Restriction of RAP% in HMA Based on Aggregate Gradation and Binder Properties

The use of recycled asphalt pavement (RAP) in pavement construction reduces the project cost and helps in conserving the naturally occurring aggregates. To incorporate RAP in hot mix asphalt, it is vital to know the amount and quality of the reclaimed binder. Three new asphalt binders were selected for this investigation. RAP material from one source was blended in different proportions with VG-10 and VG-30. Penetration, softening point, G */sin δ, G * sin δ and binder fatigue life Nf (from Linear Amplitude Sweep test) values of different blends were compared. The milled RAP aggregate gradation varied from source to source due to factors such as the gradation of the mix used in the existing layer, milling method and processing of RAP material. This variability controls the use of higher proportions of RAP in new mixes. To investigate the effect of RAP gradation on the proportion of RAP that can be used in the new mix, RAP sources with different gradation (three dense and two gap gradations) were selected. The proportion of RAP that can be used for preparing mixes with these gradations varied significantly with the source of RAP, and the target gradation. In most cases, it was found that allowable RAP percentages are smaller for the gap gradations compared to those permitted for dense gradations. The proportion of RAP in a mix can be increased by selecting an appropriate gradation for a RAP source or by using a suitable RAP source for a given gradation

A Method for the Determination of Mixing Temperatures of Different Components of Recycled Hot Mix Asphalt Mixtures

To produce reclaimed asphalt pavement (RAP) mixes in plant using hot recycling technique, virgin aggregate is super-heated to heat the RAP by conduction. The temperature to which virgin aggregates are to be heated will depend on the RAP percentage in the mix, quality of RAP and the quantity and quality of virgin binder and RAP preheat temperature. In the present study an investigation has been carried out to examine the heat transfer characteristics of RAP mixes to propose a simple method for determination of superheated virgin aggregate and RAP temperatures to be adopted for preparation of RAP mixes. For this purpose an empirical equation has been developed for estimating the super-heating temperature of virgin aggregates as a function of RAP content, RAP preheat temperature and mixing temperature. Effect of mixing temperature on bulk density and mechanical properties was also evaluated in this study. Correlations were developed between mixing temperature and bulk density, mechanical properties (Indirect tensile strength and resilient modulus). Effect of RAP preheat temperatures and virgin aggregate temperatures are having higher effect on mechanical properties for lower RAP content when compared with higher RAP content. It is also observed that using higher percentages of RAP will require either higher preheating temperatures of RAP or higher virgin aggregate temperatures. From the ANOVA analysis it was observed that for lower RAP contents (up to 25%) preheat temperature of RAP material had significant effect on mechanical properties, on the other hand for higher RAP contents (40%) both RAP preheat and superheated virgin aggregate temperature played an equal role on the mechanical properties. © 2022, The Author(s), under exclusive licence to Chinese Society of Pavement Engineering