Thermal management has become a critical challenge in electronics and portable devices. To address this issue, polymer composites with high thermal conductivity (TC) and low dielectric property are urgently needed. In this work, we fabricated perfluoroalkoxy (PFA) composite with high anisotropic TC and low dielectric constant by aligning boron nitride nanosheets (BNNs) via hot pressing. We characterized the thermal stability, microstructure, in-plane and through-plane TCs, heat dissipation capability, and dielectric property of the composites. The results indicate that the BNNs–PFA composites possessed good thermal stability. When the BNNs content was higher than 10 wt %, the BNNs were well layer aligned in the PFA matrix, and the composites showed obvious anisotropic TC. The in-plane TC and through-plane TCs of 30 wt % BNNs–PFA composite were 4.65 and 1.94 W m−1 K−1, respectively. By using the composite in thermal management of high-power LED, we found that alignment of BNNs in composite significantly improves the heat dissipation capability of composite. In addition, the composites exhibited a low dielectric property. This study shows that hot pressing is a facile and low-cost method to fabricate bulk composite with anisotropic TC, which has wide applications in electronic packaging.

In this work, the settlement deformation of the soft-soil subgrade and the deformation law of the geogrid were studied based on field tests carried out on the pile-supported reinforced embankment of the Rongwu Expressway in the Xiong’an New Area. The settlement and deformation law of the reinforcement area and the underlying layer of the pile-supported reinforced embankment, the settlement law of the transverse and longitudinal sections of the subgrade, and the deformation law of the bidirectional geogrid were analyzed. The results show that reducing the pile spacing and embankment height can effectively reduce the foundation settlement. The change in the pile spacing mainly affected the settlement in the reinforcement area, while the embankment height mainly affected the substratum settlement; the differential settlement in the subgrade cross-section was mainly caused by the settlement in the reinforcement area. The settlement at the center of the subgrade was obviously higher than that at the shoulder. In terms of the geogrid deformation law of the subgrade cross-section, the geogrid deformation at the center line of the subgrade was the largest. With the increase in the distance from the center line, the geogrid deformation gradually decreased. In terms of the deformation law of the biaxial geogrid, the tensile deformation of the geogrid in the center of two piles was greater than that in the center of four piles. The transverse tensile deformation of the geogrid was greater than the longitudinal tensile deformation. The tensile stress of the reinforced materials was calculated according to four specifications, and the applicability of various methods was evaluated.

No abstract

With the increase of coal mining in China, a large amount of waste coal gangue is produced. How to reuse waste coal gangue is an important research direction. The research results showed that the improvement of base asphalt mortar by coal gangue powder could improve the performance of matrix asphalt, however, search of rubber asphalt mortar modified by coal gangue powder is rarely reported. High and low-temperature performance is the critical performance of asphalt mortar. So the limestone powder modified base asphalt mortar (LPMBAM), limestone powder modified rubber asphalt mortar (LPMRAM), and coal gangue powder modified rubber asphalt mortar (CGPMRAM) are prepared, the high and low-temperature performance of asphalt mortar are analyzed by cone penetration tests and bending beam rheological tests (BBR). The results show that the cone penetration of asphalt mortar decreases with the increase of the filler-asphalt ratio and the decrease of the temperature. The shear strength and the stiffness modulus increase with the rise in the filler-asphalt ratio and the decrease in temperature. At the same filler-asphalt ratio and temperature, the order of cone penetration is CGPMRAM < LPMRAM < LPMBAM, and the order of shear strength is CGPMRAM > LPMRAM > LPMBAM, so the high-temperature performance of CGPMRAM is better than that of LPMRAM, much better than LPMBAM, the order of stiffness modulus is LPMRAM < CGPMRAM < LPMBAM so the low-temperature performance of LPMRAM and CGPMRAM is better than that of LPMBAM. By the double linear model, the optimum filler-asphalt ratio is determined to be 0.44~0.46 for LPMRAM and 0.42~0.43 for CGPMRAM. Microscopic tests show that the surface of coal gangue powder is rougher than that of limestone powder. The content of active oxides such as SiO2 and Al2O3 in coal gangue is about 7.8 times that of limestone powder. These physical and chemical properties make coal gangue powder able to adsorb rubber asphalt better and improve the high-temperature performance of CGPMRAM while slightly worsening the low-temperature performance of CGPMRAM but still better than LPMBAM.

The softening point of evaporation residue of ordinary emulsified asphalt is low, which is adhered to the wheel during construction and cannot play the role of interlayer bonding. The author prepared Trackless tack coat materials by base asphalt with higher softening point and modifier with improved high temperature performance, thus the softening point of evaporation residue of emulsified asphalt is improved. Its physical and chemical properties were analyzed and compared with two kinds of emulsified asphalt. Under the condition that the physical and chemical properties remain unchanged, it has obvious effect of non-sticking wheel. The interlaminar shear and pull-out tests were carried out to study the bonding performance of three kinds of emulsified asphalt. The influence degree of different temperatures on the bonding performance of emulsified asphalt was analyzed, and the bonding performance was compared and analyzed, Trackless tack coat materials layer bond strength is higher, applicable to a wider range of conditions. Through various performance test analysis, it is shown that Trackless tack coat materials meets the requirements of the specification, has excellent interlayer bonding performance, and has a better effect of non-stick wheels.