Advances in Bituminous Road Construction
Following article is the real time project research by the author.
Engineering Activity
Research:
I began this project with a
brief introductory paragraph on bituminous road pavements and its construction
types from the basic concepts which I have learned during my first three years
of bachelor’s degree in civil engineering. However, I was still anxious to know
details, and therefore I got enrolled myself to online research publications,
where I had a good opportunity to further understand the concepts involved in
flexible road pavements. I also took part in various forum discussions with
civil engineers from other regions of the world, through which I had a chance
to share my ideas and queries. This provoked me to explore the advances of
bituminous road construction types for various soil and climatic conditions and
perform exceptionally well in this project.
I made preliminary research on sub-grade soils along
with some peculiar features of the site. I found that the soils used in the
construction should be as per the Unified Soil Classification Systems (USCS) in
ASTM D 248. I gathered some of these standards from my academic books which I
studied during my bachelor’s degree, while for the rest I used the publications
on road pavements. I made investigations on soil conditions with the combination
of soil samples collected from several sources and soil borings. I tried to
understand and memorise requirements of an ideal pavement including materials,
design mixes, and maintenance costs that I have studied during my engineering
degree. Then, I moved with the traffic evaluation on the pavement with a
selection of Design Index.
Vehicular traffic
calculations:
Calculations
are made as per the road pavement thickness that helps to with stand the
anticipated traffic. It is further categorised by the weight of the vehicle,
average daily volume, and design type of the pavement. Once all the necessary
assumptions and values were considered, I calculated ultimate stress loads for
both rigid and flexible pavements. Though, there is no much difference in the
ultimate bearing capacity of both pavements, I considered only Flexible
Pavements over Rigid Pavements, as the rigid pavements uses cement on the top
layer, which is not ideal, and they are very expensive to build. Thus, I chose
flexible pavement, which provides proper wheel distribution load stresses, able
to withstand all types of stresses imposed on it and gives smooth ride to the
end users. The various layers incorporated in the flexible pavements helps to
sustain water, heavy loads, and proper bonding with all the layers.
Figure 1: Typical cross-section of Flexible Pavement
Distribution of loads:
I faced numerous difficulties and challenges
while working on this project. Some of them include finding information and
understandings on load distributions. The normal flexible pavement design is
based on magnitude of stress induced by a wheel load decreases with depth below
the surface. The below figure demonstrates the single wheel load distribution
on two sections of flexible pavement. The subgrade layer in the flexible
pavement can carry any different type of loads based on the thickness of
subgrade. If the subgrade thickness is reduced, the load distribution is
limited to smaller surface area and thus increases the stress levels on the sub-grade
significantly. The flexible pavements normally transfer load to lower layers and
the top layers can sustain the maximum compressive stress.
Figure 2: Distribution of stress produced by multiple
assemblies
Flexible pavements distribute the wheel load acting on
the surface to a wider area by decreasing the stress with the depth as shown in
figure 3. Hence, with its unique feature of stress distribution characteristic,
the concept of flexible pavements is called layered system.
Figure 3: Load transfer in flexible
pavement deep layers (granular structure)
Flexible Pavement construction:
As soon as I completed with all the design parameters
and calculations for the road construction, the next objective was to develop
the road construction operations where the work is set by planning the schedule
and to maintain the quality of the road. Some of the methods introduced such as
fine grinding, hauling, placing, mixing, spreading, and blending are used to
maintain the quality of the road construction. The method called Macadam bases
is used particularly in the construction process during the mixing of the
ingredients. For the Macadam the aggregate is placed and is spread carefully to
make sure hauling vehicles do not add objectionable material to the aggregate.
The roller is used on the top of the aggregate to ensure the stability of the
surface. The regular sprinkling and rolling on the mixture help to fill all
voids and assembles the small wave before each other for the smooth surface
finish.
Figure 4: Compacting top surface with steel-wheeled rolling
Testing and Quality Control:
As soon as the construction work finishes the tests
are performed to check the quality of the road. The tests like gradation,
mixing proportions, plasticity characteristics, moisture content, field density,
lift thickness and CBR values are taken while running these tests. Even though
I had many obstacles while performing the testing activities, with the help of
my teammate and project supervisor I was able to overcome all the hurdles and
able to complete project successfully. My team provided me with professional
atmosphere where I was able to tell my thoughts and ideas freely, which helped
us to produce better result at the end. The project was completed according to
the schedule as planned.
Figure 5: Finished top surface of Flexible Pavement
