of 2 inches specified for the wearing course is on the basis of a course 2 to 3 inches in thickness after consolidation. The chips should be used to fill the surface voids after the first application of bituminous material has been made and also as a cover for the second application or seal coat. Roads of this type may be maintained with surface treatments of bituminous material, covered with material conforming to Specification RS-1 or RS-2. General. Physical SPECIFICATION RBC-1. Broken Stone for One-size Stone Bituminous Concrete Wearing Course. The broken stone shall consist of angular fragments of rock, excluding schist, shale, and slate, 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 requirements: 8 8 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 Aggregate. That portion of the product of the crusher which, when tested by means of laboratory screens, will meet the following requirements: Methods of Tests of the physical properties of the rock and of the sizes of broken-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. Toughness, U. S. Department of Agriculture Bulletin 347, p. 15. 3. 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 bituminous concrete wearing course and seal coat. The broken stone aggregate for the concrete proper is a single size of crusher product with no exact grading limitations. It may therefore produce what is commonly known as an open mix, and will carry from 5 to 7 per cent bitumen. Such mixture may be placed on a well-compacted broken stone or gravel foundation or a cement-concrete foundation so as to produce after rolling a wearing course 2 inches in depth. A seal coat of bituminous material should then be applied and covered with chips in sufficient quantity to take up all excess of bitumen. Such roads may be maintained with surface treatments of bituminous materials, covered with material conforming to Specification RS-2. SPECIFICATION RBC-2. Broken Stone, Sand, and Filler for Coarse Aggregate Bituminous Concrete Wearing Course. BROKEN STONE. The broken stone shall consist of angular fragments of rock, excluding General. schist, shale, and slate, 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 requirements: French coefficient of wear, not less than. Physical 8 Properties. 8 That portion of the product of the crusher, which, when tested by Chips. means of laboratory screens, will meet the following requirements: Passing 1-inch screen, not less than__ Per cent. 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: Aggregate. The sand for fine aggregate shall be composed of sound, durable stone General. particles, free from a coating of clay or loam. When tested by means of laboratory screens the sand shall meet the Grading. following requirements: Passing 3-inch screen.. Total passing 40-mesh sieve.......... Retained on 200-mesh sieve, not less than__. MINERAL FILLER. Per cent. 100 30 to 70 The mineral filler shall consist of limestone dust, dolomite dust, Port- General. land cement, or natural cement. It shall be free from foreign or other objectionable material. When tested by means of laboratory sieves, the mineral filler shall meet Fineness. the following requirements: Passing 30-mesh sieve--- Total passing 200-mesh sieve, not less than__. Per cent. 100 65 Tests of the physical properties of the rock and of the size or mechan- Methods of ical analysis of broken stone, sand, and mineral filler shall be made in Testing. accordance with the following methods: 1. French coefficient of wear, U. S. Department of Agriculture Bulletin 347, p. 5. 2. Toughness, U. S Department of Agriculture Bulletin 347, p. 15. 3. Size of broken stone, U. S. Department of Agriculture Bulletin 555, p. 32. 4. Mechanical analysis of sand and mineral filler, U. S. Department of Agriculture Bulletin 555, p. 33. This specification is intended to cover the mineral constituents of a roughly proportioned bituminous concrete consisting of from 45 to 60 per cent broken stone coarse aggregate, from 30 to 45 per cent and (fine aggregate), from 3 to 5 per cent mineral filler, and from 5 to 8 per cent bitumen. Such a concrete is similar in character to that described under Specification RBC-1, but is a closer mix. It should preferably be placed upon a cement concrete foundation 58683-18-Bull. 704-2 so as to produce, after rolling, a wearing course 2 inches in depth. A seal coat of bituminous material should then be applied and covered with chips in sufficient quantity to take up all excess of bitumen. Such roads may be maintained with surface treatments of bituminous material, covered with material conforming to Specification RS-2. General. Size. SPECIFICATION RBC-3. Broken Stone, Sand, and Filler for Fine Aggregate Bituminous Concrete BROKEN STONE. The broken stone shall consist of angular fragments of rock, excluding schist, shale, and slate, 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. It shall be that product of the crusher which, when tested by means 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 20 General. Size. General. Fineness. General. Grading. SAND. The sand shall be composed of sound durable-stone particles, free from a coating of clay or loam. When tested by means of laboratory screens the sand shall meet the following requirements: The mineral filler shall consist of limestone, dust, dolomite dust. Portland cement, or natural cement. It shall be free from foreign or other objectionable material. When tested by means of laboratory sieves, the mineral filler shall meet the following requirements: Passing 30-mesh sieve Total passing 200-mesh sieve, not less than.. Per cent. 100 65 TOTAL MINERAL AGGREGATE. The total mineral aggregate shall consist of a uniform mixture of the broken stone, sand, and mineral filler, the required grading of each being such as to produce, when properly proportioned, a mixture conforming to the following limitations for grading. The exact proportion of each constituent producing a total mineral aggregate within these limitations shall be as directed by the engineer. When tested by means of laboratory screens and sieves the total mineral aggregate shall meet the following requirements: Tests of the size or mechanical analysis of broken stone, sand, and Methods of mineral filler shall be made in accordance with the following methods: Testing. 1. Size of broken stone, U. S. Department of Agriculture Bulletin 555, p. 32. 2. Mechanical analysis of sand and mineral filler, U. S. Department of Agriculture Bulletin 555, p. 33. 3. Grading of total mineral aggregate, U. S. Department of Agriculture Bulletin 555, pp. 32 and 33. This specification is intended to cover the mineral constituents and grading for bituminous concrete of a modified Topeka, or stone-filled, sheet asphalt type. It is so drawn that from 10 to 50 per cent of broken stone will be required and the mixture of very fine broken stone and sand will possess a satisfactory sheet asphalt grading. Such an aggregate will carry from 7 to 11 per cent of bitumen. It should preferably be placed upon a cement concrete foundation to a compacted depth of 2 inches. No seal coat will ordinarily be required, and maintenance should consist only in patching with bituminous concrete until it is necessary to replace the entire wearing course. SPECIFICATION RBC-4. Broken Stone, Sand, and Filler for Binder Course and Sheet Asphalt BROKEN STONE FOR BINDER COURSE. The broken stone shall consist of angular fragments of rock, excluding General. schist, shale, and slate, 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, and when tested all of the broken stone shall pass a 1-inch laboratory screen. The stone shall meet the following requirement: Toughness, not less than__- SAND FOR BINDER COURSE. Physical 8 The sand shall be composed of sound durable stone particles, free from General. a coating of clay and loam, which when tested shall all pass a inch laboratory screen. TOTAL MINERAL AGGREGATE FOR BINDER COURSE. The total mineral aggregate shall consist of a uniform mixture of the General. broken stone and sand, the required grading of each being such as to produce, when properly proportioned, a mixture conforming to the following Imitations for grading. The exact proportion of each constituent prodbeing a mineral aggregate within these limitations shall be as directed by the engineer. When tested by means of laboratory screens and sieves the total min- Grading. eral aggregate shall meet the following requirements: Passing 1-inch and retained on 1-inch screen. Per cent. 15 to 65 20 to 50 15 to 35 SAND FOR SHEET-ASPHALT WEARING COURSE. General. Grading. The sand shall be composed of sound, durable, angular stone particles, free from a coating of clay or loam. When tested by means of laboratory sieves the sand shall meet the following requirements: General. Fineness. Methods of Passing 30-mesh and retained on 40-mesh sieve- MINERAL FILLER FOR SHEET-ASPHALT WEARING COURSE. The mineral filler shall consist of limestone dust, dolomite dust, Portland cement, or natural cement. It shall be free from foreign or other objectionable material. When tested by means of laboratory sieves, the mineral filler shall meet the following requirements: Tests of the physical properties of the rock and of the size, mechanical analysis, or grading of broken stone, sand, and mineral filler shall be made in accordance with the following methods: 1. Toughness, U. S. Department of Agriculture Bulletin 347, p. 15. 3. Mechanical analysis or grading of sand and mineral filler, U. S. This specification is intended to cover the mineral constituents and rough grading of the mineral aggregate of a binder course and the sand and mineral filler for a sheet-asphalt wearing course. The gradings are essentially those included in Specifications for Sheet Asphalt Paving adopted by the American Society of Municipal Improvements in 1915. The aggregate for binder course will carry from 4 to 7 per cent bitumen. It should be laid upon a concrete base so as to produce a thickness after compaction of about 1 inches. In order to secure the specified sand grading for the wearing course it may be necessary to combine two or more sands in predetermined proportions. The surface mixture should be composed of sand, mineral filler, and asphalt cement. It should carry from 6 to 20 per cent filler and from 9 to 13 per cent bitumen. It should be laid upon the binder course so as to produce a compacted wearing course 1 or 2 inches thick as desired. Maintenance of the wearing course should consist only in patching with sheet asphalt topping until it is necessary to replace the entire course. |
