Hongjuan Wu’s research while affiliated with Minzu University of China and other places

Nano-clay has the potential to improve the properties of cement-based materials. However, the effectiveness of this improvement is influenced by the dispersion of the nano-clay. The effects of different nano-clay dispersion techniques on cement-based material properties and pore structure complexity were studied. The samples were prepared using manual and mechanical dispersion methods. The mechanical properties of the specimens were evaluated, and the pore characteristics of the cement-based materials were analysed using mercury intrusion porosimetry. The study investigated the effect of the dispersion method on the nano-clay dispersion. The complexity of the pore structure was evaluated using a fractal model, and the relationship between the fractal dimension, mechanical properties, and pore structure was analysed. The findings indicate that mechanical dispersion results in better dispersion than manual dispersion, and the mechanical properties of mechanical dispersion are superior to those of manual dispersion. Nano-clay particles can improve the internal pore structure of cement materials. Through mathematical calculation, the surface fractal dimension is between 2.90 and 2.95, with good fractal characteristics. There is a good correlation between the surface fractal dimension and the mechanical properties. The addition of nano-clay can reduce the complexity of the pore structure, and the fractal dimension has an excellent linear relationship with the pore structure.

Aiming at the problems of low strength and easy cracking of concrete with large dosages of fly ash, SSF, ARF, and PPF were mixed into concrete respectively according to the same volume ratio. Various indexes were tested and the change rule was analyzed. Besides, the fiber spacing theory was adopted to explore the anti-cracking mechanism of fiber on concrete. The results indicate that the compressive strength and flexural strength of concrete were improved by three kinds of fiber in different dosage; the RFC of 7d was between 14% and 18%, and that of 28d was between 13% and 20%; SSF in concrete would produce strong bonding force and mechanical bite force. ARF has a small impact on the compressive strength of concrete, but a significant impact on the flexural strength of concrete. PPF can be more evenly dispersed in concrete to disperse and release a certain amount of stress and play a reinforcing role. Combined with SEM Microscopic Morphology Analysis of Concrete, a concrete mix ratio of three fibers 1:1:1 is recommended.

To exploretheeffects of physical, mechanical, anti-deterioration properties of graphene oxide (GO) on cement-based cementitious materials, GO sheet dispersions areprepared by the improved Hummers method and ultrasonic dispersion method. The influence of theGO content on the compressive and flexural strengths of cement paste is investigated, and the penetration process of chloride ions in graphene oxide concrete is discussed by the electric accelerated erosion method. Combined with the rapid freeze-thaw test, the deterioration of graphene oxide concrete ismethodically analyzed. Theobtained results reveal that an appropriate amount of GO improves both the compressive and flexural strengths of cement pastev. In the chloride environment, the chloride diffusion coefficient of 0.03% GO concrete is 18.75% less than that of ordinary concrete.Under the action of freeze-thaw cycles, with the increase of salt freezing times, the deterioration mode of GO concrete is a combination of mortar shedding, micro-crack expansion, denudation, and block shedding; The stress-strain curve of the specimen tends to be flat with the growth of salt freezing times. The peak stress gradually lessens, the peak strain gradually grows, and the elastic modulus remarkably reduces. Compared with ordinary cement paste, theGO is capable of promoting the growth of cement paste hydration crystals, changing the size and shape of crystals, and realizingthe regulation of cement paste microstructure. Incorporating an appropriate amount of theGO could promote the cement hydration process and enhance the chemical water-binding amount in the cement paste. The optimal GO content is reported to be 0.03% of the cement mass.

The traditional addition method of rejuvenating agent used in the laboratory is inconsistent with the actual situation of the project, which reduces the reliability of the test results. In this paper, the way of premixing rejuvenating agent and Reclaimed Asphalt Pavement (RAP) and extracting asphalt binder is selected, and the modification effect, mechanism, and optimal content of rejuvenating agent on Styrene-Butadiene-Styrene Block Copolymer (SBS) modified asphalt are studied. In this paper, the asphalt in RAP is recycled and restored with different content of regenerant, and the conventional technical performance and Performance Graded (PG) grade of regenerated asphalt was tested. The composite equation of regenerated viscosity of SBS-modified asphalt was analyzed, and the pavement performance of regenerated SBS-modified asphalt mixture with different content of rejuvenating agent and RAP was tested, such as high-temperature stability, low-temperature crack resistance, and water stability. Finally, the determination method of the optimal content of rejuvenating agent was discussed. The results show that it is reliable to predict the viscosity, penetration, and softening point of regenerated asphalt by viscosity logarithmic composite equation. The content of rejuvenating agent has a certain influence on the PG classification of SBS-modified asphalt, which is mainly reflected in the low-temperature critical temperature. There is a certain content of rejuvenating agent to make the high-temperature stability of regenerated SBS-modified asphalt mixture reach the maximum. When the content of rejuvenating agent reaches a certain value, the low-temperature crack resistance and water stability of regenerated SBS-modified asphalt mixture no longer increase significantly with the increase of the content of regenerant. Using the three-level determination method of the optimal content of rejuvenating agent proposed in this paper, the optimal content and reasonable content range of rejuvenating agent can be obtained, which makes the technical performance of regenerated asphalt, PG grade, and the pavement performance of regenerated SBS-modified asphalt mixture meet the specification requirements.

Old cement pavement directly overlaid with an asphalt layer produces many reflection cracks. Using microcrack homogenization technology to treat old cement pavement can effectively reduce the occurrence of reflection cracks. Micro-crack homogenization is relatively mature at the technical level; however, there is relatively little research on its mechanism. To evaluate the microcrack effect of old cement pavement, we conducted core sampling on a project road section after the appearance of microcracks. The core samples were sliced by X-ray tomography (X-ray CT). The mesostructure of the core samples was obtained. The core sample was further divided into microscopic cracks and macroscopic cracks according to the length and width of the crack. The development characteristics of cracks were subdivided into type I-III microcracks and type I-IV cracks. The core-drilling sample was divided into 5652 CT images. The statistical results showed that there were 3582 type-I microcracks, 3197 type-II microcracks, and 1835 type-III microcracks. Among the specimens, the minor proportion of microcracks was 32.87%, the most significant proportion was 100.00%, and the average ratio was 47.51%. Furthermore, the cracks development law and formation mechanism were analyzed based on CT images and cracking statistics. The results showed: (1) The microcrack homogenization process produced many microcracks in the test section and achieved a specific microcrack effect. (2) The cracks produced by the microcrack homogenization process tended to develop along the transition zone of the aggregate–cement mortar interface. The development of microcracks was mainly related to the aggregates’ shape and gradation, as well as the energy required to generate cracks. The research conclusions of this paper can be used as a theoretical basis for the optimization and improvement of the microcrack homogenization process.

In this paper, aromatic petroleum resin (APR) was used as raw material. The fluorescence microscopic photography of styrene-butadiene-styrene block copolymer (SBS) modified asphalt with different contents of APR was carried out, and the effect of APR on the dispersion of SBS modified asphalt was quantitatively studied. The nano-surface morphology of SBS modified asphalt with different APR contents was tested by atomic force microscope (AFM), and the effects of APR content on AFM nanoscale parameters such as roughness and maximum amplitude were analyzed. In addition, this paper also tested the basic technical indexes of SBS modified asphalt with different APR contents and revealed its improvement law on the pavement performance of SBS modified asphalt. The results show that the use of APR is beneficial to the shearing of SBS into smaller particles. The larger the amount of APR, the smaller the maximum particle size and average particle size of SBS in asphalt and the smaller the roughness and maximum amplitude of SBS modified asphalt. APR can improve the viscosity and low-temperature ductility of SBS asphalt to a certain extent. High-temperature storage stability is improved obviously; SBS modified asphalt mixed with APR has a more dense spatial cross-linking structure after thorough development. The research results are helpful to reveal the mechanism of APR improving the performance of SBS polymer asphalt.