EFFECTS OF USING WASTE PLASTIC ON FATIGUE AND RUTTING CHARACTERISTICS IN FLEXIBLE PAVEMENTS

Abstract

Indian highways are experiencing several irregularities such as surface distresses (fatigue and rutting) which reduce their expected service life significantly. The present study is aimed at eradicating such irregularities by changing the rheology of conventional bitumen. Normally, conventional binders are temperature susceptible and the pavements lying in the vicinity of higher temperature differential are observed to show their proneness to fatigue and rutting. On the other hand, concerned authorities are facing problems in finding suitable places for disposal of plastic waste. Utilization of waste plastic at optimum proportions in the bituminous mixtures would rectify both the aforementioned problems and lower the project cost of pavements. Since, Bitumen as a binder behaves in a visco-elastic manner which can be studied using DSR (Dynamic Shear Rheometer) in wide ranges of frequency and temperature through rheological parameters like (G*, δ, G*×sinδ and G*/sinδ) and through some improved test procedures like MSCR (Multiple Stress Creep and Recovery) and LAS (Linear Amplitude Sweep) to evaluate rutting and fatigue performance respectively. Study of properties of binder alone cannot suffice the criteria for judging the overall performance of pavement unless it is accompanied by the volumetric properties of different aggregates required in bituminous mixtures. Marshall method of mix design is followed for evaluating the volumetric properties of the mixes prepared and the characteristics of the mixes with respect to distresses like rutting and fatigue are evaluated using wheel rut tester and four point bending beam respectively. This work outlines the conventional and rheological properties of binders and mixes. The work begins with the preparation of modified binder from shredded waste plastic fibres from carry bags and cement carry bags at different contents of 4%, 5%, 6% and 7% by weight of bitumen. After blending, phase separation (storage stability) test was carried out in order to determine the optimum modifier content for performing further tests. In the present study the samples modified with 4% modifier showed the desired difference of less than 3 0C. In this way three different samples were prepared namely: base bitumen (VG-10), VG-10 + 4% carry bags (CB) fibres, and VG-10 + 4% cement carry bags (CCB) fibres, which were tested for conventional tests and rheological tests including Rotational Viscometer test, DSR test, Performance grading (PG) test, LAS test, MSCR test. iv As per IRC: SP: 53-2010, any modified sample should have a temperature of minimum 760C for possessing minimum value of rutting factor (G*/sinδ) as 1.0 kPa for original binder. Since, with the introduction of waste plastic fibres as modifier to bitumen that minimum value of 1.0 kPa was found at 80.50C for VG-10+4%CB while it was greater than 1000C for VG-10+4%CCB which indicates that waste plastic as modifier fulfilled the criteria of being a suitable modifier. While evaluating the rutting susceptibility of binders using MSCR test procedure (with spindle geometry having 25mm diameter and 1 mm gap between the spindle and base plate) as lower values for non-recoverable creep compliance (Jnr) are favorable, by modifying base bitumen with waste plastic fibres the average values of Jnr get reduced approximately by 2.27 times, 4.69 times, 5.18 times and 3.5 times the corresponding values of base bitumen at creep stress level of (0.1 kPa), and for higher creep levels (3.2 kPa) the reduction in values achieved were 3 times, 3.8 times, 3.95 times and 3 times at temperatures of 400C, 500C, 600C and 700C respectively. Fatigue performance of binders were compared by performing LAS test procedure (with spindle geometry having 8mm diameter and 2mm gap between the spindle and base plate) where at lower strain level of 2.5%, the improvement obtained by modifying the bitumen over that of base bitumen was found better by 2.1times, 2.3 times and 1.8 times while for higher strain condition (5%) that improvement was approximately of the order of 1.46 times, 1.87 times and 1.37 times at 100C, 200C and 300C respectively. The improvement achieved by modifying base bitumen was quite significant in all aspects of binder performance when compared with the parameters of base bitumen. However, 4%CB as modifier proved superior to 4%CCB, in fatigue as well as rutting performance parameters. Second part of the study deals with the bituminous mixtures where the ingredients for mixes were VG-10 as base binder, aggregates corresponding to Bituminous Concrete (BC Grade 1) and 4% CB as modifier. In this way samples of four different cases namely: [VG-10 + aggregates as per BC (Grade 1) and the mix was treated as a control mix], [VG-10 +aggregates as per BC (Grade 1) + waste plastic mixed as per dry procedure of mixing], [VG-10 +aggregates as per BC (Grade 1) + waste plastic mixed as per wet procedure of mixing] and [VG-10 +aggregates as per BC (Grade 1) + pre-compressed waste plastic boards] were prepared and tested for Marshall stability, Marshall flow, Indirect tensile strength (ITS), volumetric properties (volume of air voids (%Vv), volume of voids in mineral v aggregates (%VMA), volume of voids filled with bitumen (%VFB), etc.). Some durability tests of the mixes [Retained Marshall Stability (RMS) and Tensile Strength Ratio (TSR)] were also conducted. The susceptibility of the mixes to distresses like rutting and fatigue were evaluated by performing wheel rut test at temperature of 600C and four point bending beam (4PBB) test at 200C respectively by compacting the specimens at around target void contents of 4%. In last part of study, plate load test was performed over pavement test track prepared as an overlay of 50 mm BM (Grade-2), 50 mm DBM (Grade-2) and 30 mm BC (Grade-2). Two times BC layer was modified by waste plastic carry bags once via dry procedure of mixing and once by wet procedure of mixing. Once the waste plastic boards were introduced between BM and DBM layers. So in total four different cases were tested under plate bearing assembly. Among the four dry procedure of mixing the shredded fibres to bitumen was found to be the best.