recycling pavement mix design methods

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A SEMINAR REPORT ON ASPHALT RECYCLING METHODS & DESIGN OF PAVEMENT WITH CENTRAL PLANT HOTMIX RECYCLING METHOD (CPHMR) l` l` l` l` .!!!`I`.l .!!!`I`.l .!!!`I`.l .!!!`I`.l ABSTRACT: Signified the use of RAP towards the pavement rehabilitation particularly for pavement recycling, discussed recycling methods and focused hot mix recycling (CPHMR) A case study of pavement design with central plant hot mix recycled asphalt mixes is discussed where laboratory investigations carried over the Recycled mix and virgin mix by comparing its Marshal values, Creep and Fatigue performances. Finally the cost comparison is tabulated shows the immediate implementation of recycling mixes in India for the economical benefits. INTRODUCTION: Any in-service road needs maintenance. The maintenance of roads can be done in the form of minor repair, overlay, recycling or reconstruction. Given the fund constraint for any maintenance job, an engineer needs to equip himself on various techniques of evaluation of pavement, alternative rehabilitation measures and systematic approach to allocate maintenance funds. Pavement recycling is expected to be a major thrust in pavement rehabilitation in India, soon. Significant advancement has been achieved in mix design and construction practices of bituminous pavement recycling in various countries. Recycling of existing roadway materials is a highly attractive option for rehabilitation. Recycling can not only save in costs of materials, but in most cases, can also lead to significant savings in time of construction, and in all cases, lead to reduction in disposal, and environmental benefits. Interestingly, not much of pavement recycling works at present being carried out India, though basic initiative was taken quite sometime back. The present workshop proposes to share the knowledge of state of the art tools and techniques of bituminous pavement recycling which is vital for proper utilization of the most appropriate recycling method for optimum utilization of funds The bituminous pavement rehabilitation alternatives are mainly overlaying, recycling and reconstruction. In the recycling process the material from deteriorated pavement, known as reclaimed asphalt pavement (RAP), is partially or fully reused in fresh construction. Some of the advantages associated with pavement recycling are less user delay conservation of energy preservation of environment Reduced cost of construction Conservation of aggregate and binder Preservation of existing pavement geometrics etc. Recycled mix has higher resistance to shearing and scuffing, which in turn increase the rutting resistance Chances of reflective cracking are found to be less with recycled mix The purpose of the bituminous recycling is to regain the properties of the RAP, such that it tends to perform as good as fresh mix. Thus, the process of bituminous recycling involves mixing of the RAP, fresh bitumen, rejuvenators and new aggregates in suitable proportions. Rejuvenators are low viscosity oily substance, which helps to bring down the high viscosity of aged bitumen. Recycling Methods: central plant recycling: If the RAP is modified at a plant, away from construction site In-situ recycling. In this the RAP is modified in place, from where it is available If heat is applied then the process is known as hot mix recycling. In case of cold mix recycling, old materials are conditioned using recycling agent (like, low viscosity emulsion) without application of heat. Fig.1 classification system Based on the depth of removal: Surface recycling: Done when the top layers fail, and recycling is done to that failure portion. Full depth reclamation: Done when pavement layers up to base layer is removed and constructed again. Hot in-place recycling: Initially the pavement intended to be recycled is heated to a higher temperature using suitable heating arrangement. This facilitates easier removal of materials. After heating, the pavement surface is scarified to the required depth. Further, depending on the requirement fresh aggregate and binder are added. The material is mixed well and compacted to the required thickness. As this process consumes less time, least disruption to traffic is caused. Also the transportation cost is less, as materials need not be taken away. Machinery required for this purpose being bulky in nature, sufficient right-of-way is required. This becomes an important consideration for in-place recycling within the city areas. Cold in place recycling The pavement is scarified with a scarifier. The scarified material is crushed to the required gradation. Then the required amount of fresh aggregates and binder in cold form (emulsion or cutback) is added. It is compacted and left for aeration. During this process additives like, cement, quick lime, fly ash may be used. The cold mix recycling takes care of local geometric correction of pavement distresses like surface cracks being an in-situ process the hauling cost is considerably low. The air quality related problems during construction is almost negligible as compared to hot mix process Similar to hot in place recycling process, the machinery required being bulky, sufficient maneuvering space should be available for operating the equipment. Also, the lane needs to be closed for certain time so that sufficient time is available for curing of freshly laid course. Moisture content (when bitumen emulsion is used) needs to be given importance as it influences gradation control, mixing and workability of recycled mix to a large extent Hot central plant recycling In this process, RAP is combined with required quantity of bituminous binder, and fresh aggregates in a hot mix plant. The resultant mix is heated to an elevated temperature and mixed thoroughly. The hot mix is transported to paving site, placed, and compacted to the required compaction level. The main advantage of this process is that the mix properties and performance is comparable to that of virgin mix especially have noted that the quality control due to the fact that constituents are mixed under controlled conditions and it is possible to monitor mixing process continuously. Less workspace is required for laying the recycled mix; hence this is suitable for the roads where the right of-way is somewhat restricted. The RAP should not be exposed to extremely high temperature as it causes pollution due to smoke emission. As RAP is susceptible to moisture and care needs to be taken while storing it. Cold central plant recycling This is the similar process as is the hot central plant mixing, except it does not involve any heating, and therefore emulsion bitumen is used binder in most of the cases. Precise control on the mixing time is important. Over-mixing may cause premature breaking of emulsified bitumen and under-mixing results in insufficient coating of aggregates. CASE STUDY: The investigations are done for the hot mix recycling process since large number of studies has been reported a conflicting conclusions like the performance of hot mix recycled mixes in fatigue ,rutting or stiffness could be better, worse or similar compared to the corresponding virgin mix. Two RAP samples are collected at Kanpur city for the recycling investigations are carried out on the design of the recycled mix and laboratory tests Marshal, fatigue and fatigue done and compared their performance with the virgin mix. Laboratory investigation The basic requirements of the recycled mix design can be summarized as follows: The quantity of old aggregates and new aggregates are to be adjusted in such a way that the resultant gradation of aggregates conforms to the specified gradation. The quantity of the aged asphalt binder, virgin asphalt binder and the rejuvenator, if any, are to be adjusted in such a way that the resultant viscosity becomes equal to the desirable viscosity at operating temperature. The total quantity of asphalt binder should be adjusted in such a way that it satisfies the desired asphalt binder quantity of the target mix. The other volumetric and strength parameters of the mix should also be satisfied. The RAP samples are collected, proportioned, and mixed with virgin asphalt binder and new aggregates, for various target bitumen contents. Standard Marshall testing is conducted for estimation of the possible optimal binder content. Further, creep and fatigue tests are performed on the recycled samples in order to assess their performance. The same tests are conducted for virgin mixes, with same specification, in order to have a comparative idea of mix performance. The schematic plan of the Study is presented in fig.1 PROCEDURE& DESIGN CALCULATIONS: The representative RAP samples are cleaned for deleterious materials and aged asphalt binder and old aggregates are separated using Centrifuge Bitumen Extractor(CBE) as per ASTM D2172 The average asphalt binder content of the RA


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