Hardening Of Bitumen Research Articles

Polymer modified bitumen

Standard methods of characterisation of bitumen (BIT) and polymer modified bitumen (PMB) do not provide sufficient information. We propose to rely on determination of rheological properties which are much more informative. Along theses lines, we have determined rheology before and after the rolling thin film oven test. The materials studied were BIT, BIT+linear (L), styrene–butadiene–styrene (SBS), block copolymer, BIT+radial (R) and SBS copolymer. The rheological properties of the modified binders are characterised using a dynamic shear rheometer, over wide ranges of temperatures at a fixed traffic frequency of 10 rad s−1. The SBS block copolymers increase the elasticity of the BIT at high temperatures and contribute to a better flexibility at low temperatures. Polymer modified bitumens have higher resistance to permanent deformation. After aging, the hardening of BIT and PMBs occurred and the elastic response decreases as a consequence of degradation. The determined rheological properties are in agreement with the results of conventional tests.

Aging Effect on Mechanical Characteristics of Bituminous Mixtures

Traditionally, asphalt concrete requirements are based on recipe specifications for bituminous mixtures; these specifications do not consider changes in the mechanical properties of materials over time. A considerable hardening of bitumen occurs with age, a characteristic that must be considered in the evaluation of bituminous materials. In asphalt concrete evaluation work, such as pavement design or end-product contracts, the age of asphalt materials may have a considerable impact on the outcome. This investigation was undertaken to aid the development of a performance specification that is based on the structural functional properties of asphalt concrete. Properties of asphalt concrete cores from various road sections were evaluated with respect to changes in stiffness and creep over several years, with an emphasis on hardening during the early life of the pavement. Relationships between mechanical properties of bituminous mixtures and age have been established. The results make it possible to take into...

Steric Hardening and the Ordering of Asphaltenes in Bitumen

Steric hardening is the hardening of bitumen over time at room temperature. It occurs after bitumen is melted, and it often leads to poor reproducibility in standard testing. Modulated differential scanning calorimetry shows that asphaltenes order when bitumen is cooled from the melt and that this phenomenon is time-dependent. This paper establishes the link between the ordering of the asphaltenes in bitumen and its steric hardening. It is suggested that at least 24 h elapse between the melting and pouring of bitumen and its subsequent testing by standardized methods.

Time-Dependent Microstructure of Bitumen and Its Fractions by Modulated Differential Scanning Calorimetry

Bitumen fractions were analyzed by modulated differential scanning calorimetry (MDSC) before and after annealing at room temperature. MDSC allowed for separating glass transitions (Tg's) from order−disorder transitions. All fractions showed at least two Tg's and different states of order. Saturates were semicrystalline, aromatics were amorphous, resins, and asphaltenes were mesophasic. In bitumen, the fractions order in four stages upon cooling from the melt. In the first stage, all fractions order rapidly into a weakly organized phase. In the second stage, low molecular weight saturated segments crystallize. In the third stage, high molecular weight saturated segments crystallize. In the fourth stage, resins and asphaltenes order into a mesophase. The third and fourth stages are responsible for the room-temperature (steric) hardening of bitumen.