24 



BULLETIN 949, TJ. S. DEPARTMENT OE AGRICULTURE. 



(41) The consistency of standard mortar shall depend on the amount of water 

 required to produce a paste of normal consistency from the same sample of cement. 

 Having determined the normal consistency of the sample, the consistency of standard 

 mortar made from the same sample shall be as indicated in the following table, the 

 values being in percentage of the combined dry weights of the cement and standard 

 sand. 



Percentage of water for standard mortars. 





For 1 to 





For 1 to 





For 1 to 





For 1 to 



For 



3 mor- 



For 



3 mor- 



For 



3 mor- 



For 



3 mor- 



neat 



tars of 



neat 



tars of 



neat 



tars of 



neat 



tars of 



ce- 



stand- 



ce- 



stand- 



ce- 



stand- 



ce- 



stand- 



ment 



ard Ot- 



ment 



ard Ot- 



ment. 



ara Ot- 



ment 



ard Ot- 



paste. 



tawa 



paste. 



tawa 



paste. 



tawa 



paste. 



tawa 





sand. 





sand. 





sand. 





sand. 



18 



9.5 



21 



10.0 



24 



10.5 



27 



11. 



19 



9.7 



22 



10.2 



25 



10.7 



28 



11.2 



20 



9.8 



23 



10.3 



26 



10.8 



29 



11.3 









DETERMINATION OF SOUNDNESS. 



(42) A steam apparatus, which can be maintained at a temperature between 98° 

 and 100° C, or one similar to that shown in figure 11, is recommended. The capacity 

 of this apparatus may be increased by using a rack for holding the pats in a vertical 

 or inclined position. 



(43) A pat from cement paste of normal consistency about 3 inches in diameter, 

 one-half inch thick at the. center, and tapering to a thin edge, shall be made on clean 

 glass plates about 4 inches square, and stored in moist air for 24 hours. In molding 

 the pat, the cement paste shall first be flattened on the glass and the pat then formed 

 by drawing the trowel from the outer edge toward the center. 



(44) The pat shall then be placed in an atmosphere of steam at a temperature 

 between 98° and 100° C. upon a suitable support 1 inch above boiling water for 5 hours. 



(45) Should the pat leave the plate, distortion may be detected best with a straight- 

 edge applied to the surface which was in contact with the plate. 



DETERMINATION OP TIME OP SETTING. 



(46) The following are alternate methods, either of which may be used as ordered : 



(47) The time of setting shall be determined with the Vicat apparatus described 

 in paragraph 39 (see fig. 10). 



(48; A paste of normal consistency shall be molded in the hard-rubber ring G as 

 described in paragraph 40, and placed under the rod B, the smaller end of which 

 shall then be carefully brought in contact with the surface of the paste, and the rod 

 quickly released. The initial set shall be said to have occurred when the needle 

 ceases to pass a point 5 mm. above the glass plate in one-half minute after being re 

 leased; and the final set when the needle does not sink visibly into the paste. The 

 test pieces shall be kept in moist air during the test. This may be accomplished by 

 placing them on a rack over water contained in a pan and covered by a damp cloth, 

 kept from contact with them by means of a wire screen; or they may be stored in a 

 moist closet. Care shall be taken to keep the needle clean, as the collection of cement 

 on the sides of the needle retards the penetration, while cement on the point may 

 increase the penetration. The time of setting is affected not only by the percentage 

 and temperature of the water used and the amount of kneading the paste receives. 

 but by the temperature and humidity of the air, and ils determination is therefore 

 only approximate. 



