Abstract
ABSTRACT: Hot and arid regions characterized by its high normal maximum temperature and low precipitation rate. North Africa and Middle East are a typical example of this climate. The performance of Asphaltic Concrete Pavement in such region showed a unique phenomenon of distress and early hardening and deterioration. The main distress modes are premature surface cracking, Research devoted to this region showed that, the main fatal factor contributing to this problem was the increase of applied thermal and traffic tensile stress compared with the own bitumen tensile strength. Tensile strength is probably one of the main properties which bitumen must possess to perform successfully in pavement structural composites. Bitumen forms thin films between the aggregate surfaces. The physical properties of thin films of most materials are different from those of materials in bulk. Because tensile strength is very important to ensure adequate performance, it is desirable to evaluate the tensile strength of bitumen thin films in the range of thickness expected to be encountered in bituminous composites. All tests were carried out using a Howden Universal Testing Machine, with a load capacity of 50kN. The output of the machine is connected to an X -Y plotter, where y-axis represents the load in (kN) and the X-axis represents the displacement in (mm). The variables studied in this investigation were selected from the available information related to the general behavior of material in thin films. These variables were film thickness over a range from 30 to 200 microns, testing temperature used were (0, 20, and 60 °C) and three different types of binders one base bitumen of 100 penetration and two polymer modified binders. The two polymers were Styrene - Butadiene - Styrene (SBS) and Acrylic (ACR). SBS was incorporated into 200 penetration bitumen and ACR was incorporated into 100 penetration bitumen. All experiments were carried out at a constant rate of extension 100 mm/min. The shape of tensile strength-film thickness curves indicates a variation in the behavior of the bitumen at different film thickness. Observation of these Figures indicates clearly that as the film thickness and temperature decrease the tensile strength increases. Statistical analysis of the results allowed to obtain regression equation which give numerical values between tensile strength, temperature and film thickness. Also, the thin film tests on the polymer-modified binders have shown that the addition of ACR polymer increases the tensile strength of bitumen. The obtained results showed good promise enhancing the tensile strength of the asphalt mixes and hence their performance and durability in hot and arid regions. Keywords: Hot and arid regions, premature surface cracking, bitumen tensile strength, Howden Universal Testing Machine, polymer modified binders, and Statistical analysis