A Closer Look at Prevailing Civil Engineering Practice - European ...
A Closer Look at Prevailing Civil Engineering Practice - European ...
A Closer Look at Prevailing Civil Engineering Practice - European ...
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A <strong>Closer</strong> <strong>Look</strong> <strong>at</strong> <strong>Prevailing</strong> <strong>Civil</strong> <strong>Engineering</strong> <strong>Practice</strong>, Wh<strong>at</strong>, Why and How<br />
Vincent T. H. CHU<br />
forces its way to expand to pavement surface. Too much asphalt binder in<br />
bituminous m<strong>at</strong>erial is also a common cause of bleeding. Bleeding is an<br />
irreversible process (the bleeded asphalt on pavement surface would not<br />
withdraw in winter) so th<strong>at</strong> the amount of asphalt binder on pavement<br />
surface increases with time.<br />
Bleeding forms a sticky and shiny surface which results in the loss of skid<br />
resistance for vehicles in wet we<strong>at</strong>her.<br />
16. Why is anti-skid dressing sometimes applied to pavement<br />
surface<br />
Skid resistance of road pavement plays an importance role when vehicles<br />
take a bend or brake. The use of anti-skid dressing increases the friction to<br />
reduce the possibility of skidding. Anti-skid dressing refers to the road<br />
surface tre<strong>at</strong>ment which includes high-friction calcined bauxite as the high<br />
Polished Stone Value artificial aggreg<strong>at</strong>e, together with a resin (epoxy,<br />
polyurethane) instead of bitumen to tie the aggreg<strong>at</strong>e to the road surface. It<br />
is more expensive but is more durable in difficult sites such as crossing and<br />
roundabout. Moreover, it also has side benefits of good acoustic quality.<br />
Anti-skid dressing has normally a different colour to the road surface and<br />
used to be red in colour. Anti-skid dressing is commonly used in areas<br />
which require higher friction values such as approach to roundabouts and<br />
traffic lights.<br />
The ability of the road surface to resist skidding is a combin<strong>at</strong>ion of the<br />
surface texture of the road surface and the Polished Stone Value of the<br />
aggreg<strong>at</strong>e in the road surface. The higher the Polished Stone Value the<br />
higher resistance the aggreg<strong>at</strong>e has to polished, and hence the gre<strong>at</strong>er the<br />
capability the aggreg<strong>at</strong>e of retaining its own texture. Surface texture of the<br />
road surface is often referred to as macrotexture while texture actually on<br />
the surface of the aggreg<strong>at</strong>e is known as microtexture.<br />
17. Wh<strong>at</strong> is the purpose of road studs in roads<br />
In nighttime, car drivers could not see where the road ends and where the<br />
alignment of road changes in direction. Without sufficient number of road<br />
lightings, it is necessary to provide some means to guide the drivers along<br />
dark roads. Hence, in 1933 Percy Shaw invented the c<strong>at</strong>’s eye (i.e. road<br />
studs) which is based on the principle of c<strong>at</strong>’s eyes. When a ray of light<br />
enters the eyes of a c<strong>at</strong>, the light shall be reflected back towards to the<br />
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