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Half warm mix asphalt (H-WMA) is one of the alternatives to conventional asphalt due to its special production conditions.  Half warm mix asphalt (H-WMA) manufactured with high proportions of reclaimed asphalt pavement (RAP). Half warm mix asphalt (H-WMA) are produced and compacted at the temperature range of 60-100 ° C, which requires less temperature for production process of hot mix asphalt (HMA) for example cold mix asphalt (CMA) manufactured at a temperature lower than 60 ° C; (ii) half warm mix asphalt (H-WMA) manufactured at less than 100 ° C, normally at 60-100 ° C; (iii) warm mix asphalt (WMA) manufactured at temperatures of 100-140 ° C. The aim of this study is to investigate the effects of high percentages of reclaimed asphalt pavement (RAP) on the volumetric and mechanical properties of Half warm mix asphalt (H-WMA) mixtures. In this research, bitumen emulsion (CSS-1) and conventional bitumen 60/70 were used. The siliceous aggregates were obtained from a mine near Tehran and reclaimed asphalt pavement (RAP) were obtained from an asphalt plant and its granulation before and after extraction was done according to report number 234.  Generally speaking, in H-WMA, aggregates are heated to temperatures of 100-110 ° C and then mixed with emulsion, which has previously been heated to 60-80 ° C and RAP are heated to 90-100 ° C. To determine the most suitable mixing time in the tests, the coating was visually analyzed after mixing times of 1 and 2 min and the mixing temperature was 95-85 ° C. Thus, a laboratory analysis was carried out in which the behavior of half warm mix asphalt (H-WMA) manufactured with 100%, 70% and 0% reclaimed asphalt pavement (RAP) was compared with that of a control mix, Hot mix asphalt (HMA). Optimum bitumen content for hot asphalt mixture (HMA) and optimum bitumen emulsion content for half warm mix asphalt (H-WMA) were calculated. Then indirect tensile tests (IDT) (at 25° C), moisture damage (TSR) and Semi-Circular Bending (SCB) Tests (at 25° C and -20° C) were performed on half warm mix asphalt (H-WMA) and hot mix asphalt (HWA). indirect tensile tests (IDT) yielded acceptable results, the IDT resistance increased with increasing the reclaimed asphalt pavement (RAP) content. Following this, the moisture damage (TSR) of half warm mix asphalt (H-WMA) improves by increasing the reclaimed asphalt pavement (RAP) content, which can be due to the complete covering of the surface of the aggregates with aged bitumen and the high adhesion force between the aged bitumen and the aggregates and the lack of moisture penetration into the aggregates. emulsified bitumen exhibited proper volumetric (e.g., air voids and density) and mechanical behavior in terms of moisture damage and IDT. On the other hand, the results of SCB tests at medium and low temperatures showed that by increasing the RAP content the samples become brittle, which means that resistance to crack propagation reduced, and it may be the reason for fracture energy reduction. These findings encourage greater confidence in promoting the use of these sustainable asphalt mixes for their use in road pavements or urban streets.

Keywords: Half-Warm Mix Asphalt (H-WMA), Recycled Asphalt Pavement (RAP), Bitumen Emulsion, Indirect Tensile Test (IDT), Moisture Damage, Semi Circular Bending (SCB) Tests

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