Humboldt H-1686 Void Content Apparatus for Coarse Aggregate - Manual (Page 3)

Refer to AASHTO TP56 for details of above Methods A, B and C.
The method of using the H-1686 Void Content Apparatus is the same
for all methods and proceeds as follows:
1. Position the cylindrical measure under the cylindrical hopper, being sure
that the measure is rested on the centering pin. Piece entire apparatus
in a suitable overflow pan
2. Close and lock the gate of the hopper.
3. Mix the sample until it appears homogeneous. Then pour it into the
hopper. The H-4308 Material Handling Pan works well for weighing
sample fraction makeup, mixing and pouring into hopper.
4. The sample must fall freely from the hopper by rapidly opening the
hopper gate, and the gate doors must swing away quickly and remain
out of the flow of sample. The operator should develop a technique of
accomplishing this result. It may be helpful to hold the gate shut while
releasing the latch, then releasing the gate manually.
5. Strike off excess heaped aggregate from the cylindrical measure being
careful to avoid vibration or other disturbance that could cause
compaction of sample in the cylinder. Insert strike-off bar across cylin-
der diameter at center of heap and work to sides. When a large piece
of aggregate must be removed leaving an unusual void below the rim,
replace it with one or more smaller pieces that fit below the rim.
NOTE: This replacement procedure is not mentioned in AASHTO TP56,
but is recommended.
6. Determine the mass of the cylindrical measure and contents to the
nearest 0.1g. Also record the mass of the empty measure.
7. Recover all aggregate particles for a second test run. Repeat as above,
since reported void contents will be an average of two tests.
8. Calculate uncompacted voids percent to the nearest one tenth percent
for each determination as follows:
U = (V - F/G) ~ x 100
Where: V = volume of cylindrical measure, ml
F = net mass of coarse aggregate in measure, g
G = bulk dry specific gravity of coarse aggregate
(by AASHTO T85 procedure)
U = uncompacted voids, percent in the material