Characterization and Identification of Bituminous Materials Modified with Montmorillonite Nanoclay

Montmorillonite (Mt) nanoclay is a layered silicate mineral with a 2:1-type layer structure, two tetrahedrals sandwiching one octahedral. In recent decades, it is successfully introduced into polymer systems to form polymer-clay nanocomposites (PCN) in which the silicate layers of the Mt are randomly and homogeneously dispersed at a molecular level in the polymer matrix. Due to the addition of Mt, some properties of PCN, such as the mechanical, thermal and gas barrier properties, were superior to those of pristine polymers. Based on this idea, natural and organo Mts were used to modify bitumens with different penetration grades in this study. Some rheological, ageing and fatigue properties of the modified bitumens and mortars were characterized. High-shearing mixing method was used to prepare the modified bitumen; X-ray diffraction and micro-CT scanning were employed to observe structures of Mts in bitumen; DSR equipment was adopted to characterize the rheological properties; the rolling thin film oven (RTFO) and pressure ageing vessel (PAV) methods were used to simulate the short term and long term ageing on base and Mt modified bitumens, respectively. Fatigue tests were performed on bitumen and mortar samples which consisted of bitumen, filler and sand at a weight ratio of 0.34:0.30:0.36, as well as on a dense graded asphalt mixture. XRD results indicated an intercalated structure of organo Mts in the bituminous matrix. A phase separated structure of natural Mt was found in the base bitumen. Micro-CT images further proved that natural Mt acted like a conventional filler at micrometer level. The interaction between the Mts layers and bitumen changed its viscosity and dynamic response as characterized by means of the DSR. Reinforced shear thinning was observed on the modified bitumens at a liquid state, which implies a better drainage resistance of asphalt mixture during transportation. The results indicated that organo Mts improve the short term ageing resistance of base bitumen. The main reason for this improvement is that the barrier properties of Mt particles hinder the penetration of oxygen. Meanwhile, the reduction of volatilization of the oil components of bitumen due to these barrier properties can be another reason. However, a less effective improvement was observed for the long term ageing using the PAV. That is because organo Mt platelets automatically accumulated to reduce their surface area under tough testing conditions in the PAV. This accumulation weakened the barrier properties of the Mts. It is believed however that organo Mts will improve the long term ageing behaviour of bitumen in the field because the state of the Mt will be very stable and no accumulation as occurred in the PAV will happen. The addition of organo Mts can change the fatigue properties of bitumen and even mortar. This change was influenced by the type of the surfactant on the Mt which determined the interfacial interaction between the bitumen and the Mt. Because of the heterogeneous character of asphalt mixtures and their complicated failure mechanism, the fatigue test on the asphalt mixture with the modified bitumen only gave a limited improvement of this property. Finally, some important aspects are given for further research. Based on the present research results, the organo Mt can be an alternative to modifiers used in the bitumen to sustain the durability of asphalt pavements