Humboldt H-1686 Void Content Apparatus for Coarse Aggregate - Manual (Page 2)

INTRODUCTION
The void content of coarse aggregate measurement provides an indication
of angularity, sphericity and surface texture compared to other aggregates of
the same grading. The test aggregate is allowed to free fall 115mm from the
funnel bottom of a cylindrical hopper into a 154mm diameter by 160mm high
cylindrical measure. Excess heaped aggregate is struck off using a bar, and the
miss is measured.
Uncompacted void content is computed as the difference between the
volume of the cylindrical measure and the absolute volume of tho coarse
aggregate collected in the measure (Based on bulk dry specific gravity
as determined by AASHTO T85). Higher void content in samples of
equal size gradation by this procedure indicate, a combination of greater
angularity, less sphericity. or rougher surface texture.
CALIBRATION OF CYLINDRICAL MEASURE
Apply a light coat of grease to the top edge of the dry, empty, cylindrical
measure. Determine the mass of measure, grease and glass plate. Fill
the measure with freshly boiled, deionized water at 18 to 24°C. Record
water temperature. Place the glass plate on the measure, taking care
that no air bubbles remain. Dry all outer surfaces and determine the
mass of the measure, glass plate, grease, and water to the nearest 0.1g.
Also determine the mass of the clean. dry, empty measure. for
subs equant tests.
Calculate the volume of the measure as follows:
v =1000 (MID)
Where:
v = volume of cylinder, ml
M = net mass of water, g
D = density of water at temperature used. kg/m3
(see table in AASHTO T19)
Determine the volume to the nearest 0.1 ml.
PROCEDURE
AASHTO TP·56 provides three methods of void content measurement,
the differences in method differing by the type of sample used:
Method A: Sample is of standard grading made up from several specified
gradations in specific masses totaling 5000g.
Method B: Separate 5000g samples are tested for each of three sieve
Gradations, then averaged.
Method C: An as-received 5000g sample is used, taken after
removing material finer than the #4 (4.75mm) sieve.