InstroTek
22
8. Apparent Specific Gravity of Fine and Coarse
Aggregates ASTM D7370
The following procedure can be used to calculate the apparent specific gravity
of fine and coarse aggregates in approximately 7 minutes using the CoreLok
system. In this procedure a sample of oven dry aggregate is placed inside a
bag and vacuum-sealed inside the CoreLok machine. The bag is opened
under water and weighed while submerged. The dry weight and the
submerged weight can be used to calculate the apparent specific gravity. To
determine the bulk specific gravity and percent absorption of the aggregate,
additional testing using the optional AggPlus™ system is necessary.
Note: For large aggregates (0.5 in (12.5 mm) or larger) use two bags. Use the
rubber sheets if necessary. The procedure outlined for asphalt G
mm
can be used
for large aggregate apparent specific gravity determination.
Procedures
1.
Set the CoreLok to Program # 2. In Program #2, the Dwell time is set at 300
seconds, thus making sure that all trapped air is removed out of the bags
2.
Place all three filler plates into the CoreLok chamber. The sliding plate is
not needed.
3.
Weigh an empty large bag and record the weight in column A of the
Max/Apparent Gravity Data Collection Table (
pg. 25
).
4.
Select a representative sample of approximately 1000 to 1500 grams.
Make certain the sample is completely dry. Record the sample weight in
column B.
5.
Place the dry aggregate sample in the bag. Support the bottom of the
bag on a tabletop to support against puncture and impact points.
6.
Place the bag containing the sample into the CoreLok.
7.
Place your hand inside the channel bag and gently and evenly spread
the sample within the channel bag.
Do not try to spread the sample by
squeezing down on the bags. Putting pressure on the bags will create
punctures.
8.
Place the open side of the bag over the seal bar and close the chamber
door.
9.
After the door opens, place the sample in the water for water
displacement analysis.
10.
Cut one corner of the bag, the cut should only be about 1” long. Cutting
the bag too far can cause the fines to escape into the water tank. Make
sure the bag is completely submerged before cutting. Introducing air
into the bag will produce inaccurate results.
