The National Academies Press

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From page 174... ... In order to provide increased durability, GGHMA has a relatively high asphalt binder content. This leads to the third principle of GGHMA mix design, which is that the aggregate must have a high VMA value -- typically 18 to 20%. Read the entire page →
From page 175... ... The asphalt binder content that produces 4% air voids is selected as optimum asphalt binder content. The final step in the mix design procedure is to evaluate the moisture susceptibility, draindown sensitivity, and rut resistance of the designed mixture. Read the entire page →
From page 176... ... Step 1 -- Materials Selection As with most HMA mixes, suitable coarse aggregate, fine aggregate, and asphalt binder must be selected for GGHMA. However, two additional materials are also typically needed for GGHMA designs: commercial mineral filler and stabilizing additives. Read the entire page →
From page 177... ... Likewise, mineral fillers can also be considered a stabilizing additive, since these small particles help "soak up" the asphalt binder. However, the most effective stabilizing additive is a fiber. Read the entire page →
From page 178... ... 178 A Manual for Design of Hot Mix Asphalt with Commentary should be no less than 76 and the binder should be polymer modified. This ensures that GGHMA mixes will exhibit the exceptional rut resistance that pavement engineers expect from this mix type. Read the entire page →
From page 179... ... Mineral fillers with very high Rigden voids can sometimes cause excessive stiffening in SMA mixtures. The equipment and test method for conducting the Dry Compaction Test can be found in the National Asphalt Pavement Association's Information Series 127, "Evaluation of Baghouse Fines for Hot Mix Asphalt." Other requirements for mineral fillers can be found in AASHTO M-17, "Mineral Fillers for Bituminous Paving Mixtures." However, the gradation requirements stated in AASHTO M-17 should only be used for guidance. Read the entire page →
From page 180... ... Percent by mass retained on each sieve. Stockpile and Percent Passing Based on Mass, % Sieve, mm Aggregate A Aggregate B Aggregate C Mineral Filler 25.0 100.0 100.0 100.0 100.0 19.0 95.0 100.0 100.0 100.0 12.5 66.0 71.0 97.4 100.0 9.5 43.0 46.0 84.6 100.0 4.75 9.0 6.0 48.9 100.0 2.36 5.0 4.0 27.8 100.0 1.18 2.0 4.0 16.6 100.0 0.60 2.0 3.0 10.7 100.0 0.30 2.0 3.0 7.6 100.0 0.075 1.0 1.5 4.6 72.5 Gsb 2.616 2.734 2.736 2.401 Table 10-4. Read the entire page →
From page 181... ... Convert Percent Mass Retained to Volume per Sieve In this step of developing an SMA gradation, the values for percent mass retained determined previously are converted to volumes per sieve. To make this conversion, the bulk specific gravity of the individual stockpiles is needed. Read the entire page →
From page 182... ... To perform the blending, select the estimated percentages of the different stockpiles to be used. For this example, the following percentages will be evaluated first: The percent of each stockpile in the blend is multiplied by the volume retained on a given sieve for each stockpile to determine the total volume retained on Stockpile % Blend Aggregate A 30 Aggregate B 30 Aggregate C 30 Mineral filler 10 Volume of Aggregate Retained per Sieve, cm3Sieve, mm Aggregate A Aggregate B Aggregate C Mineral Filler 25.0 0.00 0.00 0.00 0.00 19.0 1.91 0.00 0.00 0.00 12.5 11.09 10.97 0.95 0.00 9.5 8.79 8.78 4.68 0.00 4.75 13.00 14.63 13.05 0.00 2.36 1.53 0.73 7.71 0.00 1.18 1.15 0.00 4.09 0.00 0.60 0.00 0.37 2.16 0.00 0.30 0.00 0.00 1.13 0.00 0.075 0.38 0.55 1.10 11.45 -0.075 0.38 0.55 1.68 30.20 Table 10-6. Read the entire page →
From page 183... ... This is accomplished for a given sieve by dividing the volume retained on that sieve by the total volume of the blend. The following equation illustrates this calculation for the 4.75-mm sieve. Read the entire page →
From page 184... ... Stockpile % Blend Aggregate A 40 Aggregate B 41 Aggregate C 10 Mineral Filler 9 Sieve, mm Gradation Band Requirements Blend Percent Passing 25.0 100 100 19.0 90-100 98.5 12.5 50-88 80.1 9.5 25-60 62.3* Read the entire page →
From page 185... ... The percent passing the 0.075-mm sieve should be approximately 10 percent for each trial gradation. Determination of VCA in the Coarse Aggregate Fraction For best performance, the GGHMA mixtures must have a coarse aggregate skeleton with stone-on-stone contact. Read the entire page →
From page 186... ... , and Gca = bulk specific gravity of the coarse aggregate fraction VCA G G DRC ca w s ca w = −γ γ γ 100 10 1( ) Figure 10-5. Read the entire page →
From page 187... ... For example, for a GGHMA mixture to be made with an aggregate blend having a combined bulk specific gravity of 2.75, the minimum asphalt content is 6.0% by mass, and the target asphalt content would be 6.0 + 0.3 = 6.3% by mass. The minimum binder content values given in Table 10-11 have been calculated so that, in most cases, the resulting mixes will meet the suggested minimum VMA of 17.0% at 4.0% air voids for GGHMA mixtures. Read the entire page →
From page 188... ... However, although these temperatures work for neat asphalt binders, the selected temperatures may need to be changed for polymer-modified asphalt binders. The asphalt binder supplier's guidelines for mixing and compaction temperatures should be used. Read the entire page →
From page 189... ... The optimum asphalt binder content is chosen to produce 4.0% air voids in the mixture; because of typical error in volumetric analysis, air void contents within ± 0.5% of this target are acceptable. The optimum asphalt binder content should meet the minimum asphalt content requirements in Table 10-11. Read the entire page →
From page 190... ... A summary of performance testing requirements and their application to GGHMA mixtures is given below. The design procedures set forth in this manual -- including that for GGHMA -- are structured to provide HMA mix designs that exhibit a high level of rut resistance. Read the entire page →
From page 191... ... Air Voids The amount of air voids in the mixture can be controlled by the asphalt binder content. However, a problem occurs when low voids exist at the minimum asphalt binder content. Read the entire page →
From page 192... ... However, if other aspects of the mix design are changed, the volumetric composition might change significantly, which will require further refinement of the mix prior to further rut resistance testing. Bibliography AASHTO Standards M 17, Mineral Filler for Bituminous Paving Mixtures M 320, Performance-Graded Asphalt Binder M 325, Standard Specification for Designing Stone Matrix Asphalt (SMA) Read the entire page →
From page 193... ... (2008) NCHRP Report 629: Ruggedness Testing of the Dynamic Modulus and Flow Number Tests with the Simple Performance Tester, Transportation Research Board, National Research Council, Washington, DC, 130 pp. Read the entire page →

From page 174...

... In order to provide increased durability, GGHMA has a relatively high asphalt binder content. This leads to the third principle of GGHMA mix design, which is that the aggregate must have a high VMA value -- typically 18 to 20%.