1 a means toward standardizing not only specifications for broken stone but also plant practice in the production of broken stone for highway work. The forms of specification adopted for broken stone as well as other nonbituminous road materials are, in general, those recommended by the First Conference of State Highway Testing Engineers and Chemists.1 Following each specification is a brief descriptive paragraph, stating the general conditions governing its uses and what modifications may in certain instances be made. More detailed information and advice relative to methods of construction may be obtained upon application to the Bureau of Public Roads. It is realized that all classes and types of nonbituminous road materials have not been covered, and it is intended to add to the number of these specifications from time to time. For the convenience of engineers, and in order to make this bulletin complete in itself, the methods of test to which reference is made in the specifications, and directions for sampling, are given in an appendix. TABLE I. Relation of commercial revolving screens to laboratory screen requirements for broken stone. General. Physical Screenings. SPECIFICATION RW-1. Broken Stone for Water-bound Macadam. The broken stone shall consist of angular fragments of rock, excluding granite, gneiss, sandstone, quartzite, schist, shale, and slate, of uniform quality throughout, free from thin or elongated pieces, soft or disinte grated stone, dirt, or other objectionable matter. The stone shall meet the following requirement: French coefficient of wear, not less than... 7 That portion of the product of the crusher, including the dust of frac ture, which when tested by means of laboratory screens will meet the following requirements: Top Course Bottom Course Methods of Passing 1-inch screen-- Total passing 1-inch screen.. Per cent. 100 40 to 80 That portion of the product of the crusher which when tested by means of laboratory screens will meet the following requirements: Passing 2-inch screen, not less than. Total passing 11-inch screen-- Per cent. 95 25 to 75 85 Retained on 1-inch screen, not less than---- That portion of the product of the crusher which when tested by means of laboratory screens will meet the following requirements: Passing 3-inch screen, not less than_. Per cent. 95 25 to 75 85 Retained on 2-inch screen, not less than___ Tests of the physical properties of the rock and of the sizes of brokenstone products shall be made in accordance with the following methods: 1. French coefficient of wear, U. S. Department of Agriculture Bulletin 347, p. 5. 2. Size, U. S. Department of Agriculture Bulletin 555, p. 32. This specification is intended to cover stone to be used in the construction of a broken-stone road by the usual water-bound macadam methods. In certain instances the use of granite, gneiss, sandstone, or quartzite may be allowed in the bottom course, provided the material otherwise meets the specification. These types would be excluded from the wearing course, owing to lack of binding qualities found in materials of this nature. The French coefficient of wear of 7.0 is to be considered here in the light of a minimum requirement under rather light traffic conditions, unless the road is to be maintained with a bituminous wearing mat or carpet. The exact value to be inserted should be governed by the character of available material and estimated traffic conditions. For an ordinary water-bound road subjected to moderate traffic, a coefficient of from 9 to 15 would be more satisfactory, while for heavy traffic a value as high as 16.0 might be required. A coeffi cient of wear of not less than 7.0 is satisfactory when the road surface is to be maintained with a bituminous material. It is estimated that for an average rock a bottom course 5 inches and a wearing course 3 inches in thickness, before consolidation, will utilize practically the entire product of an ordinary portable crushing outfit and provide sufficient screenings to properly bind the surface, with a slight excess of screenings in the case of the softer grades of rock, which may be used if desired in filling the bottom course. SPECIFICATION RW-2. Broken Stone for Water-bound Base. The broken stone shall consist of angular fragments of rock, excluding General. granite, gneiss, sandstone, quartzite, schist, shale, and slate, of uniform quality throughout, free from thin or elongated pieces, soft or disintegrated stone, dirt, or other objectionable matter. The stone shall meet the following requirement: French coefficient of wear, not less than__ Physical 5 That portion of the product of the crusher, including the dust of frac- Screenings. ture, which, when tested by means of laboratory screens, will meet the following requirements: Passing 1-inch screen, not less than_ Total passing 1-inch screen--- That portion of the product of the crusher which, when tested by means of laboratory screens, will meet the following requirements: Passing 3-inch screen, not less than__ Total passing 2-inch screen-- Retained on 1-inch screen, not less than.. Per cent. 40 to 80 Coarse Stone. 95 25 to 75 85 Tests of the physical properties of the rock and of the sizes of broken- Methods of stone products shall be made in accordance with the following methods: Testing. 1. French coefficient of wear, U. S. Department of Agriculture Bulletin 347, p. 5. 2. Size, U. S. Department of Agriculture Bulletin 555, p. 32. This specification provides primarily for stone to be used in the construction of water-bound base upon which some higher type of wearing course will be placed, preferably after the base has been finally compacted by traffic. For the softer grades of rock it may also serve for both foundation and wearing courses, provided the thickness of each is not less than 4 inches. In case the broken-stone base is not to be water bound, granite, gneiss, sandstone, and quartzite may be allowed. SPECIFICATION RS-1. Coarse Broken Stone for Bituminous Surface Treatment. The broken stone shall consist of angular fragments of clean, hard, General. tough, durable rock of uniform quality throughout, free from soft or disintegrated stone, dirt, or other objectionable matter. It shall be that product of the crusher, which when tested by means Size. of laboratory screens, will meet the following requirements: Passing 1-inch screen, not less than.. Retained on 1-inch screen, not less than_ Per cent. 95 85 Tests of the size of broken stone shall be made in accordance with the Method of fellowing method: Size, U. S. Department of Agriculture Bulletin 555, p. 32. This specification provides for a broken-stone product which may be used as cover for a bituminous material applied hot to a road surface. For this purpose it should be evenly spread at the rate of 1 cubic yard to every 50 to 75 square yards of treated road surface, depending upon the amount of bituminous material which has been applied per square yard. Under traffic, preferably preceded by rolling, it is expected to produce, in combination with the bituminous material, a wearing mat or carpet. When the treatment of bituminous material is less than gallon per square yard a product meeting Specification RS-2 is to be preferred. Testing. General. Size. Method of SPECIFICATION RS-2. Fine Broken Stone or Gravel for Bituminous Surface Treatment. The broken stone or gravel shall consist of clean hard tough durable stone, free from soft or disintegrated particles, dirt, or other objectionable matter. When tested by means of laboratory screens it shall meet the following requirements: Passing 1-inch screen, not less than___ Per cent. 85 85 Tests of the size of broken stone or gravel shall be made in accordance with the following method: Size, U. S. Department of Agriculture Bulletin 555, p. 32. This specification provides for a product to be used as cover for a bituminous material applied to a road surface. For this purpose 1 cubic yard should cover from 50 to 150 square yards of treated road surface, depending upon the amount of bituminous material which has been applied per square yard. Under traffic it is expected to produce, in combination with the bituminous material, a thin wearing mat or carpet. It may be considered as an alternate for Specification RS-1 and preferable to the latter when the treatment of bituminous material is less than gallon per square yard. General. Physical Screenings. SPECIFICATION RB-1. Broken Stone for Bituminous Macadam. The broken stone shall consist of angular fragments of rock, excluding granite, gneiss, sandstone, quartzite, schist, shale, and slate, of uniform quality throughout, free from thin or elongated pieces, soft or disinte grated stone, dirt, or other objectionable matter, occurring either free or as a coating on the stone. The stone shall meet the following requirements: That portion of the product of the crusher, including the dust of fracture, which, when tested by means of laboratory screens, will meet the following requirements: Chips. That portion of the product of the crusher which, when tested by means of laboratory screens, will meet the following requirements: Per cent. Passing 1-inch screen, not less than_. 95 85 Top Course That portion of the product of the crusher which, when tested by means of laboratory screens, will meet the following requirements: That portion of the product of the crusher which, when tested by Bottom Course means of laboratory screens, will meet the following requirements: Stone. Methods of Tests of the physical properties of the rock and of the sizes of broken- Testing. stone products shall be made in accordance with the following methods: 1. French coefficient of wear, U. S. Department of Agriculture Bulletin 347, p. 5. 2. Size, U. S. Department of Agriculture Bulletin 555, p. 32. This specification is intended to cover stone to be used in the construction of a water-bound broken-stone base, and a bituminous broken-stone wearing course constructed by the penetration method. If the base is not to be water bound, the use of granite, gneiss, sandstone, or quartzite may be allowed, provided the material otherwise meets the specifications. Practically the entire output of an ordinary portable crushing outfit will be utilized if a bottom course filled with screenings is constructed 5 inches thick and a top course from 2 to 3 inches thick. The chips should be used to fill the surface voids in the top course after the first application of bituminous material has been made and also as a cover for the second application or seal coat. Such roads may be maintained with surface treatments of bituminous material, covered with material conforming to Specification RS-1 or RS-2. SPECIFICATION RB-2. Broken Stone for Bituminous Macadam Wearing Course. The broken stone shall consist of angular fragments of rock, excluding General. schist, shale, and slate, of uniform quality throughout, free from thin or elongated pieces, soft or disintegrated stone, dirt, or other objectionable matter, occurring either free or as a coating on the stone. The stone shall meet the following requirement: Physical French coefficient of wear, not less than_-_ 7 That portion of the product of the crusher which, when tested by means Chips. of laboratory screens, will meet the following requirements: Per cent. Passing 1-inch screen, not less than. 95 Retained on 1-inch screen, not less than. 85 That portion of the product of the crusher which, when tested by means Coarse of laboratory screens, will meet the following requirements: Stone. Passing 2-inch screen, not less than. Per cent. Total passing 13-inch screen_---. Retained on 1-inch screen, not less than-- 25 to 75 Tests of the physical properties of the rock and of the sizes of broken Methods of stone products shall be made in accordance with the following methods: Testing. 1. French coefficient of wear, U. S. Department of Agriculture Bulletin 347, p. 5. 2. Size, U. S. Department of Agriculture Bulletin 555, p. 32. This specification covers stone to be used in the construction of a bituminous broken-stone wearing course in which the bituminous material is applied by the penetration method. The maximum size |