Multi-objective optimization of nitrile rubber and thermosets modified bituminous mix using desirability approach

A variety of materials, including waste and rubber products, have been used in road construction to improve the performance of bituminous pavements. The present investigation is focused on modifying bitumen using Nitrile rubber (NBR) with different thermosets namely Bakelite (B), Furan Resin (FR), and Epoxy resin (ER). The emphasis of the problem is to arrive at a mix to achieve maximum Marshall Stability (MS) and minimum flow value of Modified Bituminous Concrete. Taguchi DOE technique has been used to design the experiments using Minitab software. Analysis of Variance (ANOVA) and Multi-objective optimization has been performed using the desirability approach in Design expert software. ANOVA analysis predicts that NBR, B, ER, and FR are the major significant parameters for Marshall Stability (MS) and Flow Value (FV). It has also been analyzed from SEM and EDS images of modified bitumen that sample S1 (5% NBR, 10% Bakelite, 10% FR, 2.5% ER) has a fine surface with small pores as compared to sample S34 (10% NBR, 0% Bakelite 10% FR, 2.5% ER). Multi-optimization results suggested the optimal conditions are achieved at NBR-7.6%, Bakelite-4.8%, FR-2.5%, and ER-2.6% for MS and FV. The maximum MS is 14.84 KN and the minimum FV is 2.84 mm is obtained using optimum conditions. To validate the optimization results, the confirmation runs have been conducted, and obtained results are within 5% error with optimal conditions.