Resilient Behavior of Fly ash Treated Reclaimed Asphalt Pavements

Javvadi, S C P (2014) Resilient Behavior of Fly ash Treated Reclaimed Asphalt Pavements. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

This study evaluates the use of reclaimed asphalt pavements (RAP) as a base course in flexible pavements. This study looked at the resilient behavior of RAP mixtures with addition of fly ash and virgin aggregates. The effect of fly ash dosage, aggregate content and curing period on resilient modulus were clearly studied. The reclaimed asphalt pavements material used in this study came from an ongoing project at Nellore district in Andhra Pradesh on National Highway 5 (NH5), the fly ash came from Neyveli Lignite Corporation (NLC), a thermal power station at Tamil Nadu, and virgin aggregates were taken from nearby quarry in Kandi village at Andhra Pradesh. MORTH gradation was used as a control materials. Physical properties were determined in the laboratory in controlled environment and the whole RAP and virgin aggregates were divided according to MORTH specified sizes. Modified proctor compaction tests were performed on the mixtures prepared by maintaining MORTH gradation to determine optimum moisture content – maximum dry unit weight relationship of 100% RAP material. For mixing the fly ash in mixture two different techniques (addition technique and replacement technique) were tried and addition method is considered to be appropriate technique. The specimens were prepared with 100% RAP material with fly ash dosage from 10% to 40% in 10% interval for resilient modulus (Mr) test, unconfined compressive strength (UCS) test and California Bearing Ratio (CBR) test. After casting, the specimens were stored in a specially designed stability chamber for curing. The specimens were tested for 1, 7 and 28 day curing periods. The resilient modulus tests were performed in a fully automatic cyclic triaxial equipment in accordance with test procedure given in AASHTO T 307-99, 2003. For gaining better strength the aggregates were mixed in the mixture and the same tests were performed on all the mixtures. The effect of fly ash content on the resilient modulus of RAP and RAP – virgin aggregates (VA) were evaluated. Increase in resilient modulus was observed in both mixtures. The similar trends were observed with increase in deviatoric stress, confining stress and curing period. For evaluating the effect of virgin aggregate on resilient modulus of RAP mixtures, two different mix compositions were considered. One mix composition vii consists of 80% RAP material and 20% VA material and another mix composition consists of 60% RAP material and 40% VA. A decreasing trend was observed in the resilient modulus of RAP mixtures with increase in aggregate content. It was observed that with increase in fly ash content UCS was increased. The similar trends were observed with increase in aggregate content, and curing period. The retained strength and CBR were also shown similar results. From the CBR values, the resilient modulus values were calculated using correlations given in IRC: 37, 2012 and compared with resilient modulus values which were directly determined by using fully automatic cyclic triaxial equipment. The comparison has shown that the calculated resilient modulus were showing comparatively very less resilient modulus than experimental results. From the experimental results of resilient modulus, the design parameters (layer coefficients and regression coefficients) were calculated, which are the main design inputs for the software like KENLAYER and IITPAVE for the design of flexible pavements. Overall, it was found that the RAP cannot be used as base materials in its original composition due to lack of bonding and shearing resistance. However, better mixes can be prepared by replacing certain portion of RAP with VA. Further improvement can be achieved by stabilizing the mixes with calcium rich fly ashes.

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