Applied Mechanics and Materials Vols. 204-208

Abstract: Aiming at determining the durability of concrete in very salty regions, this study examines the performance of various high performance fine aggregate concretes in a sulfate environment, such as high performance concrete inside a composite additive, and Portland cement concrete and sulfate resistant cement concrete, all of which experienced dry-wet cycles in sodium sulfate solutions. By examining the changes of elastic moduli and analyzing the SEM of the concrete, this paper has found that the salt resistance of sulfate resistant cement concrete is no better than that of Portland cement concrete in the extremely aggressive dry-wet cycle environment but high performance concrete containing a composite additive has better resistance in a sulfate environment. Besides, the composite additive can create the environment for a second hydration to reduce the amount of Ca(OH)2 inside the concrete, and build additional C-S-H gel to reform the microstructure of concrete effectively. Finally, the paper offers some advice for mixing concrete in salt regions.

Abstract: The paper analyzed external deformation, deep deformation and stability of slope with weak intercalated layers in detail through field monitoring of Mayanpo slope at Xiangjiaba Hydropower Station. The results show that: ① Displacement deformation increases with time and decreases with increasing depth, and displacement rate decreases with time. ② Dislocation position exists in weak intercalated layers. Dislocation rate first increases and then decreases until basically stable, and local fluctuations are mainly affected by rainfall and dynamic equilibrium adjustment of the slope internal deformation. ③ Through stability analysis of Mayanpo slope by strength reduction FEM, stability coefficient is 1.72.

Abstract: Effect of surface applied inhibitor on the durability of chloride contaminated reinforced concrete has been investigated in this paper. The C30 concrete samples contaminated with 0.5%,1.0%,1.5% NaCl by mass of the cementitious materials in the mixing process were experienced adequate curing and subjected to 1 months exposure tests after painting with 400 g/m2 MCIs. The corrosion behavior of the steel rebar in concrete samples was monitored by using electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and corrosion currents. The results indicate that, after painting the MCIs for 28d on the surface of concrete samples with 0.5% and 1% NaCl, the average corrosion rate of reinforcements in concrete samples （0.34μA/cm2 ）is lower than that of the control one (No.0, no painted inhibitor), and about 1/4 of the initial corrosion current of the samples with 0.5% and 1% NaCl before painting MCI. But the corrosion current of rebar in No.3 sample with 1.5% NaCl is still higher than that of the control one (No.0). Therefore, painting MCIs on the surface of samples is very effective to inhibit the corrosion of steel bar in concrete at low or middle chloride conditions, but it is not enough to repair severely corroded steel bar in high chloride contaminated concrete.

Abstract: The mechanical performance of concrete structures closely relates to the propagation of cracks. Depth studying energy dissipation of concrete in fracture process zone not only contributes to comprehensive understanding fracture failure mechanism of concrete, but also has significant in detecting and forecasting the cracks in actual structure. In view of this, a general equation for calculating at any time’s mean energy dissipation per unit length was given. After that, we further simplified and deduced the general equation and got a simple, practical and high accuracy numerical solution, with which Gauss integration method was used. At last, the specific steps of calculating mean energy dissipation were given by taking 10 three-point bending beams of different crack-depth ratios for an example. Compared with test dates, we found that calculated results are in good agreement with the test dates. According to results, influence of crack-depth ratio on the fracture energy was also discussed.

Abstract: Based on the construction process of the structure stress, especially the construction of continuous beam linear control plays a role in determining the characteristics, based on the deflection reliability safety risk identification method, is introduced into the deflection reliability index.Give the calculating formula and example to verify the applicability of the method.

Abstract: Based on the test of 7 reinforced concrete beam reinforcement test data comparison analysis shows that only the ordinary reinforced concrete beams with externally bonded CFRP, effectively improve the bearing capacity of members, but due to the lower tensile reserves and the upper compression reserve is relatively insufficient, make a component similar over-reinforced beam brittle failure, its ultimate bearing capacity was significantly lower than the upper part at the same time a laminated layer of the RC beam. Laminated paste CFRP composite reinforced RC beam damage characteristics and common reinforced concrete beam was no essential difference, but the laminated layer thickness reaches to a certain degree, the CFRP can also occur with sudden local cleavage fracture.

Abstract: This study concerns the experimental and numerical researches on the temperature field of CFST which is subjected to periodic solar radiation and ambient temperature. The study gives the detailed temperature and heat flux which vary with time, and the results indicate that temperature distribution caused by solar radiation is nonlinear, and is significantly varied with time and sections. The peak temperature of measure points in the surface of steel tube and in the center of concrete occur at different times, the largest temperature difference is over26.3°C. The variations of temperature lag obviously when the measuring points are more close to center in the same series. And the temperature of the center point is affected by various directions, especially the strongest direction.

Abstract: Choosing appropriate acoustic emission (AE) sensors is crucial for the research of concrete damage failure processes using AE technology. In this paper, concrete testing under axial tension and compression is used as the main research method, and the choices of AE sensors in monitoring the fracture process of concrete are studied using digital parameters-waveform AE acquire system and four different types of AE sensors. The result showed that the broadband sensor received more signals and their frequency is wider, Broadband sensor shows certain technical advantage in monitoring the damage process of concrete under different stress conditions, embodied as collecting wider frequency range of AE signal, especially the high frequency produced in the anaphase of loading.

Abstract: The prediction of pitting corrosion-induced structural performance degradation is limited by the inspection means and experimental data. Incomplete information and tempral and spatial uncertainties of corrosion are integrated to develop the time-dependent pit depth model. The reinforcement corrosion is divided into two stages in this model. The approach is illustrated by a removed concrete bridge. The evolutionary characteristic of probability density function of the pit depth is analyzed, and the probabilistic distribution pattern and distribution parameters are also obtained. Besides, The sensitivity of input parameters on the pitting model are also discussed. The results show that under appropriate conditions of concrete strength (>25MPa), increase the same percentage of concrete strength is more sensitive to the pit depth than improvement the same percentage of concrete cover thickness. The effects of continuous improvement of concrete strength or increase the thickness on corrosion depth gradually decreases. The proposed procedure can be used to evaluation of existing reinforced concrete bridge.

Abstract: The earthquake often leads to the damage of stabilizing concrete pile. In order to analyze the damage mechanism of the reinforced concrete stabilizing pile, this article uses the developed concrete model piles, studies the seismic deformation of a slope reinforced with stabilizing piles and the dynamic broken damage phenomenon of pile by using the dynamic centrifuge model test without groundwater. The results show that the earthquake action leads to the obvious increase of dynamic excess bending moments, eventually results in the pile’s breaking damage.