Performance and viscoelastic assessment of high-recycle rate cold foamed bitumen mixtures produced with different penetration binders for rehabilitation of deteriorated pavements

Abstract

The paper investigates the influence of the binder penetration grade on the volumetric, mechanical and viscoelastic properties of cold recycled mixes with foamed bitumen. Cold recycled mixtures produced with foamed bitumen differ significantly from other bituminous paving materials (e.g. hot mix asphalt) in terms of aggregate coating and bonding with the bituminous binder. What is more, hydraulic binders usually contribute to the strength of those mixtures. These factors result in a decreased viscoelastic response of cold recycled mixtures, which may impact the sensitivity of these mixtures to the type of binder used, which has not been thoroughly studied yet. The main body of the conducted experiments included complex stiffness moduli measurements under cyclic uniaxial compressive loading, supplemented by assessment of air void content, indirect tensile strength, resistance to moisture damage, indirect tensile stiffness and static creep modulus. The composition of investigated mixtures with high rate of recycled materials was designed to reflect a common scenario in rehabilitation of deteriorated pavements subjected to low and medium traffic loads. The three utilized binders were graded as 35/50, 50/70 and 70/100 penetration road paving bitumen, and were added as foamed bitumen in 2.5% amounts to the cold mix. The recycled mixes contained 50% of reclaimed asphalt pavement material, 30% of reclaimed crushed stone base and 20% of virgin aggregates. A hydraulic binder in form of Portland cement was used as a binding agent in amounts of 2%. Each of the investigated mixtures exhibited significantly distinct results in terms of air void content, indirect tensile strength and creep stiffness modulus. The performance of mixtures with 50/70 and 70/100 binders was similar in indirect tensile stiffness moduli and complex stiffness moduli. It was found, that the binder type had significant effects on the compactability of investigated mixtures, which resulted in different mechanical performance. At the same time the influence of the binder type on the viscoelastic properties of the cold mixtures was attenuated. It was concluded that the limited influence of the binder used was caused by the significant amount of reclaimed asphalt material in the evaluated mixtures and the effects of cementitious binding of the Portland cement. The results showed that a wide range of penetration grade bitumen can be used for producing cold recycled mixtures with foamed bitumen with only minor effects on their performance and viscoelastic properties.