HIGHWAY ENGINEERING AND TRAFFIC ENGINEERING CENG 95

The bituminous pavement is a combination of mineral aggregate and bituminous binders. The mixture of rock material particles with asphalt has created so many names such as: BITUMINOUS PAVEMENT

–Plant mix –Asphalt sheet –Road mix – Armor coat –Oil mat, etc. –Asphalt macadam –Asphaltic concrete –Mastic –National paving

Qualities of asphalt road The surface must free from cracks or raveling due to shrinkage and fatigue failure It must withstand weather condition, including the effect of surface water, heat, cold and oxidation

It must be resistant to internal moisture such as water vapor It must posses a tight or porous impermeable surfaces the case may be suitable to underlying base on sub-base It must be smooth riding and skid free surface

The success of an asphalt pavement lies or depends of the construction quality of the sub-grade, and the base course. On the contrary, pavement failure would be considered as a forgone conclusion.

A satisfactory asphalt pavement could be attained under the following construction procedures:

Viscous asphalt binder is heated to a fluid condition and mixed with heated aggregates. The mixture is then laid and compacted while still hot. Mixing liquid or emulsion asphalt with aggregates at normal temperature is either by plant or road mixing. The mixture is laid and compacted at the normal temperature before the solvent evaporates or the emulsion breaks.

Spread and compact the clean crushed stones, sprayed with heated or emulsified asphalt binder over it. Cover the sprayed pavement with fine aggregates. This process is referred to as the penetration method.

BITUMINOUS CONCRETE PAVEMENT

Term asphalt concrete refers to a dense graded road surface made of hot mineral aggregates, mixed with hot asphalt and laid at high temperature with about 275 degree farenheight to 300 degree farenheit.

Highest type of dense bituminous pavement concrete suitable for the most heavily traveled roads. A prime coat is first applied and treated base before asphalt concrete is laid. The purpose is to bind any loose particles of the base and likewise act as bond between the base and the pavement to deter rising moisture from penetrating the pavement.

The thickness of compacted asphalt concrete pavement ranges from 2 inch for lightly traveled road to 6inch or more for roads where traffic is considerably heavy.

BITUMINOUS CONCRETE PAVEMENT FAILURES

Caused by excessive loads. Heavy loads creates deflection on the road surface, with insufficient underlying strength. Repetitious underlying of the excessive load with roughen and crack the road pavement will ultimately result to complete failure of the roadway

. Deflection on the road surface may be the effect of the elastic deformation from the consolidation of the base or subsoil or from the combination of elastic and plastic deformation. Repeated heavy wheel load on highly resilient soil causes deflection leading to fatigue failureof the asphalt surface.

Alligator or the map cracking of the surface will be substantially evident. Elastic deformation in the sub-grade penetrate to depth of 6meters although mostly to a depth from the surface.

Surface failure Base failure Basement failure

MACADAM

John Loudon McAdam was born in Ayr, Scotland in In 1787 he became a trustee of the Ayrshire Turnpike in the Scottish Lowlands and during the next seven years this hobby became an obsession. As Surveyor-General of roads for the Bristol Turnpike in 1816, McAdam first put his ideas about road construction into major practice. MACADAM

He also began to actively propagate his ideas in two booklets called Remarks (or Observations) on the Present System of Roadmaking, (which ran nine editions between 1816 and 1827) and A Practical Essay on the Scientific Repair and Preservation of Public Roads, published in 1819.

MACADAM is a type of road construction pioneered by the Scotsman John Loudon McAdam in around The method simplified what had been considered state-of-the- art at that point. Single sized aggregate layers of stone with a coating of binder as a cementing agent are mixed in an open-structured macadam.

McAdam's method was simpler, yet more effective at protecting roadways: he discovered that massive foundations of rock upon rock were unnecessary, and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear. [9] [9]

MCADAM'S METHODS McAdam's method was more simple and yet more effective at protecting roadways: he discovered that massive foundations of rock upon rock were unnecessary, and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear.

Size of stones was central to the McAdam’s road building theory. The lower 200 mm road (7.8 inches) thickness was restricted to stones no larger than 75 mm. (2.9 in) The upper 50 mm (1.9 in) layer of stones was limited to 20 mm size (.787 in ) and stones were checked by supervisors who carried scales.

A workman could check the stone size himself by seeing if the stone would fit into his mouth. The importance of the 20 mm stone size was that the stones needed to be much smaller than the 100 mm width of the iron carriage tires which traveled on the road.

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