SAMPLING AND TESTING HIGHWAY MATERIALS. 



27 



(55) Immediately after mixing, the standard mortar shall be placed in the molds, 

 pressed firmly with the thumbs, and smoothed off with a trowel without ramming. 

 Additional mortar shall be heaped above the mold, and smoothed off with a trowel; the 

 trowel shall be drawn over the mold in such a manner as to exert a moderate pressure 

 on the material. The mold shall then be turned over and the operation of heaping, 

 thumbing, and smoothing off repeated. 



Fig. 13.— Form of briqustte as recommended by the committee on uniform tests of cement of the American 



Society of Civil Engineers. 



( 56) Tests shall be made with any standard machine . The briquettes shall be tested 

 as soon as they are removed from the water. The bearing surfaces of the clips and 

 briquettes shall be free from grains of sand or dirt. The briquettes shall be carefully 

 centered and the load applied continuously at the rate of 600 pounds per minute. 



(57) Testing machines should be frequently calibrated in order to determine their 

 accuracy. 



(58) Briquettes that are manifestly faulty, or which give strengths differing more 

 than 15 per cent from the average value of all tests pieces made from the same sample 



Fig. 14.— Gang mold. 



and broken at the same period, shall not be considered in determining the tensile 

 strength. 



STORAGE OF TEST PIECES. 



(59) The moist closet may consist of a soapstone, slate, or concrete box, or a wooden 

 box lined with metal. If a wooden box is used, the interior should be covered with 



