Key Engineering Materials Vol. 871

Abstract: Geotechnical materials are complex materials with very strong structures, but their structural problems have always been difficult problems in this field. In this paper, by studying the structural problems of geotechnical materials, we understand and master this kind of structural materials. Methods for describing complex materials, as well as the nature, characteristics, and changes of the material after being affected by the environment, especially the influence of the structure of the material on the macroscopic properties of the material. Starting from the basis of the material-material particles, fully consider the particle Geometry, surface characteristics and material characteristics, further analysis of the mechanical and geometric characteristics of structural materials composed of particles, a porosity model describing the pore size distribution is proposed, and the two-dimensional and three-dimensional The experimental data of pores in the space shows that the predicted value of the porosity model agrees well with the measured value in the three-dimensional space.In two-dimensional space, the validity of the model is closely related to the corresponding number of pores and the fractal dimension of the pore size distribution.

Abstract: Ethylene-acrylic acid copolymer (EAA) has been demonstrated to be a suitable additive for modifying the properties of asphalt. EAA mixed with metal hydroxides/oxides form EAA-M ionomers, which increase the polarity of EAA, improving its adhesive properties and affecting its mechanical and rheological characteristics. The present work investigates the mechanical and rheological characteristics of asphalt modified by EAA in conjunction with either Ca (OH)2, NaOH, or ZnO. The high-temperature properties of the modified asphalts, including the softening point, and needle penetration, were evaluated. Rheological characteristics of modified asphalts were investigated by rotary rheometer. Moreover, the storage stability at high temperature, morphology and chemical structure were also analyzed. Results indicate that a 4wt% EAA-M ionomer concentration in the base asphalt is adequate for providing the enhanced properties studied. For an equivalent concentration of EAA, the properties of modified asphalts were affected by very small additions of the metal hydroxides/oxides. The best overall mechanical and rheological performance was obtained for EAA-Ca modified asphalt with 4wt% EAA and 2.5wt‰ Ca (OH)2. EAA-Zn modified asphalt provided the most stable high-temperature storage. Compared with 6wt% pure EAA-modified asphalt, which is not stable, the EAA-Zn modified asphalt (2.7wt‰ ZnO) demonstrated reasonable high-temperature storage stability. Compared with asphalt modified with 6wt% pure EAA, the softening point increased from 55.81 °C to 58.05 °C with the addition of 2.7wt‰ NaOH. However, while the mechanical and rheological properties of EAA-Na modified asphalt were very good, its high-temperature storage stability due to the strong reactivity of NaOH, which led to the crosslinking of EAA-Na ionomers, making it difficult to disperse.

Abstract: Sand erosion is a serious problem in the relatively arid and semiarid areas. A novel chemical sand fixing agent (LSUF) synthesized by lignosulfonate graft urea-formaldehyde was introduced in this study. It was made by polymerization of lignin sulfonate, urea and formaldehyde. The newly synthesized product had good water solubility, potentially good biodegradation, and produced no additional pollution. The results showed that the strength test, water-retaining test and wind erosion test of LSUF was better than the sand fixing agent composition by urea-formaldehyde (UF). The LSUF is an environment-friendly products and, it can be considered as an ideal sand fixing agents to control sand erosion in the relatively arid and semiarid areas.

Abstract: Microorganisms can effectively heal the cracks of cementitious materials through the formation of calcium carbonate by microbial mineralization deposition, which has a wide application prospect in cementitious materials. In order to analysis the activity change and distribution of microorganisms in cementitious materials, this paper prepared cement pastes incorporated microbial powder, and extracted microorganisms by pre-crushing, grinding and ultrasonic, at the age of 3, 7 and 28 days respectively. The relationship between the optical density and effector cells is near linear fit, reflecting the activity change and specific distribution of microorganisms in cement paste specimen of different ages. The in-depth research on the activity change and distribution of microorganisms in the microbial cementitious materials can effectively characterize the microorganisms in the cementitious materials, which has a guiding role in microbial self-healing cementitious materials.