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Abstract Thermal fatigue cracking is one of the major distress modes in Egypt because of the significant variation in temperature between day and night (during the day) or between summer and winter (during the year) in many regions of the country. This type of distress is manifested as a series of transverse cracks that extend across the pavement surface in response to multiple cycles of temperature change. With increasing use of asphalt concrete mix ”Type 4B” in Egypt as an alternative to the asphalt concrete mix ”Type 4C”, it is essential to compare between the performance of these two mixes under different environmental conditions. The main objective of this study is to compare between the above mentioned two mixes in resisting thermal fatigue cracking under the Egyptian conditions. In order to achieve this purpose, a refrigerating-warming unit was fabricated. Through this unit asphalt concrete specimens can be exposed to different temperatures; maximum + 110°C minimum -20°e. Asphalt mixture specimens were prepared for both mixtures (4B, 4C) using three different percentages of bitumen (Marshall optimum percent. Marshall optimum percent + 0.5%, Marshall optimum percent - 0.5%) to study the effect of bitumen content on the resistance of thermal stresses. The specimens were tested under three di fferent temperature cycles compatible with those actual in three main regions in Egypt (north middle, and south). The deformation occurring in specimens due to the temperature change was recorded and then the number of thermal cycles that can be applied on each specimen before cracks initiation was predicted. The study concluded that mix 4C is better than mix 48 in resisting thermal fatigue cracks especially in the northern and middle regions of the country, while both mixtures can be used without a significant effect on the pavement service life in the southern region. The study also concluded that increasing the bitumen content above the optimum determined by Marshall testing procedures by 0.25% (the maximum allowable tolerance according to the Egyptian code) leads to increasing the number of temperature cycles that can be applied on both mixtures (48, 4C) before crack initiation. |