106.3.2.81 TM-81, Specific Gravity and Absorption of Aggregate Using Automatic Vacuum Sealing Method

Figure

EPG 106.3.2.81.11 Worksheet

This method determines the specific gravity and absorption of fine aggregates by Method A and coarse and blended aggregates by Method B. The values are stated in SI units and are regarded as the standard units.

A multi-laboratory precision and bias statement for coarse and combined aggregate tests in this method has not been developed at this time. Therefore, this method should not be used for acceptance or rejection of coarse and combined aggregate materials for purchasing purposes.

Aggregate, Specific Gravity

Report 2006

See also: Research Publications

This standard may involve hazardous materials, operations and equipment and does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

106.3.2.81.1 Referenced Documents

106.3.2.81.1.1 AASHTO Standards

• M43, Sizes of Aggregate for Road and Bridge Construction

• M 29, Wire-Cloth Sieves for Testing Purposes

• M 132, Terms Relating to Density and Specific Gravity of Solids, Liquids and Gases

• M 231, Weighing Devices Used in the Testing of Materials

• T 2, Standard Practice for Sampling of aggregates

• T 19, Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate

• T 27, Test Method for Sieve Analysis of Fine and Coarse Aggregates

• T 85, Standard Test method for Specific Gravity and Absorption of Coarse Aggregate

• T 84, Standard Test Method for Specific Gravity and Absorption of Fine Aggregate

• T 248, Standard Practice for Reducing Samples of Aggregate to Testing Size

106.3.2.81.1.2 ASTM Standards

• D4753, Standard Specification for Evaluating, Selecting, and Specifying Balances and Scales for Use in Testing Soil, Rock and Related Construction Materials

• C 670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials

• C 691, Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method

• C29/ C29 M, Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate

• C 127, Standard Test method for Density, Relative Density (Specific Gravity), and

Absorption of Coarse Aggregate

• C128, Standard Test Method for Density, Relative Density (Specific Gravity), and Absorption of Fine Aggregate

• C 125, Terminology Relating to Concrete and Concrete Aggregates

• C 702, Standard Practice for Reducing Samples of Aggregate to Testing Size

• D 75, Standard Practice for Sampling of Aggregates

• D 136, Test Method for Sieve Analysis of Fine and Coarse Aggregates

Aggregate, Specific Gravity

Report 2006

See also: Research Publications

106.3.2.81.1.3 Other Standards

• CoreLok Operational Instructions (InstroTek, Inc.)

106.3.2.81.2 Terminology

Absorption - the increase in the mass of aggregate due to water in the pores of the material, but not including water adhering to the outside surface of the particles, expressed as a percentage of the dry mass. The aggregate is considered “dry” when it has been maintained at a temperature of 110° ± 5ºC for sufficient time to remove all uncombined water.

Specific gravity - the ratio of the mass (or weight in air) of a unit volume of a material to the mass of the same volume of water at stated temperatures. Values are dimensionless.

Apparent specific gravity—the ratio of the weight in air of a unit volume of the impermeable portion of aggregate at a stated temperature to the weight in air of an equal volume of gas-free distilled water at a stated temperature.

Bulk specific gravity — the ratio of the weight in air of a unit volume of aggregate (including the permeable and impermeable voids in the particles, but not including the voids between particles) at a stated temperature to the weight in air of an equal volume of gas-free distilled water at a stated temperature.

Bulk specific gravity (SSD) — the ratio of the mass in air of a unit volume of aggregate, including the mass of water within the voids filled to the extent achieved by vacuum saturating (but not including the voids between particles) at a stated temperature, compared to the weight in air of an equal volume of gas-free distilled water at a stated temperature.

106.3.2.81.3 Summary of Method

Sufficient aggregate sample is dried to constant mass. For each test, two representative dry aggregate samples of the same material are selected for testing. One sample is evacuated in a vacuum chamber inside a plastic bag and opened under water for rapid saturation of the aggregate. The dry mass and submerged mass of the sample is used for calculation of apparent specific gravity. The second sample of the same aggregate is tested in a known volume metal pycnometer. The known mass of the pycnometer with water, mass of the dry aggregate, and mass of the aggregate and pycnometer filled with water is used for calculation of bulk specific gravity oven dry (OD.) The results from the two samples tested are then used to calculate absorption, and bulk specific gravity saturated-surface-dry (SSD.)

This test can be completed in less than 30 minutes and can be used for rapid determination of aggregate properties in construction testing laboratories.

This test can be performed on fine, coarse and blended (combined) aggregates by using appropriate plastic bag and pycnometer sizes.

106.3.2.81.4 Significance and Use

Bulk specific gravity is the characteristic generally used for calculation of the volume occupied by the aggregate in various mixtures containing aggregate, including Portland cement concrete, hot mix asphalt, and other mixtures that are proportioned or analyzed on an absolute volume basis. Bulk specific gravity is also used in the computation of voids in aggregate in test T 19. Bulk specific gravity SSD is used if the aggregate is wet, that is, if its absorption has been satisfied. Conversely, the bulk specific gravity OD is used for computations when the aggregate is dry or assumed to be dry.

Apparent specific gravity pertains to the solid material making up the constituent particles not including the pore space within the particles that is accessible to water.

Absorption values are used to calculate the change in the mass of an aggregate due to water absorbed in the pore spaces within the constituent particles, compared to the dry condition, when it is deemed that the aggregate has been in contact with water long enough to satisfy most of the absorption potential. The laboratory standard for absorption is that obtained after submerging dry aggregate for a prescribed period of time.

106.3.2.81.5 Apparatus

1) Balance, A balance that conforms to M 231. The balance shall be sensitive, readable and accurate to 0.1% of the test sample mass. The balance shall be equipped with suitable apparatus for suspending the sample in water.

2) Water Bath, A container with minimum dimensions (Length × Width × Depth) of 610 mm × 460 mm × 460 mm (24 in. × 18 in. × 18 in.) or a large cylindrical container with a minimum diameter of 460 mm and 460 mm (18 × 18 in.) deep, for completely submerging the sample in water while suspended, equipped with an overflow outlet for maintaining a constant water level. Temperature controls may be used to maintain the water temperature at 25° ± 1° C (77° ± 2 °F).

It is preferable to keep the water temperature constant by using a temperature controlled heater. Also, to reduce the chance for the bag to touch the sides of the water tank, it is preferable to elevate the water tank to a level at which the sample can be placed on the weighing mechanism while the operator is standing up (waist height), and the placement of the sample and the bag in the water tank can easily be inspected.

3) Sample holder, for water displacement of the sample, having no sharp edges.

4) Vacuum Chamber, with a pump capable of evacuating a sealed and enclosed chamber to a pressure of 6 mm Hg, when at sea level. The device shall automatically seal the plastic bag and exhaust air back into the chamber in a controlled manner to ensure proper conformance of the plastic to the specimen. The air exhaust and vacuum operation time shall be set at the factory so that the chamber is brought to atmospheric pressure in 80 to 125 seconds, after the completion of the vacuum operations.

5) A Vacuum Measurement Gauge, independent of the vacuum sealing device, that could be placed directly inside the chamber to verify vacuum performance and the chamber door sealing condition of the unit. The gauge shall be capable of reading down to 3 mm Hg and readable to ± 1 mm Hg.

6) Plastic Bags, used with the vacuum device, shall be one of the two following sizes: The smaller bags shall have a minimum opening of 235 mm (9.25 in.) and maximum opening of 260 mm (10.25 in.) and the larger bags shall have a minimum opening of 375 mm (14.75 in.) and a maximum opening of 394 mm (15.5 in.). The bags shall be of plastic material, shall be puncture resistant, and shall be impermeable to water. The bags shall have a minimum thickness of 0.127mm (0.005 in.). The manufacturer shall provide the apparent specific gravity for the bags.

7) Small metal pycnometer, 137 mm ± 0.13 mm (5.375 in. ± 0.005 in.) inside diameter (ID) and 89 mm ± 0.41 mm (3.5 in. ± 0.016 in.) tall, for testing fine aggregates. The pycnometer shall be machined to be smooth on all surfaces. The inside of the lid shall be machined at a 5° angle to create an inverted conical surface. The pycnometer shall be equipped with a temperature strip to allow the user to monitor temperature during testing.

8) Large metal pycnometer, 198 mm ± 0.13 mm (7.776 in. ± 0.005 in.) ID and 114 mm ± 0.8 mm (4.5 in. ± 0.03 in.) tall, for testing coarse and blended aggregate. The pycnometer shall be machined to be smooth on all surfaces. The inside of the lid shall be machined at a 5° angle to create an inverted conical surface. The pycnometer shall be equipped with a temperature strip to allow the user to monitor temperature during testing.

9) Fine aggregate fixture to hold and secure the lid on the small metal pycnometer from lifting during fine aggregate tests. The fixture shall be provided with a level indicator.

10) Accessories, A bag cutting knife or scissors, spray bottle filled with isopropyl alcohol, a bucket large enough to allow the pycnometer to be fully submerged in water, water containers to dispense water into pycnometer during testing, syringe with a needle no larger in diameter than 3 mm (0.125 in.), small paint brush and 25 mm (1 in.) wide aluminum spatula.

11) Rubber sheets, for protecting the plastic bags against punctures caused by sharp edges on coarse and blended aggregate samples. The manufacturer shall provide the apparent specific gravity for the rubber sheets.

106.3.2.81.6 Verification

106.3.2.81.6.1 System Verification

The vacuum settings of the vacuum chamber shall be verified once every 12 months and after major repairs and after each shipment or relocation.

Place the gauge inside the vacuum chamber and record the setting, while the vacuum unit is operating. The gauge should indicate a pressure of 6 mm Hg (6 TORR) or less. The unit shall not be used if the gauge reading is above 6 mm Hg (6 TORR).

Vacuum gauge used for verification shall be verified for accuracy once every three years.

In line vacuum gauges, while capable of indicating vacuum performance of the pump, are not suitable for use in enclosed vacuum chambers and cannot accurately measure vacuum levels.

106.3.2.81.6.2 Calibration of the Small Pycnometer

Step 1, Prior to testing, condition the pycnometer to 25° ± 1°C (77° ± 2°F) by placing it inside a bucket of water that is maintained at 25° ± 1°C (77° ± 2°F). Place the fine aggregate fixture on a level surface. Use a level indicator or the provided level to level the fixture.

Step 2, Remove the pycnometer from the water bucket and dry it with a towel. Place the pycnometer in the fixture and push it back until it makes contact with the stops.

Step 3, Fill the pycnometer with 25° ± 1°C (77° ± 2°F) water to approximately 10 mm (0.375 in.) from the top. Using the alcohol spray bottle, spray the surface of the water to remove bubbles.

Step 4, Gently place the lid on the pycnometer and close the clamps on the fixture.

Step 5, Using a syringe filled with 25° ± 1°C (77° ± 2°F) water, slowly fill the pycnometer through the large fill hole on the lid post. Make sure the syringe tip is far enough in the pycnometer to be below the water level. Gentle application in this step prevents formation of air bubbles inside the pycnometer.

Step 6, Fill the pycnometer until water comes out the 3 mm (1/8 in.) hole on the surface of the lid.

Step 7, Wipe any remaining water from the top of the lid with a towel.

Step 8, Place the entire fixture with the pycnometer on the scale and record the mass. Record the mass in the top portion of the Aggregate Worksheet. See EPG 106.3.2.81.11 Worksheet.

Step 9, Clean the pycnometer and repeat Steps 1 through 8 two more times and average the calibration masses obtained in Step 8.

Step 10, If the range for the 3 calibration masses is larger than 0.5 grams, then the test is not being run correctly. Check to see if the fixture is level. Make certain the water injection with the syringe is done below the pycnometer water surface and is applied gently. Check the water temperature. Check the pycnometer temperature. Repeat the above procedure until you have three masses that are within ± 0.5 gram.

Step 11, Re-calibrate the pycnometer daily.

106.3.2.81.6.3 Calibration of the Large Pycnometer

Step 1, Prior to testing, condition the pycnometer to 25° ± 1°C (77° ± 2°F) by placing it inside a bucket of water that is maintained at 25° ± 1°C (77° ± 2°F).

Step 2, Remove the pycnometer from the water bucket and dry it with a towel. Set the pycnometer on a level surface.

Step 3, Fill the pycnometer with 25° ± 1°C (77° ± 2°F) water to approximately 10 mm (0.375 in.) from the top. Using the alcohol spray bottle, spray the surface of the water to remove any air bubbles.

Step 4, Gently place the lid on the pycnometer. Using a syringe filled with 25° ± 1°C (77° ± 2°F) water, slowly fill the pycnometer through the large fill hole on the lid post. Make sure the syringe tip is far enough in the pycnometer to be below the water level. Gentle application in this step prevents formation of air bubbles inside the pycnometer. Fill the pycnometer until water comes out the 3 mm (1/8 in.) hole on the surface of the lid.

Step 5, Wipe any remaining water from the top of the lid and sides with a towel. Place the pycnometer on the scale and record the mass. Record the mass in the top portion of the EPG 106.3.2.81.11 Worksheet.

Step 6, Clean the pycnometer and repeat Steps 2 through 5 two more times and average the calibration masses obtained in Step 5.

Step 7, If the range for the 3 calibration masses is larger than 1 gram, then the test is not being run correctly. Check to see if the fixture is level. Make certain the water injection with the syringe is done below the pycnometer water surface and is applied gently. Check the water temperature. Check the pycnometer temperature. Repeat the above procedure until you have three masses that are within 1 gram range.

Step8, Re-calibrate the pycnometer daily.

106.3.2.81.7 Sampling

106.3.2.81.7.1 Fine aggregate samples (Method A)

Sampling shall be done in accordance with T 2. For fine aggregate testing thoroughly mix the sample and reduce it to obtain one 1000 g ± 10 gram sample for apparent specific gravity and two 500 g ± 3 gram samples for bulk specific gravity determination. For aggregate reduction use the appropriate procedures described in T 248.

106.3.2.81.7.2 Coarse aggregate samples (Method B)

Sample the aggregate in accordance with T 2.

Dry the aggregate to constant mass and thoroughly mix the sample of aggregate and reduce it to one 2000 g ± 10 gram sample for determination of apparent specific gravity and two 1000 g ± 10 gram samples for determination of bulk specific gravity. For reduction of the aggregate samples, use the appropriate procedures in T 248.

If the sample is tested in two or more size fractions, determine the grading of the sample in accordance with test T 27, including the sieves used for separating the size fractions for the determinations in this method.

When testing coarse aggregate of large nominal maximum size requiring large test samples, it may be more convenient to perform the test on two or more sub samples, and the values obtained combined for the computations.

106.3.2.81.8 Procedures

106.3.2.81.8.1 Method A, Fine Aggregate Test

Make certain water temperature used for this test remains at 25° ± 1°C (77° ± 2°F).

Prior to testing, condition the pycnometer to 25° ± 1°C (77° ± 2°F) by placing it inside a bucket of water that is maintained at 25° ± 1°C (77° ± 2°F).

106.3.2.81.8.1.1 Determine Bulk Specific Gravity

Step 1, Make certain the samples are dried to constant mass.

Step 2, For a single test select and separate two 500 g ± 3 gram samples (samples A and B) for the test in the pycnometer and one 1000 g ± 10 gram sample for vacuum saturation test.

Step 3, Allow the sample to cool to room temperature.

Step 4, Place the empty pycnometer in the fixture and push it back until it makes contact with the stops.

Step 5, Weigh a 500 g ± 3 gram dry sample that is at 25° ± 1°C (77° ± 2°F) and record in column A of EPG 106.3.2.81.11 Worksheet.

Step 6, Steps 8 through 15 shall be completed in less than 2 minutes.

Step 7, Place approximately 500 ml (halfway full) of 25° ± 1°C (77° ± 2°F) water in the pycnometer.

Step 8 Slowly and evenly pour the sample into the pycnometer. Make certain aggregate is not lost in the process of filling the pycnometer. Use a brush if necessary to sweep any remaining fines into the pycnometer. If any aggregate is lost during the process of filling the pycnometer, start the test over.

Step 9, Use a metal spatula and push it to the bottom of the pycnometer against the inside circumference. Slowly and gently drag the spatula to the center of the pycnometer, removing the spatula after reaching the center. Repeat this procedure 7 more times so that the entire circumference is covered in 8 equal angles, i.e. every 45 degrees until the starting point is reached. If necessary, use a squeeze water bottle to rinse any sample residue off the spatula into the pycnometer.

Step 10, Fill the pycnometer with 25° ± 1°C (77° ± 2 °F) water to approximately 10 mm (0.375 in.) of the pycnometer rim. It is important that the water level is kept at or below the 10 mm line to avoid spills during lid placement.

Step 11, Use the spray bottle filled with isopropyl alcohol and spray the top of the water to remove air bubbles.

Step 12, Gently place the lid on the pycnometer and lock the clamps. Using the syringe, slowly fill the pycnometer through the center hole on top of the lid post. Make sure the syringe tip is far enough in the pycnometer to be below the water level. Gentle application in this step will prevent formation of air bubbles inside the pycnometer.

Step 13, Fill the pycnometer until water just comes out the 3 mm (1/8 in.) hole on the surface of the lid.

Step 14, Wipe any remaining water from around the 3 mm (1/8 in.) hole with a towel.

Step 15, Weigh the sample, pycnometer and the fixture. Record this mass in column B of EPG 106.3.2.81.11 Worksheet.

Step 16, Repeat Steps 6 through 15 for the second 500 g ± 3 gram sample, Sample B.

Step 17, Average the mass in each column of EPG 106.3.2.81.11 Worksheet for sample A and sample B.

Step 18, Record the average weight of the pycnometer from Step 9 from EPG 106.3.2.81.6.2 Calibration of the Small Pycnometer in column C.

106.3.2.81.8.1.2 Determine Apparent Specific Gravity

Step 1, Set the vacuum device according to manufacturer’s recommendation.

Step 2, Use a small plastic bag and inspect the bag to make sure there are no holes, stress points or side seal discontinuities in the bag. If any of the above conditions are noticed, use another bag.

Step 3, Weigh the bag and record in column D of EPG 106.3.2.81.11 Worksheet.

Always handle the bag with care to avoid creating weak points and punctures.

Step 4, Weigh 1000 g ± 10 grams of oven dry aggregate and record the mass in column F.

Step 5, Place the sample in the bag. Support the bottom of the bag on a smooth tabletop when pouring the aggregate to protect against punctures and impact points.

Step 6, Place the bag containing the sample inside the vacuum chamber.

Step 7, Grab the two sides of the bag and spread the sample flat by gently shaking the bag side to side. Do not press down or spread the sample from outside the bag. Pressing down on the sample from outside the bag will cause the bag to puncture and will negatively impact the results. Lightly spray mist aggregates with high minus 75-μm (No. 200) sieve material to hold down dust prior to sealing.

Step 8, Place the open end of the bag over the seal bar and close the chamber door. The unit will draw a vacuum and seal the bag, before the chamber door opens.

Step 9, Gently remove the sample from the chamber and immediately submerge the sample in a large water tank equipped with a balance for water displacement analysis. It is extremely important that the bag be removed from the vacuum chamber and immediately placed in the water bath. Leaving the bag in the vacuum chamber or on a bench top after sealing can cause air to slowly enter the bag and can result in low apparent specific gravity results.

Step 10, Cut one corner of the bag, approximately 25 mm to 50 mm (1 in. to 2 in.) from the side while the top of the bag is at least 2 in. below the surface of the water. Make sure the bag is completely submerged before cutting. Introducing air into the bag will produce inaccurate results.

Step 11, Open the cut portion of the bag and hold open for 45 seconds. Allow the water to freely flow into the bag. Allow any small residual air bubbles to escape. Do not shake or squeeze the sample, as these actions will cause the fines to escape from the bag.

Step 12, After water has filled in, cut the other corner of the bag approximately 25 mm to 50 mm (1 in. to 2 in.). Squeeze any residual air bubbles on top portion of the bag through the cut corners by running your fingers across the top of the bag. Do not completely remove corners from bag nor allow any portion of the bag to reach the surface of the water.

Step 13, Place the bag containing the aggregate on the weighing basket in the water to obtain the under water mass. The bag may be folded before placing it on the basket. However, once on the basket under water, unfold the bag and allow water to freely flow into the bag. Keep the sample and bag under water at all times. Make certain the bag or the sample are not touching the bottom, the sides, or floating out of the water tank. If the bag contacts the tank it will negatively impact the results of this test.

Step 14, Allow the sample to stay in the water bath for a minimum of 15 minutes.

Step 15, Record the submerged mass in column G of EPG 106.3.2.81.11 Worksheet.

Step 16, Results may be obtained using software developed by the equipment manufacturer. Alternatively, users can develop their own software and correlations for calculation of the results with equations given in EPG 106.3.2.81.9 Calculations.

106.3.2.81.8.2 Method B, Coarse and Combined Aggregate Test

Make certain water temperature used for this test remains at 25° ± 1°C (77° ± 2°F)

Prior to testing, condition the pycnometer to 25° ± 1°C (77° ± 2°F) by placing it inside a bucket of water that is maintained at 25° ± 1°C (77° ± 2°F).

106.3.2.81.8.2.1 Determine Bulk Specific Gravity

Step 1, Make certain the samples are dried to constant mass.

Step2, Allow the sample to cool to room temperature.

Step 3, For a single test select and separate two 1000 g ± 10 gram samples (samples A and B) for the test in the pycnometer and one 2000 g ± 10 gram sample for vacuum saturation test.

Step 4, Make certain the pycnometer is set on a level surface.

Step 5, Weigh a 1000 g ± 10 gram dry sample (sample A) that is at 25° ± 1°C (77° ± 2°F) and record in column A of EPG 106.3.2.81.11 Worksheet.

Step 6, Steps 9.2.3.8 to 9.2.3.15 shall be completed in less than 2 minutes.

Step 7, Place approximately 1000 ml (halfway full) of 25° ± 1°C (77° ± 2°F) water in the pycnometer.

Step 8, Slowly and evenly pour the sample into the pycnometer. Make certain aggregate is not lost in the process of filling the pycnometer. Use appropriate pouring techniques to help in transferring the aggregate into the pycnometer. If any aggregate is lost during the process of filling the pycnometer, start the test over.

Step 9, Use a metal spatula and push it to the bottom of the pycnometer against the inside circumference. Slowly and gently drag the spatula to the center of the pycnometer, removing the spatula after reaching the center. Repeat this procedure 7 more times so that the entire circumference is covered in 8 equal angles, i.e. every 45 degrees until the starting point is reached. If necessary, use a squeeze water bottle to rinse any sample residue off the spatula into the pycnometer.

Step 10, Fill the pycnometer with 25° ± 1°C (77 ± 2°F) water to approximately 10 mm (0.375 in.) of the pycnometer rim. It is important that the water level is kept at or below the 10 mm line in order to avoid spills during lid placement

Step 11, Use the spray bottle filled with isopropyl alcohol and spray the top of the water to remove air bubbles.

Step 12, Gently place the lid on the pycnometer. Using the syringe, slowly fill the pycnometer through the center hole on top of the lid post. Make sure the syringe tip is far enough in the pycnometer to be below the water level. Gentle application in this step will prevent formation of air bubbles inside the pycnometer.

Step 13, Fill the pycnometer until you see water coming out the 3 mm (1/8 in.) hole on the surface of the lid.

Step 14, Wipe any remaining water from around the 3 mm (1/8 in.) hole with a towel.

Step 15, Weigh the pycnometer and the fixture. Record this mass in column B of EPG 106.3.2.81.11 Worksheet.

Step 16, Repeat Steps 6 through15 for the second 1000 g ± 10 gram sample, Sample B.

Step 17, Average the mass in each column of the worksheet, for Sample A and Sample B.

Step 18, Record the average weight of the pycnometer from Step 6 of EPG 106.3.2.81.6.3 Calibration of the Large Pycnometer in column C of EPG 106.3.2.81.11 Worksheet.

106.3.2.81.8.2.2 Determine Apparent Specific Gravity

Step 1, Set the vacuum device according to manufacturers recommendation.

Step 2, Use one small and one large plastic bag. Inspect both bags to make sure there are no holes, stress points or side seal discontinuities in the bag. If any of the above conditions are noticed, use another bag.

Step 3, Weigh both bags and record the mass in column D of EPG 106.3.2.81.11 Worksheet.

Always handle the bag with care to avoid creating weak points and punctures.

Step 4, Weigh the two rubber sheets and record the mass in column E.

Step 5, Weigh 2000 g ± 10 grams of aggregate and record the mass in column F.

Step 6, Place the sample in the small bag. When filling, support the bottom of the bag on a smooth tabletop to protect against puncture and impact points.

Step 7, Place the large bag into the vacuum chamber, then place one of the rubber sheets inside the large bag. The rubber sheet should be flat, centered, and pushed all the way to the back of the large bag.

Step 8, Place the small bag containing the sample into the large bag centered on top of the rubber sheet. Manually spread the sample inside the small bag. Be sure the area taken up by the sample inside the small bag remains completely contained within the area of the rubber sheets. Lightly spray mist aggregates with high minus 75-μm (No. 200) sieve material to hold down dust prior to sealing.

Step 9, Place the other rubber sheet on top of the small bag, inside the large bag. The small bag should be between the two rubber sheets.

Step 10, Place the open end of the large external bag over the seal bar and close the chamber door. Make certain the rubber sheets are not over the seal bar.

Step 11, After the chamber door opens, gently remove the sample from the chamber. Immediately place the sample in the water, for water displacement analysis.

Step 12, Cut one corner of the bag, approximately 70 mm to 100 mm (3 in. to 4 in.) from the side. Make sure the bag is completely submerged before cutting. Introducing air into the bag will produce inaccurate results.

Step 13, Open the cut portion of the large bag and the small bag with your fingers and hold open for 25 seconds. Allow water to freely flow into the bags. Allow any small residual air bubbles to escape from the bags.

Step 14, After water has filled in, cut the other corner of the bag approximately 70 mm to 100 mm (3 in. to 4 in.). Squeeze any residual air bubbles out of the cut corners by running your fingers across the top of the bag. Do not completely remove corners from bag nor allow any portion of the bag to reach the surface of the water.

Step 15, Place the bags containing the rubber sheets and the aggregate on the provided weighing basket under water. You may fold the bag to place it on the basket. However, once on the basket under water, unfold the bag and allow water to freely flow into the bag.

Step 16, Make certain the bag or the sample are not touching the bottom, the sides, or floating out of the water tank. If the bag contacts the tank during mass measurement, it will negatively impact the results of this test. Allow the sample to stay in the water bath for a minimum of 20 minutes.

Step 17, Record the submerged mass in column G of EPG 106.3.2.81.11 Worksheet.

Step 18, Results may be obtained using software developed by the equipment manufacturer. Alternatively, users can develop their own software and correlations for calculation of the results with equations given in EPG 106.3.2.81.9 Calculations.

106.3.2.81.9 Calculations

106.3.2.81.9.1 Initial Specific Gravity

106.3.2.81.9.1.1 Initial Bulk Specific Gravity

Calculate the bulk specific gravity, 25°C (77°F) as follows:

CorG_sb = ${\frac {A}{C-(B-A)}}$

Where:

A = Mass of oven-dry sample 1 in air, g

B = Mass of pycnometer and oven-dry sample in water, g

C = Average mass of pycnometer filled with water, g

D = Mass of plastic bag(s), g

E = Mass of 2 rubber sheets, g

F = Mass of oven-dry sample 2 in air, g

G = Mass of saturated sample 2 in water, g

ρbag = Density of plastic bag(s)

ρrbr = Density of rubber sheets

sa, sb = sample A or sample B.

Cor = represents for Corelock. The CorG_sa, CorAbs, and CorG_sb are all values obtained from vacuum testing in a Corelock machine. The corelock values are not accurate and are corrected using equations in EPG 106.3.2.81.9.1.

106.3.2.81.9.1.2 Initial Apparent Specific Gravity

Calculate the bulk specific gravity, 25°C (77°F) as follows:

CorG_sa = F / ((D + E + F – G) – ((D/ρ_bag) – (E/ρ_rbr)))

106.3.2.81.9.1.3 Initial Absorption

Calculate the absorption, percent, as follows:

CorAbs = $100\times {\frac {CorG_{sa}-CorG_{sb}}{CorG_{sa}\times CorG_{sb}}}$

106.3.2.81.9.1.4 Initial Bulk Specific Gravity (Saturated-Surface-Dry)

Calculate the bulk specific gravity, 25°C (77°F) on the basis of saturated-surface-dry aggregate as follows:

CorG_sb (SSD) =(1+ (CorAbs /100)) × CorG_sb

106.3.2.81.9.2 Predicted properties

Predicted properties account for the effects of absorption during the measurement of the dry aggregate volume by correlating the results to those obtained by T 85 using absorption. When an aggregate does not contain a coarse fraction, e.g. natural sand, T 84 absorption may be used.

Development of regression equations for correlation of properties may be found in MoDOT Report OR06.016. These equations may be substituted for correlation to local aggregates.

The result of equations in EPG 106.3.2.81.9.1.1, Initial Bulk Specific Gravity and EPG 106.3.2.81.9.1.2, Initial Apparent Specific Gravity are used to calculate the following:

106.3.2.81.9.2.1 Predicted Bulk Specific Gravity

G_sb= 0.342355 + 0.8751137CorG_sb - 0.051843 Abs_T85

Where:

AbsT 85 = Absorption from T 85

106.3.2.81.9.2.2 Predicted Apparent Specific Gravity

G_sa = 0.24680896 + 0.90993947CorG_sa - 0.02031058Abs_T85

106.3.2.81.9.2.3 Predicted Absorption

Abs = $100\times {\frac {G_{sa}-G_{sb}}{G_{sa}\times G_{sb}}}$

106.3.2.81.9.2.4 Predicted Bulk Specific Gravity (Saturated-Surface-Dry)

G_sb(SSD) = (1+ (Abs /100)) ×G _sb

106.3.2.81.9.3 Average Specific Gravity Values

When the sample is tested in separate size fractions, the average value for bulk specific gravity, bulk specific gravity (SSD), or apparent specific gravity can be computed as the weighted average of the values as computed in accordance with EPG 106.3.2.81.8.2 Method B, Coarse and Combined Aggregate Test using the following equation:

G = $\left[{\frac {1}{{\frac {P_{1}}{100\times G_{1}}}+{\frac {P_{2}}{100\times G_{2}}}...+{\frac {P_{n}}{100\times G_{n}}}}}\right\rbrack \;$

Where:

G = average specific gravity (All forms of expression of specific gravity can be averaged in this manner.);

G₁, G₂…G_n = appropriate specific gravity values for each size fraction depending on the type of specific gravity being averaged; and

P₁, P₂…P_n = mass percentages of each size fraction present in the original sample.

Some users of this method may wish to express the results in terms of density. Density may be determined by multiplying the bulk specific gravity, bulk specific gravity (SSD), or apparent specific gravity by the density of water (997.5 kg/m³ or 0.9975 Mg/m³ or 62.27 lb/ft³ at 23ºC). Some authorities recommend using the density of water at 4ºC (1000 kg/m³ or 1.000 Mg/m³ or 62.43 lb/ft³) as being sufficiently accurate. Results should be expressed to three significant figures. The density terminology corresponding to bulk specific gravity, bulk specific gravity (SSD), and apparent specific gravity has not been standardized.

106.3.2.81.9.4 Average Absorption Value

When the sample is tested in separate size fractions, the average absorption value is the average of the values as computed in EPG 106.3.2.81.8.2 Method B, Coarse and Combined Aggregate Test, weighted in proportion to the mass percentages of the size fractions in the original sample as follows:

A =(P₁ x A₁/ 100)+(P₂ x A₂/ 100)+ …(P_n x A_n/ 100)

Where:

A = average absorption, percent;

A₁, A₂…A_n = absorption percentages for each size fraction; and

P₁, P₂…P_n = mass percentages of each size fraction present in the original sample.

106.3.2.81.10 Report

Report predicted specific gravity results to the nearest 0.001, and indicate the type of specific gravity, whether bulk, bulk (SSD), or apparent.

Report the predicted absorption result to the nearest 0.1 percent.

106.3.2.81.11 Worksheet

EPG 106.3.2.81.11 Worksheet