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Recycling of asphalt pavements dates back to 1915; however, it first became popular in the U.S. in the 1970s during the oil embargo when the cost of crude oil skyrocketed. While the industry may have originally used RAP for the economic benefits it provided, RAP is just one way the asphalt industry is pushing to become more sustainable, as it has economic, environmental, and social benefits. The industry has long touted the economic and environmental benefits of using RAP, such as reductions in virgin material cost, carbon emissions, and use of non-renewable natural resources.

Reclaimed asphalt pavement (RAP) is the term given to removed and/or reprocessed pavement materials containing asphalt and aggregates. These materials are generated when asphalt pavements are removed for reconstruction, resurfacing, or to obtain access to buried utilities. When properly crushed and screened, RAP consists of high-quality, well-graded aggregates coated by asphalt.

RAP can be acquired in one of two ways: either by milling or by full depth removal. In developed countries, milling produces the largest quantity of RAP and is the preferred method of obtaining it because it keeps material of differing qualities separate and improves the surface smoothness of the milled pavement. Full-depth removal involves ripping and breaking the pavement using a rhino horn on a bulldozer and/or pneumatic pavement breakers. The broken material is then processed using a series of operations, including crushing, screening, conveying, and stacking.

Due to heavy traffic loads and environmental conditions that are not considered in the design of asphalt pavements, more and more asphalt pavements are failing prematurely, as a result overlaying or replacing failing pavements becomes a necessity. Overlaying a pavement is a simple process, where a new asphalt layer is added, the problem with overlaying is the nature of the asphalt mix materials, which will take the form of the lower layer and most distress will be reflected on it after opening the road for traffic. The best solution is replacing failing pavements by breaking or milling the surface of the old pavement to remove the affected part of the pavement and constructing a new layer of asphalt pavement in place using reclaimed materials obtained from existing pavements. 

With RAP technology asphalt pavements can be constructed at a reduced cost as it involves the usage of old asphalt pavement materials. The construction of new pavement or overlays involves a huge consumption of aggregates of different sizes along with asphalt. This leads to the high cost of the project. Consumption of natural aggregate can be reduced by using Reclaimed asphalt pavement (RAP) materials. The amount of asphalt can also be reduced in asphalt paving mixes by using Reclaimed asphalt pavement (RAP) materials. Studies have revealed that the performance of pavement by using up to 30% RAP material is similar to that of pavement constructed with natural aggregates without RAP materials. Increased demand of aggregates and binder supply can be meet out up to certain extent by using Reclaimed asphalt pavement (RAP) materials in hot mix material and other courses of the flexible pavements like sub-base and base. Last but not least recycling asphalt pavements creates a cycle of reuse that optimizes the use of natural resources and sustains the asphalt industry. 

Economy, ecology, and energy conservation are all achieved when the two main components i.e. asphalt and aggregate are reused as construction materials to provide a strengthened and improved pavement. The conventional method of providing asphalt surfacing on flexible pavements require significant amount of energy for production of bituminous binder, drying aggregates and subsequently production of asphalt hot mix at asphalt mixing plant. For example, approximately 5-6 liters of fuel is used for drying and heating one ton of aggregates, which would expand to enormously huge quantities considering lakhs of tons of aggregates that are used for road construction every year. The heating of bituminous binder, aggregates and production of huge quantities of hot mix material releases a significant amount of greenhouse gases and harmful pollutants. The amount of emissions becomes twofold for every 10o C increase in mix production temperature, and increasingly, higher temperature is actually being used for the production of hot mix material with modified binders. Also, there is a problem of the scarcity of aggregates, which forces the transportation of materials from long distance. The use of diesel for running trucks leads to the emission of pollutants.

Many studies had been conducted to evaluate the effect of RAP on the performance of asphalt pavements and showed that RAP increases the stiffness of asphalt mixes, due to the aged asphalt binder. Resulting in an improvement of rutting resistance and better performance at high temperatures. Based on the laboratory testing work carried out on virgin mixes and mixes with 20 % RAP, it was found that addition of RAP improves all the properties of the asphalt mixes. This indicates that mixes with 20 % RAP would perform better than the virgin mixes under similar conditions. The properties of RAP materials can be improved by the blending of aggregates and by the addition of chemical stabilizers.

Both asphalt batch plants and asphalt drum-mix plants can incorporate RAP into hot mix asphalt. RAP can be added into the drum, hot elevator, or directly in the mixer of the asphalt batch plant, depending on the percentage of RAP is to be used or the design of the asphalt plant. The inlet at which RAP is added to the drum mixer relies on the mixer type (parallel flow versus counter-flow versus double drum) and whether or not a separate mixer is included in the drum mix operation