Towards sustainable road infrastructure: framework and strategy for construction materials

Abstract

All road agencies worldwide design their roads based on traffic levels and existing soil conditions very often regardless of the availability of materials. This results in the depletion of very scarce resources and ever-increasing hauling distances from quarries to the road alignment. In some countries in Africa, such as Libya, Mali, Cote d’Ivoire, Chad and Senegal, the hauling distances in some remote areas can reach over 500 km. A national level inventory of available sand pits and quarries is frequently not performed and therefore, there is commonly no national strategy to protect scarce aggregate resources, which are taken for granted despite that they are nonrenewable recourses. The preliminary estimation by engineers of the capacity power of the potential quarries for a road project is predominantly not available or otherwise inaccurate until the contract is awarded. This “last minute” investigation of good quality construction materials can no longer be an acceptable solution in today's sustainable culture. As such, it is paramount to identify all the existing road construction materials in a country by performing the inventory of potential source materials such as sand and gravel before any design or major road construction is undertaken. This requires developing a framework to manage and control the use of basic materials to meet current and future needs. To formulate an effective strategy requires acquiring and organizing an extensive amount of information, including an inventory of the potential road construction materials available. This inventory would also need to contain the total existing road network and the projected roads, and estimations of the quantities of materials required for new road construction and rehabilitation of existing roads. This thesis develops a methodology to establish the inventory of existing road construction materials in any country and to determine road construction material needs for the next 50 years. This is paramount to justify and develop a national framework to align available geological resources to new road material needs. The validation of the methodology is conducted in Libya. This research is divided into three main parts: 1) identifying the potential aggregate resources by using Google Earth Pro and its application for Libya, 2) determining the future construction materials demand for the next 50 years from the projected road network expansion and a pavement design catalogue, and 3) establishing a sustainable aggregate materials strategy. The application of the methodology for Libya shows that 38.3 million tons of aggregates are available for road construction from 21 active quarries and, the projected expansion of the road network will be around 95,180 km over the next 50 years. This translates to over 250,000,000 m3 of materials that will be required for road construction, maintenance, and rehabilitation. The analysis also shows that there is a substantial gap in the availability of materials and the future demand for road construction materials. Therefore, there is a need to develop a national strategy to optimize the use of the scarce aggregates available. The proposed strategy is intended to better manage new material consumption by optimizing the pavement design catalogue in order to reduce the specified material quantities to a minimum by utilizing material stabilization that maximize pavement strength with limited amounts of materials, with the objective of protecting scarce resources as dictated by the environmental and social performance standards of the International Finance Corporation. This aforementioned strategy of optimizing pavement design structures could save around 85,000,000 m3 of virgin material over the next 50 years or around 1,785 m3/km of virgin materials for a typical median road. The savings in virgin materials reach 3,750 m3/km for the projected trans-Libyan highway. In addition to saving non-renewable and scare material resources, the optimized design proposed in this research also reduces the cost of the 1,400- km trans-Libyan highway by 400-550 M$ based on 75-100$/m3, depending on the distance to the quarry. Also, the modified design would additionally have environmental benefits by reducing greenhouse gas emissions. The study concludes that reducing pavement thicknesses by resorting to cement reduces the overall pavement cost and is a cost-effective and sustainable solution for meeting future local demand for aggregate materials in countries with limited aggregate resources. While this research validates the study only on Libya, the established sustainable aggregate material strategy will also help pavement management decision-makers in other developing countries to produce four significant benefits. These benefits include improved pavement performance, diminishing the usage of virgin materials, reducing construction and maintenance costs, and minimizing environmental damage.

Date	2 Jun 2024
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Gabriel J. Assaf (Supervisor)