الفهرس 
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Abstract
The main purpose of this study is to evaluate the effect of adding recycled tire rubber with variable percents (by aggregate weight) instead of an equal sand percents (dry process) in order to improving the mechanical properties of asphalt concrete mixtures and studying the ability of using the rubberized mixes in pavement construction. The rubber is used with two aggregate gradations, Dense Graded 4C and Open Graded 3B. Rubber was added to each gradation at three different percents (1.0, 2.0 and 3.0 percent by aggregate weight) instead of an equal sand. Marshall mix design method was employed for designing both conventional and rubberized mixtures. For conventional and rubberized mixes, six percents of asphalt cement content (4.0, 4.5, 5.0, 5.5, 6.0, and 6.5 percents) were used to determine the optimum asphalt content. Marshall test at curing temperature of 70 <U+F0B0>C and indirect strength test at curing temperature of 10 <U+F0B0>C were performed on both control and rubberized mixes to evaluate its performance against climatic temperature changes. Rubber percents by aggregate weight and gradation type were the variables used in this investigation for both Marshall and indirect tensile strength. The asphalt cement contents were taken as optimum asphalt content and (R+ (B0.5% around the optimum asphalt content for each conventional and rubberized asphalt mixes. The research proved that the adding of rubber to the asphalt mix aggregates exhibited an improvement of mechanical properties of asphalt concrete mixture. The optimum asphalt content, which gave the best mechanical properties For the conventional Dense Graded 4C and Open Graded 3B mixes, were 5.25 and 5.50 % (by aggregate weight) respectively. The optimum asphalt contents for rubberized Dense Graded 4C mixes (%R 1.0, 2.0 and 3.0) were 5.25, 5.0, 4.8 % (by aggregate weight) respectively while for rubberized Open Graded 3B mixes (%R 1.0, 2.0 and 3.0) were 5.25, 5.2, 5.1 % (by aggregate weight) respectively. It was found that the addition of rubber improved the stability/flow ratio of the mixes at high temperature (70 (R@(BC) especially at rubber percent 1.0% (by aggregate weight) for both aggregate gradations. It was found also that the addition of rubber improved the indirect tensile strength at low temperature (10 (R@(BC) for both aggregate gradations especially at rubber percent 1.0 %.