Applied Mechanics and Materials Vol. 470

Abstract: This paper presented the results of an investigation into effects of reagent removal by activated carbon, regrinding and combined depressant on the separation of chalcopyrite and galena. With the utilization of a selective collector called Z-200, a separation test of mixed copper-lead concentrate was conducted. By adopting single-stage roughing, two-stage scavenging, two-stage cleaning, a copper concentrate of containing 21.72% Cu, 7.81% Pb with the copper recovery of 91.28%, and a lead concentrate of containing 62.16% Pb, 0.82% Cu with the lead recovery of 95.24% were obtained.

Abstract: Fine aggregates are sensitive parts to skeleton structure of mixture and decrease rutting resistance of asphalt mixtures. In order to evaluate the high temperature performance of mixtures with different fine aggregate (2.36mm and 1.18mm) content, 16 gradations were investigated. Flow number test and rutting test was conducted to evaluate anti-rutting performance of mixtures. Then, interference coefficient was put forward to analyze interference rule of high temperature performance. The results show that high temperature performance was improved with the increasing size of nominal maximum aggregate size; the interference effects of fine aggregate ( 2.36mm and 1.18 mm ) is inversely proportional to nominal maximum aggregate size.

Abstract: The primary objective of this paper was to study the mechanical properties of the cement stabilized gravel by different compact method which added rubber particles by using macroscopic and microscopic test. Through test of compression, relationships of mechanical properties of samples were studied. Pore structure and fractal characteristic of mixture was analyzed quantitatively using mercury intrusion porosimetry (MIP), scanning electron microscope (SEM) was applied to analyze the micro-morphology of samples. The tests results showed that the compressive strength of samples which prepared by using vibrating method was greater than that by static pressure method. Compressive strength of samples from vibrating method or static pressure method decreased with the rubber particles volume fraction increase. MIP tests showed that the mean pore diameter and porosity of mixture increased from about 70nm to 250nm and 9% to 24% with the rubber particles content increasing, respectively. SEM tests showed that the interface bonding between sand and hardened cement paste was better than that of between rubber particles and hardened cement paste.

Abstract: In order to visually observe the damage evolution of the asphalt mixture, and analyze the damage evolution accurately and quantitatively, the CT image of asphalt mixture image was processed for image enhancing and segmenting, the entire or partial image features can be effectively improved. The dynamics gray-scale range of the image was adjusted by the histogram equalization and provision. Image gray-scale transformation is enhanced by using Matlab software. At the same time, when the algebraic operations and noise filtering is used to process, the mixture image segmentation and boundary identification are achieved. The results show that the contrast and gray scale dynamic range of the gray scale image can be effectively improved by provision and equalization of histogram. The gap, aggregates and binder can be extracted by segmentation technology from asphalt mixture CT images. The real microstructure obtained can accurately reflect the evolution of asphalt damage.

Abstract: For the purpose of researching the natural bonding behavior of different interfaces between steel and concrete in SRC structures, four specimens are designed to launch the monotonic push-out loading test. Each specimen is used to consider one case, including the bonding of the external flange, internal flange, web and whole cross-sections with the concrete. Failure process and modes of these specimens were observed during the test. Load-slip curves and ultimate bond strength are obtained and the bonding strength between different interfaces of steel and concrete was analyzed. The results show that the bonding strengths of different interfaces in SRC members are not equal. The minimum bonding strength occurs in web, the bonding strength of external flange is higher, and the maximum bonding strength occurs in internal flange, the ratio of the strength is 1:1.39:1.59.

Abstract: Low temperature early strength cement slurry is a slurry in order to meet the well cementation in low-temperature conditions. Daqing weather is characterized by the silica fume, solid alcohols, amines and anionic polymers prepared a certain proportion, got a new low temperature early strength agent, It can greatly accelerate the hydration rate of cement and promote the formation of the cement paste early strength; and no chlorine ions, able to overcome the problem caused by traditional chlorine early strength agent casing corrosion.

Abstract: This paper researches law of reinforcement corrosion under chloride environment based on method the simulated accelerated test. Test the self-corrosion current density and electrode potential quantitative index of concrete reinforcement under chloride environment and establish quantitative model of corrosion time and reinforcement corrosion quantity by means of advanced linear polarization method and electrochemical testing method. Corroded reinforcement weight loss ratio under chloride environment is detected in physical way, combined with reinforcement corrosion layer microstructure and composition characteristics detected by scanning electron microscope. Both of the above deeply reveals corrosion mechanism and corrosion characteristics of the reinforcement. Corrosion rate theoretical model and statistical model have been revised. The research results prove that reinforcement corrosion rate has increased by an average of 4-5 times under chloride environment, weight loss ratio has increased by 15% compared with that under no-chloride environment, and due to chlorine’s effect, partial and uneven corrosion rust layer appears on surface of the reinforcement, which will be the direct cause of inducing accelerating corrosion of reinforcement at the later stage.

Abstract: In order to make model loading plan reasonably, point loads and moving loads are used in the finite element calculation model of subway tunnel, and the result shows that: the time-history curves of acceleration are uniform under two conditions of point loads and moving loads in the U-shaped Metro tunnel orthogonal with the ground fissure, and they are consistent with the load curve. Under two conditions of point loads and moving loads, the maximum displacement along the tunnel arch bottom are at the end of the tunnel and the minimum displacement are at the middle. In these two conditions, the distributions of the displacements are agreement. The vertical acceleration of lining arch bottom has much difference with the loading frequencies changed. In point load conditions, the maximum acceleration curve of 3Hz, 8Hz take on inverted V shaped and the maximum acceleration curve of 5Hz, 10Hz, 15Hz and 20Hz take on a V shape; in moving loads case, the maximum acceleration curve of 5Hz is inverted V shaped; the maximum acceleration curve of 20Hz is V shaped; the maximum acceleration curve of 8Hz is lower left upper right; and the maximum the acceleration curve of 10Hz and 15Hz are upper left lower right.

Abstract: A method of predicting safe distance between tunnel and karst cave based on support vector machine was proposed, 10 parameters (rock density,elasticity modulus E, poisson ratio, friction angle, cohesion C, lateral pressure coefficient , the karst cave span L,rate between height and span of the Karst cave R, tunnel deep H,cave position) were chosen for safe distance influence factors, then an intelligent predicting model of safe distance between tunnel and karst cave was built, this predicting model can predict 7 kinds position of safe distance between tunnel and concealed karst cave and was feasible and high prediction precision, which was verified by engineering example.

Abstract: Based on the actual project example of high pressure gas pipeline crossing earthquake rupture area, the paper shows and explains the way to make stress analysis and strength checking calculation for the high pressure gas pipeline in the earthquake rupture area by the method of finite element.