Low-temperature Properties Of Asphalt Research Articles

Laboratory Study and Molecular Dynamics Simulation of High- and Low-Temperature Properties of Polyurethane-Modified Asphalt

This study investigated the modification mechanism of polyurethane (PU) on the high- and low-temperature properties of asphalt based on experimental and molecular dynamics (MD) simulations. PU-modified asphalt was prepared using an in situ polymerization method. The high- and low-temperature properties of asphalt containing various PU contents were investigated via a series of laboratory tests. The asphalt molecular model, the PU molecular model, and the PU–asphalt mixes system were modeled using software. Based on reasonable models, the influence of PU content on the physical modulus and molecular motion of asphalt at high temperatures was researched using MD simulations. The glass transition temperature of PU-modified asphalt with different contents was obtained using software, and the free volume theory and molecular diffusion movement were used to interpret the improvement mechanism of PU content on the low-temperature performance of asphalt. The results indicate that PU effectively can improve the high- and low-temperature properties of asphalt. PU has a significant positive effect on the physical modulus of asphalt, and the effect becomes more significant with the increase of PU content. In addition, PU can form a tight structure with asphalt and increase the stability of the asphalt system. The free volume ensures the free movement of PU molecules in the asphalt, allowing PU to be dispersed homogeneously in the asphalt. However, the free volume decreases when the PU content exceeds 15% by weight, which limits the improvement of the low-temperature performance of asphalt. The results of molecular simulation can explain the enhancement mechanism of PU, providing a reference for the performance enhancement of PU-modified asphalt.

Study on the Properties and Morphology of Nano-ZnO Modified Asphalt Based on Molecular Dynamics and Experiments

Plenty of research has verified that nano-ZnO particles could improve the properties of asphalt, but studies on nano-ZnO-modified asphalt haven’t been conducted at the molecular level. Therefore, to investigate the effect of ZnO particles on the properties, structure and morphology of asphalt, the molecular dynamics (MD) methods were carried out. In this study, the models of asphalt, ZnO cluster and ZnO/asphalt blending systems with different particle sizes were built using Materials Studio software. Then, the interaction energies of ZnO/asphalt blending systems under different temperatures were calculated, and the effect of ZnO particles on the modulus and glass transition temperature of matrix asphalt was simulated. The results indicated that the bulk modulus of asphalt increased by ZnO with particle size at 4 Å, 6 Å, 8 Å and 10 Å increased by 15.09%, 12.46%, 10.06% and 8.51%, respectively, which can illustrate that the shear resistance ability and low-temperature properties of asphalt were enhanced. Compared with matrix asphalt, the glass transition temperature of the ZnO/asphalt system decreased by less than 0.1 K, indicating that ZnO’s effect on the low temperature of asphalt was not apparent. With the increase of ZnO particle size, the diffusion coefficient decreased sharply. Compared to matrix asphalt, when the particle size increased to 8 Å and 10 Å, the diffusion coefficient decreased by 13% and 22%, respectively. So, in practice projects, to achieve better dispersion of particle materials in base bitumen, a smaller particle size would be recommended. The results of the radial distribution function (RDF) and AFM simulation indicated that ZnO particles changed the micro-structure of asphalt and increased the roughness of the asphalt surface. As a result, ZnO particles bring matrix asphalt better physical properties.

Polyolefin Elastomer Modified Asphalt: Performance Characterization and Modification Mechanism

The rapid growth of traffic load and volume has put forward higher requirements for road durability. To extend the service life of roads, this work investigated the feasibility of using polyolefin elastomers with a two-phase molecular structure to simultaneously improve the high and low-temperature performance of asphalt. The characteristics of the polyolefin modifier were evaluated by differential scanning calorimetry first. Following evaluation, the storage stability, workability, and rheological properties of modified polyolefin-modified asphalt were measured through softening point difference, rotary viscosity, dynamic shear rheometer, and bending beam rheometer. Additionally, the engineering performance of modified asphalt mixtures was also investigated through Marshall stability, wheel-tracking, and three points bending experiments. The results show that polyolefin has two glass transition points which facilitate the simultaneous improvement of the high and low-temperature properties of asphalt. Meanwhile, no concerns are found about the storage stability and workability of polyolefin-modified asphalt. Furthermore, the results of rheological properties indicate that polyolefin can significantly enhance the deformation resistance at high-temperature and cracking resistance at low-temperature of asphalt binders. While the fatigue performance of the polyolefin-modified asphalt is slightly reduced, the residual Marshall stability, dynamic stability, and ultimate tensile strain of the asphalt mixture containing 8% polyolefin are 1.05 times, 1.31 times, and 1.17 times those of the control sample, respectively. The results of infrared spectroscopy demonstrate that there is no chemical reaction between the polyolefin-modified and the virgin asphalt. The improvement of polyolefin on asphalt performance can be explained by the existence of both “rigid” and “flexible” structures in polyolefin.

Polyacrylate Thermoplastic Elastomer Replacing SBS for Modified Asphalt

Poly (styrene-butadiene-styrene) block copolymer (SBS) is the most common thermoplastic elastomer (TPE) used for modified asphalt. The unsaturated double bond of its polybutadiene block is prone to crosslinking and aging, which affects the performance and service life of modified asphalt. To solve this problem, acrylate soft monomers are used to replace butadiene, and hard monomers with high glass transition temperature (<I>T</I>_g) are used to replace styrene. Such new TPEs are designed to improve the chemical stability of the soft segment and improve the modification high and low temperature properties of asphalt. Firstly, the monomers used for flexible block and rigid block are screened out based on monomer price and <I>T</I>_g, and the polymerization method of each monomer is analyzed. Then, the polymerization methods and topological structures of block-type TPE prepared by rigid and flexible monomers are summarized and compared. The most suitable topological structure is linear or comb type. For linear TPE, a living polymerization method should be used, and each block is selected for copolymerization with monomers to adjust <I>T</I>_g. For comb-type TPE, the proposed synthetic route is: firstly prepare the telechelic graft chain, and then carry out free radical copolymerization. Finally, several schemes for the preparation of telechelic graft chains are proposed. A synthesis scheme of polyacrylate thermoplastic elastomer is proposed by summarizing the existing monomers, polymerization methods and initiator molecular structures, which provides a guideline for replacing SBS and for improving the comprehensive performance and service life of modified asphalt.

Low-temperature performance of asphalt based on temperature stress tests in dynamic cooling conditions

To investigate the low-temperature crack resistance of asphalt mixtures, the low-temperature properties of asphalt must be accurately evaluated. In this study, asphalt temperature stress variation curves corresponding to the cooling process were plotted based on dynamic thermomechanical analysis (DMA). Four new low-temperature asphalt performance evaluation indexes were derived. The DMA test and simulation calculation results were compared and analyzed. The comparison results show that DMA can directly determine the temperature stress, freeze-break temperature, and freeze-break strength of asphalt during the cooling process. These parameters can be used to assess the low-temperature performance of asphalt. The difference between the simulated and measured freeze-break temperature was less than 10%. However, the simulated temperature stress was significantly lower than the measured value.

Investigation on preparation and rheological properties of grafted organic long-chain carbonitride (CNDC) modified asphalt

In order to improve the high temperature and low temperature properties of asphalt and its ultraviolet (UV) aging resistance, a type of modifier grafted organic long-chain carbonitride (CNDC) was prepared. The modifier was characterized using various methods, such as Fourier transform infrared spectroscopy, scanning electron microscope and thermogravimetric analysis. The performance of CNDC modified asphalt was analyzed through conventional item tests and dynamic shear rheological tests. In addition, the dispersion characteristics of CNDC in asphalt was analyzed by optical microscope. The test results showed that the organic long-chain was grafted onto the carbonitride surface successfully and the thermal stability of CNDC was good. The dynamic shear rheological tests results demonstrated that the addition of CNDC could improve the high temperature performance of asphalt. The low temperature crack resistance of asphalt was best when the CNDC content is 3%. Furthermore, the fatigue resistance can be improved by 30% when the CNDC content was 1%. The UV aging resistance of asphalt could be improved when the content of CNDC was less than 3%. The optical microscopy test results showed that the CNDC particles did not agglomerate when the content was less than 3%. The results of the softening point difference indicated that the storage stability of the modified asphalt was good. In this study, CNDC modified asphalt had reached a balance between high and low temperature performance, which was to improve the rutting resistance of asphalt without reducing the low temperature performance. Moreover, the addition of CDNC could improve the UV aging resistance of asphalt. This study can give some help for the research of inorganic material asphalt modifiers.

Performance evaluation of new warm mix asphalt and water stability of its mixture based on laboratory tests

To confirm the reliability of self-developed ZYF-1 warm mix additive and provide some references for the promotion and application of ZYF-1, the conventional performance test and Strategic Highway Research Program (SHRP) test of SK90# asphalt and SBS modified asphalt containing ZYF-1 were conducted. The commonly used warm mix additives of Sasobit and Aspha-min were also tested. Meanwhile, the splitting test and Cantabro test of warm mix asphalt mixture before and after freeze-thaw cycles were conducted to evaluate the long-term water stability. The beam fatigue test and Wheel Tracking test were also carried out to verify other road performance of asphalt mixture with ZYF-1. The results show that ZYF-1 greatly improves the low temperature property of asphalt and has little adverse effect on high temperature performance. After mixed with Sasobit and Aspha-min additive, the high temperature property of asphalt is improved, but the low temperature performance is weakened. ZYF-1 and Sasobit significantly reduces the high temperature viscosity of asphalt binder, while Aspha-min makes the viscosity slightly increase. 4% by the weight of asphalt is recommended as the reasonable dosage for ZYF-1 based on the variation of asphalt performance. Freeze-thaw cycle simulation obviously influences the water stability of warm mix asphalt mixture, and 15 freeze-thaw cycles are recommended for the evaluation of water stability. Among tested additives, the deterioration range of water stability for asphalt mixture caused by ZYF-1 is the smallest. The warm mix asphalt mixture containing ZYF-1 effectively reduce the construction temperature while ensuring the road performance.

The research for SIS compound modified asphalt

To improve the properties of styrene-isoprene-styrene (SIS) modified asphalt and decline the SIS content in asphalt further, SIS compound modified asphalt has been prepared by the addition of SIS, polyphosphoric acid (PPA) and sulfur. The physical and rheological properties of modified asphalts were studied and the structural characteristics were analyzed by adopting morphology observation, infrared spectroscopy and thermal analysis. The research showed the suitable addition of PPA improved the high- and low-temperature properties of asphalt and declined the SIS content without negative effect. The use of sulfur can improve the storage stability of modified asphalt greatly and increase the susceptibility to ageing. The morphology and infrared analysis indicate the effects of PPA, sulfur and ageing on the structural characteristics of asphalt. The calculation for the characteristic peaks of enthalpy curves in thermal analysis was used to investigate the influence of PPA and sulfur on the distribution of molecule weight and constitutes of SIS modified (SM) asphalt before and after ageing efficiently.

Investigation on the low temperature property of asphalt fine aggregate matrix and asphalt mixture including the environmental factors

Asphalt fine aggregate matrix (FAM) is an important component of hot-asphalt mix (HMA) pavements at the meso-scale, but the relationship between FAM and HMA is not clear with respect to thermal stress and relaxation capacity at low temperatures. Thus the bending beam rheometer (BBR) was adopted to investigate the low temperature property of FAM and HMA beams. The asphalt content in FAM was calculated by keeping the filler-bitumen (FB) ratio the same as it in the known HMA specimens. FAM and HMA beams were cut and trimmed to meet the geometry requirements. Virgin beams, beams subjected to four freeze-thaw cycles, and aging beams were tested by mean of a constant creep load using BBR. In this study, the time-aging superposition principle was developed to comprehensively interpret the data. Results show that the optimal compaction is a decisive factor to generate a strong asphalt pavement. The size of air voids in FAM and HMA beams contributes to different mechanisms of moisture damage caused by the freeze-thaw cycle. FAM is more sensitive to the sunlight aging, and the time-aging superposition principle is a useful tool to quantitative the effect of aging.

Short-Term Aging Effect on Properties of Sustainable Pavement Asphalts Modified by Waste Rubber and Diatomite

Waste utilization has gained more and more interest. In this study, crumb rubber and diatomite were used to modify asphalt binder and the short-term aging effects on the properties of modified asphalts were evaluated. Three kinds of modified asphalt were prepared; they are diatomite modified asphalt (DA), crumb rubber modified asphalt (RA), and diatomite and crumb rubber compound modified asphalt (DRA). Thin film oven test (TFOT) was used to simulate short-term aging in the laboratory. Penetration, softening points, ductility, viscosity, elastic recovery, low temperature creep, and rutting susceptibility were tested and analyzed before and after TFOT. The results indicated that the softening point, viscosity, elastic recovery, creep stiffness, and G*/sinδ of DA, RA, and DRA are all linearly increased with increasing age, while the penetration and ductility are linearly decreased with increasing age. High temperature properties of asphalt are obviously improved by the addition of crumb rubber. Low temperature properties of asphalt are affected more seriously by the addition of diatomite. DRA could combine the advantages of diatomite and crumb rubber and achieve better performance in short-term aging resistance than DA and RA.

Investigation of Road Performance and Colloidal Structure of Tourmaline Modified Asphalt

Tourmaline modified asphalt (TMA) was prepared by melt-blending process. The modified effect of tourmaline on base asphalt was studied systematically by penetration test, softening point test, ductility test and bending beam rheometer (BBR) test. Based on this, the chemical components of the samples were tested and the colloidal structures of the asphalt were analyzed. Experimental results showed that the temperature susceptibility of asphalt could be improved significantly with the addition of tourmaline. Softening point test revealed that the softening point of TMA was constantly increased with the increasing amount of tourmaline. BBR test indicated that the low temperature properties of asphalt were improved with the addition of tourmaline. The colloidal structure of the asphalt was not changed due to the addition of tourmaline, remaining Sol-Gel type, and a stronger stability happened with the increasing mixing amount of tourmaline.

Experimental Investigation on Related Properties of Asphalt Mastic Containing Recycled Cement Mortar Powder

Some properties of asphalt mastic containing recycled cement mortar powder (CMP) were investigated in this paper. CMP was used as filler in asphalt mastic. The investigated mastic consisted of asphalt and filler at a mass ratio of 1:1. Penetration, softening point and high-temperature viscosity were tested. Dynamic Shear Rheometer (DSR) was used to conduct frequency sweep test of asphalt mastic. The introduction of CMP resulted in reduced penetration, increased softening point, apparent activation energy, complex shear modulus in the low frequency area and high-temperature viscosity. Results indicate that CMP may have some positive effect on high-temperature properties but some negative effect on low-temperature properties of asphalt mastic. It is also believed that the average mixing and compacting temperature of asphalt mixture containing CMP is higher than that containing limestone mineral filler (LMF).

Study on the Freeze-to-Crack Test of Asphalt Modified by Waste-PE in Packing

The purposes of this study are to modify asphalt by retrieved waste-PE in packing (WPP) and to investigate the low temperature properties of the modified asphalt. The traditional testing methods such as low temperature ductility, low temperature penetration degree, penetration or Fraass breaking point think that PE can not improve the low temperature properties of asphalt effectively, while this study adopts a new method to test the low temperature properties of WPP modified asphalt through the freeze-to-crack test. The result indicated that, after the modification, the low temperature properties of asphalt are improved, which coincides with the fact. And the improvement of the low temperature properties can be explained by the function of Shear yield and crack pinning.

Cracking of asphalt at low temperature as related to bitumen rheology

A laboratory investigation of the influence of bitumen rheology on low temperature behaviour of asphalt mixtures is described. Five bitumens from four sources and three different mixture types were studied. Rheological characteristics of the binders were measured using conventional methods (penetration, softening point and viscosity) as well as dynamic mechanical analysis (DMA). Low temperature properties of asphalt characterized by the fracture temperature were measured using thermal stress restrained specimen test (TSRST). Statistically significant relations between rheological characteristics of bitumens and TSRST fracture temperatures of asphalt specimens were established. © 1998 Chapman & Hall

Relationships between bitumen chemistry and low temperature behaviour of asphalt

A laboratory investigation of the relationships between bitumen chemistry and low temperature behaviour of asphalt mixtures is described. Five bitumens from four sources (Venezuela, Saudi Arabia, Mexico, Russia) and three different mixture types (dense graded, stone mastic and porous asphalt) were studied. Chemical characteristics of the binders were measured using Thin Layer Chromatography (TLC) and Gel Permeation Chromatography (GPC). Low temperature properties of asphalt characterised by the fracture temperature were measured using Thermal Stress Restrained Specimen Test (TSRST). Statistically significant relations between chemical characteristics of bitumens and fracture temperature of asphalt specimens are presented, indicating that the bitumen chemistry may have a significant influence on the low temperature behaviour of asphalt pavements.