Key Engineering Materials Vols. 629-630

Abstract: A probabilistic analysis is performed where the pressure change inside a concrete tube is probabilistically estimated considering the uncertainties inherent in the material, system discontinuity and outside pressure. A set of uncertain variables that are related to the equivalent system air permeability and the atmospheric pressure are defined as random variables with specific distributions. The pressure change inside a concrete tube is then probabilistically described using both analytical and simulation approaches. The analysis confirms the need of probabilistic approach for evaluation of the airtightness performance of vacuum tube structures.

Abstract: This paper deal with concrete behavior under chemical and mechanical degradation. Experimental investigations were described where the effects of the calcium leaching process of concrete on its mechanical properties were highlight. The compressive strength and the stress-strain relationship of leached concrete with different leaching degradations were investigated experimental. As leaching grew, a loss of stiffness and of strength were observed and an obviously decrease of peak strain was noted. Then the micromechanical damage constitutive model of the leached concrete was proposed. The proposed model was applied to simulate typical laboratory tests. And it was shown that the proposed model was able to describe the main features of mechanical behavior of concrete in sound and leaching degraded states. And the parameters in the proposed model can be got by testing the pH value of pore solution, which it is easier to measure from the existing concrete.

Abstract: Abstract: Affected by various external factors, the tensile force of prestressed anchorage structures presents loop and fluctuation characteristics in practical engineerings, which will cause severe impact on the inner anchoring section of the prestressed anchorage structures. On this base, PFC2D discrete element program was established for numerical simulation analysis of microscopic physical and mechanical changing characteristics of stress, porosity, angle, etc. of different interfaces locations for prestressed anchor cable under cyclic loading. The results showed that: at locations of the front-middle, the grouting body near interfaces were divided into tensile stress area of the inside part and compressive stress area of the outside part, and two locations of y-direction stress concentration were located at the two end of inner anchoring section; The interfaces had the feature of progressive failure and the characteristic of shear stress peak shifting; While loading finish, particles at different locations of interfaces basically generated clockwise rotation angle, but at two locations of y-direction stress concentration, the particles rotation angle, which was very small at the other locations, was very large; At y-direction tension and compression stress boundary, the particles spinning direction showed instability characteristic and the ultimate rotation angle was small.

Abstract: The usage of autoclaved PHC pile in chloride environment becomes common, so how to evaluate the resistance to chloride ion penetration of autoclaved PHC pile becomes urgent. This article Compare the resistance to chloride ion penetration of pile and pile concrete specimens based the Rapid Chloride Migration Synthesis Method and RCM. The results show that the Rapid Chloride Migration Synthesis Method is not suitable for pile, RCPT and RCM are suitable for pile; the resistance to chloride ion penetration of the pile inner and outer lateral concrete has a rather large different, so the sample must distinguish the direction when testing. Steel bar has little influence on the resistance to chloride ion penetration of autoclaved PHC pile, and the resistance to chloride ion penetration of pile outer lateral concrete is similar with pile concrete specimen, using pile concrete specimen to test the resistance to chloride ion penetration of autoclaved PHC pile is suitable. The chloride diffusion coefficient values have a good relationship with the electricity value, using the electricity value of square pile concrete specimen as commonly quality control way are suggested. The resistance to chloride ion penetration of pile can test the outer lateral concrete of pile or pile head, using the electricity value as daily quality control method and basis for project acceptance, and using RCM method as life assessment and basis for project acceptance.

Abstract: In order to evaluate the quality of air entraining agent quickly and effectively. Air void parameters of fresh concrete with different air entraining agents were studied by Air Void Analyzer (AVA). The spacing factor and durability index of hardened concrete were tested and the relationship between the surface tension of air entraining agent and frost resistance of concrete was compared. The results showed that, the quality of air entraining agent can be evaluated quickly and effectively by diameter distribution of air bubbles in fresh concrete and spacing factor of fresh concrete. AEA2 introduced much more big air bubbles into concrete which is bad for the frost resistance of concrete. The quality of AEA2 was the worst, so the durability index of hardened concrete was 58.7%. Quality of air entraining agent cannot be characterized by properties of air entraining agent, but air entraining ability can be characterized by surface tension of air entraining agent. Keywords: air entraining agent (AEA), air void parameter, fresh concrete

Abstract: This paper in detail introduces basic principles and technical development process of inspecting the material strength of high performance concrete by rebound method and Ultrasonic-rebound combined method. The strength-inspected curves of high performance concrete in Beijing region are given by using above mentioned two methods. Existing problem that 2.207J rebound device could not be used to inspect the strength of concert at grades 50MPa and above, has been solved. This article is one of the research results in “ Technical specification for strength testing of high strength concrete ”JGJ/T 294-2013 during compiling, which can be used in inspecting the material strength of high strength concrete in Beijing region.

Abstract: The glutinous rice-lime mortar (M_GRL) is a high performance organic-inorganic composite, which has been commonly used as a building material since ancient times in China. However, the knowledge of nonlinear structure of M_GRL is limited. In this work, the nonlinear structure of traditional M_GRL was investigated. The particle size distribution (PSD) of fine and micro-aggregate were evaluated by fuzzy fractal set. The microstructure of M_GRL were tested by electron backscattered diffraction (EBSD) and field emission scanning electron microscope (FESEM) analysis. Results shown that the structure of M_GRL is a fuzzy fractal system. And the fuzzy fractal dimension of the system is correlated to the fracture resistance of M_GRL.

Abstract: Methylene blue value (MBV) is an effective index for detecting harmful clay in manufactured sand (MS) and it’s of great importance for quality control of MS concrete. In order to verify relationship between MBV and concrete properties and feasibility of using MBV to confine clay harmfulness, influences of MBV on fresh and hardened mortar properties were investigated under constant flow by means of adjusting water and water reducer content, respectively. The results indicate that water and water reducer demand and drying shrinkage increase while frost resistance decreases with increasing MBV. Meanwhile, compressive strength and permeability resistance decrease significantly with increasing MBV when water content is increased and they are not greatly negatively affected when W/C is held constant. Certain relationships can be established between MBV and mortar properties and adverse effect of clay is relatively limited when MBV is within 1.0g/kg.