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From page 46... ... The asphalt binder content of a mixture, for example, is often given in terms of percent of total mix weight, whereas air void content is always given as a percent of total volume -- it must be given this way, since the mass of air voids in an asphalt concrete specimen is essentially zero. Although composition of asphalt concrete mixtures can be given in terms of weight, traditionally the most common and most important method of describing and analyzing asphalt concrete composition is by volume. Read the entire page →
From page 47... ... When discussing the air void content of asphalt concrete mixtures, it is first necessary to specify what type of specimen or sample we are testing or analyzing. We can measure the air void content of asphalt concrete in the following types of specimens: • Specimens compacted in the laboratory when developing a mix design • Specimens compacted in the laboratory from material produced at the plant as part of quality assurance testing Mixture Volumetric Composition 47 0% 20% 40% 60% 80% 100% Lean Base Course Surface Course Stone Matrix Asphalt Voids Asphalt Aggregate Figure 5-1. Read the entire page →
From page 48... ... However, once the pavement is opened to traffic, the repeated loading as trucks pass over the pavement will tend to further compact the material in the wheel paths of the pavement. Many engineers assume that the air void content in the wheel paths of an asphalt concrete pavement should, within a few years, reach about the same value as was used in the laboratory mix design, but, as documented in NCHRP Report 573, this is not always the case. Read the entire page →
From page 49... ... First and most important, it is the asphalt content by volume and not by weight that dictates performance, and asphalt content by total mix weight is a function of both asphalt content by volume and aggregate specific gravity. Consider two asphalt concrete mixtures, both with an air void content of 4.0% and an asphalt binder content of 12.0% by volume. Read the entire page →
From page 50... ... As discussed below, one way to specify effective binder content by volume is to control both air void content and voids in the mineral aggregate at the same time. Voids in the Mineral Aggregate Voids in the mineral aggregate (VMA) Read the entire page →
From page 51... ... Therefore, establishing a single design air void content (such as the 4.0% used in Superpave mixtures) and then controlling VMA is the same as controlling effective binder content. Read the entire page →
From page 52... ... Rut resistance of asphalt concrete mixtures increases as VMA decreases and aggregate fineness increases. Because binder content decreases with decreasing VMA, this means that rut resistance should increase 52 A Manual for Design of Hot Mix Asphalt with Commentary 40 50 60 70 80 90 100 5 10 15 20 25 VMA, Volume % VF A , % 3% 5% 4% (a) Read the entire page →
From page 53... ... Agencies that choose to specify film thickness for asphalt concrete mixtures should take special care to ensure that there are no unintended conflicts with any simultaneous requirements for VMA, design air void content, or aggregate gradation. Mixture-Specific Gravity Specific gravity has the same meaning when applied to asphalt concrete mixtures as it does when applied to aggregates and other materials -- the ratio of the density of a material to the density of water at 25°C and at standard air pressure. Read the entire page →
From page 54... ... Furthermore, use of multiple procedures for determining specific gravity of aggregates and HMA mixtures should be discouraged, since this can only increase the variability in the test results and in the subsequent volumetric analyses. Theoretical Maximum Specific Gravity The theoretical maximum specific gravity of an asphalt concrete mixture is the specific gravity of the mixture at zero air void content. Read the entire page →
From page 55... ... Maximum specific gravity is determined by measuring the specific gravity of the loose paving mixture, after removing all of the air entrapped in the mixture by subjecting the mixture to a partial vacuum (vacuum saturation) Read the entire page →
From page 56... ... A set of variables similar to those given in Figure 5-9 can be defined for the mass terms used in volumetric analysis: Mbe = Mass of effective asphalt binder Mba = Mass of absorbed asphalt binder Ms = Mass of aggregate, total Mb = Mass of asphalt binder, total Mse = Mass of aggregate, effective (excluding surface pores filled with asphalt) Ma = Mass of air voids Mmb = Mass of specimen, total 56 A Manual for Design of Hot Mix Asphalt with Commentary vacuum container vapor traps calibrated gage vacuum pump Figure 5-8. Read the entire page →
From page 57... ... ( ) Mixture Volumetric Composition 57 ai r aspha lt bi nde r absorbed asphalt a ggr egat e be V ba V sb V b V se V mm V mb V a V VMA V be = Volume of effective asphalt binder VBE = Effective asphalt content, percent by volume V ba = Volume of absorbed asphalt binder VBA = Absorbed asphalt binder, percent by total mix volume V ma = Volume of voids in mineral aggregate VMA = Voids in mineral aggregate, percent by volume V sb = Volume of aggregate, bulk (including all permeable surface pores) Read the entire page →
From page 58... ... Asphalt binder content can be calculated in four different ways: total binder content by weight, effective binder content by weight, total binder content by volume, and effective binder content by volume. Total asphalt content by volume is calculated as the percentage of binder by total mix mass: where Pb = Total asphalt binder content, % by mix mass Mb = Mass of binder in specimen Ms = Mass of aggregate in specimen Total asphalt binder content by volume can be calculated as a percentage of total mix volume using the following formula: where VB = Total asphalt binder content, % by total mix volume Pb = Total asphalt binder content, % by mix mass Gmb = Bulk specific gravity of the mixture Gb = Specific gravity of the asphalt binder The absorbed asphalt binder content by volume is also calculated as a percentage of total mix volume: where VBA = Absorbed asphalt content, % by total mixture volume Gmb = Bulk specific gravity of the mixture VBA G P G P G G mb b b s sb mm = ⎛⎝⎜ ⎞⎠⎟ + ⎛⎝⎜ ⎞⎠⎟ − ⎛⎝⎜ ⎞⎠⎟⎡ 100 ⎣⎢ ⎤ ⎦⎥ ( ) Read the entire page →
From page 59... ... VB = Asphalt binder content, % by total mixture volume (see Equation 5-6) Pba = Absorbed asphalt binder, % by total mixture mass VMA is simply the sum of the air void content and the effective asphalt binder content by volume: where VMA = Voids in the mineral aggregate, % by total mixture volume VA = Air void content, % by total mixture volume (Equation 5-4) Read the entire page →
From page 60... ... Ss = Aggregate specific surface, m3/kg Ps = Aggregate content, % by total mix weight = 100 − Pb Gmb = Mixture bulk specific gravity Aggregate Specific Surface. The surface area of aggregate contained in a mixture, expressed as specific surface, is needed to calculate apparent film thickness. Read the entire page →
From page 61... ... Material Specific Gravity Percent by Mass in Aggregate Blend Percent by Mass in Total Mix 12.5-mm limestone 2.621 28.0 26.6 12.5-mm sandstone 2.668 28.0 26.6 Manufactured sand 2.595 44.0 41.8 Asphalt binder 1.030 -- - 4.9 Table 5-1. Mixture composition for example problem. Read the entire page →
From page 62... ... Calculate the absorbed asphalt binder content by mix volume using Equation 5-7: Step 7. Calculate the effective asphalt binder content by volume by subtracting the absorbed asphalt from the total asphalt content (Equation 5-8) Read the entire page →
From page 63... ... . % Mixture Composition Factor Value Total asphalt binder content, % by mix weight 4.9 Absorbed asphalt binder, % by mix weight 0.5 Aggregate content, % by mix weight 95.1 Average aggregate bulk specific gravity 2.622 Mixture bulk specific gravity 2.357 Mixture maximum specific gravity 2.451 Air void content, % by total mix volume 3.8 Effective asphalt binder content, % by total mix volume 10.7 VMA, % by total mix volume 14.5 VFA, % by total mix volume 73.8 Aggregate specific surface, m2/kg 5.1 Apparent film thickness, μm 9.4 Table 5-4. Read the entire page →
From page 64... ... NCHRP Report 573: Superpave Mix Design: Verifying Gyration Levels in the Ndesign Table, TRB, National Research Council, Washington, DC, 73 pp. 64 A Manual for Design of Hot Mix Asphalt with Commentary Read the entire page →

From page 46...

... The asphalt binder content of a mixture, for example, is often given in terms of percent of total mix weight, whereas air void content is always given as a percent of total volume -- it must be given this way, since the mass of air voids in an asphalt concrete specimen is essentially zero. Although composition of asphalt concrete mixtures can be given in terms of weight, traditionally the most common and most important method of describing and analyzing asphalt concrete composition is by volume.