the terms gmm or maximum specific gravity or rice … plant 1/08... · gradation and is influenced...

The terms Gmm or Maximum Specific Gravity or Rice gravity are often used interchangeably

Module 6 - Maximum Specific Gravity

Release 10 4/19/2016

Asphalt Plant Level 1

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The maximum specific gravity test is one of the most important tests run on the mix. It is the basis for all volumetric calculations including air voids and density. It Aaccounts for the specific gravity of the aggregate gradation and is influenced by the source of the aggregate, and also accounts for the asphalt binder in the mix. It is crucial that proper procedures are used since the test is the basis for many other values used in the determining the quality of the mix.


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Listed Aon the next two slides is the equipment needed to conduct this test. The test method is FM 1-T 209.


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More equipment.


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Shown here is a typical setup in a production lab. Other setups are used and vary in piping and the location of the pump/manometer. But, it is important that all the required elements are present in any setup.


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A close-up picture of the orbital shaker, vacuum lines, desiccators, and vacuum pump. One of the keys for longevity of the vacuum pump is a series of moisture traps that include the use of a desiccant (moisture absorbing material). Allowing moisture to get into the pump will cause it to fail, and good quality pumps are expensive.


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The remainder of the equipment needed to run this test is shown.


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Shown here iAs a typical setup showing the testing equipment needed to conduct the maximum specific gravity test. This method is also commonly referred to as the Rice test, named after the inventor, Jim Rice.


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The first step in conducting this test is to calibrate the flask. A capable and accurate scale meeting these requirements is needed. A scale like this will be common in the asphalt testing lab.


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The next step is to determine the volume of the inside of the flask. Weigh the empty dry flask and cover plate to get a dry weight. Fill the flask completely with water and use a cover plate. Make sure the water temperature has stabilized to 77 + 2oF. Slide on the cover plate.

Getting the cover plate on properly (no entrapped air in the flask) takes a little practice, but can be mastered in a short time. Once the flask is full of water and the outside of the flask wiped dry, it is weighed again. Subtracting the empty flask weight from the flask plus water weight leaves the water weight. The water weight in grams is equal to the volume of the flask in cubic centimeters, as 1 gm = 1 cc, at a standard temperature of 77ºF. This step should be done ahead of time prior to the mix samples arriving, so there is no delay.

Calibrate once a month, or if dry weight change is > 0.4g.• Fill flask with water at 77° + 2°F.• Use a cover plate to get accurate filling.• Do not trap air.• Weigh flask (with cover plate) and water.


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The next step is to obtain the mix samples, as shown in an earlier module. Secure a sample size of 2,000-2,200 grams. The test consists of running two complete samples weighing 1,000 to 1,100 grams each. These samples are conditioned in the oven for one hour to simulate haul time.

From the Specifications. Sampling and Testing Requirements: … Prior to testing volumetric samples, condition the test-sized sample for one hour ± five minutes at the target roadway compaction temperature in a shallow, flat pan, such that the mixture temperature at the end of the one hour conditioning period is within ±20° F of the roadway compaction temperature.

Once the conditioning period is completed, the Rice samples are cooled and tested, as shown in the following slides.

Obtain by FM 1-T 168. Total sample size = 2,000 to 2,200 grams. Divided into two 1,000 to 1,100 gram samples. Condition samples. Cool and separate particles.


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Revised: January 12, 2015

Florida Method of Test for

MAXIMUM SPECIFIC GRAVITY OF ASPHALT PAVING MIXTURES

Designation: FM 1-T 209

1. SCOPE

This method covers the determination of the maximum specific gravity ofuncompacted bituminous paving mixtures.

2. REFERENCED DOCUMENT

FM 1-T168 Sampling Bituminous Paving Mixtures.

AASHTO M 231

3. APPARATUS

3.1 Balance - A balance, with a capability of 8 kg or greater, accurate to 0.1 g conforming to the requirements of AASHTO M231, Class G2.

3.2 Container - A glass volumetric flask having a capacity of at least 2000 ml. Side arm flasks will not be acceptable. Containers shall be sufficiently strong to withstand a partial vacuum and shall have a rubber stopper with a hose connection. A small piece of fine wire mesh covering the hose opening shall be used to minimize loss of fine material. The top surfaces of all containers shall be smooth and substantially plane.

3.3 Thermometers – a) Calibrated liquid-in-glass, total immersion type, of suitable range with gradations at least every 0.2°F (0.1°C) and a maximum scale error of 0.2°F (0.1°C) as prescribed in ASTM Specification E1 or b) electronic thermometric device meeting the same gradation and scale error requirements as the liquid-in-glass, total immersion type.

3.4 Vacuum Pump – Capable of evacuating air from the vacuum container to a residual absolute pressure of 30 mm of Hg.

3.5 Manometer - A mercury or digital type suitable for measuring, to the nearest 1 mm, the vacuum being applied to the system. The manometer shall be placed at the farthest location within the system from the vacuum pump and shall be placed higher than the flasks (see Figure 1). The manometer shall be equipped with an adjustable valve to regulate the level of vacuum during testing.

3.6 Moisture Trap - A suitable moisture trap of one or more 1000 ml filter flasks

FM 1-T 209 1

Module 6 - Maximum Specific GravityAsphalt Plant Level 1

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(FIG. 1), or equivalent, shall be installed between the vacuum vessel and vacuum source to reduce the amount of water vapor entering the vacuum pump. A refrigerated cold trap is acceptable.

3.7 Orbital Shaker Table - A shaker table with a orbit of 3/4 inch (19.0 mm) with sufficient load capacity to shake at least two containers and specimens.

4. CALIBRATION OF FLASKCalibrate the volumetric container by accurately determining the mass of the container and the water required to fill it at 77.0 ± 2.0°F (25.0 ± 1.0°C). A cover plate will be used to ensure accurate filling of the container, taking care not to entrap air beneath the cover plate. Designate this mass as (D).

Due to the use of an orbital shaker table, abrasion inside the volumetric container will occur. This shall be corrected by calibrating the container once per month or sooner if the dry weight of the flask changes by more than 0.4 g since the last calibration.

5. TEST SPECIMENS

5.1 The sample shall be obtained in accordance with FM 1-T168, the Method ofSampling Bituminous Paving Mixtures. The test sample shall consist of two specimens of approximately 1000 g to 1100 g each.

6. PROCEDURE

6.1 Separate the particles of each specimen, taking care not to fracture the mineralparticles, so that the conglomerates of the fine aggregate are no larger than 1/4 in. (6.0 mm). If the mixture is not sufficiently soft to be separated manually by hand, place it in a large flat pan and warm in an oven only long enough to allow the mix to be broken apart with bare fingers. If the mix is too hot to handle with bare hands, a spatula may be used to separate the particles until the mix cools enough to allow it to be broken apart with bare fingers.

6.2 Cool the specimens to room temperature, then place each specimen in separate containers and weigh. Designate the mass of each specimen, excluding the mass of the container, as (A). Shake the container vigorously until the specimen moves freely inside the container. Add sufficient water and wetting agent to cover the specimens. Caution: From this point forward care must be taken to ensure no particles are lost which will affect the results.

Note 1: To facilitate the release of entrapped air, a suitable wetting agent such as

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Aerosol OT in concentration of 0.01 percent (1 ml of 10% solution in 1000 ml of water) will be used.

6.3 Remove entrapped air by subjecting each specimen to a partial vacuum of 30 ± 2 mm Hg absolute pressure. The correct vacuum should be achieved within 2 minutes. Once the correct vacuum is achieved, agitate the containers and contents continuously at 270 ± 10 rpm for 15 ± 2 minutes and release the vacuum as soon as agitation is complete.

6.4 After releasing the vacuum in Section 6.3, slowly fill each flask to within 0.5 in (13 mm) of the top of the flask with water at a temperature of 77.0 ± 2.0°F (25.0 ± 1.0°C), taking care not to introduce air into the specimen. Determine the temperature of the water within each container to verify that it is within the allowable temperature range 77.0 ± 2.0°F (25.0 ± 1.0°C). If the temperature is outside of this range, then adjust the temperature through the addition of warm or cold water as needed.

6.5 Between 9 and 11 minutes after releasing the vacuum in Section 6.3, perform and complete the following steps: a) remove the thermometers from the containers and completely fill each container with water at a temperature of 77.0 ± 2.0°F (25.0 ± 1.0°C) using a cover plate, taking care not to entrap air beneath the cover plate, b) wipe the excess moisture from the exterior of the container and the cover plate, and c) determine the mass of the filled flasks (including the cover plate), designating this mass as (E). If the surface dry portion of the test is not to be performed, then this is the final step in the test procedure.

To determine the surface dry mass of the specimen, complete steps 6.6 and 6.7.

6.6 Drain water from the specimens. To prevent loss of fine particles, decant water through a No. 200 sieve (75 μm).

6.7 Spread each specimen in a pan before an electric fan to remove surface moisture. Conglomerations of mixture should be broken apart and stirred at frequent intervals to facilitate uniform drying. Care must be taken to prevent loss of particles of mixture. Weigh each specimen at 15-minute intervals. When the loss in mass for a specimen is less than 0.5 g for this time interval, the specimen may be considered to be in the surface-dry condition. Transfer each specimen into a tared pan and obtain the mass. Designate this final surface-dry mass of each specimen as (B). This procedure requires about 2 hours but may be more or less depending on the mixture.

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Note 2: If the final surface-dry mass of a specimen (B) is less than the original mass of the dry specimen (A), then use the original mass (A) in-place of the surface-dry mass (B) in the maximum specific gravity calculation.

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7. CALCULATIONS7.1 Calculate the specific gravity of each specimen as follows:

7.1.1 When the dryback procedure is used, the maximum specific gravity (Gmm,SSD) is calculated as follows:

Gmm, SSD =A/(B+D-E)

Where: A = mass of dry specimen in air, g. B = final surface-dry mass of specimen, g. D = mass of flask filled with water at 77.0 ± 2.0°F (25.0 ± 1.0°C), g,

and E = mass of flask filled with water and specimen at 77.0 ± 2.0°F (25.0 ± 1.0°C), g.

7.1.2 When the dryback procedure is not used (in situations where a correction factor will be used), the formula in 7.1.1 is modified as follows:

Gmm, dry =A/(A+D-E)

Where: A = mass of dry specimen in air, g. D = mass of flask filled with water at 77.0 ± 2.0°F (25.0 ± 1.0°C), g,

and E = mass of flask filled with water and specimen at 77.0 ± 2.0°F (25.0 ± 1.0°C), g.

A correction factor should be developed and applied to the Gmm, dry in accordance with Section 7.4.

7.2 Calculate the difference between the specific gravities of the two specimens. If the difference between the two specimens is more than 0.013 the test is considered invalid and shall be performed again with new specimens. This applies to the specific gravities determined using either formula as given in Sections 7.1.1 or 7.1.2.

7.3 The specific gravity of the test will be the average of the specific gravities of both specimens. This applies to the specific gravities determined using either formula as given in Sections 7.1.1 or 7.1.2.

7.4 During production the dryback procedure will not be performed and the Gmm,dry will be used. At the mix design stage, it is necessary to calculate a correction factor to determine an accurate maximum specific gravity value. The correction factor will be included on the mix design and used during production. Determine

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the correction factor using two Gmm tests (four flasks). The correction factor is determined using the dryback procedure and calculated as given in Sections 7.1.1, 7.2, and 7.3. This value is referred to as Gmm, SSD. Additionally, for the same two tests, the maximum specific gravity is calculated as given in Section 7.1.2, 7.2, and 7.3. This value is referred to as Gmm, dry. For each of the two tests, the Gmm, dry is subtracted from the Gmm, SSD. These two differences are then averaged to obtain the correction factor. During production, the correction factor is then added to the Gmm, dry values to obtain corrected Gmm, SSD values. The correction factor is either a negative value or equal to zero.

Gmm, SSD #1 – Gmm, dry #1 = Difference #1 Gmm, SSD #2 – Gmm, dry #2 = Difference #2

Diff. #1 + Diff. #2 = Sum of Differences

Sum of Differences ÷ 2 = Correction Factor

Gmm, dry + Correction Factor = Corrected Gmm, SSD

Note 3: All calculations in Section 7 should be rounded to the third decimal place (0.001).

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8. PRECISION

8.1 Criteria for judging the acceptability of specific gravity test results obtained by this method are given in the table entitled "Specific Gravity Test Results." The figures given in column 2 are the standard deviations that have been found to be appropriate for the conditions of test described in column 1. The figures given in column 3 are the limits that should not be exceeded by the difference between the results of two properly conducted tests. For single-operator precision, a test result is defined as the maximum specific gravity for one specimen (i.e., one flask). For multi-laboratory precision, a test result is defined as the average maximum specific gravity of two specimens (i.e., two flasks). These precision values were determined through a round-robin interlaboratory study using plant-produced asphalt mixtures and include the variability associated with sampling, splitting and testing the asphalt mixture. Separate analyses were conducted for the dryback and non-dryback procedures and the results were not significant enough to warrant two precision statements. Therefore, the precision values given below apply to tests conducted using either the dryback or non-dryback procedure.

Specific Gravity Test Results

Test and Type Index Standard Deviation (1S) Acceptable Range of Two Test Results

(D2S)

Single-operator precision 0.00449 0.013 Multi-laboratory precision 0.00557 0.016

Basis of estimate: 4 replicates, 6 materials, 13 laboratories

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FIGURE 1 An example of the correct arrangement of testing apparatus (Note - The purpose of the train of small filter flasks is to trap water vapor from the vacuum vessel, that otherwise would enter the vacuum pump and decrease the pump’s ability to provide high vacuum).

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As the mix cools, the agglomerations or chunks of asphalt need to be separated by hand. Simply rubbing the mix between your hands is normally sufficient. The goal is to separate any chunks of fine sand and asphalt binder to less than ¼ inch in size. We do not want trapped air bubbles left in the mix at this stage. It will affect the test results. If the mix cools off too rapidly, it may need to be warmed enough to separate the chunks.

Separate particles to less than ¼ inch. Warm if necessary.


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Once the mix is sufficiently separated, add the sample to the flask (make sure you get the entire sample from the pan) and weigh. Again, we are going to run two flasks and then compare and average the results. Each flask will contain ½ of the Rice sample.

Add cooled sample to flask and weigh.


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Shake the container gently to make sure the mix has not recombined or chunked up again. No trapped air pockets.

Shake container until mix moves freely.

Do not pound on the flask! This can cause it to break. A broken flask means start over. And it can cause a serious injury.


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The next step is to partially fill the flask, covering the sample completely. A wetting agent, such as aerosol, is used at the rate of 1 ml per 1,000 ml of water. The water and aerosol is mixed (see picture) and poured into the flask.

Add wetting agent to water to help remove air. 1,000 ml H2O + 1 ml aerosol.


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The next step is to partially fill the flask, covering the sample completely.


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Most laboratories are using digital manometers. Shown is the mercury-filled type. If broken and the mercury spills, proper clean up and disposal procedures are required.

The stopper is placed into each flask and they are loaded in the orbital shaker. The pump is turned on and the manometer is adjusted to read a residual pressure of 30 mm of mercury ± 2 mm within 2 minutes. Shown here is a residual manometer. You calculate the total pressure by adding up each “leg” of column of mercury. There are also digital manometers available. Many labs are trying to eliminate the use of mercury.

Put stopper in and adjust vacuum to 30 + 2 mm Hg. Achieve within 2 minutes.


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Next, the sample is agitated while the vacuum pump removes the air. The orbital shaker is turned on and adjusted to 270 + 10 rpm. The duration of this part of the test is 15 + 2 minutes. Set a timer.

Shake continuously with orbital shaker (270 + 10 rpm) for 15 + 2 minutes.


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Once the 15 minutes of orbital shaking have elapsed, turn off the pump and slowly bleed the pressure off the flasks. Set the timer for 10 minutes and the next series of steps need to be completed in that time.

Slowly bleed pressure off. Remove stopper. Start a timer for 10 ± 1 minutes.


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Immediately fill the flasks slowly with water to within ½ inch of the top of the flask. Pouring slowly ensures no air is forced into the sample. The goal is to get the flasks filled and the water temperature stabilized to 77ºF + 2ºF as quickly as possible.

Slowly fill with water. Remove entrapped air.


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If the water temperature is outside that range, remove some water and adjust with either warmer or cooler water.

Determine the temperature. Adjust as necessary to 77º ± 2º F.


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Between the 9th and 11th minute after releasing the vacuum, fill the remainder of the flask with water and ease on the cover plate using caution to not trap any air. This takes a little practice to master.

Fill flask with water and cap with glass plate. Use caution not to trap air.


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Keeping some pressure on the cover plate. Wipe down the flask, including the cover plate.

Carefully dry the outside of the flask and around the cover plate.


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Weigh the filled flask. The requirement is to complete this entire process in 10 minutes + 1 minute.

Weigh the flask with contents and the plate. Complete between 9-11 minutes.


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The dryback procedure, which is used to determine the saturated surface dry (SSD) weight, will not be performed during production. The Gmm correction factor will be determined at the mix design stage. The correction factor will be included on the mix design and used during production.

For reference: When the dryback procedure is used, the maximum specific gravity (Gmm, SSD) is calculated as follows: Gmm, SSD =A/(B+D-E)

When the dryback procedure is not used (in situations where a correction factor will be used), the formula is modified as follows: Gmm, dry =A/(A+D-E)

The correction factor is determined from two Gmm tests (four flasks) using the dryback procedure. This value is referred to as Gmm, SSD. Additionally, for the same two tests, the maximum specific gravity, Gmm, dry, is calculated. For each of the two tests, the Gmm, dry is subtracted from the Gmm, SSD. These two differences are then averaged to obtain the correction factor.

During production, the correction factor is then added to the Gmm, dry values to obtain corrected Gmm, SSD values. The correction factor is either a negative value or equal to zero.

Gmm, SSD #1 – Gmm, dry #1 = Difference #1Gmm, SSD #2 – Gmm, dry #2 = Difference #2

Difference #1 + Difference #2 = Sum of DifferencesSum of Differences ÷ 2 = Correction FactorGmm, dry + Correction Factor = Corrected Gmm, SSD


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Following the weighing, start the dryback process. Drain the water through a 200 mesh sieve so that no particles are lost.

Drain the water through a 75 mm (200 mesh) sieve.


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Once the water is removed, dump the mix into a flat rimmed pan. Rinse the flask out over the sieve. We need to get ALL the mix out of the flask.

Empty as much mix as possible into a clean pan. Rinse the flask over the sieve.


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Rinse out flask onto sieve. Once the flask is completely empty, rinse the mix particles caught on the sieve into the pan. There should be no mix left in the sieve.

Rinse any mix material left in the sieve into the pan.


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Tilt the pan slightly and let the excess water drain to one end. Blot out water being careful not to remove any of the mix sample.

Remove as much water as possible without losing any sample.


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As shown in the picture, spread the mix out in the pan into one thin layer and place in front of a fan. The mixture should be stirred at frequent intervals to facilitate uniform drying.

Spread and dry the sample in front of a fan.


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Set a timer and weigh the pan at 15 minute intervals. The saturated surface dried (SSD) condition is reached when the weight loss is less than 0.5 grams in 15 minutes. Stir the mix intermittently. Once SSD condition has been reached, obtain the final weight and proceed to the calculations that follow.

Weigh every 15 minutes. SSD is when the weight loss is less than 0.5 grams. Stir intermittently.


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The Gmm, SSD formula shown here is used when the dry back procedure is performed.


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Here is an example of the Gmm, SSD formula. The weights are in grams.


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During production, the Gmm, dry values are calculated using the above formula. A correction factor is calculated during the mix design process. This correction factor is added to the Gmm, dry values to obtain the corrected Gmm, SSD values. The correction factor is either a negative value or equal to zero.

Next is an example of the Gmm, dry formula. The weights are in grams.


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Here is an example of the Gmm, dry formula. The weights are in grams.

The correction factor for this particular mix is -0.015.

Gmm, dry + Correction Factor = Corrected Gmm, SSD


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The precision of the test method is shown here.


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There also needs to be a comparison made between the two Gmm tests conducted. The test results must be within 0.013 of each other to be considered a valid test.


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This comparison is shown on based on the example problem. The difference between the two tests is 0.008, which is less than the 0.013 allowed. The test results are considered OK. (They compare). Finally, the two test results are averaged together. This is the final Gmm of the sample.


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An example of multi-lab precision is shown above. The difference of 0.012 (actual) is less than 0.016 (allowed) so the test results compare. This is used is when the VT Gmm test results are compared to the QC Gmm test results.

Also see the Table for Between-Laboratory Precision Values in Specification 334.


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Now that we have the Gmm results, what do we do with them? Again, these are the basis of the air void and density tests. We use the bulk specific gravity (Gmb) of the pills or the cores to calculate these. Shown in the next slide.


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The formula shown here is used to calculate the % air voids. This is covered in more detail in the Asphalt Plant Level 2.


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The formula shown here is used to calculate the roadway density. The Gmb in this case would be the average of the cores from the sublot compared to the Gmm from that same sublot. This is covered more in the Asphalt Paving Level 2.


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the terms gmm or maximum specific gravity or rice … plant 1/08... · gradation and is influenced...

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