VITRIFIED BRICK PAVEMENTS FOR COUNTRY ROADS. 25 



Office of Public Roads Bulletin No. 44, shall satisfactorily meet the following 

 requirements : 



Hardness not less than ten (10), toughness not less than five (5), and per 

 cent of wear not more than twelve (12). 1 



The crushed stone for use in the concrete curb shall be clean, sound, and 

 durable, and shall be composed of all that part of the product of the crusher 

 which is retained on a screen having circular openings one-fourth (J) inch in 

 diameter, or a one-fourth (i) inch mesh screen, and which passes a screen hav- 

 ing circular openings one and one-fourth (li) inches in diameter. A sample of 

 the stone, when subjected to the physical tests as described in the United States 

 Office of Public Roads Bulletin No. 44, shall satisfactorily meet the following 

 requirements : 



Hardness not less than twelve (12), toughness not less than six (6), and per 

 cent of wear not more than ten (10). 1 



Slag. — The slag for use in the concrete base shall be steel-furnace slag, broken 

 to such sizes that all of the particles will pass a screen having circular openings 

 two (2) inches in diameter and will be retained on a screen having circular 

 openings one-fourth (!) inch in diameter, or a one-fourth (I) inch mesh screen. 

 Not more than seventy-five (75) per cent of the particles shall pass and not 

 more than seventy-five (75) per cent shall be retained on a screen having cir- 

 cular openings three-fourths (f ) inch in diameter. 



The material shall be reasonably uniform in character, and a sample, when 

 subjected to the physical tests, as described in United States Office of Public 

 Roads Bulletin No. 44, shall satisfactorily meet the following requirements: 



Specific gravity not less than two and one-tenth (2.1), hardness not less than 

 fifteen (15), toughness not less than five (5), and per cent of wear not more 

 than fifteen (15). 



A sample of the slag proposed to be used, weighing not less than one hun- 

 dred (100) pounds, shall be .furnished to the engineer by the contractor at least 

 thirty (30) days before It is proposed to use the slag in the work. Test speci- 

 mens of concrete, composed of one (1) part of cement, two and one-half (2£) 

 parts of sand, and five (5) parts of the slag, may be made, and they shall have a 

 compressive strength, when tested at any age not exceeding twenty-eight (28) 

 days, equal to that of a concrete composed of one (1) part of cement, two and 

 one-half (21) parts of sand, and five (5) parts of crushed stone of the quality 

 herein specified for the concrete base. 



Water. — The water used in the mixing of concrete or grout shall be free from 

 oil, acid, alkali, or vegetable matter, and fairly free from clay or silt. 



Brick. — The brick shall be standard wire-cut lug or re-pressed paving block. 

 The standard size of brick shall be three and one-half (3i) inches in width, 

 four (4) inches in depth, and eight and one-half (82) inches in length. The 

 brick shall not vary from these dimensions more than one-eighth (J) inch in 

 width and depth and not more than one-half (i) inch in length, and in brick 

 of the same shipment the maximum width or depth shall not vary from 

 the minimum width or depth more than one-eighth (J) inch. All brick must 

 be thoroughly annealed, regular in size and shape, and evenly burned. When 

 broken they shall show a dense, stonelike body, free from lime, air pockets, 

 cracks, and pronounced laminations. No surface of any brick shall have kiln 

 marks more than three-sixteenths ( h ) inch in depth or cracks more than three- 

 eighths ( I ) inch in depth, and the wearing surface of the brick shall not have 



1 The values given for hardness, toughness, and per cent of wear are intended to exclude 

 unsatisfactory stone, but in communities where better stone is readily available the re- 

 quirements should be made more rigid. 



