 CA-4 CA-5 Source Location Indiana Indiana Indiana North Carolina Virginia Nominal Maximum Size (mm) 12.5 12.5 12.5 12.5 12.5 Percent Passing 19.0 100 12.5 100 100 100 100 89.0 9.5 87.0 87.9 84.1 90.0 60.0 4.75 25.0 24.7 18.1 23.0 7.0 2.36 1.4 4.7 1.1 4.0 2.0 1.18 0.4 2.0 0.2 3.0 0.6 0.60 0.4 1.7 0.2 2.0 0.6 0.30 0.3 1.5 0.2 1.0 0.6 0.15 0.3 1.4 0.2 1.0 0.6 Si ev e Si ze (m m) 0.075 0.2 1.3 0.2 0.5 0.6 Dry Bulk Specific Gravity (ASTM C127) 2.734 2.550 2.598 2.649 2.897 Apparent Specific Gravity (ASTM C127) 2.825 2.752 2.742 2.705 2.981 Water Absorption, % (ASTM C127) 1.2 2.9 2.0 0.8 0.7 Flat or Elongated Particles (ASTM D4791), % 2:1 Ratio 3:1 Ratio 5:1 Ratio Flat and Elongated Particles (ASTM D4791), % 3:1 Ratio 5:1 Ratio 44.9 4.6 0.7 21.7 6.3 48.4 6.0 1.3 28.0 8.1 28.8 2.6 0.0 13.2 1.8 47.5 3.3 0.0 20.1 2.7 34.2 5.8 0.0 18.6 2.3 Uncompacted Voids, % Method A – AASHTO TP56 Method B – AASHTO TP56 51.2 49.8 48.2 49.6 42.2 42.9 48.9 49.1 46.8 48.4 Micro-Deval (AASHTO TP58), % 7.0 10.9 8.8 5.5 5.1 LA Abrasion Test (Type C Gradation - ASTM C96), % 23.0 24.8 18.8 18.9 13.6 Percent Fractured Particles (ASTM D5821), % 1 or more than 1 2 or more than 2 100 100 100 100 15 12 100 100 100 100 Clay Lumps and Friable Particles (AASHTO T112), % 0 0 0 0 0 Magnesium Sulfate Soundness Test, 5 cycles (AASHTO T104), % 0.8 6.3 6.6 0.4 0.9 Traprock #88 CA-5b Virginia 12.5 100.0 100.0 85.4 11.2 1.3 0.6 0.6 0.6 0.6 0.6 2.910 2.989 0.9 35.5 2.0 0 11.6 2.7 48.0 48.8 4.6 14.3 100 100 0 1.0 Table 6. Coarse aggregate description, location, and properties.

to 9.5-mm, 375 g of 9.5-mm to 6.7-mm, and 375 g of 6.7-mm to 4.75-mm aggregate sizes. The total, combined specimen was placed in the Micro-Deval metal container and filled with approximately 2 liters of water. The sample was soaked for a minimum of 1 hour. After soaking, 5,000 g of steel balls were introduced into the container. The con- tainer was then placed on the Micro-Deval machine and rotated for 105 minutes. After this, the sample was washed over the 4.75-mm and 1.18-mm sieves, recombined, and oven dried. The loss is the amount of material passing the 1.18-mm sieve expressed as a percentage of the original sample mass. Los Angeles abrasion loss (ASTM C 96) was determined on a Type C specimen consisting of 2,500 g of 9.5-mm to 6.3- mm and 2,500 g of 6.3-mm to 4.75-mm size particles. Magnesium sulfate soundness loss (AASHTO T 104) val- ues were measured on material retained on the 9.5-mm and 4.75-mm sieves and are reported as the weighted average on the basis of the original gradations. The bulk specific gravity and water absorption values of the coarse aggregates were determined according to the ASTM C 127 method. Field Results In addition to testing aggregate samples received from the producers for mixture design purposes, flat and/or elongated tests were conducted on aggregate samples taken from the HMA plant stockpiles, aggregate recovered from plant-produced mixtures, and aggregate recovered from APT test section cores after binder extractions. Table 7 lists the flat and/or elongated values of the coarse aggregates from these sources. The data in Table 7 show that the 2:1 flat or elongated ratios (FOE21) are somewhat variable throughout the con- struction process. The FOE21 may show some changes in particle shape from the stockpiles through the HMA mix- ture production and construction process, but it is not con- clusive. Some of the variability could result from coring because it is often difficult to discard all the aggregate pieces on the edge of the core that were cut by the core barrel dur- ing the coring procedure. As shown in Table 7, the uncom- pacted voids measured on samples taken from the HMA plant stockpiles indicated little change except for dolomite and granite. 12 Flat or Elongated Particles, 2:1 Ratio Mixture CA-1 CA-2 CA-3 CA-4 CA-5b Coarse Aggregate Dolomite Limestone Gravel Granite Traprock#88 Mixture Design 49 48 27 46 34 HMA Plant Stockpile 45 45 35 55 34 HMA Plant Mixture 41 50 29 38 34S am pl e So ur ce APT Cores 37 49 35 41 33 Flat or Elongated Particles 5:1 Ratio Mixture CA-1 CA-2 CA-3 CA-4 CA-5b Coarse Aggregate Dolomite Limestone Gravel Granite Traprock#88 Mixture Design 1 1 0 0 0 HMA Plant Stockpile 1 1 0 0 0 HMA Plant Mixture 2 2 0 1 0S am pl e So ur ce APT Cores 1 0 0 0 0 Flat and Elongated Particles 5:1 Ratio Mixture CA-1 CA-2 CA-3 CA-4 CA-5b Coarse Aggregate Dolomite Limestone Gravel Granite Traprock#88 Mixture Design 6 8 2 3 3 HMA Plant Stockpile 6 8 1 7 3 HMA Plant Mixture 8 8 1 4 2S am pl e So ur ce APT Cores 5 4 2 6 2 Uncompacted Voids Content, Method A, % Mixture CA-1 CA-2 CA-3 CA-4 CA-5b Coarse Aggregate Dolomite Limestone Gravel Granite Traprock#88 Mixture Design Material 51.2 48.2 42.2 48.9 48.0 Sa m pl e So ur ce HMA Plant Stockpile 48.8 48.3 42.7 50.6 48.5 Table 7. Coarse aggregate test data.

13 40 45 50 55 25 35 45 55 65 FOE21, % U V A ,% CA-1 CA-2 CA-3 CA-4 CA-5b UVA = 0.27FOE21 + 36.31 R2 = 0.55 Note: Large symbols are data from mixture design phase. Small symbols are from HMA plant stockpiles. Figure 4. Coarse aggregate UVA and FOE21 relationship. Figure 4 shows the relationship between coarse aggregate UVA and FOE21. Data obtained during the HMA mixture design phase are shown by the larger symbols and those from HMA plant stockpiles are shown by the small symbols. There is a positive correlation between UVA and FOE21. As FOE21 increases, so does the UVA. Fine Aggregate Description, source location, and properties of the fine aggregates used in the study are listed in Table 8. Initially, six fine aggregate types were used in the HMA mixture designs, but acceptable mixture designs could not be obtained using the FA-5 and FA-6 aggregates. As a remedy, different dolomite (FA-5b) and traprock (FA-6b) sands were used. Mixtures using these alternate sands produced desirable vol- umetric properties. Mixtures with the original dolomite (FA-5) and traprock (FA-6) fine aggregates were not used in the study. Aggregate Type Natural Sand A Crushed Gravel Sand Natural Sand B Granite Sand Dolomite Sand1 Traprock #161 Designation FA-1 FA-2 FA-3 FA-4 FA-5 FA-6 Source Location Indiana Indiana Ohio North Carolina Indiana Virginia Percent Passing 9.5 100 100 100 100 100 100 4.75 100 100 100 99.0 98.4 95.0 2.36 89.9 81.8 85.3 83.0 71.6 57.0 1.18 59.2 50.6 61.9 57.0 31.7 34.0 0.60 30.4 30.8 37.5 40.0 15.0 20.0 0.30 9.0 17.2 18.0 27.0 6.0 12.0 0.15 1.6 7.3 6.1 19.0 1.7 6.0Si ev e Si ze (m m) 0.075 0.8 3.5 3.2 13.0 0.7 2.7 Dry Bulk Specific Gravity (ASTM C128) 2.585 2.660 2.586 2.639 2.665 2.911 Apparent Specific Gravity (ASTM C128) 2.714 2.782 2.735 2.689 2.830 3.003 Water Absorption, % (ASTM C128) 1.8 1.6 1.9 0.7 2.2 1.0 Particle Size of p0.075 Materials D60, microns D30, microns D10, microns 20.2 9.7 2.8 14.3 7.0 2.2 12.2 5.6 2.0 13.4 6.6 2.8 17.9 8.4 2.7 11.6 5.4 2.0 Uncompacted Void Content, % Method A - ASTM C1252 Method B - ASTM C1252 VTM5 40.3 43.1 44.0 46.1 50.4 51.6 41.9 46.4 47.3 49.1 53.0 54.4 45.0 49.9 51.4 48.8 53.6 55.0 Methylene Blue Value (AASHTO TP57) 3.3 1.3 5.0 8.0 0.5 6.8 Clay Content by Sand Equivalent (AASHTO T104), % 98 90 82 70 100 86 Magnesium Sulfate Soundness, 5 cycles (AASHTO T104), % 9 13 24 13 9 7 Micro-Deval (Ontario Test Method LS-619), % 10.0 17.0 20.4 10.6 5.8 12.1 1Used during the initial HMA mixture design Dolomite Sand2 Traprock #132 FA-5b FA-6b Indiana Virginia 100.0 100.0 100.0 96.0 81.3 70.1 51.7 49.1 33.4 35.6 19.5 25.7 10.5 16.8 5.7 9.7 2.634 2.892 2.820 3.007 2.5 1.3 18.4 8.2 2.5 10.9 5.0 1.8 46.8 50.9 51.9 49.2 53.6 55.1 2.8 5.1 79 70 30 13 18.1 14.5 Table 8. Fine aggregate description, location, and properties.

Laboratory Sample Results Before completing mixture designs, samples of each of the fine aggregates were received in the laboratory from the aggregate producers. These samples were tested for the vari- ous properties shown in Table 8. The fine aggregate test results in Table 8 show a wide range in test values. The uncompacted voids contents were meas- ured by three methods, Methods A and B of ASTM C 1252, and the VTM5 method. Equipment for the VTM5 method is basically a larger scale of the ASTM C 1252 apparatus. In Method A, voids were determined using a standard fine aggregate specimen consisting of 44 g of 2.36- to 1.18-mm, 57 g of 1.18- to 0.60-mm, 72 g of 0.60- to 0.30-mm, and 17 g of 0.30- to 0.15-mm size fractions. In Method B, the voids of three individual size fractions were determined (i.e., 2.36 mm to 1.18 mm, 1.18 mm to 0.60 mm, and 0.60 mm to 0.30 mm). These three individual measurements were averaged and reported as the Method B value. The VTM5 procedure is sim- ilar to the ASTM C 1252, Method B, procedure. Three size fractions, 2.36 to 1.00 mm, 1.00 to 0.60 mm, and 0.60 to 0.30 mm, were used. Results indicate that using 1.00 or 1.18 mm as a size break was insignificant because sieving the 2.36- to 1.18-mm fraction on the 1.00-mm sieve produced a negligi- ble number of particles. Particle size analyses were conducted on the p0.075 mate- rial using a Horiba LA500 Particle Size Analyzer. The sizes at 60 (D60), 30 (D30), and 10 (D10) percent of the fraction smaller than 0.075 mm were determined. The MBV test is used to determine the amount and nature of potentially harmful materials, such as clay and/or organic material, that may be present in the p0.075 fraction. The sand equivalent test is used to measure the relative amount of clay- sized particles in a fine aggregate. Tests were performed on material passing the 4.75-mm sieve. Magnesium sulfate soundness of each material was determined for material passing the 4.75-mm sieve. Mate- rial retained on the 2.36-, 1.18-, 0.60-, and 0.30-mm sieves were tested separately. The sample mass of each size frac- tion was approximately 300 g. Each sample was soaked for 16 to 18 hours and oven dried for 6 to 8 hours. After five cycles of soaking and drying, each sample was washed over the same sieve on which it was retained before the test. Material loss of each size fraction was computed as the per- centage of the original mass. Based on the individual frac- tion loss, the weighted averages were computed based on the percentage of each size fraction in the original fine aggregate gradations. Micro-Deval tests were performed in accordance with the Ontario Test Method LS-619. A 500-g mass of each sample was prepared by combining six individual size fractions of material between the 4.75- and 0.075-mm sieves. The amount of material on each size fraction was designed such that the combined sample had a fineness modulus of 2.8. In the test, samples were placed into the Micro-Deval jars and approxi- mately 750 mL of water was added. The samples were allowed to saturate for 24 hours. Approximately 1,250 g of steel balls were then put into the jars containing the sample and water. The jars were placed on the Micro-Deval machine and rotated for 15 minutes. Samples were then washed over the 0.075-mm sieve and losses computed as the amount of material passing the 0.075-mm sieve expressed as the percentage of the origi- nal sample mass. The bulk specific gravity and absorption values of the fine aggregates were determined according to the ASTM C 128 method. Field Results In addition to testing laboratory samples received from aggregate producers, aggregate samples collected from the HMA plant stockpiles and recovered from plant-produced mixtures and APT cores were also tested. The fine aggregate UVA and MBV test results are listed in Table 9. For the UVA results, there is good agreement between the field results and those obtained from laboratory samples. Some degradation did occur during mixture production and placement. Similarity of fine aggregate UVA test results obtained for the laboratory mixture design aggregate and the aggregate from the HMA plant stockpiles suggests that degradation during material handling and transportation was not sig- nificant; however, increased degradation did occur during HMA production. The UVA of fine aggregates extracted from the HMA plant mixtures were consistently lower than those from the HMA plant stockpiles. The difference between the UVA values for the HMA plant stockpiles and the HMA plant mixtures was divided by the initial UVA of the aggregate sampled from the HMA plant stockpiles. This index indicated the amount of relative degradation result- ing from HMA mixture production for each aggregate. As shown in Figure 5, the degradation is correlated to the ini- tial UVA values. Fine aggregates with initially high UVA val- ues appear to degrade more than do those with initially low UVA values. There is reasonable agreement between field MBV values and those obtained on laboratory samples, except for FA-1, FA-4, and FA-6b aggregates. According to the AASHTO TP 57 test method, the mixture design results (laboratory samples) for FA-1 and FA-6b indicate that the aggregates should have excellent performance while the stockpile results indicate they are marginally acceptable. However, for the FA-4 aggregates, the stockpile results indicated acceptable performance, but the mixture design results were marginally acceptable. For 14

these three aggregates, the materials delivered to the hot-mix plant apparently had fines that were somewhat different from the materials used in the mixture design. Mixture Designs All mixtures were designed using the Superpave volumet- ric mixture design method outlined in the Asphalt Institute Manual, SP-2, Superpave Level I Mix Design, and subsequent addendum. The number of design gyrations, Ndes, and max- imum number of gyrations, Nmax, used for all designs were 100 and 160, respectively. This compaction effort was selected based on a design Equivalent Single Axle Load (ESAL) level of 3 to 30 million. Before compaction, all mix- tures were aged for 2 hours at the compaction temperature. Design binder contents were selected at 4-percent air voids using specimens compacted to the Ndes value. Once the design binder content was selected, additional specimens were compacted to Nmax to ensure that the mixture density at this point was less than 98 percent of the maximum theoret- ical density. A 12.5-mm NMAS was used for all mixtures because of its wide use by highway agencies for HMA surface mix- tures. A single, unmodified asphalt binder, PG 64-22, was used in all mixtures, because it represents a typical neat binder grade for much of the United States and is included in most specifications. The experiments were designed to assess aggregate contribution to HMA mixture perform- ance. The complete binder and mixture design data are included in Appendix B, which is available in NCHRP Web- Only Document 82. Coarse-Graded Mixtures A natural sand with a UVA of 40.3 percent was used as the fine aggregate for all coarse HMA mixtures. The coarse- graded mixture design data are given in Table 10. Traprock #78 was initially used in the laboratory mixture design process. However, because of the low design binder content and VMA values, a different traprock stockpile (Traprock #88) was evaluated and a second mixture design conducted with this aggregate. This second mixture was used in APT testing. Fine-Graded Mixtures A natural uncrushed gravel with a UVA of 42.2 percent was used as the coarse aggregate for all fine-graded HMA mixtures 15 Mixture ID FA-1 FA-2 FA-3 FA-4 FA-5b FA-6b Aggregate Type Natural Sand A Crushed Gravel Sand Natural Sand B Granite Sand Dolomite Sand Traprock Sand Uncompacted Voids Content, % Mixture Design 40.3 46.1 41.9 49.1 46.8 49.2 HMA Plant Stockpile 39.2 47.6 42.0 48.9 46.2 49.3 HMA Plant Mixture 38.7 45.1 40.9 46.2 45.0 46.6 APT Cores 38.3 44.7 41.0 45.5 45.1 46.4 Methylene Blue Value Mixture Design 3.3 1.3 4.9 11.1 2.8 5.1 Sa m pl e So ur ce HMA Plant Stockpile 7.8 1.3 5.5 5.8 2.8 6.9 Table 9. Fine aggregate uncompacted voids content (Method A) and methylene blue values. y = 0.42x - 15.16 R2 = 0.84 0 1 2 3 4 5 6 35 40 45 50 55 Plant Stockpile UVA, % U V A R ed uc tio n % In iti al V al ue Figure 5. Fine aggregate degradation.

in the rutting and fatigue studies. The mixture design data are shown in Table 10. Mixtures FA-5 and FA-6 are dolomite and traprock fine- graded aggregate mixtures, respectively. The compacted HMA mixtures using the original dolomite (Mixture FA-5) and traprock (mixture FA-6) sands had high VMA values resulting in voids filled with asphalt (VFA) values above the maximum allowed by specification. To remedy this problem, different dolomite and traprock fine aggregate stockpiles were identi- fied. These two new fine aggregates (FA-5b, FA-6b) had higher percentages of p0.075 material than the original materials (see Table 8). Mixture design results for these mixtures are shown in Table 10. Both have VFA values within the specification lim- its. Their dust proportions also increased considerably. Moisture Susceptibility Mixtures Five of the six fine aggregates used in the rutting study were selected for the moisture susceptibility experiment. Each fine aggregate was combined with a common, crushed dolomite coarse aggregate and mixture designs were completed; mix- ture design data are given in Table 10. 16 Coarse-Graded Mixtures (Rutting and Fatigue) VMA VFA %GmmMix No. Pb (Pbe) Gmm Ndes Nmax Ndes Nmax DP Nini Nmax Gse Gsb CA-1 5.7 (4.7) 2.524 14.9 14.1 73.4 78.8 0.7 86.0 97.0 2.766 2.689 CA-2 6.1 (4.4) 2.447 14.0 13.2 71.5 76.7 0.9 85.4 96.9 2.688 2.566 CA-3 3.9 (2.9) 2.511 10.8 9.9 63.6 70.2 1.1 88.5 97.1 2.665 2.600 CA-4 5.8 (5.3) 2.461 16.0 15.1 75.1 80.8 0.7 87.0 97.1 2.691 2.652 CA-51 3.7 (3.1) 2.664 11.4 10.3 66.2 75.1 1.2 89.1 97.4 2.838 2.786 CA-5b2 4.8 (4.3) 2.630 14.3 13.6 72.0 77.5 0.6 88.2 97.0 2.853 2.808 1 Contained Traprock #78 and was not tested in the APT 2 Contained Traprock #88 and was tested in the APT Fine-Graded Mixtures (Rutting and Fatigue) VMA VFA %Gmm Mix No. Pb (Pbe) Gmm Ndes Req’d. Ndes Req’d. DP Nini Nmax Gse Gsb FA-1 6.0(4.9) 2.438 15.3 74.0 0.4 90.8 96.7 2.671 2.594 FA-2 5.7(5.3) 2.447 16.2 75.2 0.7 88.3 96.9 2.669 2.638 FA-3 5.8(4.8) 2.444 15.0 73.6 0.8 88.9 97.1 2.672 2.602 FA-4 4.9(4.5) 2.460 14.3 73.0 1.9 88.1 97.3 2.651 2.625 FA-53 7.4(5.7) 2.458 17.4 77.0 0.4 87.1 97.6 2.766 2.642 FA-63 6.3(5.8) 2.565 18.0 77.9 0.6 87.2 97.4 2.851 2.811 FA-5b4 6.3(5.1) 2.454 15.8 74.7 0.7 87.5 97.4 2.705 2.620 FA-6b4 4.9(4.3) 2.619 14.4 14.0 72.2 65-75 1.6 87.7 97.2 2.845 2.797 3 Originally designed, but not tested in the APT 4 Prepared using fine aggregates from different source or gradation and tested in the APT Fine-Graded Mixtures (Moisture Susceptibility) VMA VFA %Gmm Mix No. Pb Gmm Ndes Req’d Ndes Req’d DP Nini Nmax Gse Gsb FAM-1 6.1 2.481 15.6 74.4 0.7 90.1 96.9 2.728 2.648 FAM-2 6.4 2.485 16.8 76.4 0.9 87.6 97.2 2.748 2.687 FAM-3 5.4 2.488 15.3 74.3 1.7 87.5 97.2 2.707 2.671 FAM-45 6.5 2.588 18.3 78.4 0.8 86.8 97.3 2.894 2.848 FAM-4b6 5.3 2.650 15.0 73.3 1.4 86.7 97.3 2.904 2.835 FAM-5 6.1 2.469 15.9 14.0 74.8 65-75 0.7 88.9 96.8 2.715 2.650 5 Originally designed, but not tested in the APT 6 Prepared using fine aggregates from the same source, but different gradation and tested in the APT Table 10. Mixture design data (at 4 percent air voids).

Accelerated Pavement Test Results Accelerated pavement tests were conducted at the APT facility at the Indiana DOT Research Division in West Lafayette, Indiana. Up to four test lanes can be constructed in this facility at a time using conventional paving equipment. Details of the facility, test section construction, and data col- lection can be found in Appendix D, which is available in NCHRP Web-Only Document 82. Rutting Rutting was monitored by recording transverse surface profiles at increments of traffic applied with dual tires and without wander. These profiles were captured with software that automatically reduces and stores the data in a spread- sheet (7). An initial profile was recorded before traffic appli- cation and used as the baseline reference for determining rutting from subsequent profiles. Each test lane was trafficked until a total rut depth of 20 mm was achieved or 20,000 wheel passes were applied, whichever occurred first. Profiles were recorded at nine locations over the length of a given test section; however, three consecutive sections nearest the center of the test section (Sections 4, 5, and 6, see Figure D.8) were averaged and used as a single result in the subsequent analyses. These three locations were used because the APT wheel carriage travels at a constant speed over this portion of the test lane. Performance Coarse-Graded Mixtures. Rutting in the APT as a function of wheel passes for the coarse-graded mixtures is shown in Figure 6. In addition to total rut depth, the rut rate was also computed. Rut rate is simply the slope of the regres- sion line and has units of mm/log(N) where N is the num- ber of wheel passes. Rutting data for mixtures CA-1, CA-2, CA-3, and CA-5b exhibited a bilinear trend; these data were fitted by two logarithmic functions. The rut rate during the early traffic stage is the slope of the first regression line while the rut rate during later traffic stage is the slope of the sec- ond regression line. The regression equations for all mix- tures are given in Table 11. Rutting performance parameters for coarse-graded mix- tures are shown in Table 12. These parameters include total rut depth at 5,000 and 20,000 wheel passes as well as the rut rate during early and later traffic stages (early and late stages are defined by the N break point shown in the table). As an example, for mixture CA-2, early traffic is where N200, while late traffic is N200. For each of the rutting performance parameters, mixtures are ranked from 1 (best) to 5 (worst). The mixtures were ranked by four parameters; three of the mixtures were ranked the same by the four parameters; however, the early rut rate inverts 1 and 2, and 3 and 4. This would seem to indicate that after approxi- mately 200 wheel passes are applied with the APT, one can obtain a good indication of the relative rutting rank of an HMA mixture. Fine-Graded Mixtures. APT rutting of the fine-graded mixtures is shown in Figure 7. Testing on Mixture FA-1 (Nat- ural Sand A) was terminated at 1,000 wheel passes because of excessive total rut depth. Testing on Mixture FA-2 was termi- nated inadvertently at 12,500 wheel passes; however, the trend for this mixture shows that it would have most likely accom- modated additional passes with a minimal increase in rutting. Rut development curves for fine-graded mixtures also appear to be bilinear. As above, the first regression line repre- sents early traffic stage rutting and the second later traffic 17 0 5 10 15 20 25 30 35 1 10 100 1000 10000 100000 Number of Wheel Passes, N A ve ra ge T ot al R ut D ep th , m m CA-1 CA-2 CA-3 CA-4 CA-5b Figure 6. Coarse-graded mixture rut depth development. Mixture ID Regression Equation Condition Total rut depth = 1.56 log(N) + 0.28 for N < 400CA-1 Total rut depth = 2.25 log(N) -1.50 for N > 500 Total rut depth = 1.89 log(N) + 0.17 for N < 200CA-2 Total rut depth = 3.56 log(N) -3.74 for N > 200 Total rut depth = 4.88 log(N) – 1.27 for N < 200CA-3 Total rut depth = 14.72 log(N) – 26.02 for N > 200 CA-4 Total rut depth = 1.75 log(N) – 0.13 for all N Total rut depth = 2.09 log(N) – 0.01 for N < 200CA-5b Total rut depth = 3.27 log(N) – 2.66 for N > 200 Table 11. Coarse-graded mixture rutting regression equations.

stage rutting. Regression equations for the data are given in Table 13. Table 14 lists total rut depths at 1,000; 5,000; and 20,000 wheel passes and rutting rates for both early and later traffic stages. These rutting parameters were used as the basis for ranking mixture performance from 1 (best) to 6 (worst). Overall rank is the rank appearing the most number of times for each mixture. Three of the parameters (rut depth at 5,000 and 20,000, and rut rate at later traffic) rank the mixtures the same. The remaining two parameters rank the mixtures the same, but have 3 and 4 inverted from the previous three parameters. Again, it appears that a good indication of the rut resistance can be gained after approximately 200 wheel passes of the APT. Moisture Susceptibility Before APT testing, six cores were taken from each of the moisture susceptibility test lanes. In-place densities and air voids of the test lanes were determined from the cores, which were then used to test the plant-produced mixtures for mois- ture susceptibility in accordance with AASHTO T 283. In addition to moisture conditioning, the conditioned speci- mens were also subjected to one freeze/thaw cycle before being tested in indirect tension. The AASHTO T 283 test results are shown in Table 15.Aver- ages of VTM ranged from 7.1 to 9.9 percent. Degree of satu- ration for the conditioned specimens varied from 67.4 to 78.2 percent. The tensile strength ratio (TSR) [the ratio of the indi- rect tensile strength of conditioned specimens to that of dry (unconditioned) specimens] varied from 1.10 to 0.79. Some specimens were loaded until they cracked. The interior sur- faces were then inspected for stripping and photographs were taken. Visual observation indicated that stripping occurred. Typically, conditioned specimens lost their glossy appearance and the interior surface exhibited a brownish tint (see Figures E.1 to E.5 in Appendix E provided in NCHRP Web-Only Doc- ument 82). Stripping in terms of lost binder film was also observed in specimens with dolomite coarse aggregate. Performance Rutting accumulation for all test lanes is shown in Figure 8. A 20-mm total rut depth criteria was adopted for traffic ter- mination. Mixture FAM1 (Natural Sand A) was terminated at 1,000 wheel passes, while mixture FAM5 (Natural Sand B) reached the 20-mm total rut depth criteria and was terminated at 7,500 wheel passes. The FAM5 mixture exhibited a signifi- cant increase in rutting between 5,000 and 7,500 wheel passes. There was also an increase in rutting after 3,000 wheel passes on mixture FAM3 (Granite Sand). In general, this type of rutting does not occur in dry rutting tests and may be an indi- cation of stripping. The rutting data for mixtures FAM1, FAM2, and FAM4 do not show a change in rate of rutting accumulation. 18 Mixture ID Total Rut Depth at 5,000 Passes Total Rut Depth at 20,000 Passes Total Rut Rate (mm/log(N)) Overall mm Rank mm Rank Early traffic Rank Later Traffic Rank Rank CA-1 7.1 2 7.6 2 1.6 1 2.3 2 2 CA-2 9.5 4 11.3 4 1.9 3 3.6 4 4 CA-3 29.5 5 —1 —1 4.9 5 14.7 5 5 CA-4 6.3 1 7.2 1 1.8 2 1.8 1 1 CA-5b 9.2 3 11.1 3 2.1 4 3.3 3 3 1 Tested to only 5,000 wheel passes. Table 12. Coarse-graded mixture rutting performance. 0 5 10 15 20 25 30 35 1 10 100 1000 10000 100000 Number of Wheel Passes, N A ve ra ge T ot al R ut D ep th , m m FA-1 FA-2 FA-3 FA-4 FA-5b FA-6b Figure 7. Fine-graded mixture rut depth development.

The rutting data were also plotted as a function of the log of the number of wheel passes (see Figure 9). This plot shows that the rutting of mixtures FAM1, FAM2, FAM3, and FAM5 appears to be bilinear. As a result, data for these mix- tures were fitted with two logarithmic regression lines. The regression equations for all mixtures are shown in Table 16. Table 17 shows total rut depths for 1,000; 5,000; and 20,000 wheel passes and total rutting rates for early and later traffic stages. These rutting parameters were used in ranking per- formance. Among these rutting parameters, only total rut depth at 1,000 wheel passes and total rutting rate are available for all mixtures. Based on these rutting parameters, the mix- tures were ranked from 1 (best) to 5 (worst). Overall per- formance rank from best to worst are FAM2 (Crushed Gravel Sand), FAM3 (Granite Sand), FAM4 (Traprock Sand), FAM5 (Natural Sand B), and FAM1 (Natural Sand A). 19 Mix ID Regression Equation Condition Total rut depth = 7.26 log(N) - 2.78 for N < 100FA-1 Total rut depth = 21.10 log(N) - 33.33 for N > 200 Total rut depth = 3.81 log(N) – 0.74 for N < 200FA-2 Total rut depth = 5.00 log(N) – 3.29 for N > 300 Total rut depth = 2.78 log(N) – 0.52 for N < 200FA-3 Total rut depth = 4.02 log(N) – 3.56 for N > 300 Total rut depth = 1.06 log(N) – 0.61 for N < 200FA-4 Total rut depth = 1.63 log(N) – 1.84 for N > 300 Total rut depth = 2.75 log(N) – 0.004 for N < 400FA-5b Total rut depth = 4.45 log(N) – 4.70 for N > 500 Total rut depth = 2.10 log(N) – 0.57 for N < 200FA-6b Total rut depth = 3.31 log(N) – 3.54 for N > 300 Table 13. Fine-graded mixture rutting regression equations. Total Rut Rate (mm/log (N)) Early Traffic Later TrafficMix ID Rut Depth at 1,000 Passes (mm) R an k Rut Depth at 5,000 Passes (mm) R an k Rut Depth at 20,000 Passes (mm) R an k R an k R an k Overall Rank FA-1 30.6 6 NA1 NA1 7.3 6 21.1 6 6 FA-2 11.1 5 15.4 5 18.12 5 3.8 5 5.0 5 5 FA-3 8.6 4 11.3 3 15.5 3 2.8 4 4.0 3 3 FA-4 2.8 1 4.3 1 5.4 1 1.1 1 1.6 1 1 FA-5b 8.4 3 11.7 4 16.8 4 2.8 3 4.5 4 4 FA-6b 6.4 2 8.7 2 10.4 2 2.1 2 3.3 2 2 1Testing was terminated at 1,000 wheel passes because total rut depth was more than 20mm 2Testing was inadvertently terminated at 12,500 wheel passes; total rut depth at 20,000 wheel passes was predicted using the regression equation. Table 14. Fine-graded mixture rutting performance. Mixture ID FAM1 FAM2 FAM3 FAM4 FAM5 Aggregate Type Natural Sand A Crushed Gravel Sand Granite Traprock Natural Sand B Dry Specimens Tensile Strength, kPa 452.3 689.6 837.7 652.8 808.7 Average Air Voids, % 8.4 9.1 8.3 9.9 7.1 Conditioned Specimens Tensile Strength, kPa 499.4 621.2 708.1 537.0 640.2 Average Air Voids, % 9.1 9.2 8.2 9.4 7.5 Degree of Saturation, % 70.9 78.2 67.4 69.2 71.4 TSR 1.10 0.90 0.85 0.82 0.79 Methylene Blue Value 3.3 1.3 8.0 5.1 5.0 Table 15. AASHTO T 283 and MBV test results.

When APT traffic application was complete, cores were collected and split open to determine visually if stripping had occurred. Photographs of the split surfaces are shown in Fig- ures E.6 through E.10 (Appendix E). Visual inspection revealed no stripping of FAM1, FAM2, and FAM4 cores. There was a loss of glossiness on the split surfaces of FAM3 (Granite Sand) and FAM5 (Natural Sand B). These two mix- tures also exhibited signs of stripping in their rutting data. Signs of stripping were observed on the bottom of cores taken from all of the test lanes. Fatigue Relationships between fatigue cracking and coarse and fine aggregate properties were evaluated through construction and testing of six mixtures in the APT as indicated in Table 18. Fatigue performance was characterized by percentage of fatigue cracking in the wheel path. The experiment is similar to the rutting experiment, with the exception that a conven- tional flexible pavement was installed consisting of 100 mm of HMA and 200 mm of a crushed stone on a subgrade. An attempt was made to control the pavement test temperature at approximately 10 to 20°C. However, because of the unavail- ability of a cooling system, this temperature range was exceeded for the tests conducted in June and July. The six experimental fatigue mixtures listed in Table 18 were selected based on the earlier APT rutting performance and aggregate quality. Mixtures were selected to have as wide a range in both rutting performance and aggregate quality as possible. Of the six mixtures, three were coarse- graded and three were fine-graded. Mixture FA-1 (Natural Sand A) had the poorest aggregate qualities and exhibited the worst rutting performance. The mixture was included, even though such a mixture probably would be replaced in the field before failing in fatigue. Testing mixtures with the greatest range of aggregate quality, as determined by the aggregate test methods, were expected to provide the most useful information for determining the strength of the relationships between the aggregate properties and fatigue performance. 20 0 5 10 15 20 25 30 0 5000 10000 15000 20000 Number of Wheel Passes, N A ve ra ge T ot al R ut D ep th , m m FAM1 Natural Sand A, IN FAM2 Crushed Gravel Sand, IN FAM3 Granite Sand, NC FAM4 Traprock Sand, VA FAM5 Natural Sand B, OH Figure 8. Rut depth development. 0 5 10 15 20 25 30 1 10 100 1000 10000 100000 Number of Wheel Passes, N A ve ra ge T ot al R ut D ep th , m m FAM1 Natural Sand A, IN FAM2 Crushed Gravel Sand, IN FAM3 Granite Sand, NC FAM4 Traprock Sand, VA FAM5 Natural Sand B, OH Figure 9. Rut depth development. Mix ID Regression Equation Condition Total rut depth = 6.82 log(N) - 2.40 for N < 200FAM1 Total rut depth = 26.88 log(N) – 52.53 for N > 300 Total rut depth = 1.62 log(N) + 0.77 for N < 200FAM2 Total rut depth = 2.31 log(N) – 0.89 for N > 300 Total rut depth = 2.18 log(N) – 1.32 for N < 1000FAM3 Total rut depth = 4.88 log(N) – 10.16 for N > 2000 FAM4 Total rut depth = 2.53 log(N) – 0.69 for all N Total rut depth = 3.31 log(N) – 1.14 for N < 400FAM5 Total rut depth = 8.03 log(N) – 13.94 for N > 500 Table 16. Regression equations.

Based on rutting performance from best to worst, the fine- graded mixtures selected for the fatigue study were FA-4 (Granite), FA-3 (Natural Sand B), and FA-1 (Natural Sand A). Likewise, coarse-graded mixtures were CA-4 (Granite), CA-2 (Limestone), and CA-3 (Uncrushed Gravel). Test Section Construction The first step in constructing the fatigue test sections involved removing the previous rutting test sections. The underlying Portland concrete cement (PCC) slabs were then removed, along with the underlying pea gravel fill. Subse- quently, a subgrade soil was installed and compacted to a depth of 1.5 m. Moisture was added to the soil, and the two were mixed using two motorized tillers. Compaction was accomplished using vibrating plate compactors. The Proctor curve for the soil is shown in Figure 10. An attempt was made to compact the soil on the wet side of optimum in order to render the soil more plastic and thereby aid the pavement fatigue process. The optimum moisture content is approxi- mately 15 percent and the soil was compacted at 18- to 20- percent moisture. As can be seen from Figure 11, the California bearing ratio (CBR) value for moisture content in the desired range was approximately 2. The result was a “springy” subgrade that was indeed plastic. In fact, the sub- grade was so “springy” that construction was made difficult. It was later discovered that the drain for the APT pit was clogged and that excess moisture could not be drained from the soil. Once the drain was repaired, the excess moisture drained and the soil became stiffer. After subgrade compaction, a geotextile fabric was placed on the subgrade and an unbound, crushed stone base course was placed and compacted such that the finished base course was 200 mm in depth. The 100-mm deep HMA test section mixtures were then constructed on the base course using con- ventional HMA construction techniques as described in Appendix D (available in NCHRP Web-Only Document 82). Fatigue Testing Performance data were collected throughout the loading process, including transverse profiles when needed. Longitu- dinal and fatigue cracking were measured by counting the number of cracks that developed during loading. The fre- quency of measurement varied with test section and depended on how quickly the cracking occurred. From a fatigue standpoint, the criterion was established that a test 21 Total Rut Rate (mm/log(N)) Mix ID Total Rut Depth at 1000 Passes (mm) R an k Total Rut Depth at 5000 Passes (mm) R an k Total Rut Depth at 20000 Passes (mm) R an k Early Traffic Ra nk Late Traffic Ra nk O ve ra ll Ra nk FAM1 28.5 5 —1 —1 6.8 5 26.9 5 5 FAM2 6.1 2 7.6 1 9.2 1 1.6 1 2.3 1 1 FAM3 5.4 1 7.7 2 11.0 2 2.2 2 4.9 3 2 FAM4 7.1 3 8.8 3 9.9 3 2.5 3 2.5 2 3 FAM5 10.1 4 16.1 4 —2 3.3 4 8.0 4 4 1Testing terminated at 1,000 wheel passes; 20 mm rut depth reached. 2Testing terminated at 7,500 wheel passes; 20 mm rut depth reached. Table 17. Moisture susceptibility rutting performance. Aggregate TypeAggregate Performance Tests Category Coarse Aggregate Fine Aggregate CA-2 (Limestone) CA-3 (Uncrushed Gravel) Coarse Aggregate Test Methods Evaluation (Coarse-Graded Mixtures) CA-4 (Granite) Natural Sand A FA-1 (Natural Sand A) FA-3 (Natural Sand B) Fine Aggregate Test Methods Evaluation (Fine-Graded Mixtures) Uncrushed Gravel FA-4 (Granite) Table 18. Fatigue experiment design. 1650 1700 1750 1800 1850 5 10 15 20 25 Moisture Content (%) D en si ty (k g/ m 3 ) Figure 10. Subgrade Proctor curve.

section was considered to have failed when the center one- third of the test section had exhibited fatigue cracking exceed- ing 10 percent of the area. This center area of the test lane was chosen because it was expected to have the most uniform mixture properties. Random wheel wander was also incorpo- rated during testing to help avoid rutting; it was done by a random number generator within the APT control program. The fatigue results are shown in Table 19. The first test section to be trafficked in the fatigue experi- ment was the CA-3 (Uncrushed Gravel) mixture. Loading consisted of a 40 kN load on dual wheels with a tire pressure of 690 kPa. The section deformed quickly and failed after only 1,000 passes. The failure is shown in Figure 12. Three to four cracks appear in the center one-third of the test lane; however, inspection of the failure revealed that the subgrade failed before the fatigue properties of the mixture could be fully tested. Testing began on the next test section, CA-2 (Limestone), with a reduced load of 26.7 kN applied to the dual wheels and the tire pressure reduced to 620 kPa. After 8,000 passes, no signs of cracking were observed, so the load was increased to 33.3 kN and an additional 12,000 passes were applied. The load was then increased to 40 kN and the tire pressure increased to 690 kPa. Testing was stopped at 80,000 wheel passes because the section showed signs of subgrade failure near the edge of the test pit. Minor fatigue cracking developed in the section during application of the last 60,000 wheel passes as shown in Figure 13. Subgrade failure was repaired and traffic continued; however, damage at the edge continued to accumulate and it was necessary to discontinue trafficking of the section to avoid damage to the APT equipment. The third mixture to undergo fatigue testing was the FA-1 mixture produced using Natural Sand A. This test section proved difficult to compact during construction because of mixture tenderness and the resiliency of the section against which it was being compacted. As a result, numerous cracks occurred during compaction.These “roller”cracks were painted with a lime-water solution so as to appear white to distinguish them from cracks caused by APT loading.The existence of these cracks from the outset of the testing most certainly influenced the fatigue results of the section. The section before traffic is 22 Test Mixture Percent Cracking Average Total Rut Depth (mm) Number of Wheel Passes CA-2 1 None 80,000 CA-3 30 None 1,000 CA-4 None 40.0 20,000 FA-1 25 None 2,000 FA-3 None 33.6 20,000 FA-4 None 43.8 20,000 Table 19. Fatigue results. 0 5 10 15 5 10 15 20 25 Moisture Content (%) CB R Va lu e Figure 11. Soil CBR values. Figure 12. CA-3 test section after 1,000 wheel passes. Figure 13. CA-2 test section after 80,000 wheel passes.

shown in Figure 14. Trafficking of this test section began with an applied load of 31.1 kN and tire pressure of 690 kPa. As shown in Figure 15, the section exhibited substantial fatigue cracking when the testing was stopped after 2,000 passes. Fatigue testing of mixtures CA-2, CA-3, and FA-1 was finally completed in June 2003, and subsequently, the test sec- tions were removed. In July 2003, test sections of mixtures FA-3 (Natural Sand B), FA-4 (Granite), and CA-4 (Granite) were placed in the APT facility. Testing immediately began on the FA-3 mixture; rutting began to develop with no sign of fatigue cracking.Without the ability to control temperature in the APT facility, the test pavement temperatures were well over the desired temperature range of 10 to 20°C. This affected the 23 Figure 14. Initial FA-1 test section. Figure 15. FA-1 test section after 2,000 wheel passes. fatigue results of the last three APT test sections. Finally, in August 2003, trafficking was discontinued because 20,000 passes were applied on each section with no evidence of sig- nificant fatigue cracking; however, each section did show rut- ting. The FA-3 mixture (Natural Sand B) had an average rut depth of 33.6 mm, while the FA-4 (Granite) and CA-4 (Gran- ite) mixtures had average rut depths of 43.8 and 40.0 mm, respectively. Recently, cooling capabilities have been installed in the APT building and fatigue tests have been conducted. These tests indicate that, had the desired temperature range been maintained during the testing of the FA-3, FA-4, and CA- 4 mixtures, these mixtures probably would have sustained 80,000 to 100,000 APT wheel passes before failing in fatigue.

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TRB's National Cooperative Highway Research Program (NCHRP) Report 557: Aggregate Tests for Hot-Mix Asphalt Mixtures Used in Pavements examines performance-based procedures to test aggregates for use in pavements utilizing hot-mix asphalt (HMA) mixtures and provides guidance on using these procedures for evaluating and selecting aggregates for use in specific mixture applications. The appendices to NCHRP Report 557 are available as NCHRP Web-Only Document 82: Validation of Performance-Related Test of Aggregates for Use in Hot-Mix Asphalt Pavements: Appendixes A through F.

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