SUITABILITY OF USING POLYMER ADDITIVES S IN BITUMINOUS MIXTURE FOR SUSTAINABLE AND ECO-FRIENDLY ROAD CONSTRUCTION

Abstract

The need to improve the deficiencies of bitumen and make roads more sustainable has encouraged the development of alternative binders to modify or replace asphalt binders. This research aimed at studying the suitability of using polymer additives in bituminous mixture for sustainable and eco-friendly road construction. The polymers; Styrene-butadiene-styrene (SBS), Polyethylene Terephthalate (PET) and Ethylene-vinyl Acetate (EVA) were used separately to partially replace bitumen in percentages by weight of 10%, 20%, 30%, 40%, and 50% percentage replacements. The physical properties of bitumen and Polymer Modified Bitumen (PMB) were determined by carrying out Penetration test, Ductility test, Softening point test, Flash and fire point tests, Viscosity test and Water in bitumen test to standard specification. Fourier Transform Infrared Spectroscopy (FTIR) was performed to determine the functional chemical groups in bitumen and PMB. Rheological properties of bitumen and PMB were investigated by performing a Dynamic Mechanical Analysis (DMA) (ASTM D7175-15) with Brookfield Dynamic Shear Rheometer. The results of physical properties test revealed the hardening and stiffening effects of polymer on bitumen, which was confirmed by increase in the complex viscosities and decrease in penetration of PMB. PET modified bitumen has a high ductility, which is an indication of good adhesive properties and good performance in service. PMB exhibited an increase in hardness or stiffness, which is responsible for the increase in softening point values. FTIR analysis of bitumen and PMB showed that the functional chemical groups identified from the interpretation of FTIR spectra bitumen and PMB are C-H, C-C, CH3 and CH=CH-(cis). The DMA of bitumen and PMB showed that PMB has a very high Complex Modulus especially PET modified bitumen with the highest Complex Modulus of 5310 kPa at 30% partial replacement; this is an indication of a high resistance to thermal and plastic deformation which is as a result of the formation of a tough, rigid, three- dimensional network. It was also confirmed that PMB has an improved elastic response (reduced phase angles) compared with the base bitumen; whereas the phase angles of the base bitumen approaches 900, indicating predominantly viscous behaviour, with increasing temperature. The Loss Tangent (tan δ) which is the ratio of Loss Modulus to Storage Modulus of the PMB is infinitesimal; this is because the Storage Modulus is far greater than the Loss Modulus, which means the energy accumulating, elastic component of the complex modulus dominates the material behaviour. The result of Marshall Stability test obtained showed Stability values of 3.47 kN, 3.52 kN, 3.77 kN, 4.12 kN, 2.64 kN and 2.31 kN for 0%, 10%, 20%, 30%, 40%, and 50% percentage PET composition respectively. Comparing these values with the recommended typical Marshall Design Criteria (Asphalt Institute, 1997) given as 2.224 kN for Light Traffic, 3.336 kN for Medium Traffic and 6.672 kN for Heavy Traffic roads showed that 10%, 20% and 30% PET modified bitumen are adequate for both Light and Medium traffic roads. Likewise, Flow results obtained showed that 10%, 20% and 30% PET modified bitumen meet the criteria for both Light and Medium traffic roads. It is therefore recommended that government should encourage the use of PET modified bitumen in Nigeria to tackle the deplorable condition of Trunk B and C roads in Nigeria. Further researches into the morphology and microscopic characterisation of PMB to understand its strengthening mechanism better is recommended