12 



BULLETIN 555, U. S. DEPARTMENT OF AGRICULTURE. 



Moris 



strength test. 



M «■ t h o d s of 



sanii/Iing. 



Methods of 



testing. 



When that portion of the combined dustless screenings and 

 sand which passes a one-quarter-inch laboratory screen is mixed 

 with Portland cement in the proportion of 1 part of cement to 

 3 parts of the combination, by weight, according to standard 

 methods of making 1 : 3 mortar briquets, the resulting mortar at 

 the age of 7 and 28 days shall have a tensile strength of at least 



* per cent of that developed in the same time by mortar 



of the same proportions and consistency, made of the same cement 

 and Ottawa sand. 



Preliminary acceptance samples shall be subjected to both 

 7 and 28-day tests, and acceptance based thereupon. Samples 

 tested during the progress of the work will be accepted on the 

 basis of the 7-day test. 



Stone shall be sampled for quality in accordance with the 



method described on page , paragraphs , of these 



specifications. Dustless screenings and mixtures of the dustless 

 screenings and sand shall be sampled for grading in accordance 



with the method described on page , paragraphs , of 



these specifications ; and sand shall be sampled in accordance with 



the method described on page , paragraphs , of these 



specifications. 



Tests of the physical properties of stone shall be made in ac- 

 cordance with the method described or referred to on page 



of these specifications, test No. Tests of the grading of 



dustless screenings and of the combination of dustless screenings 

 and sand shall be made in accordance with the method described 

 or referred to on page of these specifications, test No. 



Note. — It is recommended that volumetric analyses be reported 

 by the laboratory to facilitate field control. 



SPECIFICATION FOR STONE BLOCK. 



General. 



Physical prop- 

 erties. 



Dimensions. 



Visual Inspec- 

 tion. 



The stone block shall be of (^s^.type. 8 . allowable) , of medium- 

 sized grain, showing an even distribution of constituent minerals. 

 They shall be of uniform quality and texture throughout, and 

 free from seams, scales, or disintegrated material. 

 Sample blocks shall meet the following requirements : 



Per cent of wear not more than 



(or French coefficient not less than ) 



Hardness to 



The blocks shall meet the following requirements: 



Inches. 



Length on top to 



Width on top to 



Depth to 



The stone block shall be subjected to inspection subsequent to 

 delivery at the place of use, prior to and during laying, in order 

 to cull out and reject those which fail to conform with the general 



* It is recommended that the strength ratio be 100 per cent for this 

 purpose. 



