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Nowadays, many
people feel that the temperature is hotter than before and they do not know
why. Are you live in an urban area? Do you prefer to live in a city than live
in a town? Do you prefer to drive your car on an asphalt pavement than drive on
your country normal ground? The asphalt is the main reason for the feeling that
the air and the temperature are hotter than before. There are many reasons that
the asphalt made the air and temperature hotter. First, the color of the
asphalt is very dark and it is one of the problems for hotter weather. Second,
the density asphalt made it warm long time after the sun gone and the dark
came. Last but not least, the bulk properties of the asphalt such as heat
capacity and the thermal conductivity.

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(asphalt) types

There are main
three mixes of asphalt. To start with the first type which called “Dense
Graded mixes” this type is used to allow the water to flow from the
surface area so, the impartiality of this type is useful for the drainage of storm
water. The second type is “Stone matrix asphalt” this type its
durability is high, the mixture of it expansive. It is used to carry the heavy
duty and to carry the higher load of vehicles. The third type is” open
graded mix” this type is a combined type of the first and the second type
which is permeability is high and the durability of this type is high. There
are two classifications of the third type, the first classification is used for
the course surface and the second type is used under dense graded stone mix or
Portland cement concrete for drainage.





temperature rise (urban heat island (UHI) phenomenon)

The urban heat
island (UHI) phenomenon is characterized by high air temperatures in densely
constructed areas in comparison with the surrounding rural areas. One of the
main causes of the formation of a UHI is the use of large quantities of
industrialized materials (bricks, concrete, asphalt mixtures, stones and
others) in urban zones.

Asphalt absorb
a high percentage of shortwave solar radiation during the day up to 90% and the
pavement layers also conduct heat which results in pavement temperature
rise  and then irradiate it to the
environment more easily so that the pavement and the air get to it equilibrium
stat of heat.



As we mentioned
that it is a savvier issue to the asphalt to be implemented in a very high
degrees or very low temperature location, a lot of reports and discussions were
made to find the best solution for this problem, plus that a lot of effort was
made into experiments and trials on asphalt in many locations to check for a
solution that satisfy most of the conditions.

After reviewing
many solutions in order to find the most suitable one but it was hard due to
that every location and every area is different from another in weather
conditions and climate and other geological properties.

The solutions
that we can use in order to prevent the effect of asphalt on air temperature is
as follow:


Planting, it is
directed to have planted asphalt roads all along with tree/buildings to
increase shading area and decrease the time in which the asphalt is exposed to
the sun heat (solar radiation).
unfortunately, this method is unsificiant in urban areas and doesn’t give
satisfying result however its temporary solution, however its effective in the
city’s due to the high rise buildings

Admixture Coating, this method
have gone through a lot of development in the asphalt and pavement, there have
been a lot of progress in the admixtures and mixtures field, a lot specified
mixture was developed that have materials that make the surface of the coating
(highly reflective) to solar radiation. As there is many mixtures however the
most effective ones are the ones with white color. some examples for this is:
as it have a high impact on lowering the temperature however it have a
disadvantage as the coating wear off due to the circulation of vehicles



Colored reflectance pavement, as
this work the same as the Admixture Coating however the hole pavement is highly
solar reflectance. such as CoDAM, YeDAM, RaDAM, RbDAM, GrDAM and RPC.

Smooth surface pavement, as smooth
surface the solar radiation will be reflected in several directions a single
time, while dense asphalt mixtures with a rough texture have a greater surface
area which allows a greater amount of solar radiation to be absorbed, some
example to this is :  UCF and UCZ.

Water retaining pavement, Water retaining pavement is the pavement using
porous asphalt mixture of which the void is filled with water retaining
material. The heat of vaporization by its retained water restrains the rise of
pavement temperature due to solar heat as the water absorb the solar radiation.
It can contribute to a mitigation of heat-island phenomena in summer. And the
water should be sprinkled onto the pavement.



As we learned from our studies through
the course of physics 210, energy is one of the most important thing the
mankind is trying to find new sources and trying to improve it.

As we know one of the sources is
Thermal Energy Harvesting (heat energy)
what if ?? we can develop this concept for pavement and try to harvest heat
energy from it in which the pavement will absorb the solar radiation and
converting to heat as what it do, but !! rather than it radiates the heat to
the air to get to an equilibrium state with air, (it get to an equilibrium
state with pipes filled with water) as the pavement heat will transfer to water
in the pipe and the circulation of the hot water (evaporate) will convert to
energy and by this proses will keep the pavement cooler in which it will not affect
the air temperature.


To conclude, there are three main
types of asphalt. The three types of asphalt are classified according to the
permeability and the durability. The color of the asphalt is dark and the
density of the material of asphalt stores the heat for a long time after the
sunset, both reasons causing the increases of the temperature because of the
asphalt. To solve the problem of increasing the heat caused by the asphalt we
have provided solutions for the current situation and for the future. To start
with the current situation, the first solution is to increase shade on the
asphalt, in order to do so we have to plant the asphalt roads all along with
tree or buildings. The second solution is to coat the admixture of the asphalt.
The future solutions are colored
reflectance pavement, Smooth surface pavement and water retaining pavement.