Advances in Bituminous Road Construction


Advances in Bituminous Road Construction


Following article is the real time project research by the author. 

Roads are the essential means of connectivity throughout the world, and recent advances in the construction of roads have facilitated uniform progress and better-quality service to the people. Being a civil engineer, it comes under my professional domain to explore the developments and methods deployed in the road construction activities. Any road pavement is a rigid structure consisting of several superimposed processed material layers with the functionality of distributing applied vehicle loads evenly across all sub-bases, so that the load transferred to the sub-grade (natural surface) will not exceed the ultimate bearing capacity of the natural soil. To absorb and distribute the applied loads evenly to the sub surfaces, the top layer i.e. bituminous layer plays significant role. Hence, in this technical assignment, I emphasised on the study of recent advancements in the field of bituminous road construction. The project consisted of all sequential steps followed in the construction of bituminous road pavement. It all began with the preliminary investigation of the site and ended with the quality control. The key research activities covered in this project includes kinds of materials used in the road construction, and special bituminous mixes, and I also explored on various recycling activities involved in the construction of this flexible pavements made up of bitumen.

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