Rheological Properties Of Polymer Modified Bitumen Research Articles

Structural characterization and application of bitumen modified by recycled polyethylenes

The use of recycled polyethylene as a bitumen modifier makes it possible to obtain cheap roofing and road construction materials, as well as to dispose of polyethylene waste. Here we discuss the influence of the type of recycled polyethylenes (high-density (r-HDPE), linear low-density (r-LLDPE), and low-density (r-LDPE) polyethylenes) on their compatibility with bitumen and the internal structure of obtained polymer-modified bitumens (PMB). The novel approach was used for assessing of the compatibility of r-PEs with bitumen. Two concentrations of r-PE in PMBs are chosen: 3 wt.% (as for binder in road-building materials) and 7wt.% (as for binder in roofing materials). At 3wt.% of r-PE, the internal structure and rheological properties of PMBs are the same for different types of r-PE. Thus, any type of r-PE can be used for the production of PMBs for road construction materials. The type of r-PE strongly affects the internal structure and rheological properties of PMBs at 7 wt.% of r-PE. Only r-LLDPE forms a polymer network in bitumen. Thus, it should be used for the production of PMBs for roofing materials.

Optimisation of liquid rubber modified bitumen for road pavements and roofing applications

Polymer Modified Bitumens (PMBs) are largely used for pavement and roofing membranes applications with Styrene-Butadiene-Styrene Block copolymer (SBS) playing a major role in both markets despite its constantly increasing price due to the rising demand for quality bitumen modifiers. On the other hand, there is an increasing trend of recycling end of life tyres generating Recycled Tyre Rubber (RTR) at affordable price. This investigation aims at engineering a modified bitumen with a combination of Liquid Rubber (LR), a homogeneous blend of 50–70% RTR pre-processed in combination with heavy oils, and a wax denominated Ethylene Bis Stearamide (EBS). In the first phase, the effect of LR and EBS was independently characterised and compared to PMBs. Next, the Response Surface Methodology (RSM) was used to predict the response of different combinations of LR and EBS in terms of low and high temperature properties and cost, to then be optimised targeting conventional and rheological properties of PMBs currently used in asphalt mixtures and roofing membranes in UK. As a result, an optimum combination of LR and EBS was found leading to a cost-effective modified bitumen comparable to PMBs. The work provided also analytical functions that could be of use in further design exercises.

Preparation and Characterization of Polyester Polyol Modified Bitumen for Pavement Applications

In this study, polymer modified bitumen (PMB) from polyester polyols was prepared by bis(2-hydroxyethyl terephthalate) (BHET) which was obtained by glycolysis of Polyethylene terephthalate (PET) waste. The effect of polyester polyol structure on the rheological properties of PMB was investigated. Polyester polyols obtained by the reaction of various polyols and polycarboxylic acids. POL1, synthesized from BHET and adipic acid (AA), were blended with the bitumen resulting in improved stiffness, rutting resistance and fatigue performance with respect to neat bitumen. Also, the synergistic effects of the polyester polyol addition into styrene-butadiene-styrene modified bitumen (SBS-Bitumen) were investigated where this reference mixture contains SBS loading of 3 % according to the weight of bitumen. Although the addition of POL1(1.3:1) into SBS:Bitumen mixture at 3:3:94 weight ratio didn’t alter the high temperature performance grade of PMB, POL1:SBS:Bitumen exhibited higher softening point, elastic recovery and rutting parameter than reference mixture. The early stage promising results of this study indicated the potential benefits of polyester polyol as bitumen modifier. Also, this study showed that the use of BHET obtained by PET waste as a starting material for polyester polyol synthesis could be an alternative way to utilize plastic waste.

Effect of warm mix asphalt chemical additives on the mechanical performance of asphalt binders

Warm mix asphalt (WMA) has become very popular in asphalt pavement construction because it allows reducing both energy consumptions and carbon emissions. WMA can be obtained by using different types of additives and can be produced, applied, and compacted at temperatures 20–40 °C lower than hot mix asphalt. WMA additives allow reducing the working temperatures without compromising the final performance of the asphalt concrete. Many WMA additives are available on the worldwide market and some of them reduce the viscosity of asphalts binder (organic additives or foam) whereas others do not act on this sense (chemical additives). This study focuses on the effect of chemical additives on the performance of asphalt binders for WMA production. To this purpose, a neat bitumen, a polymer modified bitumen (PMB) and two different chemical additives were selected. All the binders were characterized through conventional tests, DSR, MSCR, FTIR and microscopic analysis. The result clearly showed that the influence of the chemical additives on the neat bitumen is negligible or non-existent. On the contrary, significant changes were observed in the modified bitumen properties. Specifically, chemical additives reduce the viscosity temperature susceptibility of PMBs in the temperature range between 80 and 140 °C, increase the rutting resistance potential and the elastic response of PMBs at high temperatures. Moreover, a morphological inspection supported the modifications observed in the rheological properties of PMBs.

Identifying the rheological properties of polymer-modified bitumen based on its morphology

This paper is an attempt to identify the relationship between morphology and performance of polymer-modified bitumen (PmB) containing styrene–butadiene–styrene (SBS) copolymer and carbon nanotubes (CNTs). Morphology is defined as the partition of polymer-rich and bitumen-rich phases, which is obtained by fluorescence microscopy and atomic force microscopy. Rheological properties of PmB are captured by Master curve, Han curve, and Cole–Cole curve. Three different bitumen samples with same polymer amount were selected in this paper. The results showed that a dense network and the interlocked structure in SBS phase provided a better anti-rutting property of PmB. Han curve demonstrated that the elastic modulus improvement of PmB had a close relationship with the size of SBS phase. Cole–Cole curve illustrated that the smaller size and interlocked structure of SBS phase prevented the movement of SBS phase and presented a higher loss viscosity at low-driving speed condition. Furthermore, CNTs played a positive role on the anti-aging property, storage stability, and anti-cracking performance of SBS-modified bitumen.

Effect of cross-linking agents on the rheological properties of polymer-modified bitumen

The use of polymer-modified bitumen (PMB) has increased significantly for more than two decades. Cross-linking agents are used in PMB as an additive, mainly for improving the durability of this material as the cross-linking agent chemically reacts with the PMB by forming a covalent or ionic bond. This study tries to investigate the effect of cross-linking agents on the rheological properties of PMBs. Two types of elastomers – linear and radial – and seven types of cross-linking agents were used. A functional polyethylene (FPE) was added to all the binders. The rheological properties (creep and recovery) were studied using the dynamic shear rheometer. The viscosity and storage stability for each of the modified binder were also studied. Among all the cross-linking agents used in this study, sulphur was found to be the most effective. Two more cross-linking agents were found to have similar results as that of sulphur.

Influence of polymer modification on asphalt binder dynamic and steady flow viscosities

Asphalt pavement performance such as rutting, crack initiation and propagation as well as fatigue behaviour are substantially affected by the rheological properties of the bitumen. In this sense, the use of polymer modification in road paving applications has been growing rapidly over the last decade as it allows significant enhancements in bitumen properties with consequent improvement in road service life. In fact, the use of polymer modified bitumens (PMBs) leads to pavements characterized by higher resistance to rutting and thermal cracking and lower fatigue damage, stripping and thermal susceptibility. This paper presents a laboratory investigation concerning the effect of polymer modification on the flow behaviour of bitumens. Two different polymers, an elastomer and a plastomer, were used as bitumen modifying agents at three different percentages (2%, 4% and 6% by bitumen weight). Oscillatory mechanical analysis as well as viscosity measurements under steady state conditions were performed taking into account different testing parameters such as temperature, loading frequency and shear rate. The results confirm that the rheological properties of PMBs are strongly influenced by polymer nature and polymer content. The bitumen viscosity on the dynamic domain was combined with that in the steady-state domain, confirming the applicability of the Cox–Merz relationship for the plain bitumen and the PMBs with low polymer content. Finally, the Cross and the Carreau models were found to be suitable to fit the steady state and the dynamic results in order to determine the viscosity function of the investigated bitumens.

Influence of the processing conditions on the rheological behaviour of polymer-modified bitumen ☆

Mixing polymers into bitumen has important consequences on the engineering properties of bituminous binders. Thus, structural and chemical changes may be observed during processing of polymer-modified bitumens. Chemical compatibility and processing conditions are crucial to obtain suitable properties. Most polymers occur to be insoluble, in some degree, in the bitumen matrix, and phase separation may result. Polymer stabilization can be achieved by mechanical dispersion of the modifier and swelling by compatible components in the maltene fraction. This paper deals with the influences that processing variables exert on the rheological properties of polymer-modified bitumens. From the experimental results obtained we may conclude that a rotor–stator mixer device enhances the rheological properties of binders prepared with high-density polyethylene, low-density polyethylene, ethylene–propylene–diene monomer, and their blends, as compared to a stirred tank device.