1、Standard Practice for Designing Stone Matrix Asphalt (SMA) AASHTO Designation: R 46-08 (2012)1American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2d R 46-1 AASHTO Standard Practice for Designing Stone Matrix Asphalt (S
2、MA) AASHTO Designation: R 46-08 (2012)11. SCOPE 1.1. This standard practice covers the design of Stone Matrix Asphalt (SMA) using the Superpave Gyratory Compactor (SGC). The SMA design is based on the volumetric properties of the SMA in terms of air voids (Va), voids in the mineral aggregate (VMA),
3、and the presence of stone-on-stone contact. 1.2. The values stated in SI units are to be regarded as the standard. The U.S. Customary units in parentheses are for information only. 1.3. This standard practice does not purport to address all of the safety concerns, if any, associated with its use. It
4、 is the responsibility of the user of this standard practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1. AASHTO Standards: M 325, Stone Matrix Asphalt (SMA) R 30, Mixture Conditioning of Hot
5、 Mix Asphalt (HMA) T 19M/T 19, Bulk Density (“Unit Weight”) and Voids in Aggregate T 27, Sieve Analysis of Fine and Coarse Aggregates T 85, Specific Gravity and Absorption of Coarse Aggregate T 166, Bulk Specific Gravity (Gmb) of Compacted Hot Mix Asphalt (HMA) Using Saturated Surface-Dry Specimens
6、T 209, Theoretical Maximum Specific Gravity (Gmm) and Density of Hot Mix Asphalt (HMA) T 283, Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage T 305, Determination of Draindown Characteristics in Uncompacted Asphalt Mixtures T 312, Preparing and Determining the Density of Asphalt
7、Mixture Specimens by Means of the Superpave Gyratory Compactor 2.2. Asphalt Institute Publication: MS-2, Mix Design Methods for Asphalt Concrete and Other Hot-Mix Types 3. TERMINOLOGY 3.1. Definitions: 3.2. stone matrix asphalt (SMA)a hot mix asphalt (HMA) consisting of two parts, a coarse aggregate
8、 skeleton and a rich asphalt binder mortar. The mixture must have an aggregate skeleton with coarse aggregate-on-coarse aggregate contact (generally referred to as stone-on-stone contact). 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication
9、 is a violation of applicable law.TS-2d R 46-2 AASHTO The coarse aggregate is generally considered to be that fraction of the aggregate retained on the 4.75-mm (No. 4) sieve but may be designated as other sizes. 3.3. air voids (Va)the total volume of the small pockets of air between the coated aggre
10、gate particles throughout a compacted paving mixture, expressed as a percent of the bulk volume of the compacted paving mixture (Note 1). Note 1Term defined in the Asphalt Institute Publication MS-2. 3.4. voids in the mineral aggregate (VMA)the volume of the intergranular void space between the aggr
11、egate particles of a compacted paving mixture that includes the air voids and the effective binder content, expressed as a percent of the total volume of the specimen (Note 1). 3.5. voids in the coarse aggregate (VCA)the volume between the coarse aggregate particles. This volume includes filler, fin
12、e aggregate, air voids, asphalt binder, and stabilizing additive (if used). 3.6. SMA mortara mixture of asphalt binder, filler material passing the 0.075-mm (No. 200) sieve, and stabilizing additive. 3.7. stabilizing additiveeither cellulose or mineral fiber. 4. SUMMARY OF THE PRACTICE 4.1. Material
13、s SelectionAsphalt binder, aggregate, mineral fillers, and stabilizing additives that meet the applicable specification are selected. 4.2. Selecting Optimum GradationThree recommended trial aggregate gradations from the selected aggregates are blended. The dry-rodded unit weight for the coarse aggre
14、gate for each trial gradation is determined in accordance with T 19M/T 19. For each trial gradation, an initial trial asphalt binder content is selected and at least two specimens are compacted in accordance with T 312. Where no previous history is available, an initial trial asphalt binder content
15、between 6.0 and 6.5 percent is recommended. Gradations of the three blends are selected to ensure that minimum VMA requirements and stone-on-stone contact are achieved. 4.3. Selecting Design Binder ContentReplicate specimens are compacted in accordance with T 312 at three binder contents. The design
16、 binder content is selected on the basis of satisfactory conformance with the requirements of Section 10 (Note 2). Note 2When an SMA mix cannot be designed within the minimum binder content requirements, the guidelines given in Table X2.1 can be used to establish minimum binder content requirements
17、based on the combined-aggregate bulk specific gravity. 4.4. Evaluating Moisture SusceptibilityThe moisture susceptibility of the mixture, designed and compacted in accordance with T 312 to a Vacontent of 6.0 1.0 percent, is evaluated in accordance with T 283. 4.5. Evaluating DraindownThe mixture is
18、evaluated for sensitivity to asphalt binder draindown in accordance with T 305. If the mixture fails the moisture susceptibility or draindown tests, it must be modified so that the specification requirements are met. 5. TEST SPECIMENS 5.1. Number of SamplesA total of nine samples are initially requi
19、red; at least three samples at each of the three trial gradations are produced. Each sample is mixed with the trial asphalt binder content, and two of the three samples for each trial gradation are compacted. The remaining 2015 by the American Association of State Highway and Transportation Official
20、s.All rights reserved. Duplication is a violation of applicable law.TS-2d R 46-3 AASHTO sample of each trial gradation is used to determine the theoretical maximum density in accordance with T 209. 5.2. Preparation of AggregatesDry aggregates to a constant mass at 105 to 110C (221 to 230F), and sepa
21、rate the aggregates by dry-sieving into the desired size fractions. The following size fractions are recommended: 37.5 mm (11/2in.) to 25.0 mm (1 in.); 25.0 mm (1 in.) to 19.0 mm (3/4in.); 19.0 mm (3/4in.) to 12.5 mm (1/2in.); 12.5 mm (1/2in.) to 9.5 mm (3/8in.); 9.5 mm (3/8in.) to 4.75 mm (No. 4);
22、4.75 mm (No. 4) to 2.36 mm (No. 8); 2.36 mm (No. 8) to 0.075 mm (No. 200); and Passing 0.075 mm (No. 200). 5.3. Determination of Mixing and Compaction Temperatures: 5.3.1. The temperature to which the asphalt binder must be heated to produce a viscosity of 170 20 cSt shall be the mixing temperature.
23、 5.3.2. The temperature to which the asphalt binder must be heated to produce a viscosity of 280 30 cSt shall be the compaction temperature. Note 3While the temperatures given in Sections 5.3.1 and 5.3.2 are appropriate for neat asphalt binders, the selected temperatures may not be applicable to mod
24、ified asphalt binders. In those cases, it is recommended that the manufacturers guidelines for mixing and compaction temperatures be used. 5.4. Preparation of Mixtures: 5.4.1. A mechanical mixing apparatus shall be used. 5.4.2. An initial batch shall be mixed for the purpose of “buttering” the mixin
25、g bowl and stirrers. This batch shall be emptied after mixing, and the sides of the bowl and stirrers shall be cleaned of mixture residue by scraping with a small limber spatula but shall not be wiped with a cloth or washed clean with solvent, except when a change is to be made in the asphalt binder
26、 or at the end of a design. 5.4.3. Into separate pans for each test specimen, weigh sufficient material to produce compacted samples of the desired volume, approximately 4700 g. Mix the aggregate in each pan. Place the aggregate in an oven and heat to a temperature not exceeding the mixing temperatu
27、re established in Section 5.3 by more than approximately 28C (50F). Heat the asphalt binder to the established mixing temperature. The stabilizing additive is added to the heated aggregate prior to the introduction of the asphalt binder. Note 4It is recommended that the stabilizing additive be manua
28、lly mixed with the heated aggregate. This procedure is needed to ensure an even distribution of the stabilizing additive during the laboratory mixing process. The use of stabilizing additives generally requires slightly longer mixing times. 5.4.4. Form a crater in the dry blended aggregate and stabi
29、lizing additive, and weigh the preheated required amount of asphalt binder into the crater. Care must be exercised to prevent loss of the mix during mixing and subsequent handling. At this point, the temperature of the aggregate and asphalt binder shall be within the limits of the mixing temperature
30、 established in Section 5.3. Mix the aggregate and asphalt binder rapidly until the aggregate is thoroughly coated. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d R 46-4 AASHTO 5.5. Compaction of
31、SpecimensThe compaction temperature is determined in accordance with Section 5.3. Laboratory samples of SMA are short-term conditioned in accordance with R 30 and then compacted for 100 gyrations. Note 5When aggregates have a Los Angeles Abrasion loss value greater than 30 percent, the desirable num
32、ber of SGC design gyrations is 75. 6. SELECTION OF TRIAL GRADATIONS 6.1. The trial gradations must be selected to be within the desired specification range as defined in M 325. To design an SMA mixture, it is recommended that at least three trial gradations be initially evaluated. It is suggested th
33、at one of the trial blends fall along the coarse limits, one along the fine limits, and one in the middle of the gradation bands as defined in M 325. When the bulk specific gravities of the different aggregates to be used in the mixture vary by more than 0.2, the trial blend gradations should be bas
34、ed upon volumetric percentage. An example problem illustrating how to blend aggregates based on volume is given in Appendix X1.1. 7. SELECTION OF TRIAL BINDER CONTENT 7.1. As a starting point, for aggregates with bulk specific gravities approximately equal to 2.75, a binder content of approximately
35、6.0 percent or greater, by mass, needs to be selected. If the bulk specific gravity of the coarse aggregate exceeds 2.75, the trial binder content can be reduced by approximately 0.1 percent for each specific-gravity increment of 0.05 above 2.75. If the bulk specific gravity of the coarse aggregate
36、is below 2.75, the trial binder content can be increased approximately 0.1 percent for each specific gravity increment of 0.05 below 2.75 (see Table X2.1). 8. DETERMINATION OF VCA IN COARSE-AGGREGATE FRACTION OF MIXTURE 8.1. For best performance, the SMA must have a coarse-aggregate skeleton with st
37、one-on-stone contact. The course-aggregate fraction is that portion of the total aggregate blend retained on the 4.75-mm (No. 4) sieve for 12.5-mm (1/2-in.) and 19-mm (3/4-in.) SMA. For the 9.5-mm (3/8-in.) nominal-maximum aggregate size SMA, the coarse aggregate is that portion of the total aggrega
38、te blend retained on the 2.36-mm (No. 8) sieve. The condition of stone-on-stone contact within an SMA is defined as the point at which the VCA of the compacted mixture is less than the VCA of the coarse aggregate in the dry-rodded test. 8.2. The dry-rodded VCA of the coarse-aggregate fraction (VCADR
39、C) is determined by compacting the stone with the dry-rodded technique in accordance with T 19M/T 19. When the dry-rodded density of the stone fraction has been determined, the VCADRCcan be calculated using Equation 1: 100CA w sDRCCA wGVCAG = (1) where: GCA= the bulk specific gravity of the coarse a
40、ggregate (T 85); s= the unit weight of the coarse-aggregate fraction in the dry-rodded condition kg/m3(lb/ft3) (T 19M/T 19); and w= the unit weight of water 1000 kg/m3(62.4 lb/ft3). 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a v
41、iolation of applicable law.TS-2d R 46-5 AASHTO 9. SELECTION OF DESIRED GRADATION 9.1. After the trial samples have been compacted and allowed to cool, they are removed from the molds and tested to determine their bulk specific gravity in accordance with T 166. The uncompacted samples are used to det
42、ermine the theoretical maximum density in accordance with T 209. Using the bulk specific gravity and theoretical maximum density, the Va, VMA, and VCA of the compacted mixture (VCAmix) can be calculated using Equations 2, 3, and 4: ( )100mb sb sVMA G G P= (2) ( )mix100mb CA CAVCA G G P= (3) ( )( )10
43、0 1a mb mmV GG= (4) where: Gmb= the bulk specific gravity of the compacted mixture (T 166); Gsb= the bulk specific gravity of the total aggregate; Ps= the percent of aggregate in the mixture; GCA= the bulk specific gravity of the coarse-aggregate fraction (T 85); PCA= the percent of coarse aggregate
44、 in the total mixture; and Gmm= the theoretical maximum density of the mixture (T 209). 9.2. Of the three trial gradations evaluated, the one with the lowest percent of coarse aggregate that meets or exceeds the minimum VMA requirement, and has a VCAmixless than VCADRC, is selected as the desired gr
45、adation. The trial gradation selected, based on the above conditions, is referred to as the optimum gradation. Note 6If possible, the selected gradation should have a VMA somewhat higher than the minimum criteria to allow for some reduction in VMA during plant production. 10. SELECTION OF OPTIMUM BI
46、NDER CONTENT 10.1. Once the optimum gradation of the mixture has been chosen, it may be necessary to raise or lower the binder content to obtain the proper amount of Vain the mixture. In this case, additional samples are prepared using the selected gradation and varying the binder content. The optim
47、um binder content is chosen to produce the Vain the mixture specified in M 325. 10.2. Twelve samples are needed for this portion of the procedure. This number provides for three compacted samples and one uncompacted sample (used to determine the theoretical maximum density) at each of the three bind
48、er contents. The mixture properties are determined and the optimum binder content is selected to provide the desired Valevel. The SMA selected should have properties meeting the criteria as specified in M 325. If these criteria are not satisfied, the mixture should be modified so that the requiremen
49、ts are satisfied. 11. MOISTURE SUSCEPTIBILITY 11.1. Moisture susceptibility of the selected mixture is determined in accordance with T 283 using samples compacted in accordance with T 312 to a Vacontent of 6.0 1.0 percent. The retained tensile strength level of the SMA shall be as specified in MP 8 at 6.0 1.0 percent Va. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2d R 46-6 AASHTO 12. DRAI
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