ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. c. 10 CENTS PER COPY UNITED STATES DEPARTMENT OF AGRICULTURE BULLETIN No. 704 Contribution from the Bureau of Public Roads LOGAN WALLER PAGE, Director Washington, D. C. PROFESSIONAL PAPER. August 30, 1918 TYPICAL SPECIFICATIONS FOR NONBITUMINOUS ROAD MATERIALS. By PRÉVOST HUBBARD, Chemical Engineer, and FRANK H. JACKSON, Jr., Assistant Testing Engineer. This publication should be considered as a companion bulletin to "Typical Specifications for Bituminous Road Materials.” In it are given a number of typical specifications for the more common nonbituminous materials used in the construction and maintenance of various types of highways. These are grouped mainly according to type of road. In so far as practicable materials of the same class have also been kept together. When a single type of road requires more than one class of nonbituminous material peculiarly suited to that class, all of the materials are treated in the same specification. under appropriate subheadings. Thus in specification RC-2, where the requirements for coarse aggregate for concrete base are the same for broken stone or gravel, these materials have been specified together. Also in specifications such as RBC-2, for bituminous concrete, all of the nonbituminous constituents, including broken stone, sand, and filler, are included. 2 During the summer of 1917 a survey was made of stone quarries in certain sections of the country with the primary object of obtaining data relating to the commercial sizes of broken stone, which would enable the Bureau of Public Roads to recommend a minimum 1. S. Department of Agriculture Bulletin 691. Public Roads," vol. 1, No. 2, June, 1918. number of standard sizes necessary for the various types of roads in which broken stone is used. It was found that, within a very restricted area, revolving screens, with as many as 28 different size openings, were being used to produce broken stone for a comparatively few types of roads. As a rule, the exact size of product for any one type of road is selected by the individual engineer without reference to other products which the crushing plant may be called upon to supply, also without reference to what size or sizes the engineer himself will select for other types of roads. Moreover, great lack of uniformity in the method of specifying sizes of broken stone was found to exist so that the entire subject of broken stone specifications is at present in an almost chaotic condition. Following the very logical recommendations of the First Conference of State Highway Testing Engineers and Chemists,1 the specifications for sizes of broken stone, as given in this bulletin, are based upon laboratory screen tests, rather than upon the size of openings in the commercial screen which produces the material. Based upon data secured in the survey previously mentioned, a limited number of sizes has been selected. It is believed that for the commercial production of each size sufficient tolerance has been allowed in the specifications to make practicable the use of revolving screens with the same openings as the maximum and minimum laboratory screens specified for that size. In most cases, the amount passing an intermediate laboratory screen has also been specified with limits (from 25 to 75 per cent) sufficiently wide to include all acceptable commercial products between the maximum and minimum size but reject most products which would be unacceptable. The different size broken stone products which may be used satisfactorily in constructing various types of road are given in Table I. It will be seen that not more than five different size openings in revolving screens are required for any one type. In order to meet reasonable working conditions, a general tolerance of not less than 5 per cent retained on the maximum screen, and 15 per cent passing the minimum screen, has been allowed. In the case of screenings, when only the maximum size revolving screen would be required ordinarily, as the product would include dust and all other smaller material, from 40 to 80 per cent of material passing the 1-inch screen is specified. The only other exception is the broken stone for Topeka type bituminous concrete, where at least 20 per cent of material is required to be retained on the 1-inch screen. It is realized that just as satisfactory roads may be constructed with sizes of broken stone varying considerably from these specifications. It is believed, however, that the sizes here covered represent average practice and they are recommended for general use as |
