SPECIFICATIONS FOR NONBITUMINOUS EOAD MATERIALS. 33 



Washing Test and Grading, or Mechanical Analysis of Sand-Clay or Top- 

 Soil. (Bmlletin 555, page 35.) — A 500-gram sample of the material is dried 

 at a temperature below 350° F. (176.6° C.) to constant weight, and is gently 

 pulverized to break down soft clods or masses, but not so as to grind or break 

 hard material. The sample is then passed through a 10-mesh sieve, the coarse 

 residue weighed and recorded as " coarse material." The material passing the 

 10-mesh sieve is then used as the starting point of a percentage analysis as 

 follows : 



Two samples of 50 grams each of this material are weighed out for duplicate 

 analysis. Each is placed in a wide-mouth bottle (5 to 6 cm. diameter and 

 about 12 to 15 cm. high), and about 5 c. c. of dilute ammonia water and about 

 200 c. c. of water is added. After thoroughly shaking for about 20 minutes, 

 the sample is allowed to settle 8 minutes and the supernatant liquid de- 

 canted. The process is repeated until the supernatant liquid is clear. The 

 washings drawn off may be collected and evaporated to dryness for direct re- 

 covery of the fine sediment classed as " clay." Ordinarily the sediment loss is 

 computed as difference. 



The content of the bottle is washed into a porcelain evaporating dish and 

 carried to dryness on a water bath. The dried residue is then passed through 

 a nest consisting of a 20, 60, 100, and 200 mesh sieve. The residue retained on 

 each sieve is weighed and recorded as sand of the respective size. Their sum 

 constitutes the " total sand." The residue passing the 200-mesh sieve and 

 caught in the pan is weighed and recorded as " silt." Duplicate samples should 

 check within 1 per cent. 



Tests for Portland Cement. (A. S. T. M. Standard Test C9-17.)— The gen- 

 erally adopted standard methods of testing Portland cement have been so 

 widely circulated through Bureau of Standards Circular No. 33, and publica- 

 tions of the American Society for Testing Materials, that it is thought unneces- 

 sary to include them in this bulletin. These tests cover chemical analysis, 

 specific gravity, fineness, soundness, time of setting, and tensile strength. 



Mortar Tensile Strength Test for Sand. (Based on A. S. T. M. Standard 

 Test C9-17.) — This test is preferably made with the same brand of cement 

 that will be used in construction, but any Portland cement which meets the 

 standard specifications will serve. Briquets composed of three parts of the 

 sand, which has first been passed through a i-inch laboratory screen, to one 

 of cement are made of as near as possible the same consistency as ordinary 

 standard mortar briquets, a set of which should be made at the same time. 

 Such consistency can only be obtained by trial. In general, slightly more 

 water will be required for an ordinary concrete sand than for the standard 

 Ottawa sand. The mortar should be of such consistency after thorough mix- 

 ing that after squeezing in the hand it will stick together and still retain its 

 shape. If the consistency is other than this, a fresh batch of mortar should 

 be made with more or less water as indicated and the trial repeated until the 

 proper consistency is secured. This is preferable to adding water to a batch 

 of mortar which may have been found to be too dry. 



Immediately after mixing, the mortar is placed in the standard molds, 

 pressed in firmly with the thumbs and smoothed off with a trowel without 

 ramming. Additional mortar should be heaped above the mold and smoothed off 

 with a trowel, which should be drawn over the mold in such a manner as to 

 exert a moderate pressure on the material. The mold should then be turned 

 over and the operation of heaping, thumbing, and smoothing off repeated. 

 The briquets must be kept in molds on glass plates in a moist closet for 



