Geopolymers are prepared by alkali solution‐activated natural minerals or industrial waste materials, which have been widely used as new sustainable building and construction materials for their excellent thermal and mechanical properties. The thermal and mechanical properties of geopolymers at high temperature have attracted great attention from many researchers. However, there are few systematic works concerning these two issues. Therefore, this work reviewed the thermal and mechanical behaviors of geopolymers at high temperature. Firstly, the thermal properties of geopolymers in terms of mass loss, thermal expansion, and thermal conductivity after high temperature were explained. Secondly, the mechanical properties of residual compressive strength and stress‐strain relationship of fly ash geopolymers and metakaolin geopolymers after high temperature were analyzed. Finally, the microstructure and mineralogical characteristics of geopolymers upon heating were interpreted according to the changes of microstructures and compositions. The results show that the thermal properties of geopolymers are superior to cement concrete. The geopolymers possess few mass loss and a low expansion ratio and thermal conductivity at high temperature. The thermal and mechanical properties of the geopolymers are usually closely related to the raw materials and the constituents of the geopolymers. Preparation and testing conditions can affect the mechanical properties of the geopolymers. The stress‐strain curves of geopolymer are changed by the composition of geopolymers and the high temperature. The silicon‐type fillers not only improve the thermal expansion of the geopolymers but also enhance mechanical properties of the geopolymers. But, they do not contribute to reducing the thermal conductivity. the different raw materials, aluminosilicate precursor and reinforcement materials, result in different geopolymer damage during the heating. However, phase transitions can occur during the process of heating regardless of the raw materials. The additional performance enhancements can be achieved by optimizing the paste formulation, adjusting the inner structure, changing the alkali type, and incorporating reinforcements.

Image segmentation has been implemented for pavement defect detection, from which types, locations, and geometric information can be obtained. In this study, an integration of a fully convolutional network with a Gaussian‐conditional random field (G‐CRF), an uncertainty framework, and probability‐based rejection is proposed for detecting pavement defects. First, a fully convolutional network is designed to generate preliminary segmentation results, and a G‐CRF is used to refine the segmentation. Second, epistemic and aleatory uncertainties in the model and database are considered to overcome the disadvantages of traditional deep‐learning methods. Last, probability‐based rejection is conducted to remove unreasonable segmentations. The proposed method is evaluated on a data set of images that were obtained from 16 highways. The proposed integration segments pavement distresses from digital images with desirable performance. It also provides a satisfactory means to improve the accuracy and generalization performance of pavement defect detection without introducing a delay into the segmentation process.

Low atmospheric pressure (LAP) can enormously affect properties of cement concrete in plateau areas. There are fewer studies and attendances on this issue than those of cement concrete in normal atmospheric pressure (AP), because of the limitations of both environmental conditions and instruments. In order to improve properties of cement concrete under LAP, influences of LAP on properties of cement concrete were reviewed in this work. The influence rules and mechanism on properties of cement concrete were summarized. The corresponding mechanism and techniques were put forward for enhancing the properties of cement concrete. The results of researchers show that LAP can significantly reduce the air entraining ability of the air entraining agent (AEA). Air content in concrete linearly decreases with the decrease of AP when other conditions are constant. If the initial air content is high, the decrease rate of air content increases with the decrease of AP. When the initial air content in cement concretes is similar, the greater the slump of cement concrete, the stronger its resistance to the decrease of air content caused by the decrease of AP. In addition, the condition of the bubble characteristics of hardened cement concrete under LAP is worse than that under normal AP. Therefore, the change of concrete properties under LAP is mainly attributed to these bubble characteristics, such as air content, bubble spacing coefficient, bubble radius and bubble specific surface area. In this work, nano-silica (negative charges) with cationic oligomeric surfactants is recommended as a new type of AEA to optimize the bubble characteristics under LAP in plateau areas.

The use of waste tires to prepare rubberized asphalt has been a hot trend in recent years, and the characteristics of adhesion between rubberized asphalt and aggregates are important factors affecting the performance of asphalt pavement. However, there is a lack of uniform results on the adhesion characteristics of rubberized asphalt. Therefore, crumb-rubber-modified asphalt (CRMA) with 15%, 20%, and 25% rubber contents was prepared in this work, and the basic rheological parameters and cohesive energy of the rubberized asphalt were characterized by DSR. The adhesion properties between rubberized asphalt and aggregates were characterized based on macroscopic binder bond strength (BBS), surface free energy (SFE) theory, and nanoscale atomic force microscopy (AFM) tests. The results show that crumb rubber (CR) can improve the high-temperature elastic properties of asphalt; secondly, CR can have a negative impact on the maximum tensile strength of asphalt and aggregates. CR can improve the SFE parameter of asphalt. The work of adhesion of rubberized asphalt and limestone is the highest, followed by basalt and, finally, granite. Finally, CR can cause the catanaphase in asphalt to gradually break down and become smaller, and the adhesion of rubberized asphalt can be reduced. Overall, CR can reduce the adhesion performance of asphalt, and this work provides a reference for the application of rubberized asphalt.

The aging of bitumen seriously affects the service life of bituminous pavements. At present, there are many related researches on bitumen aging, but most of them focus on aging endured in indoor surroundings and conditions. Therefore, the conclusions obtained cannot reflect the actual aging changes of bitumen in bituminous pavements in service. In order to study the comprehensive aging process and mechanism of bitumen under the influence of service, we studied bridge deck, traffic lane, and ramp with bituminous pavement structures in service. The bitumen samples obtained from the core samples in different bituminous pavement structures were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), dynamic shear rheometer (DSR), and fluorescence microscope (FM). The aging degree of different bitumen was analyzed, and conclusions were drawn on changes to bitumen aging from different pavement structures. The results showed that the aging degree of bitumen from the upper layer was the most serious, the aging degree of bitumen at the middle layer was weaker than that of bitumen from the upper layer, and the aging degree of bitumen from the bottom layer was the weakest for the different bituminous pavement structures. The aging of bitumen mainly occurred due to oxygen absorption. After aging, viscoelastic components of bitumen changed, and bitumen became harder. The macromolecule of bitumen could be divided into small molecules, and the small molecular weight of bitumen became large. The styrene-butadiene-styrene (SBS) modifier in the modified bitumen became granular after aging, and it appeared as a single phase in bitumen. The aging changes characterized by different analytical methods showed that the aging degree of bitumen from different layers of bituminous pavement structures in service was different. Effective measures should therefore be taken in time to decrease further aging of bitumen from the upper layer of bituminous pavements due to its inevitable early aging in service.

Temperature sensitivity characteristics of bitumen can be evidently influenced by modifier types and natural aging processes. Many types of modifiers have been used to improve the temperature sensitivity performance of bitumen, but their effects are different. Therefore, different bitumen specimens as well as SBS/CRP (Styrene-butadiene-styrene polymer/crumb rubber powder)-modified bitumen were prepared and the temperature sensitivity characteristics of bitumen after different aging processes were analyzed in this study. A dynamic rheological property test and performance test at low temperature were carried out to analyze temperature sensitivity and low temperature rheological properties of bitumen. An infrared spectrum test was adopted to study the effect of functional groups under different aging process on the properties of bitumen. The relationship between macroscopic properties and microstructures of bitumen was analyzed. The results show that SBS/CRP-modified bitumen has a strong anti-aging ability in that its flexibility and structure remain in a good condition after long-term aging. The aging process has no significant effect on SBS/CRP-modified bitumen. SBS/CRP-modified bitumen has an excellent low-temperature relaxation ability and low-temperature crack resistance. In contrast to original bitumen and SBS-modified bitumen, the temperature sensitivity performance of SBS/CRP-modified bitumen is evidently enhanced. The physical blending effect is dominant in the bitumen modified process and there is no evident chemical reaction between bitumen and crumb rubber powder. SBS/CRP-modified bitumen is recommended for wide use in plateau areas with ultraviolet and cold surroundings.