﻿22 BULLETIN 23, U. S. DEPARTMENT OP AGRICULTURE. 



Stone curbing. — All stone curbing shall have the shape and size shown 

 on the plans, and shall be hauled and set before the subgrade is com- 

 pleted. The stone used shall be hard, tough, and of a homogeneous 

 texture, and no section of curbing shall have a length less than 4 

 feet. Stone curbing shall be set true to line and grade, and shall be 

 securely bedded in either broken stone or gravel. 



Concrete curbing. — All concrete curbing shall be constructed before 

 the subgrade is completed. It shall have the cross section shown on 

 the plans, and shall be composed of Portland cement concrete, mixed 

 hi the proportion 1 part of cement, 2 parts of sand, 4 parts of broken 

 stone or washed gravel, and sufficient water to make a quaky mixture. 

 The specifications as to quality of the materials, mixing and placing 

 the concrete, etc., hereinafter given under "Concrete foundation/' 

 shall apply also to concrete curbs. 



Forms for concrete curbs shall be constructed of dressed lumber, 

 and the curb shall be constructed in sections not less than 4 feet nor 

 exceeding 12 feet in length. When complete the curb shall present 

 a smooth, neat, uniform appearance, and shall be true to line and 

 grade. • 



Marginal curb. — Marginal curbs shall be constructed at the ends 

 of the pavement and at all intersections with other roads and drive- 

 ways. The marginal curbs shall conform to the specifications given 

 above for the kind of curbing employed, except that they shall be 

 shaped to conform to the cross section of the pavement. 



Broken stone or gravel foundation. — If a broken stone or gravel 

 foundation is called for, it shall be constructed of sound, durable 

 material, and to the compacted depth shown on the plans. The 

 material shall be well graded in size between that which will just be 

 retained on a screen having |-inch circular openings and that which 

 will just pass a screen having 1^-inch circular openings. After the 

 broken stone or gravel has been spread, sufficient clean sand or stone 

 screenings to fill the voids shall be spread over it and flushed in by 

 means of sprinkling and rolling. When completed the foundation 

 shall be well compacted, free from depressions, and uniform in grade 

 and cross section. 



Concrete foundation. — If a concrete foundation is called for, it shall 

 be constructed to the depth shown on the plans in the following 

 manner: 



The subgrade shall be completed for a distance of at least 50 feet 

 in advance of the foundation work. The foundation shall be con- 

 structed of Portland cement concrete mixed in the proportions 1 part 

 of Portland cement, 3 parts of sand, 6 parts of broken stone, and 

 sufficient water to bring the mass to a condition commonly described 

 as quaky. The concrete shall be thoroughly mixed to the satisfac- 

 tion of the engineer, either by hand or in a mechanical mixer approved 



