STUDY ON STABILIZED FLY ASH LIME SLUDGE COMPOSITE AS BASE COURSE LAYER

Abstract

newlineIn the present work, two potential industrial waste materials, Fly Ash (FA) and Lime Sludge (LS) that are generated in bulk quantities from thermal power plants and water treatment plants respectively and poses environmental hazards were stabilized using Commercial Lime (CL) and Gypsum (G) in order to make them suitable for use in Civil Engineering construction applications. Different compositions of FA, LS, CL and G (39 combinations) were studied and tested for Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR) and Split Tensile Strength Test (STS). The quality of composite is judged based on these parameters and two composites (optimum mix 1, 95%FA+5%LS) and (optimum mix 2, 50%FA+50%LS) stabilized with 12%CL and 1%G have resulted well. newlineThe optimum mix 1 and optimum mix 2, acquired UCS of 6.6 MPa and 5.8 MPa and STS of 1.3 MPa and 1.1 MPa, respectively, after 28 days of curing. The unsoaked and soaked CBR values after 28 days of curing were observed to be 89% and 75%, respectively, for optimum mix 1. Similarly, CBR values were observed to be 91% and 82%, respectively, for unsoaked and soaked condition after 28 days of curing optimum mix 2. Both the composites sustained the durability tests performed as per American and British standards. For example, the loss in weight of the samples after twelve cycles of wetting and drying was only 1.12% and 1.05% for mix 1 and 2, respectively and were within the prescribed ranges of standards. Further, the heavy metal concentration leached from the 28 days cured composites was found to be negligible. Moreover, the formation of cementitious compounds with curing was studied through Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). newlineHowever, these stabilized composites were brittle in nature. To suppress the brittleness, fibers were added to these composites and their effects on ductility and strength was studied. After trails with different percentages of fibers, it was observed that 0.3% of fiber addition to both the composites imparts ductility to the mix and also enhances the strength. The enhancement in strength and ductility was measured in terms of strength index and deformability index, respectively. It has been observed that addition of fibers increases the strength by nearly 40% and failure strain by 80%. The results suggested application of composite as base course layer material in flexible pavements as it acquired requisite strength, durability and ductility essential for base course layer material. newlineIn addition, the reliability based decision making of total pavement thickness is advocated with due consideration of uncertainty in input parameters, i.e., design traffic load (in terms of Million Standard Axle, MSA) and soil bearing capacity (in terms of CBR value). Design charts, with due consideration of uncertainty in the input parameters, were prepared for deciding total thickness of flexible pavement that can ensure certain level of reliability in the pavement performance. Moreover, issues of uncertainty in distress analysis (in terms of fatigue and rutting failure) of flexible pavement were also studied through reliability based approach utilizing combination of Mechanistic-Empirical approach, Monte Carlo Simulation (MCS) and First Order Reliability Method (FORM). A three layered flexible pavement model was analysed through PLAXIS 2D code software to compute strain at critical locations for fatigue and rutting failure and reliability index (and#946;) was computed to access the performance of the pavement. newlineThe developed composites, optimum mix 1 [(95%FA+5%LS), 12% CL, 1% G and 0.3% F] and optimum mix 2 [(50%FA+50%LS), 12% CL, 1% G and 0.3% F] satisfy all the criteria required for strength, durability and ductility. For a 450 mm thick base of optimum mix 2, the compressive and tensile strain value at critical location were obtained as and#603;c = 13.42 x 10-5 and and#603;t = 18.11 x 10-5, respectively. The probabilistic based approach suggests that the performance of the pavement was excellent (and#946;R and and#946;F gt5) for 10 MSA of design traffic load, however, for higher traffic load the pavement shows above average performance under fatigue and rutting. newline