Presentation on theme: "Ms Ikmalzatul Abdullah BITUMINOUS MATERIALS. Definitions: Binder: A material used to hold solid particles together, i.e. bitumen or tar. Bitumen: A heavy."— Presentation transcript:
Ms Ikmalzatul Abdullah BITUMINOUS MATERIALS
Definitions: Binder: A material used to hold solid particles together, i.e. bitumen or tar. Bitumen: A heavy fraction from oil distillation (also occurs as part of natural asphalt). Tar: A viscous liquid obtained from distillation of coal or wood. Rarely used in construction currently in the UK. Asphalt: A mixture of bitumen and mineral filler. Note that Hot Rolled Asphalt is a road surfacing material. Mastic: An adhering asphalt which is placed with trowelling. Macadam: A road construction material with binder and coarse aggregate. Tarmacadam was the first road surfacing material.
SAFETY The flash point is the temperature at which vapour given off from the surface will burn. The fire point is the temperature at which the binder will burn. Water will spread a bitumen fire. The materials are generally used at temperatures high enough to cause severe burns. Both the materials and the vapours are potentially carcinogenic.
Binder Properties Adhesion Bituminous materials adhere to clean dry surfaces. Viscosity All bituminous materials are viscous, i.e. when subject to a long term load they deform continuously. Softening point This is the temperature at which the binder softens to a pre- determined point.
Bitumens are: Intrinsically durable, they oxidise, polymerise and lose light oil components when exposed to air and heat but all of these processes just make then harder Virtually impermeable if well compacted Intrinsically resistant to plant growth Softened by high temperature and solvents (often by fuel spills)
Cracking of thin surface
BINDER MIXTURES Cutbacks This term is used to describe a mixture of a binder and a light volatile oil. They are liquid at low temperatures until the volatile oil evaporates.. Due to the release of solvents into the atmosphere they are now rarely used. Emulsions When mixed with water binders will generally settle out. An emulsifier must be added to give a stable solution. Bitumen paints are made this way. The water evaporates and the bitumen remains on the surface. The current types of cold rolled materials are based on emulsions.
Rubberised bitumens The viscosity and softening point are increased and penetration is decreased. The elasticity is increased. The sensitivity to temperature changes is decreased. The beneficial properties are lost with prolonged heating. The increased elasticity and penetration resistance makes this material ideal for expansion joints and repairs in roads.
The four components of a typical mix are: Coarse aggregate (retained on 2.36mm sieve) Fine aggregate (passing 2.36mm sieve but retained on 75 ) Filler (passing 75 ), may be cement. Binder: Bitumen etc.
Asphalt Mixing Plant
Adding aggregate to a binder has the following general effects The cost is reduced. The strength is generally increased. If the mix has to be laid hot the aggregate must also be heated (at considerable cost) May fail due to loss of adhesion between aggregate and binder
Surfacing materials Hot rolled asphalt: Coarse aggregate dispersed in a mortar composed of sand, filler and bitumen. This is gap graded. Asphaltic concrete: Asphalt in which the aggregate particles are continuously graded to form an interlocking structure. Surface dressing: Sprayed bitumen binder with stone chippings rolled on. This is used for repair work. Slurry surfacings and micro asphalts: Bitumen emulsions with selected aggregate combinations. Also used for repair. Stone mastic asphalt: gap graded asphalt composed of a coarse crushed aggregate skeleton with mastic mortar.
Hot Rolled Asphalt Surface
Failure mechanisms. Wearing course: –Rutting (shear failure) –Potholes (bond failure) –loss of skid resistance (viscous flow) Lower courses –Cracking (Fatigue failure) –Breakdown due to failure of lower courses (e.g. reflected cracking from dry-lean concrete)