112n STEEL HIGHWAY BRIDGES. CHAP. III. 



Bituminous Wearing Surface on Timber Sub-Floor. The bituminous wearing surface may 

 be put on hot by the standard method, or by a cold process. The specifications adopted in 1917 

 by the Illinois Highway Commission are as follows: 



Bituminous Wearing Surface Hot Penetration Method. Illinois Highway Commission. 



Asphalt. The asphalt used for bituminous wearing surface shall conform to the following 

 requirements: Asphalt shall have a specific gravity at 25 C. of not less than 0.97 nor more than 

 unity. It shall be soluble in cold carbon disulphide to the extent of at least 98 per cent. Of the 

 total bitumen, not less than 22 per cent nor more than 30 per cent shall be insoluble in 86 B. 

 naphtha. When 20 grams (in a tin dish 2| in. in diameter and in. deep with vertical sides) are 

 maintained at a temperature of 163 C. for 5 hours in a N. Y. testing laboratory oven, the evapora- 

 tion loss shall not exceed 2 per cent and the penetration shall not have been decreased more than 

 25 per cent. The fixed carbon shall not exceed 16 per cent by weight. The penetration as de- 

 termined with the Dow machine using a*No. 2 needle, 100 g. weight, 5 seconds time, and a tem- 

 perature of 25 C. shall be not less than 30 nor more thah 50. The asphalt shall contain not to 

 exceed 6 per cent by weight of paraffine scale. 



Aggregate. The aggregate shall consist of screened gravel, which shall have been approved 

 by the engineer, dry, free from dust, dirt and clay, and graded in size from f in. to in. 



Cleaning Sub-Planking. Before placing the wearing surface, the sub-planking shall be thor- 

 oughly cleaned from all foreign material and the cracks shall be filled and the plank covered to a 

 depth of approximately | in. with asphalt of the character herein specified, which shall be applied at 

 a temperature of not less than 400 F. The sub-planking shall be dry when the asphalt is applied. 



Placing Wearing Surface. The gravel shall be spread on the asphalt covering while the same 

 is hot and in a quantity which will just cover the asphalt. The thickness must not exceed that 

 which will be formed by a single layer of the gravel pebbles. 



Upon the material thus spread, -there shall be poured hot asphalt until the interstices are all 

 filled, the asphalt being at a temperature of not less than 400 F. 



Upon the layer of asphalt thus poured there shall be spread a second layer of gravel which shall 

 not exceed the thickness of a single layer of pebbles, but which must be spread in sufficient quantity 

 to cover completely the layer of asphalt. 



Upon the layer of gravel thus spread there shall be poured hot asphalt until all the interstices 

 are filled, the asphalt having a temperature of not less than 400 F. 



Finish. The surface shall then be covered with a layer of pebbles just sufficient to cover th$ 

 asphalt, the pebbles to be well rolled or tamped into the asphalt and the surface finally covered 

 with coarse sand sufficient to take up any free asphalt. After the surface has stood for one day, 

 it may be opened to traffic. 



Bituminous Wearing Surface Cold Mixing Method, using an Asphalt Emulsion. Illinois 

 Highway Commission. 



Asphalt Emulsion. The emulsion shall consist of asphalt, water and fatty or resin soap thor- 

 oughly emulsified. It shall conform to the following requirements: 



Total bitumen Not less than 60.0 per cent 



Specific gravity of dehydrated material Not less than i.ooo 



Penetration of dehydrated material, 25 C., 100 gm., 5 sec 150 to 200 



Total Bitumen. The total bitumen shall be considered as being 100 minus the sum of the 

 percentages of water, of fatty or resin acids, of organic matter insoluble in carbon disulphide other 

 than fatty or resin acids from the soap, or mineral matter (ash), and of ammonia. 



For percentages of water, fatty or resin acids, organic matter insoluble in carbon disulphide, 

 mineral matter (ash), and ammonia, see United States Department of Agriculture Bulletin 314, 

 p. 41. 



Specific Gravity. Standardized pycnometers, United States Department of Agriculture 

 Bulletin 314, p. 4. 



Penetration A.. S. T. M. Stand. Test D 5-16. 



Aggregate. The aggregate shall consist of crushed stone chips uniformly graded from f in. 

 down to dust with all dust removed, to which shall be added sufficient sand to fill all remaining 

 voids, but not to exceed 20 per cent of the volume of the aggregate. 



Cleaning Sub- Planking. Before placing the wearing surface, the sub-planking shall be 

 thoroughly cleaned from all foreign material and all cracks shall be filled with wood strips or oakum. 



Mixing Materials. The aggregate and the asphalt emulsion shall be mixed cold in the pro- 

 portions of I gal. of emulsion to I cu. ft. of aggregate. To facilitate mixing, water to the extent of 

 20 per cent may be added to the emulsion. The proportions given above for mixing the aggregate 

 and the emulsion are based on the undiluted emulsion. The mixing shall be done on a tight 

 mixing board or in a batch concrete mixer, and shall continue until all particles of the aggregate 

 are thoroughly coated. 



