16 



BULLETIN 704, U. S. DEPAETMENT OF AGRICULTUEE. 



General. 



Quality. 



Uethod of 

 Testlag. 



SPECIFICATION GW-1. 



Ch-avel for Water-'bound Gravel Roails. 



The gravel shall be composed of fragments of hard, durable rock, of 

 high resistance to abrasion, together with sand and clay or other binding 

 material, and shall be free from thin or elongated pieces. 



Per cent. 

 Cementing value of material under J-inch mesh shall be not 



less than !50 



1. For base course : 



(a) The gravel, when tested by means of laboratory screens, 

 shall meet the following requirements : 



Passing a 3-inch screen, not less than 95 



Total retained on J-inch screen 50 to 75 



(6) The material retained on the J-inch screen is known as 

 coarse aggregate. The coarse aggregate, when tested 

 by means of a laboratory screen, shall meet the fol- 

 lowing requirement : 



Total retained on IJ-inch screen 25 to 75 



(c) The material passing the |-inch screen is known as fine 

 aggregate. The fine aggregate, when tested by means 

 of a laboratory sieve, shall meet the following re- 

 quirement : 



Total passing 200-mesh sieve 15 to 35 



2. For wearing course : 



(a) The gravel, when tested by means of laboratory screens, 

 shall meet the following requirements : 



Passing a 2-inch screen, not less than 95 



Total retained on J-inch screen 50 to 75 



(6) The material retained on the |-inch screen is known as 

 coarse aggregate. The coarse aggregate, when tested 

 by means of a laboratory screen, shall meet the fol- 

 lowing requirement : 



Total retained on 1-inch screen 25 to 75 



(c) The material passing the i-inch screen is known as fine 

 aggregate. The fine aggregate, when tested by means 

 of a laboratory sieve, shall meet the following require- 

 ment : 



Total passing 200-mesh sieve 15 to 35 



Tests of the quality and grading of the gravel shall be made in accord- 

 ance with the folowing methods : 



Cementing value, U. S. Department of Agriculture Bulletin 345, p. 19. 

 Grading, U. S. Department of Agriculture Bulletin 555, p. 32 (9). 



This specification covers the quality and grading of a sand- 

 clay-gravel suitable for use in the construction of a water-bound 

 gravel road. It applies to gravels composed mainly of fragments 

 of quartz or other nonbinding roclf types. In cases where the 

 gravel is composed essentially of limestone or other materials 

 which will bond under traffic, considerably less material under 

 200-mesh may be allowed. The sizes specified contemplate a base 

 cour.se of at least 4 inches, and a wearing course of at least 3 

 inchas in thickness after consolidation. The relative proportions 

 of the various intermediate sizes have been drawn so as to exclude 

 only gravels of manifestly poor grading. In cases where the 

 gravel, although otherwise acceptable, is deficient in sand or 

 clay, such materials, if available, and of a suitable character, 

 may be added in sufficient quantities to bring the grading and 

 cementing value of the gravel to within the limits specified. This 

 should be done by spreading the sand or clay uniformly over the 

 loose gravel surface and thoroughly harrowing with a spike-tooth 

 harrow, after which the surface is consolidated. 



