INVESTIGATING CONDUCTIVE FIBER AND INDUCTION HEAT ENERGY EFFECTS ON FATIGUE RESISTANCE AND RESILIENT MODULUS OF HOT MIX ASPHALT

Abstract

ABSTRACT Cracks in flexible pavement are inevitable due to traffic loading, fatigue, construction deficiencies and environmental factors. It causes water ingress which ultimately leads to the failure of the pavement structure. This study investigated conductive fiber and induction heat energy effects on fatigue resistance and resilient modulus of hot mix asphalt. The materials used include, coarse and two variants of fine aggregates, bitumen, and kitchen steel wool as the conductive fibre. Preliminary tests such as particle size analysis, specific gravity, flash and fire point determinants were carried out to evaluate the properties of the materials. Marshall test was used to determine the optimum bitumen content (OBC) and optimum steel wool content (OSWC) of the asphalt matrix samples. Steel wool content (SWC) in the asphalt samples was varied from 0 to 6% at 2% interval. Scanning electron microscopy (SEM) and X-ray fluorescence (XRF) test were used to evaluate the microstructure of the asphalt samples. Self-healing properties of these samples under microwave induction heating at 110 ⁰C were examined by evaluating their electrical conductivity, heat transmission rate (HTR) and extent of closure of induced cracks. The indirect tensile fatigue test (ITFT) was carried out to determine the fatigue resistance and resilient modulus performance of the samples under three different tensile loading stresses of 250, 400 and 550 kPa. The preliminary tests of the aggregates revealed that coarse aggregate had a specific gravity of 2.68 and was classified as uniformly graded. The two variants of fine aggregates, sharp sand and stone dust, were well graded soil and had specific gravities of 2.64 and 2.57 respectively. The kitchen steel wool had a specific gravity of 6.61. The bitumen material had a specific gravity of 1.01 with flash and fire points of 256.7 and 325 ⁰C, respectively. The OBC of the sample was 5.94% while OSWC by weight of OBC was 2.83%. In comparison with the control mix, the stability of the modified asphalt mix with the OSWC decreased by 15.36% from 9.24 to 8.01 KN while that of flow of the mix decreased by 2.37% from 3.88 to 3.79 mm. The SEM and XRF analysis results revealed variations in the quantities of the elemental constituents of the modified mix, as the SWC increases. The electrical conductivity increased from0.1x10-7 to 0.1x10-1 μS/cm with increase in SWC from 0 to 2% and remained constant with further increase to 4%. The HTR of 0.10, 0.14 and 0.18 ⁰C/min were respectively obtained for 0, 2 and 4%. The average resilient modulus of the asphalt mixes obtained from the ITFT increased from 4084.06 to 5578.76 MPa as SWC increased from 0 to 2% and remained relatively constant with further increase to 4%. Also, the asphalt mix with 2% SWC performed optimally in fatigue resistance and resilient modulus. The study concluded that the fiber enhanced the self-healing properties of the asphalt.