Performance Evaluation of Bakelite as an Additive in Hot Mix Asphalt Mixes

Abstract

Pakistan is heading towards a major infrastructure growth especially the highway and motorway network system. Most of the roads are flexible pavements which have higher susceptibility to rutting, moisture damage and stripping. To overcome this we have to find ways to solve these problems. Keeping in view the current economic conditions, one must find solution which is cost effective and locally available. One such solution is the addition of cheap additives in the available asphalt being produced by our refineries. Therefore research should be carried out on additives which are cheap and locally available. This study investigates the effects of Bakelite as an additive, on various mechanical properties such as Marshall Stability, flow, quotient, retained stability and resilient modulus of asphalt concrete mixes. Bakelite is a high density plastic, industrially manufactured for making buttons, electrical switch boards, car bumpers and telephone sets etc. It is cheap and locally available material. The modified asphalt concrete mix was prepared by wet process which involves the direct mixing of bitumen (60/70 penetration grade) and Bakelite at high temperature (160˚C-165˚C) followed by aggregate during mixing process. The modified asphalt concrete specimens were prepared with following Bakelite percentages (2%,4%,6%,8%,10%,12%). Both modified and un modified samples were prepared by Marshall mix design (ASTM D6926), using NHA Class B gradation. Prior to sample preparation, the bitumen (60/70 penetration grade) and aggregates (Margalla aggregate) were tested to check their compatibility according to the standards of NHA. The optimum bitumen content (OBC) was found using Marshall Mix design (ASTM D6926), which was then used in the preparation of both conventional and modified samples. Performance tests including resilient modulus (ASTM D4123), Marshall Stability, flow (ASTM D6926) and retained stability (AASHTO T283) were performed to check performance of modified mixes. The test results revealed that modified mix containing 6% Bakelite by weight of optimum bitumen content provides best resistance against moisture damage, rutting and enhances the stability of asphalt concrete, than the other modifier percentages. In the end resilient modulus (ASTM D4123) test was performed under variable Bakelite (0% & 6%), temperature (25˚C &40˚C) and load duration (100 ms& 300 ms) conditions. The xiii experimental investigation of these conditions and their interaction was analyzed by full factorial design experiment. The factorial analysis showed that Bakelite content was the most significant factor influencing the resilient modulus and ultimately the strength of the asphalt concrete mix. Therefore it is concluded that addition of Bakelite as an additive in hot mix asphalt mixes gives better results regarding pavement performance.