HIRENG MT 07: Bituminous materials

bitumen

• Any various occuring mixtures ofhydrocarbons and their nonmetallic derivatives

• Composed of decomposed marine organisms that settled to the bottom of the sea mixed with silt and sand

• Transformed over time into petroleum and natural gas

Examples of bitumen

• Crude petroleum

• Asphalt

• Tar

Petroleum deposits

• Found in sediment basins rich in organic material that buried long enough for oil to form

Asphalt

• Black, cement-like material varying in consistency of solid to semi-solid

• Found in natural deposits in pits or lakes as residue from crude petroleum or now commercially derived from petroleum

Refining process in obtaining petroleum asphalt; fractional distillation

• Removes the diff volatile materials in crude oil at high temp until petroleum asphalt is obtained as residue

Refining process in obtaining petroleum asphalt: destructive distillation

• Involve application of high temperature and pressure resulting in chem changes that convert raw materials to useful chemicals

Thermal cracking

• Process developed to increase yield of distillation

• The heavier portions of crude oil were heated under pressure at higher temperatures

Types of asphalt binders

• Asphalt cement

• Asphalt cutbacks

• Asphalt emulsions

Asphalt cement

• Obtained after separation of lubricating oils

• Semisolid hydrocarbons with physicochemical characteristics that make them good cementing agents

• Used in manufacture of hot-mix, hot-laid asphalt concrete

Uses of asphalt concrete in construction

• Highway pavement

• Airport pavement surface and base

• Parking areas

• Industrial floors

Asphalt cutback

• Combination of asphalt cement and petroleum solvent

• Used in cold-laid plant mixes, road mixes, and as surfac etreatments

Types of asphallt cutbacks

• Slow curing asphalt

• Medium curing asphalt

• Rapid curing asphalt

Slow curing asphalt

• Obtained through distillation of crude petroleum or cutting back or reduction of amount of asphalt cement with heavy distillate diesel

Medium curing asphalt

• Produced by cutting back residual asphalt with light fuel oil or kerosene

Rapid curing asphalt

• Made by blending asphalt cement with a petroleumdsitillate that will evaporate easily like gasoline or naptha

Emulsified asphalts

• Produced by breaking asphalt cement into minute particles and dispersing them in water with emulsifier

• Classifications of asphalt emulsions:

  • Anionic - negatively charged

  • Cationic- positively charged

  • Nonionic- neutrally charged

• Used in cold laid plant mixes and road mixes - construction of highway pavement surfaces, bases,a dn surface treatments

Properties of asphalts

• Consistency

• Aging and temperature sustainability

• Rate of curing

• Resistance to water action

Conditions inn determining asphalt connsistency

• Variation of consistency with temperature

• Consistency at specified temperature (indicated that state of asphalt within temperature range

Aging and temperature sustainability

• Asphalt material exposure to environmental elements lead to deterioration due to weathering - loss in material plasticity and brittleness

Durability

• Resistance of asphalt material to resist weathering

Factors influencing weathering in asphalt

• Oxidation

• Volatilization

• Temperature

• Surface area

Oxidation

• Chemical reaction that takes place when asphalt material is attacked by oxygen in the air

• Causes asphalt hardening

Volatilization

• Evaporation of lighter hydrocarbons from asphalt

• Causes loss of plasticity

Temperature

• Rate of oxidation and volatilization changes as temperature changes

Surface area

• Rate of oxidation and volatilization changes as surface area changes

Curing

• Defined as the process through which an asphalt material increases its consistency as it loses solvent by evaporation

Inherent factors affecting the rate of curing cutbacks

• Volatility of solvent

• Quantity of solvent in cutback

• Consistency of base material

External factor affecting rate of curing of cutbacks

• Temperature

• Ratio of surface area to volume

• Wind velocity across exposed surface

Resistance to water action

• Asphalt must sustain ability to adhere to aggregates even in the presence of water

• Otherwise, asphalt will strip off resulting in pavement deterioration

• No preventive action in hot mix hot laid

• Commerical antistri additives added in hot mix cold laid

Consistency test

• Consistency at a temperature indicates grade of material

• Viscosity property used to describe consistency of asphalt material

• Viscosity tests:

  • Saybolt furol test- temp of 25, 50, 60

  • Kinematic viscosity- temp of 135

  • Rotational viscosity- temp of 60-200, 20rpm

Penetration test

• Gives empirical measurement of consistency of material in terms of distance a standard needle sinks into that material under prescribed loading and time

Float test

• Used to determine the consistency of semisolid asphalt materials with so high viscosity

• 50C water bath

• Float test value time required for after to force its way through bitumen plug

Ring-and-ball softening point test

• Used to measure susceptibility of asphalt to temperature changes by determining temp which material will be adequately softened to allow standard ball to sink through it

• Measure resistance to temperature shear

• Softening point temp at which asphalt material touches bottom of bath

Durability test

• Thin-film oven test used to measure susceptibility characteristics of asphalt to abnormal temperature and atmospheric changes

Rate of curing test

• Uses volatility and quantity of solvent to indicate rate of curing

• Determined from distillation test

• Used for cutbacks and emulsions

Rheological test

• Uses dynamic shear rheometer to charaterize viscous and elastic behavior of asphalt binders at med-high temps

• Bending beam rheometer provides measure of low temp stiffness and relaxation properties

  • Give asphalt binder’s ability to resist low temp crackling

Specific gravity test

• Specific gravity determines the weight of a given volume of material , the amount of voids in compacted mixes, and corrects volumes measured at high temperatures

• Theoretical maximum specific gravity determined by taking sample of hot mix-asphalt, weigh, then determine its volume through vole of water displaced

Ductility test

• Indicate the extent to whihc the material can be deformed without breaking

• ductility is distance a standard sample of asphalt material will stretch without breaking at 25C

Solubility test

• Measures the amount of impurities in the asphalt material

Flashpoint test

• Flash point is the temp at which vapor will ignite instantaneously in presence of open flame

Loss-on-heating test

• Determines amount of material that evaporates from sample under a specified temperature and time

• Determines whether asphalt material has been contaminated with lighter materials

Asphalt mixtures

• Uniformly mixed combination of asphalt cement, coarse aggregate, fine aggregate, and other materials

• Types:

  • Hot mix hot laid

  • Hot mix cold laid

  • Cold mix cold laid

Hot mix hot laid asphalt

• Used for high-type pavement construction

• Open graded, coarse graded, dense graded, or fine graded

Hot mix cold laid

• Manufactured hot and then shipped and laid immediately or stockpiled for future use

• Suitable for patching

Objective of mix design

• Determine optimum blend of different components that will satisfy the requirements of the given specifications

  • Adequate mount of asphalt for durable pavements

  • Have satisfactory mix stability to prevent unacceptable distortion and displacement

  • Voids in total compacted mixture should be adequately balanced to permit small amount of compaction

  • Workability of mixture sufficient to facilitate placement of mix without segregation

Phases in mix design

• Mechanical stabilization selection and combination of aggregates for satisfactory gradation

• Achieving optimum percentage of asphalt

Design asphalt content

• Selected as asphalt content resulting in highest durability without dropping stability

Methods used to determine optimum asphalt content for stability

• Marshall method Bruce Marshall, Mississippi highway dept, 1939 most widely used method

• Hveem method Francis Hveem, California division of highways, late 1920s

Low void low stability

• Increase amount of coarse aggregate

• Or reduce asphalt content

Low voids satisfactory stability

• Add more quality aggregates

High voids satisfactory stability

• Increase amount of mineral dust filler in mix to reduce void

Satisfactory void low stability

• Use quality aggregates

High voids low stability

• Increase amount of mineral dust filler

• Or use quality aggregates

Cold mix cold laid

• Utilizes emulsified asphalts and low viscosity cutback asphalts as binders

• Applications

  • Seal coat

  • Prime coat

  • Tack coat

Seal coat

• Single application of asphalt material that may or may not contain aggregates

• Type:

  • Fog seals

  • Slurry seals

Fog seal

• Thin application of emulsified asphalt

• No aggregates added

Slurry seals

• Uniformly mixed combination of slow-setting asphalt emulsion, fine aggregate, mineral filler, water

Prime coat

• Application of low viscosity asphalt to granular base, preparing for initial later of asphalt

• Spraying asphalt binder materials to non-asphalt base courses

• Purpose:

  • Provide waterproof surface

  • Fill capillary voids

  • Facilitate bonding of loose mineral particles

  • Facilitate adhesion of surface treatment to base

Tack coats

• Thin layer of asphalt sprayed over old pavement to facilitate bonding of old pavement to ew course played over old pavement