Evaluation of flexible and rigid pavements construction in Bangladesh

Abstract

The aim of this study was to find the pavement type which would be more cost effective and would give good serviceability in the long run in the context of Bangladesh. In this regard field investigations were carried out to identify the problems associated with the various stages of quality control in the construction of pavements. Samples were collected from two construction sites for both field and laboratory experiments. The performance evaluation of few completed flexible road construction projects was made. In order to assess the level of understanding regarding the proper way of constructing flexible pavement, all together 12 Engineers from different Government Organizations as well as from the Contractor’s side were interviewed. In addition to that 15 field staffs particularly from the Contractor’s side were also interviewed. Unit costs of flexible and rigid pavements were estimated by determining life cycle cost (LCC) of a few completed projects. Finally, a comprehensive comparative analysis between flexible and rigid pavements was made from the viewpoint of locally available binding material, amount of aggregates and type of equipment requirements, construction and maintenance cost, quality control issues and above all performance under submerged condition. From the field and laboratory investigations it was found that due to improper way of heating and mixing bitumen, its properties change significantly particularly with the manual method of construction. Aggregate gradation is hardly maintained in the preparation of pavement mixtures and thereby lower Marshall stability and flow values along with higher void contents are obtained in the laboratory investigation. Also temperature measurements in the field at different stages of construction process show that bitumen quality is deteriorated significantly at the time of heating and mixing with aggregates. Overall, it is observed that in every stage of pavement resurfacing works there is a serious lack of quality control particularly in maintaining appropriate temperature of aggregates and bitumen as well as of placing and compaction of mixture. In reality, serious ignorance exists both with the field engineers and contractors related to pavement construction works. They have little ideas about the compliance of maintaining specific temperature at a particular step of pavement construction works. Field observation revealed that where both flexible and rigid pavements are built side by side by different organizations, the performance of rigid pavements is relatively better. Rigid pavement as constructed by LGED in Sunamganj district has found to be performing well under daily tidal submergence cyclic loading pattern. It was observed that for per km construction of a standard 2-lane width road, material requirement is almost 50% higher in case of flexible pavement as compared to the rigid pavement. From the unit rate analysis of binders, it was found that over a period of four years (2004-2008) the cost of bitumen has increased by two and half times as compared to the cost of cement, which has increased by nearly one and half times during the same period of time. It was found that in 2004 the unit cost of flexible paving mix was lower than that of the cost of cement concrete paving mix and after that its price has been increasing very rapidly and has crossed the price of concrete pavement by 2006. Now, the unit cost of bituminous pavement is more than one and half times as compared to the unit cost of concrete mix. From the evaluation of different completed projects it was revealed that though overloading and drainage are the main causes of premature pavement failure in Bangladesh, manifestation of lack of poor quality of work, use of excessive binder, bonding problem between new and old layers are also found to be contributory factors for premature failure of flexible pavement. From the questionnaire survey it was observed that the persons concerned with the construction of flexible pavements, both the client and contractor’s side, have poor understanding on the proper way of doing the construction of flexible pavement job. As such, there is a need for pavement construction method which is simple and requires no heating requirement, compaction work and above all not so sensitive to the quality control, which essentially suggests that rigid pavement construction would be the appropriate method of road construction for the local conditions. In the end recommended areas of applying rigid pavement instead of flexible pavement are also presented.