SAMPLING AND TESTING HIGHWAY MATERIALS. 
21 
may be used with slight modification in making tests for con- 
crete for wearing resistance, bond between concrete and steel, 
impermeability, etc. The investigation of machine-mixed concrete 
will require certain obvious changes in the method. 
2. Materials shall be brought to room temperature (65° to 70° 
P.) before beginning tests. Cement shall be stored in a dry 
place, preferably in covered metal cans. The cement shall be 
thoroughly mixed in advance, in order that the sample may be 
uniform throughout the tests. It shall be sifted through a No. 16 
sieve and all lumps rejected. Aggregates shall be in a room-dry 
condition when used in concrete tests. 
3. Representative samples of all concrete materials shall be 
secured for preliminary tests prior to the proportioning and 
mixing of the concrete. Cement test samples may be made up 
of a small quantity from each sack used in the concrete tests. 
Test samples of aggregates may be taken from larger lots by 
quartering. 
4. Cement shall be subjected to test, using the methods de- 
scribed in the standard specifications and tests for Portland 
cement. 
5. Fine aggregates shall be subjected, when required, to the 
following tests : 
(a) Sieve analysis test made in accordance with the test for 
mechanical analysis of aggregates for concrete. 
(5) Test for organic impurities (natural sand only) made in 
accordance with the test for organic impurities in sands for 
concrete. 
(c) Test for quality of silt, clay, or dust made in accordance 
with the test for quantity of clay and silt in sand for highway 
construction. 
(d) Test for unit weight made in accordance with the test for 
unit weight of aggregate for concrete and percentage of voids. 
(e) Strength test of 1:3 mortar at 7 and 28 days in com- 
parison with standard sand mortar, in accordance with the com- 
pression and tension tests of fine aggregate for concrete. 
6. Coarse aggregates shall be subjected, when required, to the 
following tests: 
(a) Sieve-analysis test as specified under section 5 (a). 
(b) Test for quantity of silt, clay, or dust, in accordance with 
the test for quantity of clay and silt in gravel for highway con- 
struction. 
(c) Test for unit weight as specified under section 5 (d). 
7. The unit weight of mixed fine and coarse aggregates as used 
in concrete tests shall be determined in accordance with the 
method specified in section 5 (d). 
8. The quantities of each size of aggregate to be used in each 
batch shall be determined on the basis of the sieve analysis and 
the unit weight of the mixed aggregate. The exact quantities of 
cement and of each size of aggregate for each batch shall be de- 
termined by weight. The quantity of water for each batch shall 
be accurately measured. The quantities of materials may be ex- 
pressed as (a) 1 volume of cement to - volumes of total aggregate 
mixed as used, or (b) 1 volume of cement, - volumes fine aggre- 
gate, and - volumes of coarse aggregate. 
9. Compression tests of concrete shall be made on cylinders of 
a diameter equal to one-half the length. The standard shall be 
6 by 12 inch cylinders where the coarse aggregate does not ex- 
ceed 2 inches in size; for aggregates larger than 2 inches, 8 by 
16 inch cylinders shall be used ; 2 by 4 inch cylinders may be used 
for mixtures without coarse aggregate. 
10. (a) Concrete shall be mixed by hand in batches of such 
size as to leave a small quantity of concrete after molding the test 
pieces. The batch shall be mixed as follows : 
(b) The cement and fine aggregate shall be mixed dry until 
the mixture is homogeneous in color. 
(c) The coarse aggregate shall be added and mixed dry. 
Tests of 
materials. 
Preparation 
of test 
specimen. 
