Bituminous Materials The term bitumen is a generic name applied to various mixtures of hydrocarbons They may be gaseous, liquid, semisolid, or solid Most common materials within the family of bitumen’s are tars, pitches, and asphalts Destructive distillation is carried out on natural materials produces tar Partial evaporation or fractional distillation of tar produces the solid or semi-solid residue of pitch Asphalts are dark brown or black solids or semi solids which are found in the natural state and are also produced by the refining of petroleum Some natural deposits of asphalts are found in Kentucky, Utah, Colorado, and California 95% of asphalt materials used in North America are derived from the refining of petroleum
Test of Flow of Properties
The viscous or flow properties of bitumen’s are of importance, both at the high temperatures encountered in processing and application and at the low temperatures to which bitumen’s are subjected in service. Flow properties are complex, and as a result, tests have been formulated to measure the consistency of the materials at temperatures comparable to those encountered during the service life of the bitumen.
Test of Flow of Properties
The penetration test Measures the depth of penetration in tenths of millimeters of a weight needle into a bitumen during a period of time at a given temp. Softening point test Measures the temperature degrees Celsius at which a steel ball falls a known distance through the bitumen Ductility Test Are conducted to determine the amount a bitumen will stretch at temperatures below its softening point Viscosity Tests Are used to determine the flow characteristics of asphalts in the range of temperatures used during application Flash Point Test Indicates the temperature to which asphalt cement can be safely heated without danger of flash. A brass cup is partially filled with cement and heated at a prescribed rate. A small flame is place over the surface of the sample Thin Film Oven Test Test is used to obtain a general indication of the amount of hardening which may be expected to occur in an asphalt cement during the plant operation. Viscosity Test Penetration Test
Types of Bitumen’s Tar and Pitch
Most of the tar and pitch used in construction is made by the distillation of coal. Tar is used to saturate felt paper and coated kraft paper to produce a waterproof membrane. Coal – tar pitch oxidizes quite rapidly when exposed to ultra violet rays of the sun.
Types of Bitumen’s Asphalt
A large percentage of the asphalt used results from the refining of crude oils There are three main groups of asphalt products produced from straight run asphalts
Asphalt Hot asphalt- those soften by heat
Hot asphalt can be used directly or it can be processed further to produce a harder material Hot asphalts have good resistance to the transmission of water and water vapor when they are applied to dry surfaces and the heating process is controlled Hot asphalts bond poorly to damp or wet surfaces, have relatively poor flexibility, oxidize under the sun’s rays and are brittle at low temperatures
Asphalt Cut back asphalts – those dissolved in mineral solvents
Cutback asphalts are of three types Straight run asphalt and solvent Heavily filled cutback made by adding a large amount of filler and fiber to asphalt cut with solvent Primer type cutback asphalt in solution with no filler or fiber
Asphalt Emulsion asphalts – those dispensed or suspended in a water base Three types Soap type in which soap is used as the emulsfier Clay modified soap type – clay and soap are used as emulsfier Clay based type Advantages Easy to handle Addition water is all that is necessary to decrease viscosity Drying involves the loss of water by evaporation No heating is required Good bonding to damp or wet surfaces
Uses of Bitumen’s Waterproof coating and membranes Asphalt pavement
Used to provide a waterproof coating for walls and to make waterproof membranes in buildings Asphalt pavement Asphalt cutbacks and emulsions have their greatest use in road construction Accounts for about 85% of amount produced in North America Asphalts in pavements acts as a binder for the aggregates, in this capacity as a cement, the asphalts are usually semisolid Before it can be mixed with the aggregate the asphalt must be made liquid by heating, and cutting with solvent or by emulsifying with water
Uses of Bitumen’s Liquid paving asphalts
Most of the liquid asphalts used for paving are cutbacks Three types Gasoline used as a solvent rapid curing liquid asphalt Kerosene – produces a medium curing asphalt Heavier fuel oils produce a slow curing asphalt Types refer to the rate at which solvent is lost, either during construction or after pavement has been laid The liquid asphalt to be selected for any given project depends on the construction conditions In general a rapid curing grade can be used as a binder for open graded aggregates that coat quickly during mixing or for surface treatments Medium curing grades are required for dense graded aggregates which require longer mixing time Slow curing grades are used with aggregates requiring a long mixing time and for projects where the pavement may have to be torn up and reworked from time to time
Uses of Bitumen’s Asphalt paving cements
The binders for the more expensive asphalt pavements are usually asphalt cements These semisolid materials are also separated into grades having different ranges of hardness Asphalt canal liner and bank erosion control The versatility of asphalt has led to its employment in many types of hydraulic structures Mixes made with the harder asphalts
Uses of Bitumen’s Asphalt shingles Built up roofing
Asphalt shingles are made from heavy rag felt, saturated with asphalt and coated with high melting point flexible asphalt Ceramic coated mineral granules are pressed into the asphalt coating on the exposed face to provide a fire resistant surface. Built up roofing Built up roofing is term applied to a type of roofing made by building up successive layers of felt paper and asphalt over a solid roof deck Five types Type 1 – consists of asphalted felt paper, asphalt and gravel or slag Type 2 – consists of tarred felt paper pitch and gravel Type 3 – consists of asbestos felt, asphalt felt and a smooth flood coat of asphalt Type 4- requires heavy slate surfaced roofing paper as well as asphalt saturated felts Type 5 – called cold process – felts are cold process felts saturated with cold asphalt emulsion and the asphalt top coating is applied cold.
Uses of Bitumen’s Rolled roofing Sprayed on asphalt roofing
Rolled roofing consists of very heavy asphalt saturated felt paper, with or without finely crushed slate embedded in one surface put up in rolls. Sprayed on asphalt roofing A new technique for the application of asphalt roofing involves the use of special equipment for apply the material A special gun with three nozzles and a fiber cutting chamber is used Glass fibers are fed into the chamber where they are cut to predetermined lengths and blown out through a center nozzle
Uses of Bitumen’s Asphalt flooring Fiberboard
Asphalt mastic flooring – is made by mixing an emulsifed asphalt with Portland cement, sand and gravel or crushed stone to form a plastic mixture. This is spread over the floor screened compacted and floated to a depth of ½ in. Asphalt tile – are composed of fibers bond together by a blend of selected asphalt binders Fiberboard Insulation boards composed of asphalt impregnated wood fibers used in built up roofing systems
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