الفهرس 
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Abstract
Phosphogypsum is a solid by-product waste generated from phosphoric acid industry. The worldwide amount of phosphogypsum is ranging between 100 and 280 million tons. Otherwise, iron and steel slag is a solid by-product waste resulted from iron and steel industry. The estimated worldwide amount of iron and steel slag is 400 million tons. Therefore, these solid wastes are causing negative effect on the environment and surrounding communities. On the other hand, the demand for road construction, widening and maintenance works also construction of other structures increased by time, which means increasing in demand for conventional aggregates that threatened by depletion. Therefore, many studies were conducted around the world by utilizing these solid by-product wastes in road construction which proved the ability to use these wastes either with underlying layers or asphaltic layers. This study aims to form and test mixtures of these wastes with locally available traditional base course aggregates to determine and evaluate the effect of adding these solid wastes on some of mechanical characteristics of the base course materials. Therefore, all used materials subjected to validation tests to determine some of its physical and mechanical characteristics. Seven percentages (0, 5, 10, 15, 20, 25 and 30%) of phosphogypsum were mixed with crushed limestone. Further, three percentages (25, 50 and 75%) of crushed steel slag blended with crushed dolomite stone and six percentages (0, 5, 7.5, 10, 12.5 and 15%) of phosphogypsum at each percent of steel slag. These mixtures subjected to modified compaction test, un-soaked California bearing ratio penetration test, soaked California bearing ratio penetration test, California bearing ratio swelling test and California bearing ratio penetration test after a series of wetting-drying cycles. The results of tests demonstrated that using phosphogypsum and crushed steel slag improves some mechanical characteristics of traditional base course materials. Whereas, a mixture containing 20% phosphogypsum and 80% crushed limestone showed improving in some mechanical characteristics comparing with control mix 100% crushed limestone. Further, some mechanical characteristics of a mixture consisting 10% phosphogypsum from mixture dry weight, crushed steel slag and crushed dolomite stone with ratio 75%:25% were enhanced compared with control mix 100% crushed dolomite stone. Therefore, utilizing these solid by-product wastes in road base enhance the mechanical properties of conventional construction aggregates.
Key words: phosphogypsum, steel slag, limestone, dolomite stone, California bearing ratio, wetting-drying cycles and base course.