The bending and tensile properties of asphalt mixture affect the service quality and life of asphalt pavement, and its internal stress determines the bending and tensile performance. In order to investigate the internal stress characteristics of asphalt mixtures, this paper adopted the discrete element method to quantitatively evaluate the force chains of each component in asphalt mixtures under the three-point bending mode. Firstly, it constructed a template library of coarse aggregates based on image recognition and realized efficient three-dimensional modeling of asphalt mixture specimen and proposed a three-point bending simulation method. Then the internal force chain distribution of asphalt mixture was visually represented, and data of force chains of each component were extracted. The force chain characteristics were analyzed from the three aspects of composition, strength, and angle. The results show that under the three-point bending mode, the internal force chain field of asphalt mixture exhibits tension and compression zones, and the extrusion of aggregates only takes effect in the compressed zone. 70.8% of the internal contact force of SMA 13 asphalt mixture is provided by the asphalt mortar, and that of AC13 asphalt mixture is 83.2%, indicating that coarse aggregates have little effect under bending and tensile stress and asphalt mortar plays a major role in resisting external loads. The proportion of force chains decrease as the strength increased, and the proportion of strong force chains in the interior of the mortar and the mortar-aggregate interface position is basically the same. The stress between coarse aggregates is uneven, and the mortar plays a significant role in ensuring uniform stress within the asphalt mixture. The strength of horizontal force chains at the aggregate-mortar interface is slightly higher than that in the vertical direction, and the strength of aggregate force chains fluctuates greatly with the change of angle. Asphalt mortar bears the main load during bending and tensile force of asphalt mixture and the research findings can serve as a reference for the structural design and performance evaluation of asphalt mixtures.

Municipal solid waste incineration bottom ash (IBA) shows large heterogeneity because of different garbage composition, incineration process and storage conditions. The effective cooperation for one batch of recycled concrete (mortar) may be ineffective for another batch, resulting in large dispersion of recycled concrete (mortar) performance, which limits its application. In order to explore the heterogeneity of IBA from different sources and the strength variability of recycled mortar, this study collected a total of 14 batches of IBA samples from different incinerators and different monthly sources and tested for their physical and chemical properties. And it investigated the workability, compressive strength, and splitting tensile strength of IBA recycled mortar. Statistical analysis was conducted to assess the level of strength variability in IBA recycled mortar. The test results showed that the crushing index, porosity, sulfide, and chloride content of IBA did not meet the specifications for recycled fine aggregates, and there is significant heterogeneity in IBA from different origins. When the recycled cement mortar below M20 strength grade is prepared with a substitution rate of 50% IBA which is from a single incineration plant of different months, the strength is not significantly reduced compared with that of natural aggregate mortar, and the strength variability is similar to that of ordinary recycled aggregate concrete and the standard deviation is also lower than the recommended value of the specification. However, when used to prepare the recycled cement mortar above M20, the reduction in compressive strength was significant (reduced by 23%~32%). Due to higher compressive strength variability of IBA recycled mortars from two different incineration plants, it was not recommended to use IBA recycled mortars from different incineration plants together.

Steel slag contains metallic iron and its oxide, which are high value‐added renewable resources, and it can be utilized as a mineral admixture in the building materials industry. After different cooling treatment processes, the phase of steel slag evolves, thus affecting the recovery of iron in steel slag and the cementitious activity of tailings. In order to improve the recycling of iron resources in steel slag and the effective utilization of tailings, this paper studied the steel slag of three different treatment processes, namely, hot splash, roller crushing‐pressurized hot stewing and roller crushing‐hot splash. It used petrography analysis, XRD, SEM‐EDS, and chemical phase‐selective dissolution, and other methods to analyze the distribution of the iron phases and the state of enrichment of steel slags, and to determine the rate of magnetic separation powder and iron grade, and the cementitious activity of tailings. The results show that: the metal iron is easier to be enriched and deposited under the hot splash process, and the iron phase is mainly in the form of FeO uniformly distributed in the RO phase and the ferrite phase, with less Fe in the phase, and the yield of magnetic separation powder is higher, but the grade is poorer, which is 32.22% and 33.43%, respectively. After roll crushing‐pressurized hot stewing, no obvious metal iron particles can be seen in the slag; Fe in the phase accounts for more, and the yield of the magnetic separation powder is low but the grade is higher, which is 28.37% and 37.12%, respectively; after roll crushing‐hot splashing, the iron phase mainly exists in calcium ferrite phase and silicate phase in the form of Fe₂O₃, Fe in the phase accounts for more and contains Fe₃O₄, and the magnetic separation powder has high yield and high iron grade, which is 37.60% and 39.69%, respectively. Under roll crushing‐pressurized hot stewing, the C₂S content in steel slag is relatively more and better developed, and has high cementitious activity, 7 d and 28 d activity index of tailings is 78% and 92%, respectively; the 7 d activity index of the roll crushed‐hot splash slag is low at 66%, but the 28 d activity index grows to 92%; the cementitious activity of the hot splash slag is in the middle.

To explore the mechanism of extension and coalescence of the defect (flaw) in rocks under complex stress state, the study simulated the cracking process of rock-like material containing double pre-existing flaws in the biaxial compression test based on 3D discrete element software (PFC3D) and the improved parallel-bond model (IPBM). The microscopic parameters of the numerical model were calibrated by matching both macroscopic mechanical properties (uniaxial compressive strength, tensile strength, and elastic modulus) and cracking pattern with the laboratory experiments. The results show that: the first cracks are tensile cracks which vary with the inclination angle of flaw，and the secondary cracks are shear; the confining stress will suppress the first cracks and promote the development of the secondary cracks; the coalescence patterns of samples are closely related to the geometries of the flaw and the confining stress. Two new shear coalescence patterns (New1 and New2) can be observed at the confining stress σ_c > 0 MPa. The number of microcracks in the numerical sample is greatly affected by the confining stress, but not by the flaw geometries. The initial stress and peak stress of crack are correlated with confining stress and flaw inclination angle, but not with bridging length and bridging angle. The crack extension is closely related to the stress distribution in the sample, and the cracks first occur in the stress concentration area around the pre-existing flaws. The study provides a reliable reference for the subsequent calibration of discrete element model parameters and the crack extension mechanism based on discrete element.

With the continuous development of electronic information technology, electromagnetic pollution is becoming increasingly serious, and the research of high-efficiency absorbing materials has received more and more attention. Using bacterial cellulose as carbon source, the study prepared CNFs/ZnO composites based on bacterial cellulose with carbonization-modification and hydrothermal two-step method, and studied the effects of zinc acetate dihydrate concentration on the microwave absorption properties of CNFs/ZnO composites. The structure, morphology and microwave absorption performance of the composites were characterized by X-ray diffraction (XRD), cold field emission scanning electron microscopy (FESEM) and vector network analysis (VNA). The results show that CNFs/ZnO composites are successfully prepared, and the carbon nanofibers (CNFs) show an amorphous state without obvious diffraction peaks. Both carbonized and modified CNFs maintain the fine microscopic morphology of nanofibers with a three-dimensional network and porous structure of bacterial cellulose, but CNFs become crimped and the diameter of the fibers decreases significantly. In CNFs/ZnO composites, ZnO is closely attracted to the surface of CNFs or randomly inserted into the gap of CNFs. By changing the concentration of zinc acetate hydrate, the content of ZnO in the composite can be controlled, which in turn regulates the electromagnetic parameters of the composite and obtains good impedance matching. When the concentration of zinc acetate hydrate is 0.25 mol/L, ZnO is most uniformly dispersed on CNFs. At this time, the resistance loss, dielectric loss and interface polarization of CNFs and ZnO are synergistic on the three-dimensional porous network structure, which increases the multiple reflection, scattering and long-range dissipation of electromagnetic waves. The CNFs/ZnO composite prepared under this condition is a reliable composite absorbing material with the best reflection loss of -57.5 dB and an effective absorption bandwidth of 7.1 GHz, at a coating thickness of 2.8 mm and a frequency of 15.1 GHz.

To investigate the performance impact mechanism of warm asphalt rubber (WAR), 2 types of asphalt rubber (AR) and 4 types of warm asphalt rubber were prepared by using 70# base asphalt, 2 types of warm mixing agents, and 2 grain sizes of crumb rubber modifier. Liquid phase and insoluble crumb rubber modifier for prepared asphalt samples were obtained by the solid-liquid phase separation. The staged extraction method was innovatively employed to systematically extract components in the insoluble crumb rubber modifier blending zone layer by layer. Through experiments, the study established the connection between the preferential absorption of crumb rubber modifier and high- and medium-temperature rheological properties represented by asphalt rubber and clarified the modification mechanism of warm asphalt rubber. Test results indicate that the improvement of asphalt rubber’s high-temperature rutting resistance and low-temperature cracking resistance performance are attributed to the particle effect generated by insoluble crumb rubber modifier in asphalt and the modification effect of the soluble components of crumb rubber modifier. The improvement of fatigue resistance at medium temperature and the increase in viscosity of asphalt rubber is mainly attributed to the particle effect generated in the insoluble crumb rubber modifier. Different types of thermal mixture have different effects on the rheological properties of asphalt rubber. The addition of the organic warm mix additive is more significant in enhancing the high-temperature resistance to rutting and medium-temperature resistance to fatigue performance of asphalt rubber. The addition of the chemical warm mix additive proves to be more effective in improving the low-temperature resistance to cracking performance of asphalt rubber. The lighter components with smaller relative molecular mass in the asphalt rubber liquid phase are more easily absorbed by the crumb rubber modifier into its blending zone. The organic warm mix additive has almost no significant effect on the preferential absorption of crumb rubber modifier, while the addition of the chemical warm mix additive not only reduces the proportion of large relative molecular mass components in the liquid phase but also weakens the preferential absorption of crumb rubber modifier. The preferential absorption of crumb rubber modifier is beneficial for improving the high-temperature and fatigue resistance properties of asphalt rubber.

Warm mix asphalt technology can reduce the production and construction temperature of asphalt mixtures, and has great application potential in energy conservation and carbon reduction. The foamed warm mix asphalt technology has the advantage of low cost, but there are some problems such as the unsatisfactory foaming effect of modified asphalt and the insignificant warm mix effect, so it has potential application prospects. Surfactants have the effects of both “asphalt lubricant” and “foam stabilizer”, which makes it possible to improve the foaming characteristics and warm mix effect of foamed warm mixed asphalt. Based on this, this study prepared surfactant additive foamed asphalt (SAFB6, SAFB8, SAF10) with different mass fractions of surfactant additives and foaming temperatures. The foaming test, dynamic shear rheology test and bending beam rheology test were used to investigate foaming properties, high temperature performance, fatigue resistance and low temperature performance. The mechanism was analyzed by Fourier infrared spectroscopy test, and the synergistic effect of both surfactant and foaming process on the performance of foamed warm mix asphalt was revealed. The experimental results show that surfactant additives had a significant synergistic effect on the foaming properties of SBS modified asphalt, especially the half-life, which reached up to 69 s. The best foaming conditions can be achieved when the foaming temperature and surfactant additives content are 170 ℃ and 8%, respectively. No complex chemical reaction occurs during the preparation of SAFB asphalt, but the foaming process resulted in a certain degree of oxidation of SBS modified asphalt. The synergistic effect of the surfactant additives and foaming process improves the high temperature performance and fatigue resistance of the SBS modified asphalt, while the low temperature crack resistance is equivalent to that of SBS modified asphalt. Generally, the combination of surfactant and foaming technology is feasible, which improves the foaming effect and road performance of SBS modified asphalt.

In the high alkaline environment of concrete, in order to improve the resistance of steel bar in concrete to chloride ion erosion, this study adopted a new environmentally friendly organic rust inhibitor-β-glycerophosphate sodium to protect the steel bar and achieve the purpose of extending the service life of reinforced concrete structures. In this study, the electrochemical measurements were used to monitor the evolution properties of the steel embedded in concrete in real time. The corresponding key parameters were obtained to explore the relationship between sodium β-glycerophosphate and steel passive film in the passivation period, as well as the relationship among sodium β-glycerophosphate, steel passive film and chloride ions during the maintenance passivation period, and then the rust resistance mechanism of this kind of organic matter was revealed. The results obtained by OCP, LPR and EIS electrochemical testing methods show that: β-sodium glycerophosphate forms a more density protective film through physicochemically interacting with Fe oxides/hydroxides on the steel surface, so as to make the surface of the steel bar form a protective film with more inhibited behavior, which also improves the resistance of the steel bar under chloride ion erosion. The resistance of the steel bar in each of the four solutions is: NaOH + 0.1 mol/L sodium β-glycerophosphate > saturated clarified Ca(OH)₂ > NaOH > saturated clarified Ca(OH)₂ + 0.1 mol/L sodium β-glycerophosphate. Among them, the critical chloride ion concentrations (c_crit) of steel bars in NaOH, NaOH + 0.1 mol/L sodium β-glycerophosphate and saturated clarified Ca(OH)₂ solutions are: 0.02 mol/L, 0.07 mol/L, and 0.04 mol/L, respectively, while no effective passive film is generated on the steel bar in saturated clarified Ca(OH)₂ + 0.1 mol/L sodium β-glycerophosphate. In addition, the addition of sodium β-glycerophosphate to Na⁺ solutions can promote the formation of a more dense passive film on the steel bar surface with a faster passivation rate. That is, more than 80% passivation film can be formed in 72 h, and the rust inhibitor rate is as high as 99.80%. Furthermore, further comparative analyses of the effects the Na⁺ and Ca²⁺ solutions themselves on the resistance of the steel bar under chloride ions erosion show that Ca²⁺ solution is more conducive to the resistance to chloride ion erosion ability, and the corrosion inhibition efficiency is more than 90%.

In order to reduce the amount of natural aggregates and cementitious material in 3D printed concrete, this study used recycled fine aggregate (RFA) to partially replace natural fine aggregate and clay brick powder (CBP) to replace cement. The fluidity and compressive strength test of cast-in-situ concretes with RFA only (0, 25%, 50%, 75% and 100% replacement ratio), with CBP only (0, 5%, 10%, 15%, 20% and 30% replacement ratio) and with both of them were firstly carried out to obtain the optimal replacement ratio of RFA and CBP. Then, it investigated the effect of the addition of 50%RFA and 10%CBP and the corresponding mix proportion adjustment methods (adding extra water and increasing water reducer dosage) on the fresh and harden properties of 3D printed concrete. The test results indicate that the decreasing amplitude of the compressive strength of cast-in-situ concrete is within 10% when the replacement ratio of RFA is less than 50%. With the increase of CBP replacement ratio from 0 to 30%, the compressive strength of cast-in-situ concrete increases first, then decreases and then slightly increases. The specimen with CBP content of 10% exhibits the highest compressive strength. Compared to the concrete with 50%RFA only, the concrete with 50%RFA and 10%CBP has higher strength, while the fluidity is almost kept unchanged. For 3D printed concrete, the addition of 50% recycled fine aggregate and 10% brick powder and additional water can keep the initial expansion of 3D printed concrete unchanged and improve the buildability of concrete, but it can decrease the slump, opening time, compressive and split tensile strength and increase intensity anisotropy. However, increasing water reducer dosage in the mixture can not only significantly improve the fluidity, opening time and compressive strength of 3D printed concrete, but also reduce the intensity anisotropy.

TC4 is widely used in aerospace field due to its high specific strength, good corrosion resistance and light weight. However, its disadvantages such as large friction coefficient and poor wear resistance greatly limit its application range. In view of the shortcomings of low hardness and poor wear resistance of TC4, a 4 kW high-power Laser4000 semiconductor laser was used to prepare different proportions of steel-based metal-ceramic hard coatings on the surface of TC4 by laser cladding technology with transition family refractory carbides HfC, TaC and ZrC as reinforcing phases and H13 steel-based powder as base powder. Then, the macro morphology, microstructure, phase composition and coating element distribution of the coatings with different proportions were compared and analyzed by means of scanning electron microscopy (SEM), EDS energy spectrometer, D/max-2500/PC X-ray diffractometer (XDR) and other test methods. The hardness of the coating was tested by Qness Vickers microhardness tester and the variation law of the microhardness of the cross section of the cladding sample was analyzed. The friction and wear properties of the coatings with different material components were studied by MMU-5G end friction and wear tester. The results show that the cladding layer of the specimen forms a good metallurgical bonding with the substrate. The microstructure of the cladding layer is mainly dendritic structure and block structure. The main phases of each cladding layer all contain TiC, and as the content of ternary ceramic powder increases, the content of MC also increases. When the carbide mixed powder is 15% (mass fraction), Hf_0.8Ta_0.2Fe₂ ternary alloy phase is detected in the cladding layer. When the content of ternary ceramic powder is 10% (mass fraction), the cladding grain is the smallest, the average hardness of the coating layer is the highest, and the average hardness is about 763.43 HV, 2.29 times the hardness of the substrate. When the content of ternary ceramic powder is 5% (mass fraction), the coating has the best wear resistance, and the relative wear resistance is 25%.

Oxidized starch gel material has become a hot material in fields such as food and biomedicine because of its advantages of hydrophilicity, chargeability, easy reaction and assembly in recent year. However, when used as a hot-extrusion 3D printing (HE-3DP) gel material, it has defects such as poor printability and low gel strength. This study investigated the influence of different chitosan addition amount on the rheological properties, printing formability and gel strength of oxidized starch-chitosan gel materials by adding different amounts of chitosan and utilizing non-covalent and chemical cross-linking between chitosan and oxidized starch. The results show that the oxidized starch-chitosan pastes exhibit typical shear-thinning characteristics. As chitosan is added in varying concentrations (0.5%~2%), non-covalent interactions such as hydrogen bonding and electrostatic attraction lead to an increase in the viscosity of the system. The thixotropic property initially increases and then decreases, while the flow stress (τ_f) first decreases, and then increases; and the yield stress (τ_y) increases first and then decreases. Compared with oxidized starch gel, oxidized starch-chitosan gel has good printing formability. Especially when the amount of chitosan added is 1%, the composite gel has the best thixotropic property, the minimum flow stress (τ_f) and the largest yield stress (τ_y), so the printing formability and printing accuracy is the best. Additionally, due to the non-covalent interaction between chitosan and oxidized starch and the schiff base chemical cross-linking, the oxidized starch-chitosan gel forms a dense network structure to improve gel stability and gel strength significantly. These effects are more significant with a higher chitosan content. The results can provide a theoretical basis and technical support for the performance improvement of oxidized starch gel material and the design and application of oxidized starch-chitosan gel materials suitable for HE-3DP.