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About the Authors Dr. Mixture density and air void content workability problems, asphalt does have some effect are directly related.
HMA mixtures with below- The durability of an asphalt pavement is a minimum VMA values will have thin films of function of the air void content of the in-place asphalt and will provide an HMA pavement with HMA pavement.
The lower the air voids, the less low durability. Therefore, reducing asphalt content permeable the mixture becomes. An air void by lowering VMA is actually counterproductive and content that is too high provides passageways detrimental to pavement quality. An air void content that is too low can lead 2. Voids Filled with Asphalt VFA is the percentage The air voids in a paving mixture see Figure of inter-granular void space between the aggregate 2.
A certain percentage effective binder see Figure 2. VFA is used to of air voids is necessary in the finished HMA to ensure proper asphalt film thickness in the mix. The of temperature increases. In general, the design acceptable range of VFA varies depending upon air void level in a laboratory-compacted sample the traffic level. For special uses, a lower or because mixture strength and stability are a greater higher design air void content may be specified.
A VFA that is too graded mixes, pavement compaction achieve an high, however, may yield a tender mix and cause air void content of less than 8 percent to minimize bleeding.
Aggregate gradation must remain high enough to achieve an adequate is directly related to optimum asphalt content. Conversely, coarser in a mix that seems to have too much asphalt.
Total area and optimum asphalt content is most asphalt content is the amount of asphalt that must pronounced when mineral filler containing high be added to the mixture to produce the desired mix percentages of particles passing the No. Effective asphalt content is based on the 0. Variations volume of asphalt not absorbed by the aggregate— in the amount and the size of mineral filler at it is asphalt that effectively forms a bonding film on a constant asphalt content will cause changes the aggregate surfaces.
Small increases in optimum asphalt content because enough asphalt filler content will use up additional asphalt and must be added to the mix to allow for absorption produce a dry, unstable mix.
Small decreases have while still coating the aggregate particles with an the opposite effect. Too little filler results in a adequate film. The maximum size aggregate is generally 3.
However, this 3. Nevertheless, any properly designed HMA mix can generally serve at any level in the pavement. Additionally, based on the local strength requirements should not be compromised materials available, traffic loading and climate, regardless of the location of the mix within the other ingredients or additives may be required pavement.
All quality pavements should be public agencies. Historical pavement 3. Mixtures degree of design, production and construction are typically designed with layer thickness, control procedures should be used to ensure proper availability of aggregates and local history in performance of the pavement. In general, surface mixtures have greater A special type of surface mixture used for asphalt content than binder or base mixtures due reducing hydroplaning and increasing skid to their greater surface area and the higher VMA resistance is an open-graded friction course requirements of smaller maximum aggregate size OGFC , also known as a porous friction course mixtures.
PFC or popcorn mix. The function of this The nominal maximum aggregate size is one mixture is to provide a free-draining layer that size larger than the first sieve to retain more than permits surface water to migrate laterally 10 percent of the material. Nominal maximum aggregate 18 percent or higher. The choice of nominal in the mix. The open-graded mixture also maximum aggregate size is often predicated provides a skid-resistant surface as its coarse on the desired surface texture, with a smaller texture provides excellent friction between the maximum aggregate size producing a smoother, pavement and the tire, while reducing noise.
Figure 3. SMA is a graded mixture. Typically lift thicknesses are durable, rut-resistant mixture that relies on stone- two to three times the NMAS. OGFC surfaces should be relatively high percentage of asphalt binder— removed prior to any subsequent overlays being often polymer-modified—for durability. To placed. The be found in Section In addition to their inherent 3.
This heavy Ultrathin bonded wearing UTBW courses are membrane seals small cracks and helps to adhere the yet another surface mixture that deserves special overlay to the existing pavement.
The grade of the attention. Please see chapter 12 for additional asphalt binder, as with other pavement designs, is guidance on the design of ultrathin bonded wearing chosen based on the climate and traffic parameters courses. An ultrathin bonded wearing course is for the project location. These are usually a part choice. Specialty equipment is required to place both of a pavement preservation program for use on the emulsion and the HMA in a single operation.
The structurally sound materials. Ultrathin overlays concept of the ultrathin bonded wearing course is are a single layer of HMA placed on a heavy asphalt that the heavy shot of asphalt membrane is wicked emulsion layer or membrane. This emulsion is up, during construction, partially into the voids of typically polymer modified, although unmodified the gap-graded mix. Binder and base mixes are The next noteworthy system was the viscosity often used interchangeably in pavement design grading method AC developed by the Asphalt and construction.
Where heavy wheel loads Institute and the Federal Highway Administration are involved, a typical binder mix for highway in the late s. The AC system was further construction can be used as a surface mix if a coarser modified into the AR system by western U. This scuffing action of tight-radius, power steering turns. For compacted subgrade or over a granular base. Base most mix designers, determining the specific mixes are characterized by larger aggregate sizes that binder to be utilized on the project will have already range up to 3 inches 75 mm.
The relative asphalt been determined before the mix design phase. For content will be lower due to the larger maximum more binder specification, selection and testing aggregate size and its smaller surface area. Maximum aggregate sizes for Pavement experts from around the world have base mixtures are often established by the locally worked with industry to better shape the future available material.
Since aggregate properties eventually enter the pavement structure. Such play an essential role in overcoming permanent open-graded base mixtures, or Asphalt Treated deformation, much effort has been directed toward Permeable Base ATPB mixes, are designed to developing two categories of aggregate properties: provide an interconnecting void structure, using consensus properties and source properties.
It is 75 mm. Positive, free drainage must be important to thoroughly understand the impacts of incorporated in the overall pavement design with aggregate gradation for these distresses, and they these layers. See section Chapter 5, section 5. Materials near the of the final mix. Samples used in the mix design pavement surface subjected to high traffic levels must be representative of the materials produced require more stringent consensus properties.
Mix The criteria are intended to be applied to a design samples that do not reasonably represent proposed aggregate blend rather than individual the average stockpile values for gradation or other components.
However, many agencies currently properties listed in this section will result in a apply such requirements to individual aggregates production mix substantially different than the mix so undesirable components can be identified. The design, in essence invalidating the mix design. The consensus properties are detailed in Table 3. Coarse aggregate angularity CAA ensures a high degree of aggregate internal friction for rutting 3. Design ESALs are the anticipated traffic level expected on the design lane over a year period.
Regardless of the ac- tual design life of the roadway, determine the design ESALs for 20 years to choose the appropriate aggregate criteria. Criterion based upon a maximum-to-minimum ratio. Flat and elongated criteria do not apply to 4. For 4. If less than 25 percent of a layer is within mm of the surface, the layer may be considered to be below mm for mixture design purposes. The fine criteria, either by mass or particle count. The aggregate bulk dry specific gravity Gsb is used to reporting format gives both the percentage of compute the fine aggregate volume.
Table 3. Flat and elongated particles degree of fine aggregate internal friction and rutting are undesirable because they have a tendency to resistance. It is defined as the percent of air voids break during construction and under traffic and present in loosely compacted aggregates smaller than they tend to reduce VMA.
The test procedure the 8 sieve 2. Higher void The procedure uses a proportional caliper device contents typically mean more fractured faces. By measuring the mass of fine arm and fixed post at position A. The swinging aggregate F in the filled cylinder of known volume arm then remains stationary while the aggregate V , the void content can be calculated as the is placed between the swinging arm and the fixed post at position B.
The flocculating solution forces the clay material into suspension above the granular aggregate. The sand equivalent value is from the coarse aggregate fraction of a standardized computed as the ratio of the sand to clay height test sample. It is performed by subjecting the coarse readings, expressed as percentage. In essence, this aggregate, usually larger than the 8 sieve 2. The test result is the mass percentage 3. The maximum allowable loss certain other aggregate characteristics are critical.
The However, critical values of these properties could not higher the value, the more friable the coarse aggregate, be reached by consensus because needed values are and the greater the breakdown degradation of the source specific. Consequently, a set of source properties aggregate from quarrying through stockpiling, HMA is recommended.
Specified values are established by manufacturing and under the rollers. The lower the local agencies. While these properties are relevant value, the better the skid resistance and tire chain wear during the mix design process, they may also be used resistance of the pavement. Those properties are Another test for toughness is Micro-Deval toughness, soundness and deleterious materials. Micro-Deval is similar to LA Abrasion except that the drum is 3. Abrasion test.
Also, the aggregate aggregate to abrasion and mechanical degradation is soaked in water before the test and water is used during handling, construction and in-service. The in the drum during the test. It is typical for magnesium Soundness tests estimate the resistance of sulfate loss to be greater than sodium sulfate loss aggregates to in-service weathering. The most on the same aggregate. It can be percentage of contaminants such as clay lumps, performed on both coarse and fine aggregate.
The shale, wood, mica and coal in the blended test is performed by exposing an aggregate sample aggregate. One immersion and drying is considered The analysis can be performed on both coarse one soundness cycle.
During the drying phase, and fine aggregate. The test is performed by wet salts precipitate in the permeable void space sieving aggregate size fractions over specified of the aggregate.
Upon re-immersion, the salt sieves. The mass percentage of material lost as a rehydrates and exerts internal expansive forces result of wet sieving is reported as the percent that simulate the expansive forces of freezing of clay lumps and friable particles. A wide range water. The test result is total percent loss over of criteria for maximum allowable percentage of various sieve intervals for a required number deleterious particles exists. Values range from of cycles. Maximum loss values typically range as little as 0.
Magnesium depending on the exact composition of the sulfate testing is typically more aggressive than contaminant. Minimum voids in the 16 The results should be B Weight after wash The exception is the S — from sieving 9. Typically, multiple stockpiles of aggregate are blended to meet the final specified requirements.
A washed sieve analysis must be performed on such as air voids and VMA are directly impacted every aggregate ingredient to be utilized in the by the amount and size of aggregate particles and mixture in order to calculate the final aggregate the resulting packing characteristics in the final blend in the mixture to be designed. Most mixture. A gradation can give insight to the final aggregate specifications are based on the final volumetric properties in a particular mixture.
However, when the specific gravities of the Calculating a blended gradation, assuming all individual aggregates differ or vary significantly aggregate fractions have a similar Bulk Specific by 0.
Based on the operations result in an aggregate size distribution gradation, it would be reasonable to assume based on percentage of mass.
An important feature of the 0. The maximum density line different aggregate specific gravities than those plots as a straight line from the maximum aggregate used in the mix design will also yield different size to the origin of the chart. This is one of the The maximum aggregate size is typically the largest reasons why most specifications require a new mix sieve size through which percent of the aggregate design when the source and characteristics of any will pass.
The maximum aggregate size is defined of the mix ingredients are changed. The NMAS is defined as one 3. The maximum evaluating aggregate gradations. The the plotted maximum density line and varies restricted zone was enforced to varying degrees. As part of the mix design Project showed that if the other Superpave process, the aggregate gradation should be plotted aggregate properties were met, then violation on the 0.
It was concluded that 0. Moreover, numerous field examples of pavements that were in violation 3. However, a designer as master ranges between which gradations must should understand the need to be cautious with pass. Control points are placed at the nominal gradations that pass through the restricted zone maximum size, an intermediate size 2. Superpave Such gradations have a greater tendency to be control point limits vary depending on the nominal tender and are to be approached with due care.
The gradation should also be made indication that there was possibly too much up of the most economical aggregates available that natural sand in the mix, resulting in possible mix are of suitable quality.
The restricted zone was introduced by the Superpave system and it has since been 3. It resided The specific gravity of an aggregate is the ratio along the maximum density line between the of the weight of a unit volume of material to the intermediate size either 4.
This property is used in mix volumetric control points and restricted zone for a Also, bulk Superpave mixture Whereas bulk various aggregates. Apparent specific gravity considers the volume note: The accuracy of specific gravity measurements as being the volume of the aggregate itself. It does for mix designs is important. Unless specific gravities not include the volume of any pores or capillaries are determined to four significant figures three that become filled with water after a to hour decimal places , an error in air voids value of as soaking.
Bulk dry specific gravity considers the much as 0. The Asphalt Institute overall volume of the aggregate particle, including the recommends the use of weigh scales whose sensitivity pores that become filled with water after a to will allow a mix batch weighing 1, to 5, grams hour soaking.
The effective specific gravity to be measured to an accuracy of 0. Many designers take this into account by determining the extent of the additional Aggregate batching and fines created during production and making a mix sample preparation corresponding adjustment to the aggregate batch There are no AASHTO, ASTM or other widely for mix design. Performing this adjustment may accepted standards for the batching of aggregates help avoid the drop in air voids and VMA often for asphalt mix design.
Many variations exist and seen in plant mixes versus laboratory mixes. This section will Therefore, a careful comparison of gradations detail several different batching methods. Conducting a mixture design using aggregate that Aggregate samples from the plant or quarry may does not meet a project specification or is not come to the lab saturated with moisture. Fine representative of field-produced material is of aggregate stockpiles tend to absorb a higher little use.
There are many different methods that can be Without completely drying the aggregate first, utilized to prepare aggregate samples for mixture the absorbed moisture will increase the aggregate testing. They can range from very accurate and weight, resulting in inaccurate material proportions time-consuming to relatively quick but with less in the batch.
Accurately prepared specimens that Prior to batching samples for the mix design, are representative of the final aggregate blend gradations should be performed on each material produced by the mixing plant will give the most submitted.
Aggregate material submitted for mix reliable mixture design data. The mix designer design should be accompanied with production should use the most accurate method practical that test results. Submitted materials should then obtains representative and reproducible results and be compared with production test results to specimen with minimal variability.
Many agencies assure the materials submitted for mix design specify certain methodologies for specimen are representative of the materials that will be preparation. Agency-specified procedures may used in the project. Softer aggregates tend to deviate from the following methods described and degrade more during the production process should be thoroughly understood by the designer. The pan material using this method becomes all of the material that passes the 1.
Large capacity, tray-type mechanical samples prior to fractionation shakers have the capacity to fractionate samples This method utilizes a process where a sample of up to 50 or more pounds. Care should be taken to aggregate is prepared by combining a predetermined prevent overloading of sieve screens. The amount amount of every stockpile sample into one combined allowed on each sieve is dependent on the nominal blend and then fractionates the combined aggregate maximum aggregate size NMAS , as outlined in sample into a chosen number of size fractions.
Method 2 is dependent on the mix design equations, and must be repeated for each stockpile aggregates submitted being representative of field of aggregate to be used: production and the accuracy of splitting out batching Determine the grams needed from each portions that are representative. Changing the percentages of Determine the amount to be contributed from aggregates used will require the process to be each individual sieve fraction: started over. Fractionate the resulting pan using a sieve shaker, making sure to limit the quantity Care must be taken to assure that the large of material on a given sieve so that all particles amounts of pan material shown are uniformly have an opportunity to reach the sieve openings blended and added to the batch sample.
Make sure that each pan is the sieves: as homogeneously mixed as possible. If the chosen sieves were For this example, the following trays were Example: used: When fractionating with fewer will need to be combined in proportion to the cold than the five tray slots typically present, fill the feed bin percentages and then sieved.
Fractionate each pan, of all aggregate materials placing each resulting size fraction into a Fractionate each aggregate source with a sieve separate pan. Using the in Table 3. Even though the particles are small, Fractionate each aggregate individually and keep there may be some level of segregation. If each fraction in a separate, labeled pan or bucket. Then batch 3 percent more of the Calculate the number of grams required of each moist fines than would be required of dry fines to size fraction to make a 5,gram batch.
The moisture will be First, calculate the number of grams needed for driven away when the aggregates are placed in the each aggregate source according to the percentage oven to bring them up to mixing temperature.
Add Taring the scales after adding each new of 5, In the oven, In order to compensate for this conglomerate and may alter the binder properties potential error, a prepared trial batch should in the recycled materials. Caution must be material added during batching. A thorough understanding of the material the temperature to a high enough level to assure being utilized by the designer is necessary when thorough mixing with the virgin aggregate.
Mix designers are encouraged to Hydrated lime is often used as a treatment use Methods 1 or 2 for ordinary production mix for the prevention of moisture damage and is design.
Hydrated lime is typically added to the prepared samples prior to heating and 3. Hydrated lime may be added as either a Many different types of additives may be added dry component or as slurry. Each method has been to a batched specimen. The reclaimed asphalt, recycled shingles, lime, ground method of adding hydrated lime to the mixture tire rubber or a number of other specialty products.
See chapter 9 for more details into the final mixture must consider the on methods to incorporate hydrated lime in field- temperature to which the aggregate will be heated. If scooping from buckets, design process, many of which are proprietary round-bottomed scoops can be used.
The supplier guidelines for use and Placing each aggregate fraction in the batching incorporation must be followed very carefully pan in distinct piles will aid in batching as shown unless otherwise specified by the owner or agency.
If the batch weight is accidentally exceeded for any particular aggregate, it is easier 3. If scooping from a pan, flat-bottomed aggregate fraction when they are all piled together. For example, basing a mix design 4. Using too many binder increments 4.
If the material source is unknown to the designer, Introduction use five trial binder contents. If the designer is Laboratory asphalt mixture testing is primarily familiar with the material source, the number of conducted to determine two fundamental asphalt trials may be reduced to no less than three. These values are utilized provide a distinction between points, but close in calculating volumetric properties discussed in enough together to avoid lengthy interpolation.
Laboratory binder percentage points is 0. However, asphalt mix specimens are also prepared for further if the designer is unfamiliar with aggregates being mixture testing such as moisture sensitivity or used, or if other materials or additives are used other recommended or specified performance such as RAP, RAS, lime, WMA, etc. The specific gravity of aggregates, binders at smaller increments over a wider range may and asphalt mixtures are determined using be needed.
The ultimate goal is to prepare batches that bracket the anticipated design binder content. The designer should evaluate the aggregate type, the 4. This method a fine aggregate gradation will require more still works well for unmodified asphalt binders.
Additionally, high compaction temperatures In the end, the designer should never extrapolate lead to potential problems in obtaining accurate a higher or lower design binder content from density data due to low mix stiffness, excess outside the range of trial points.
This frequency is the asphalt binder is determined at two test then input into an equation to calculate mixing and temperatures, establishing a relationship between compaction temperatures. The DSR Steady Shear Flow Procedure uses Compaction temperatures are determined a shear stress sweep from 50 to Pa at a where the viscosity-temperature line crosses the minimum of three test temperatures to determine compaction viscosity range of 0.
This viscosity is then Mixing temperatures are determined where the plotted as a function of temperature, from which viscosity-temperature line crosses the mixing the mixing and compaction temperatures are derived. Users should refer to other existing practices or supplier recommendations to determine appropriate mixing and compaction temperatures for GTR-modified asphalt binders. Laboratory mixing and compaction temperatures are intended for determining design volumetric properties of the asphalt mixture and are not intended to represent field mixing and compaction temperatures at the project level.
Small stainless steel pitchers from to have a valid comparison of their volumetric commercial restaurant supply stores work properties. In an asphalt mix facility, the mixing very well. Regardless of the selected contents. Mixing is typically done with either a planetary mixer see Figure 4.
To avoid excessive aging of the binder, do not allow it to stay at the mixing temperature for much over the time needed to bring it to temperature and complete the mixing operation. Keep enough molds in the oven to rotate their use, always keeping a hot mold available. R 30 specifies a 2-hour conditioning period prior to When you are ready to mix, place the mixing laboratory compaction.
Pour the characteristics can impact both Gmb and Gmm heated aggregate batch into the bowl and verify values. The maximum theoretical specific gravity the required weight see Figure 4.
Form a crater test procedure, AASHTO T , requires a in the center of the aggregate to receive the binder mixture conditioning period of at least 2 hours. In an effort to provide the most accurate mixture Add the correct number of grams of binder, dipping design results, the Asphalt Institute recommends out any excess binder with a folded paper dipper. Aggregate batches. When transferring the mixture from the sources that have high water absorption values mixing bowl to the conditioning pans, make sure to above 2.
Figure 4. The spread it to an even thickness between 25 and 50 purpose of the conditioning for volumetric millimeters in depth. Place the mixture and pan, mix design is to allow for binder absorption as shown in Figure 4. Note that testing is designed to simulate the plant-mixing the conditioning time may need to be increased to be and construction effects on the mixture.
Subject: Mix Design. Highlights: Best Seller. Buy Rent. Title information Details The manual is a practical guide based on proven technologies, incorporating the most current information in Pages: Language: English. Topics are presented in the logical progression of mix design steps.
Chapters 1 through 5 apply across all mix design methods; covering mix behavior, material selection, batching, specimen preparation, binder absorption, specific gravity testing, volumetric calculations, data interpretation and more.
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