26 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
(b) The approximate percentage of voids in the inundated fine aggregate 
may be calculated from the formula : 
400 X specific gravity— W x 1(J0 
400 (specific gravity— 1) 
where 
F=the approximate percentage of voids, 
Specific gravity=apparent specific gravity of the fine aggregate, 
]r=combined weight in grams of 400 cubic centimeters of 
water and fine aggregate in the flask. 
6. Duplicate determinations should check to within 1 per cent. Variations in, 
the composition of the rock grains of the fine aggregate which result in varia- 
tions of 0.05 in the approximate apparent specific gravity of the aggregate will 
cause an inaccuracy in results equal to from 2 to 3 per cent of voids. 
18. METHOD OF TEST FOR FIELD DETERMINATION OF 
SURFACE MOISTURE IN FINE AGGREGATE 
(A. S. T. M. tentative standard method (J), serial designation C 70-27 T) 
1. This method of test is intended for use in the field for making approximate 
determinations of the percentage of surface moisture in fine aggregate for use 
in computing the allowance to be made for water in the fine aggregate when 
proportioning concrete by the maximum water content method. 
This method determines only surface moisture; that is, moisture on the 
outside of the particles. The moisture absorbed within the particles does not 
add to the volume of the particles' and. therefore, does not make itself evident 
in this test. 
2. The apparatus shall consist of the following : 
{a) Balance. — A balance, preferably of the torsion type, having a capacity of 
2 kilograms or more and sensitive to 0.5 gram or less. 
( b > Flask. — A special graduated flask of the type, and conforming to the 
dimensions, shown in Figure 8. 
3. A sample weighing about 1 kilogram shall be selected which shall be as 
truly representative of the fine aggregate as possible. It shall be well mixed 
and spread out on a flat nonabsorbent surface. Five hundred grams shall be 
immediately weighed out, permitting moisture to evaporate as little as possible 
from the sample. 
4. The graduated flask shall be filled to the 200-cubic centimeter mark on 
the lower neck with water at room temperature. The 500-gram sample of damp 
aggregate shall then be slowly poured into the flask, and the contents of the 
flask agitated or stirred to free any entrained air bubbles. The combined 
volume, in cubic centimeters, of the water and fine aggregate shall be read on 
the scale on the upper neck of the flask. 
5. (a) This method requires that the npparent specific gravity be known of 
the fine aggregate in a room-dry, free-flowing condition, but with the voids 
within the particles of the aggregate containing moisture. If the apparent 
specific gravity of the aggregate in this condition is not known it shall be 
determined in accordance with the tentative method of test for field determina- 
tion of approximate apparent specific gravity of fine aggregate (serial designa- 
tion C 68-27 T) of the American Society for Testing Materials (5). 
(&) The percentage of surface moisture in the fine aggregate (air-dry basis) 
may be calculated from the formula : 
200 
Percentage of surface moisture = ^§^4^^ X100 
zOO-j-oOO — V 
where 
F=the combined volume in cubic centimeters of the water and fine aggre- 
gate in the flask, 
Specific gravity=approximate apparent specific gravity of the fine aggregate. 
6. Duplicate determinations should check to within 0.5 per cent. Variations 
in the composition of the rock grains of the fine aggregate which result in 
variations of 0.05 in the approximate apparent specific gravity of the aggregate 
will cause inaccuracy in results equal to from 1 to 1.5 per cent of moisture. 
