Asphalt may be found as natural deposits in lakes or pits. This appears as a residue from crude petroleum that has seeped up through fissures in the earth. For centuries it has been used for waterproofing applications.
Uses: Today, all commercially produced asphalt is derived from petroleum.
It is used industrially for community walkways, paving of footpaths, surfacing over concrete on bridge decks as a road surface and on top of a compacted bluestone
road base for suburban roads and highways.
Asphalt is black in colour and it absorbs heat thus becoming very hot in summer (one of its undesirable properties or characteristics).
On the plus side it has a high plasticity making it easy to work. It is flexible and readily forms a composite with different grades of aggregate to which it cements extremely well.
Asphalt is impervious to attack by oils, salts and most acids and is a highly wear resistant and waterproof material.
Dense Graded Asphalt is a mixture of dense graded aggregates and a bituminous binder. It is produced at around 150°C and laid and compacted hot to produce a dense smooth surface. This is the most common type and is used on roads, at airports, in car parks and school playgrounds.
This section of the New Sydney ‘Orbital’, beside the M5, has 3 layers of surfacing asphalt. Note how the joins have been staggered for increased resistance to separation
The degree of deflection in relation to the mass of a beam and its distribution about the neutral axis is a related property known as the ‘second moment of area’ and bending stress calculations involve the bending moment at the fibre under consideration and the distance from the neutral axis.
Take for example the RSJ (‘I’ beam) illustrated above. It has been designed to function best when incorporated into a structure as seen in Fig. 1. The distribution of mass and hence cross-sectional
area as seen in Fig. 2 would be less rigid.
As for all structures under load, the equilibrium of that structure is dependant upon the balance of external forces or loads and internal reactions.
Shear Forces and Bending Moments, applied externally, are resisted internally to maintain equilibrium. However, when bending occurs, minimal as it may be, outer fibres either compress or stretch (as already discussed).
Since it has been established that the neutral axis is not affected by bending, bending stress (maximum) through a section of a beam (its cross sectional area) may be calculated when the bending moment is a maximum and
the distance from the beam’s neutral axis is a maximum.
The Bending Stress is calculated using the formula:
