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Chapter3 road pavement
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4. Aggregates are a component of composite materials such as concrete and asphalt concrete
5. Aggregate serves as reinforcement to add strength to the overall composite material.
6. Due to the relatively high hydraulic conductivity value as compared to most soils, aggregates are widely used in drainage applications such as foundation and french drains, septic drain fields, retaining wall drains, and road side edge drains.
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8. The terms asphalt and bitumen are often used interchangeably to mean both natural and manufactured forms of the substance. In American English, asphalt (or asphalt cement) is the carefully refined residue from the distillation process of selected crude oils. Outside the U.S., the product is often called bitumen.
9. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time.
11. In areas with very soft or expansive subgrades such as clay or peat, thick gravel bases or stabilization of the subgrade with portland cement or lime may be required.
14. Warm mix asphalt is applied at temperatures of 200 to 250 degrees F
15. cold mix asphalt is often used on lower volume rural roads, where hot mix asphalt would cool too much on the long trip from the asphalt plant to the construction site.
16. Advantages: low noise, relatively low cost compared with other paving methods, and perceived ease of repair.
17. Disadvantages:less durability than other paving methods,less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon pollutionto soil and groundwater or waterways.BITUMEN AND ASPHALT
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20. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum into a powder to make 'Ordinary Portland Cement', the most commonly used type of cement (often referred to as OPC).
21. Portland cement is a basic ingredient of concrete, mortar and most non-speciality grout.
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23. usually formed from carbon steel, and is given ridges for better mechanical anchoring into the concrete.
24. Rebar is available in different grades and specifications that vary in yield strength, ultimate tensile strength, chemical composition, and percentage of elongation.
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26. 9 TYPES OF TESTS ON MATERIALS a.AggregateImpact Value Test b. Polished Stone Value Test c. Aggregate Crushing Value Test d. Flakiness Index Test e. Elongation Test f. Penetration Test g. Softening Test h. Viscosity Test i. Flash and Fire Point Test j. Ductility Test k.Floatation Test l. Soundness Test.
48. Aggregate to be tested is in size of 63 mm to 6.3 mmFI = Mass of aggregate passing x100 % Total mass
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50. Defined as the distance (in 1 / 10) standard needle puncture of the time, load and temperature are known.
51. Using a standard needle under the load of 100 grams for 5 seconds at a temperature of 20 degrees celsius.
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54. 18 Flash and Fire Point Test When the bitumen is heated at high temperatures, the vapor will be liberated and embrace if any sources of ignition. Flash point indicates the temperature at which bitumen can be heated without danger of fire generated in the presence of the fire. The method used is the Cleveland open cup method.
55. 19 DUCTILITY TEST This test is done to determine the ductility of distillation residue of cutback bitumen, blown type bitumen and other bituminous products as per IS: 1208 – 1978. The principle is : The ductility of a bituminous material is measured by the distance in cm to which it will elongate before breaking when a standard briquette specimen of the material is pulled apart at a specified speed and a specified temperature. The apparatus required for this test: i) Standard mould ii) Water bath iii) Testing machine
57. 21 Objectives of asphalt mix design The design of an asphalt mix is largely a matter of selecting and proportioning materials to optimise the engineering properties in relation to the desired behaviour in service. Procedures for designing asphalt mixes have been generally developed around testing of dense graded mixes and determination of optimum binder content, although most tests can be used for other mix types with suitable interpretation of results. The overall objective for the design of dense graded asphalt paving mixes is to determine (within the limits of project specifications) a cost-effective blend and gradation of aggregates and binder that yields a mix
58. 22 Characteristics of asphaltic concrete mix 1.Sufficient binder to ensure a durable pavement; 2. Sufficient mix stability to satisfy the demands of traffic without distortion or displacement; 3. Sufficient voids in the total compacted mix to allow for a slight amount of in place compaction by traffic and bitumen expansion due to temperature increases, without flushing, bleeding and loss of stability; 4. A maximum void content to limit the permeability of harmful air and moisture into the mix; 5. Sufficient workability to permit efficient placement of the mix without segregation and without sacrificing stability and performance; 6. For surface mixes, proper aggregate texture and hardness to provide sufficient skid resistance.
59. 23 An overview of the design process Asphalt mix design involves the following basic steps that are similar in concept, regardless of the actual tests and procedures used: 1. Selection of mix type. 2. Selection of component materials. 3. Combination of aggregates to meet target grading. 4. Selection of target binder content or range. 5. Mixing and compaction of asphalt mix to a density that is representative of in-service conditions. 6. Measurement of volumetric properties of compacted mix. 7. Mechanical testing of compacted samples, if required. 8. Verification of design properties on samples of manufactured asphalt, if required. 9. Selection of Job Mix.
60. 24 MARSHALL MIX DESIGN METHOD - Developed by Bruce Marshall & the U.S. Corps of Engineers. Objective: To determine the optimum asphalt content for a particular aggregate blend and asphalt to be used.
61. 25 PROCEDURES: 1. Prepare asphalt concrete specimens (4 inches in diameter & 2.5 inches in height) for a range of asphalt content at and near the estimated optimum asphalt content. (A) Mixing temperature: at asphalt viscosity of 170 ± 20 cSt (B) Compaction temperature: at asphalt viscosity of 280 ± 30 cSt (C) Compactive Effort: 35, 50 or 75 blows with a Marshall hammer (10 lbs, 18 inches drop) on each side of the specimen. (D) Number of Samples: 3 replicates at each asphalt content Typically, 5 different asphalt contents are used.
68. 32 % AC at 4% air voids: 6.7 6. Verify mix design criteria at the optimum asphalt content. The five mix criteria to check against are: (A) Marshall stability (B) Marshall flow (C) Air Voids (D) VMA (E) VFA