Design and performance of polyurethane elastomers composed with different soft segments

Thermoplastic polyurethane elastomers (TPUs) are widely used in a variety of applications as a result of flexible and superior performance. However, few scholars pay close attention on the design and synthesis of TPUs through the self‐determined laboratory process, especially on definite of chemical structures and upon the influence on properties. To investigate the properties of synthesized modifier based on chemical structure, firstly each kind of unknown structure and composition ratio of TPUs was determined by using a new method. Furthermore, the thermal characteristics and mechanical properties of modifiers were exposed by thermal characteristics and mechanics performance tests. The experimental results indicate that TPUs for use as an asphalt modifier can successfully be synthesized with the aid of semi‐prepolymer method. The linear backbone structure of TPUs with different hard segment contents were determined by micro test methods. The polyester‐based TPUs had thermal behavior better than the polyether-based TPUs; conversely, the low temperature performance of polyether‐based TPUs was superior. Most importantly, it was found that the relative molecular mass of TPUs exhibited a weak effect on the mechanical properties, whereas the crystallinity of hard segment showed a significant influence on the properties of TPUs

Preparation of Latent Heat Materials Used in Asphalt Pavement and Theirs' Controlling Temperature Performance

Abstract: In order to solve rutting diseases of asphalt concrete pavement, latent heat materials for asphalt pavement were prepared and theirs' controlling temperature performance were studied. Phase change materials (PCM), which were fitted to thermal environment of road were selected, phase change asphalt, diatomite powder and pottery sand granular composite phase change materials (CPCM) were prepared by three kinds of import modes. The CPCM were chosen by comparing the performance of above mentioned materials. Latent heat asphalt mixture (LHAM) was made by replacing mineral powder and fine aggregate with CPCM. Its controlling temperature ability was tested by temperature monitor system. The results show that, comparing to general asphalt mixture, LHAM can reduce temperature to 8-10℃. Therefore, LHAM has a good effect on adjusting road temperature. Introduction The rutting problem of asphalt concrete pavement has bored road transport administrators in the past few years, it is urgent to seek scientific and effective methods to solve the problem. The asphalt mixture is a viscoelastic material, the main factors which affect its mechanical properties are loading and temperature. Loading conditions are not easy to control, so temperature becomes the dominant factor to solve rutting. For a long time, the researchers have focused on improving temperature stability of asphalt and asphalt mixture, asphalt modifing, adding fiber and optimizing gradation and so on measures have been put forward [1-2]. All methods have changed asphalt pavement's temperature passively. Although they have solved some problems in certain domain and condition, temperature-related diseases of asphalt pavement are still very serious. Therefore, the paper was from the angle of improving temperature status of asphalt pavement, latent heat materials used in asphalt pavement were prepared, theirs' temperature performance were tested. The organic phase change materials (OPCM) were imported into inorganic porous materials to prepare composite phase change materials (CPCM). The latent heat asphalt mixture (LHAM) was prepared by mixing CPCM into asphalt mixture through different channels. CPCM is used to absorb heat of pavement constantly. Because of appropriate phase change temperature and high phase change latent heat, its self-thermostat effect performance is great. Preparation of Latent Heat Materials Used in Asphalt Pavement Phase change materials selection The phase change materials (PCM) can change phase with temperature and provide phase change latent heat (PCLH). Phase change materials can be divided into four categories which are solid-solid, solid-liquid, solid-gas and liquid-ga

Effect of Freeze-Thaw Cycles on the Internal Structure and Performance of Semirigid Base Materials

In this study, we investigate the spatial distributions of the internal structures in semirigid base materials (SRBMs) and explore their effect on the service performance of the SRBMs. X-ray computed tomography (X-ray CT) was used to conduct a spatial voids structure analysis. Three variates were selected to study the factors influencing the spatial distributions of the internal structures, including freeze-thaw cycles, curing time, and cement content. The results show that, with the increase in the number of freezing and thawing cycles, the average porosity, void area, and void number of the SRBM samples increased, and the average void diameters of all samples initially increased and then decreased. These trends led to an increase in the mass loss ratio and strength loss ratio. Increasing the cement content and extending the curing time decreased the average number of voids, average void area, and average void diameter and decreased the mass loss ratio and strength loss ratio of the SRBMs. The top and bottom of the SRBM samples were more porous than the middle of the samples, whereas the maximum value of the average void diameter was observed in the middle of the samples

Correlation model between mesostructure and gradation of asphalt mixture based on statistical method

Asphalt mixture has complex gradation and mesostructure. Accurate prediction of the relationship between gradation and mesostructure is of great significance for the establishment of mesostructure numerical simulation model and image-based gradation detection. In this paper, featurization, stepwise regression, econometric hypothesis test are utilized for establishing the predicting models. Firstly, asphalt mixtures with 64 kinds of gradation are scanned by Computed Tomography (CT) to obtain the mesostructure images; Then a series of mesostructure parameters of voids and aggregates are put forward. On this basis, the relationship model between gradation and mesostructure is established and verified by featurization and statistical modeling method. The results show that for predicting the passing percentage of the 4.75 mm sieve and the mean value of average distance between aggregate centroids for 9.5–4.75 mm aggregates, the prediction error of passing percentage is acceptable. It illustrates that the relationship model between gradation and mesostructure established by statistical method is effective, and it is significance for material design and testing under the condition of big data in the future

Evaluation of Warm-Mix Asphalt Compaction Performance by Variable-Temperature Gyratory Compaction

Abstract: For dynamic changes of viscosity reducing mechanism of different types of additives in after mixing mixture, the Warm-Mix Asphalt would present different compaction performance development with the change of paving temperature and time. The authors employed an improved variable-temperature gyratory compaction experiment to evaluate different mixtures' compaction performance. In the research, specimen preparation were tried to imitate natural cooling process of paving construction, and the development of construction energy index and the optimum compaction temperature were two ways to carry out qualitative and quantitative evaluation respectively . The authors proposed an equidensity -temperature method which based on analogous principle to determine the optimum compaction temperature of Warm-Mix Asphalt indirectly, this method fit for those mixture that their optimum compaction temperature can not be predicted by binder directly, and can also avoid defects of the direct methods by mixture. According to the experiment results, there is significant difference in the compactibility and the optimum compaction temperature to different Warm-Mix Asphalt. The overall evaluation information of Warm-Mix Asphalt compaction performance could be get by the combination used of the variable-temperature gyratory compaction and the evaluation methods in the paper

Study on application of cement substituting mineral fillers in asphalt mixture

In order to investigate the potential of cement fillers applying in asphalt pavement instead of mineral fillers, this research did a comprehensive study, including the raw materials properties tests, mix design, and verification of mixture performance. Results show that in terms of the physical and volumetric properties, the cement fillers are similar with mineral fillers. The mix design process of asphalt mixture containing cement fillers can refer to the common asphalt mixture. The optimum asphalt/aggregate ratio was 5.0% for the materials and gradation selected in this research. The residual stability of immersion Marshall stability test was 78.9%, and the TSR of freeze–thaw splitting test was 74.4%. Both of them meet the specification requirements. The dynamic stability was 1169 time/mm, the seepage coefficient was 63.4 ml/min. These larger data than the required values demonstrated the good functional performance of asphalt mixture containing cement fillers, including the rutting resistance and the anti-permeable ability. Keywords: Asphalt mixture, Cement filler, Volumetric property, Mechanical property, Functional performanc

Molecular Simulation of Minerals-Asphalt Interfacial Interaction

The interfacial interaction between asphalt binder and mineral aggregate makes different components have different diffusion behavior. It influences the performance of interface and consequently that of the mix. In this research, the models of four asphalt components (asphaltene, resin, aromatics and saturate) and five minerals were constructed individually, and then the Al2O3-asphalt interface model was constructed by adding the asphalt layer and mineral layer together. The interfacial behavior at molecular scale was simulated by setting boundary conditions, optimizing the structure and canonical ensemble. The mean square displacement (MSD) and diffusion coefficient of particles were selected as indicators to study the diffusion of asphalt components on the surface of Al2O3. The results show that when the temperature was 65 °C, asphalt binder showed more viscosity, the diffusion speed of asphalt components ranked according to their molecular mass, which was saturate > aromatics > resin > asphaltene. At 25 °C and 165 °C, the resin had the fastest diffusion speed, which was nearly twice of asphaltene. The interaction between asphalt components and Al2O3 mineral surface can make the diffusion of asphalt components independent on temperature

Evaluation of Geometric Characteristics of Fine Aggregate and Its Impact on Viscoelastic Property of Asphalt Mortar

It has long been recognized that fine aggregate (FA) plays a crucial role in the performance of asphalt mixture, especially for the viscoelastic behavior. In this research, 13 types of FA (1 natural sand, 5 stone chips, and 7 machine-made sands) were selected for investigation. Three indirect indicators (uncompact void content test, flow time test, and standard test method for index of aggregate particle shape and texture ASTM D3398) and three types of direct indicators (form, angularity, and texture) were employed to evaluate the geometric characteristics of FA and conduct comprehensive studies on the indicator system. Meanwhile, the effects of FA geometrical properties on the viscoelastic behavior of asphalt mortar were investigated. The results show that only the form indicator ratio of equivalent ellipse axis (E) and angularity indicator surface parameter (SP) can effectively distinguish different types of fine aggregates. The correlation analysis reveals that the parameters of the four elements in the Burgers model are negatively related to the form index (E) but positively related to the angularity index (SP), while the parameter retardation time ( τ r ) exhibits the opposite. This indicates that the use of less flat-elongated and more angular FA can increase both the overall stiffness and elastic component of asphalt mortar

Effective Suppression of Residual Magnetic Interference in a Conductive Shielded Room for Ultra-Low Field Nuclear Magnetic Resonance

Residual magnetic interference induced by applied magnetic field pulses inside a conductive shielded room (SR) has been a common issue in ultra-low-field (ULF) nuclear magnetic resonance (NMR). The rapid cutoff of the applied pre-polarizing field (Bp) induces eddy currents in the walls of the SR, which produces a decaying residual magnetic interference that may cause severe image distortions and signal loss. In this study, a pair of cancellation coils (CC) and control electronics were designed for the suppression of the residual magnetic interference in a SR. Simulations show that this method was effective in suppressing the residual magnetic field (Br) after removal of the pre-polarizing magnetic field. Then, a small-scale SR was designed and the effectiveness of this cancellation scheme was experimentally verified. The test results showed a good agreement with the simulation, which indicated that the cancellation scheme was capable of reducing Br field to a much lower level. The scheme proposed in this study provides a solution for suppressing the residual magnetic field in the ULF NMR system. After decoupling the eddy–current field, the effect of the suppression may be further improved by optimization of the cancellation coil in further work

Investigating fatigue life prediction of rubber asphalt mixture based on damage evolution using residual strain analysis approach

This study aims to develop the fatigue life (Nf) prediction method of rubber asphalt mixture based on residual strain (RS) analysis by using three-point bending fatigue test. The RS mechanical model established based on the modified Burgers model was used to characterize the evolution laws of RS, the residual viscoelastic strain (RVES) and the residual viscous-flow strain (RVFS), and the mechanical parameter of residual strain ratio (RSR) was defined based on the evolution laws. The correlation analysis was performed to explore the relationship between the Nf and the RSR, and the damage indication was advanced. The damage variable was defined based on the RSR evolution and the established fatigue damage model based on the ExpAssoc damage evolution model was used to perform the damage evolution analysis. The correlation analysis between the RSR and the damage evolution speed (Ds) was conducted to establish the fatigue and remaining fatigue equations. The results showed that RS mainly consisted of RVES and RVFS, and the RVFS was primarily responsible for the material damage. The RS mechanical model can characterize the non-linear evolution laws of RS, RVES and RVFS with sufficient accuracy, and the RVES can be regarded as a constant under given conditions. The RSR characterizing Ds can determine damage evolution and Nf prediction, and define the damage variable by isolating the damage factor from the viscoelastic factor. The established damage model can be capable of capturing the damage evolution of the rubber asphalt mixture. The increased Ds led to the exhibited decrease in the Nf. The established fatigue equation and remaining fatigue equation succeeded in accurately predicting the Nf and remaining fatigue life (Nfr) corresponding to the early damage evolution stage of rubber asphalt mixture, respectively