30 BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 



The specification already given for concrete curbs constructed in combination 

 with the foundation shall also apply to curbs constructed separate from the 

 foundation as regards proportioning, mixing, and placing the concrete, con- 

 structing the forms, and all other features of construction which are not 

 covered on the plans or in this specification. 



STONE CURBS. 



"Where stone curbs are required, they shall be hauled and set before the 

 subgrade is finally completed. The curbs shall be set true to line and grade 

 and shall be securely bedded in broken stone, gravel, or firm earth. In pre- 

 paring the trenches for the curbs great care shall be exercised to see that the 

 material upon which the curb is to be set is well compacted, firm, and hard. 



Stone curbing shall be quarried from hard, tough, homogeneous stone. The 

 individual blocks shall have the- cross section shown on the plans and shall 

 be not less than four (4) feet in length. Each block shall be free from seams and 

 all other imperfections and shall be neatly dressed and finished on all exposed 

 faces. 



CRUSHED-STONE BASE. 



Where a crushed-stone base is called for on the plans it shall be constructed 

 after the curbs are set and in two (2) courses of such thickness that the finished 

 base will have the required depth shown on the plans. 



The first course of stone shall consist of a single layer of No. 1 stone spread 

 uniformly to a depth of not more than eight (8) inches before compacting. The 

 stone shall be spread by hand from dumping boards or from dump wagons of a 

 type that will distribute each load of stone evenly over that part of the sub- 

 grade to be covered by the load. 



After the crushed stone of the first course has been spread to the required 

 depth, it shall be rolled until it is thoroughly compacted and firm with a power 

 roller of the macadam type, weighing not less than ten (10) tons and not more 

 than fifteen (15) tons. The rolling shall begin at the curbs and progress gradu- 

 ally toward the crown. All irregularities and depressions that may develop 

 shall be immediately corrected with No. 1 stone, and the rolling shall continue 

 until the stone is well compacted and the surface is uniform in grade and 

 cross section. 



The second course of stone shall consist of a single layer of No. 2 stone 

 spread uniformly to a depth not exceeding four (4) inches. The stone shall be 

 spread and rolled in the manner prescribed for the first course. When completed 

 the surface of the second course of crushed stone shall be smooth, firm, well 

 compacted, and continuous, and shall have the cross section and grade indicated 

 by the drawings. 



After the second course of stone has been spread, rolled, and completed as 

 above specified, screenings shall be spread uniformly over the surface to a depth 

 of approximately one-half ($) inch. The spreading shall be done with shovels 

 from piles along the road, from dumping boards, or from carts. In no case shall 

 an entire load of screenings be dumped directly upon the second course. 



After the screenings are spread they shall be dry rolled until the voids of the 

 second course are filled. The foundation shall then be sprinkled with water 

 from properly constructed sprinkling wagons and rolled with a power roller of 

 the type and weight specified for the first course. The amount of water used 

 shall be sufficient to wet the stone thoroughly, but shall be put on in such quan- 

 tity and manner as not to wet and soften the subgrade. Screenings shall be 

 added and the sprinkling and rolling continued until the surface ceases to show 



