FORMS FOR SPECIFICATIONS, ETC., FOR ROAD MATERIALS. 51 



be followed, using composite samples. Samples at the mill shall be taken by 

 any of the methods of section 18, A. S. T. M. specifications, as may be most 

 practicable. 



Field Samples of Concrete. 



(1) When taken. — Samples shall be taken regularly for the general control 

 of strength and uniformity on one day of each week of work ; and at irregular 

 intervals, whenever a complete change is noted in the character or grading of 

 one or more materials or in any element affecting the entire mix. 



(2) Number of samples. — 



(a) In taking regular samples three specimens should be molded to be 

 broken one at each of the periods, 14 days, 28 days, and 



(o) In taking irregular samples, nine specimens should be molded, three to 

 be broken at each of the periods, 14 days, 28 days, and 



How taken. — The batch sampled for general purpose should be similar in 

 consistency and general grading of the aggregate to the regular run of batches 

 being turned out. The sample from which specimens are molded should be 

 composed of several portions taken during the discharge of one batch in order 

 to represent an average of the batch ; or the batch may be dropped upon the sub- 

 grade and concrete from several points (taking care to exclude dirt), placed in 

 a clean wheelbarrow or other container, avoiding additional mixing. 



Sampling Vitrified Paving Brick. 



Inspection. — Vitrified brick may be inspected and tested at the point of 

 manufacture, or they may be sampled at the point of delivery, and representa- 

 tive samples submitted to the laboratory for testing prior to acceptance of the 

 shipment. 



Plant inspection. — Whenever practicable the inspection and testing of vitri- 

 fied brick shall be carried on at the manufacturer's plant. The choice between 

 plant inspection and sampling at point of use should be based on the average 

 number of brick to be shipped from the plant per day, and the total number 

 required for the particular piece of work. 



Whenever conditions permit, samples should be taken directly from the kiln 

 during the process of emptying. One or more sets of tests, depending upon the 

 size of the kiln, each set consisting of three separate tests, should be made 

 on each kiln. Each test in a set of three should represent approximately a 

 single degree of burning (based on the position of the bricks in the kiln), and 

 all ten of the bricks in a single test should be of the same approximate degree 

 of burning. 



The average abrasion loss in three such tests will determine whether the 

 contents of a kiln or part of a kiln meet the average maximum abrasion loss 

 specified ; and the maximum variation between the per cent abrasion losses of 

 the three sets will be used to determine what portion of the bricks represented 

 will be culled or rejected. 



Sampling from piles at the plant. — In general, samples selected from piles at 

 the plant shall be as nearly as possible representative of the entire run of the 

 brick. Samples from piles shall be taken from as many different points corre- 

 sponding to the length, breadth, and depth of the pile as possible. In no case 

 shall they be confined to the upper or outer few layers. Where controversy 

 arises regarding the admissibility of certain types or portions of the lot, entire 

 test samples may be selected from such types or portions having a characteristic 

 appearance in common. 



