Development of innovative mix design for road construction in hot regions

Abstract

Permanent deformation in the form of rutting and bleeding is one of the major mechanisms of deformation affecting asphalt pavements, with severe safety and comfort consequences and substantial associated economic cost and marginal pollution. This is a serious concern exacerbated in hot countries whereby the resistance to deformation or viscosity of the bitumen binders, at those prevailing extremely hot in-service temperatures, drops multifold. In hot countries, air temperatures can exceed 45°C and the asphalt mix may reach 70°C. Even in the construction of primary roads, bitumen 60/70 (B60/70), which is a relatively low-grade and hard bitumen, continues to be used for Hot Mix Asphalt (HMA) construction because of the lack of availability of Performance Grade Superpave asphalts. Asphalt pavement roads therefore develop extreme deformations in the form of rutting because the B60/70 is primarily based on the resistance to deformation at 25°C. As a result, flexible pavements in hot regions namely those subject to heavy loads, often show substantial rutting and shoving. These distresses are caused by heavy traffic, an inadequate viscosity of bitumen at these in-service temperatures, a poor fine gradation with less coarse aggregates and/or an insufficient aggregate angularity. In several countries of North Africa and Middle East: 1) the surface temperature of asphalt can reach 70°C, and 2) the materials available near the alignment are often very thin and rounded by wind erosion, which accentuates rutting and shoving. Road agencies have difficulties coping with these issues at a cost that makes economic sense for funding. This research investigates the use of Ordinary Portland Cement (OPC) and cellulose fiber (CF) as a filler substitute to improve the resistance to deformation or rigidity of asphalt concrete mixes made with B60/70 bitumen and readily available low quality, fine and rounded, aggregates. This amended mixture increases the pavement’s stability and resistance to high temperatures. To establish the effects of OPC on the performance of asphalt mixtures in hot climates, four different percentages of OPC (0%, 2%, 4% and 6%) are used as filler substitutes in three different mixes. CF mixes were also tested with three different percentages of CF (0.25%, 0.5%, and 0.75%) used as filler. The performance of the OPC and CF mixes are assessed using the Superpave Gyratory Compactor to ensure easiness to place, the Asphalt Pavement Rutting Analyzer to ensure lack of rutting and The Indirect Tensile Stiffness Modulus (ITSM) to prevent in-service cracking. ITSM tests were conducted at - 5°C, 10°C, 25°C to simulate adverse conditions in desertic or mountainous regions in the Middle East and North Africa and the rutting analyzer test was conducted at 60°C to simulate adverse hot temperatures in the region. Findings indicate that mixtures containing higher percentages of OPC as a filler are significantly more resistant to rutting as found with the rutting analyzer, while remaining easy to place as found with the gyratory compactor. These experimental results also show that Portland Cement Filler Asphalts (PCFA) represents a more stable alternative to conventional asphalts that also reduces thickness requirements as demonstrated with mechanistic pavement design model, because of the higher resulting modulus of rigidity. This has important cost implications in hot rural areas with scarce quarries for good quality aggregates, because of the increased stability and therefore performance and the reduced thicknesses, both of which reduce the construction and the maintenance cost of the road, to levels more in line with the savings generated by the reduction in transport cost resulting from a road in better condition.

Date	12 May 2022
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Gabriel J. Assaf (Supervisor)