Bituminous pavement is widely used in transportation construction due to its excellent road performance and driving comfort. Viscoelastic bitumen without modification is much susceptible to temperature, giving rise to high-temperature rutting and low temperature cracking. To avoid these undesirable diseases in the pavement construction, bitumen is usually modified by polymers such as styrene-butadiene-styrene (SBS), polyethylene (PE) to enhance its engineering properties.
Nowadays, heavy traffic loads and large volume of vehicles make bituminous pavement prone to suffer rutting and fatigue cracking. The intensification of Urban Heat Island (UHI) effect requires the bituminous pavement to accommodate the severe climates conditions. These harsh realities bring a serious challenge to bituminous materials, even polymer modified bitumen.
On this account, researchers led by Professor Tian Xia from Chongqing University of Technology and Dr. Jianhui Xu from Chongqing Zhixiang Paving Technology Engineering Co., Ltd. proposed a route of network structure construction in polymer modified bitumen to effectively enhance their rutting resistance and rheological stability. The underlying mechanism of the resulting network structure is viscoelastic phase separation (VPS), whose prerequisite is the large dynamic asymmetry between polymer and base bitumen.
Their previous study revealed that, adding polyethylene glycol (PEG) with different loadings in PE modified bitumen could regulate the complex modulus temperature range and stabilize the PE-rich network, further enhance the rheological stability, rutting resistance and durability of the modified bitumen. Despite the significant efforts to improve the performance of bitumen, more studies are needed to understand the effects of different modification methods.
On this account, the authors investigated the effects of annealing methods and chemical reaction on the properties and structure of PE/PEG modified bitumen. Specifically, the authors employed two methods to regulate the rheological stability of PE/PEG modified bitumen. The first approach involved physical modifications utilizing various annealing treatments for the blends. This approach allowed for the study of the influence of PE crystallinity on the rheological properties of the blends. The second approach was chemical modification comprising chemical reactions between the polar and NCO groups in the PE/PEG modified bitumen to generate the urea structure that has considerable influence on the properties of the modified bitumen. The rheological stability changes were explored via PE-based crystallization behavior and viscoelastic network evolution. Finally, the impact of the two approaches was compared. The work is published in the journal, Construction and Buildings Materials.
Results showed rheological property on each complex modulus variation with temperature curves of the PE/PEG modified bitumen. The authors, however, observed that various annealing treatments could regulate the initial temperatures at a stable complex modulus plateau. The sample annealed at a temperature of 100 °C, which is close to the crystallization temperature of PE, exhibited the best rheological stability. This was attributed to the close relationship between the crystallinity and stiffness of the PE-rich network induced via VPS. Furthermore, thermal stability, complex modulus and solvent-resistance of PE modified bitumen improved when the PEG modifier was partially replaced with the same fraction of 4,4′ -diphenylmethane diisocyanate (MDI). It also refined the PE-rich network structure, resulting in better solvent resistance.
In summary, the structure and rheological stability properties of PE/PEG modified bitumen were studied. The main factor contributing to the occurrence of rheological stability was identified to be the presence of the stiff network with crystalline PE. The rheological stability was obtained regardless of the annealing treatment method used. On the other hand, the chemical reaction between MDI and polar groups of the blend formed a large-scale urea/urethane structure, and this was the crucial reason for the network refinement and significant performance enhancement of PE/PEG/MDI modified bitumen. In a statement to Advances in Engineering, the authors stated that their study findings contribute to developing high-performance bitumen for various environmental conditions.
Xia, T., Chen, X., Xu, J., Chen, W., & Zhang, A. (2021). Effect of annealing method and chemical reaction on the structure and properties of polyethylene/polyethylene glycol modified bitumen. Construction and Building Materials, 269, 121228.