ROAD MODELS. 21 



depth made such that footing will extend to rock, hardpan, or other 

 suitable foundation material; where rock is not found the depth is 

 governed by character of soil and topographical features). 



The concrete is made of Portland cement, clean sand, and hard 

 broken stone or gravel, mixed in the following proportions: 



Superstructure, 1:2:4 (size of stone, J to 1 inch). 



Abutments above footings, 1:2^:5 (size of stone, £ to 2^ inches). 



Footings, 1:3:6 (size of stone, I to 2£ inches). 



Plate XII, figure 2, represents a reinforced concrete culvert having 

 a span of 8 feet and height of 4 feet, with 24-foot width of roadway. 

 Lettered cards are used to designate the parts, as follows: 



A, reinforced concrete floor slab, 10^ inches in thickness; B, 

 f-inch twisted steel bars, \\ inches from the underside of the floor 

 slab, spaced 6 inches center to center and parallel to the center line 

 of the roadway (there are also J-inch twisted steel bars, 12 inches 

 center to center, extending the full width of the bridge perpendicu- 

 larly to the center line of the roadway) ; C, abutment wall (thickness 

 at top, 13 inches; thickness at base, 1 foot 10 inches); D, wing walls 

 (thickness at top, 10 inches; thickness at base, 1 foot 1 inch to 2 feet 

 3J inches); E, forms (framing, 2 by 4 inches, 3 feet on centers; 

 boards, If by 8 inches); F, pipe railing (2-inch galvanized-iron pipe 

 protected by painting); G, concrete parapet (top thickness, 1 foot 

 6 inches) ; H, footing (2 feet 6 inches wide by 3 feet or more in depth, 

 depending on foundation material). 



The concrete is made of Portland cement, clean sand, and hard 

 broken stone or gravel, mixed in the following proportions: 



Superstructure, 1:2:4 (size of stone, \ to 1 inch). 



Abutments above footings, 1:2J:5 (size of stone, \ to 1\ inches). 



Footings, 1:3:6 (size of stone, \ to 2% inches). 



Any kind of surfacing or pavement may be used over these bridges. 

 ROADSIDE TREATMENT. 



Plate XIII has been designed to emphasize various methods of 

 roadside treatment. Well-trimmed trees furnish shade along the 

 roads and aid in preventing the road surfaces from drying out and 

 raveling. Neat signposts stand at the crossroads, and in place of a 

 fence the house lawn is divided from the road by a sightly hedge. 

 The use of the guardrail is shown, with the concrete retaining wall 

 where the road follows the creek bank. A well-constructed con- 

 crete arch bridge is a feature of the model. The slopes of the fill 

 extending from the bridge to the crossroad are sodded to prevent 

 slides. Traffic on the fill is protected by double guardrails. 



The schoolhouse represents a type of the modern consolidated 

 country school. Its concrete walk to the road furnishes a good 



