Influence of Relative Molecular Mass of SBS on Low-Temperature Performance of Modified Asphalt

Styrene Butadiene Styrene (SBS) is widely used in pavements because it significantly improves the performance of the modified asphalt. The dosage of SBS has an important effect on the low-temperature performance of the modified asphalt. The difference in relative molecular weight influences the magnitude of the change in low-temperature performance. In this paper, low temperature bending beams rheology test of five different relative molecular weight SBS modified asphalt is conducted at -12°C, -18°C and -24°C to evaluate the low-temperature properties of modified asphalt. Then, the experimental results are analysed. The results show that there is a certain correlation between the relative molecular mass of SBS and the low-temperature performance of modified asphalt. The creep stiffness and creep rate of the modified asphalt are influenced by the relative molecular mass of SBS and temperature. As the relative molecular mass increases, the low-temperature performance of the modified asphalt first rises and then decreases.

Rheological Evaluation of Modified Bitumen by EVA and Crumb Rubber Using RSM Optimization

In the present study, ethylene-vinyl acetate (EVA) and crumb rubber (CR) were used as bitumen modifiers. The experiment was designed by response surface methodology (RSM) at different levels of modifier additives based on the central composite design (CCD). Next, the Superpave protocol was followed to evaluate the modified bitumen performance at different temperatures compared with the unmodified bitumen. In this regard, to evaluate at high temperatures, a dynamic shear rheometer (DSR) test was performed, and G ∗ /sinδ index was examined on bitumen samples after aging. Besides, the bending beam rheometer (BBR) test was performed to evaluate the low-temperature behaviour of the modified bitumen according to the SHRP standard based on the creep stiffness and creep rate. The optimal combination of additives was evaluated using RSM and analysis of statistical values to improve the performance properties of bitumen at high and low temperatures. Moreover, based on the DSR and BBR test results, 5.6% of EVA and 3.9% of CR were selected as the optimal values for the modified bitumen behaviour at the high and low temperatures of the mixture.

High and Low-Temperature Performance Evaluation and Microanalysis of SMCSBS Compound-Modified Asphalt

The mixture of styreneic methyl copolymers (SMCs) normal temperature-modified asphalt and styrene-butadiene styrene block copolymer (SBS)-modified asphalt (SMCSBS) compound-modified asphalt was investigated in this study. The viscosity and temperature properties of compound modified asphalt (SMCSBS) were studied by Brookfield rotary viscosity test. Dynamic shear rheometer (DSR) and bending beam rheometer (BBR) were used to test SMCSBS compound modified asphalt with different SMC additions. Finally, the microstructure and physicochemical properties of SMCSBS were evaluated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR), and the modification mechanism of the SMCSBS was studied. The results show that the viscosity of the compound-modified asphalt added with SMC is improved, which is conducive to improving its workability. With the increase of SMC content, the high-temperature performance of the compound modified asphalt firstly increases and then decreases with the increase of SMC content. When the content of SMC is 12%, its high-temperature performance is the best. Compared with SBS-modified asphalt, the SMCSBS has better low-temperature performance, and the creep stiffness S and creep rate m of the SMC with different content are better than that of SBS. Finally, the microcosmic characteristics show that the SMC can give full play to its characteristics and can be uniformly dispersed in SBS modified asphalt. SMC is essentially a surfactant, which can reduce the viscosity and construction temperature by changing the surface tension and surface free energy of asphalt molecules. The curing agent of epoxy resin is slowly cross-linked and cured after contacting with air to form a certain strength, thus improving the road performance of the asphalt mixture.

Prediction of Dynamic Modulus of Hot Mix Asphalts with Reclaimed Asphalt Pavement

This study evaluated the viscoelastic properties of a performance grade (PG) binder blended with different percentages of binders recovered from reclaimed asphalt pavement (RAP) for conditions (materials, climate, and specifications) prevailing in Oklahoma. The viscoelastic properties of the blended binders were then used to estimate dynamic modulus ( E ∗ ) values of the new mixes with RAP by using the Witczak model through time-temperature superposition (TTS) principles. The recovered binder from RAP was found to be significantly stiffer than the virgin binder (PG 64-22). The addition of RAP increased the complex modulus ( G ∗ ) of the base binder, so did the E ∗ of the corresponding mix. The creep stiffness resistance of the asphalt binder at low service temperatures decreased with the addition of RAP. With up to 10% RAP binder, no notable changes were observed in the viscosity and PG grade of the virgin binder. With 25% and 40% RAP binder, the PGs of the blended binders were found to be PG 70-16 and PG 76-16, respectively. It was observed that the E ∗ master curves predicted from PGs of the blended binders were in close agreement with those estimated from the laboratory-measured E ∗ data. The dynamic shear rheometer (DSR) data of rotational thin film oven (RTFO)-aged blended binders predicted significantly lower E ∗ values compared to the measured ones. The E ∗ values predicted from rotational viscosity (RV) test data were found to be higher than the measured E ∗ values. The findings of this study are expected to provide transportation professionals with a better understanding of new mixes with high RAPs.

Evaluation of recycled asphalt mixture at low temperature using different analytical solutions

Using reclaimed asphalt pavement (RAP) in road infrastructures is crucial for mitigating the environmental impact while controlling the construction costs. However, poorer low temperature performance may be experienced for mixtures containing RAP. In this paper, the effect of RAP on the material response at low temperature is investigated through mixture creep testing with the bending beam rheometer. Three different mathematical approaches are selected for further evaluation in combination with simple statistical analysis. Based on the experimental data, creep stiffness, m-value, relaxation modulus, thermal stress, and critical cracking temperature are computed and compared. As a result, no differences are found between the virgin mixture and that designed with 15% of RAP. Poorer performance is observed when more than 25% of RAP is incorporated; however, no significant variation was observed for a further increase up to 40% suggesting that higher amount RAP could be used depending on traffic level and climate.

Effects of Carbon Fibre on Performance Properties of Asphalt Mixtures

In this study, the effects of carbon fibre on improving the performance characteristics of asphalt mixtures were investigated. To this end, four percentages of carbon fibre (0%, 0.3%, 0.5%, and 0.7% by weight of bitumen) were used as an additive in asphalt mixtures. The mechanical properties of prepared mixture specimens were investigated using tests such as Marshall Stability and flow, Indirect Tensile Stiffness Modulus, Creep Stiffness, Indirect Tensile Strength, and moisture resistance. The results of tests applied to asphalt mixtures showed that the carbon fibre additive increased the resistance to shear stress by 25%, the fatigue life by 51% at 40 °C and the permanent deformation resistance by 2.25 times at 60 °C. It also improved the resistance of mixtures to moisture damage by increasing the durability and cohesion of asphalt mixtures. Experimental results indicated that the carbon fibre provided a positive contribution to the performance properties of asphalt pavements.

Influence of the Mineral Powder Content on the Asphalt Aging Resistance in High-Altitude Areas Based on Indoor Ultraviolet Light Tests

Intense ultraviolet irradiation is an important environmental factor affecting the service performance of asphalt mixtures in high-altitude areas, and the asphalt mortar is the main factor affecting the durability of asphalt mixtures. It is of great theoretical significance and engineering value to study the performance of the asphalt mortar at medium and low temperatures under ultraviolet irradiation. Therefore, this paper focuses on the evolution of the effect of the filler content on the rheological properties of different asphalt materials at low and medium temperatures under quantitative UV irradiation. Taking the average amount of UV irradiation observed annually in Northwest China as the indoor aging condition, the matrix asphalt mortar and modified asphalt mortar with different mass ratios of asphalt mortar are selected for indoor aging tests. Physical property tests, low-temperature performance tests, and dynamic shear rheological tests are carried out. The effects of the UV irradiation intensity and mineral powder content on the low temperature performance of the asphalt mortar are studied by variance analysis method, and the reasonable mass ratio range of the asphalt mortar under UV irradiation is proposed based on the standard residual square sum (STRSS) method. The results show that the temperature sensibility and low-temperature deformation energy significantly decrease with the increase in the filler content, while the values of the softening point, fatigue factor (G*sin δ), and creep stiffness modulus of the asphalt mortar increase. In addition, the variance analysis of the creep stiffness modulus aging index (SAI) shows that the ultraviolet radiation intensity has a significant impact on the performance of the asphalt mortar. When the mineral powder content is less than 40%. When the filler content is greater than 40%, the filler content effects the performance of the asphalt mortar. According to the standard residual square sum (STRSS) method, the best mass ratio of the base asphalt mortar is 1.096, and the best mass ratio of the modified asphalt mortar is 0.9091.

Prediction of Bending Beam Rheometer Test Outputs Using Artificial Neural Networks

The major objective of this study is to investigate the possibility of using Artificial Neural Networks in creating prediction models capable of estimating Bending Beam Rheometer outputs; namely creep stiffness, and m-value based on test temperature, modifier content; in our case waste vegetable oil, and testing time interval. A feedforward backpropagation neural network with Bayesian Regulation training algorithm and an SSE performance function was implemented. It was found that the neural network model shows high predictive powers with training and testing performance of 99.8% and 99.2% respectively. Plots between laboratory obtained values and neural network predicted outputs were also considered, and a strong correlation between the two methods was concluded. Therefore, it was reasonable to state that using neural networks to build prediction models in order to find BBR test values is justified.

Size Effects of Finite Element Model for Three-Dimensional Microstructural Modeling of Asphalt Mixture

Asphalt mixture is a particulate composite material consisting of aggregate, mastic, and air voids. The computed tomography (CT) image-based finite element approach is used as an effective method to simulate micromechanical response of asphalt mixture. For finite element analysis, the accuracy of the finite results is determined by the size of the finite element. In this paper, a voxel-based three-dimensional (3D) digital reconstruction model of asphalt mixture with the CT images after being processed was proposed. In this 3D model, the aggregate phase was considered as elastic materials while the asphalt mastic phase was considered as linear viscoelastic material. Four micromechanical digital models were generated, whose voxel sizes were 0.5 mm, 0.67 mm, 1.0 mm, and 2.0 mm, respectively. The four digital models were used to conduct uniaxial creep test for predicting creep stiffness modulus to investigate the effect of voxel size. Simulation results showed that the voxel sizes had a significant effect on creep stiffness modulus. For the creep simulation test, the most appropriate voxel size whose creep stiffness modulus changes within 2.5% is 1.0 mm with regard to time steps, computational time, aggregate, and mastic shape representations.