Experimental study of the mechanical properties of an asphalt concrete with a binder modified with a hyperbranched polymer

Abstract

An epoxy resin is an important modifier in the production of polymer asphalt concretes; adding epoxy resins to bitumen increases the crack resistance, shear resistance, and the long-term strength of the final product. However, polymer asphalt concrete production is chargeable compared to that of traditional asphalt concrete due to high fraction of epoxy introduced. Hyperbranched polymers (HBP) with epoxy end groups form a highly branched spatial network at curing, their application as an active modifier in bitumen composition leads to the formation of additional spatial reinforcement architectures in asphalt concrete, which allows to strengthen the effects achieved by epoxy resins, as well as to increase impact toughness, moisture resistance, fuel resistance, and temperature stability of asphalt concrete at low fraction of the modifier. We present an experimental study of the mechanical properties of asphalt concrete with a bitumen modified by a hyperbranched polymer. The bitumen was modified with relatively low fractions (3, 5, and 8 wt.%) of the hyperbranched epoxy resin. The mechanical properties of asphalt concrete were characterized with the modulus of elasticity, compressive strength, tensile strength at break, shear strength, residual compressive strength after low-cycle loading, coefficient of residual compressive strength, and the ultimate percent compression. The results demonstrated that asphalt concrete with modified bitumen has improved characteristics compared to the original asphalt concrete, even at low fractions of the modifier. The elastic modulus and compressive strength are closely bound and, during the formation of the architecture of links in bitumen, increase almost linearly with an increase of hyperbranched modifier fraction, achieving an improvement of 9.0 and 17.7%, respectively, for samples with 8 wt.% of epoxy modifier. At the same time, asphalt concrete becomes more ductile; the ultimate percent compression increases from 2.75 to 3.5% and does not depend significantly on the amount of hyperbranched polymer. The tensile strength at break decreases as the fraction of an epoxy modifier increases, which is consistent with the literature data. However, the ductility of asphalt concrete is significantly improved, reaching the ultimate percent deformation of 1.8% at 5 wt.% of the modifier. At the same fraction of the modifier, the highest shear strength of 0.48 MPa is achieved. With an increase in the mass fraction of the epoxy modifier, the compaction under low-cycle loading decreases; the residual strength coefficient, as the ratio of the residual compressive strength after low-cycle fatigue to the static compressive strength, tends to unity for asphalt concrete, also modified with 5 wt.% of hyperbranched polymer. Thus, the best result, as a compromise of all factors under study, is achieved when 5 wt.% of epoxy hyperbranched modifier is introduced into the bitumen.