Zhiwu Yu

Practical Issues Related to the Application of Electromechanical Impedance-Based Method in Concrete Structural Health Monitoring

Here the piezoelectric Lead-Zirconate-Titanate (PZT) sensors were developed and embedded into concrete to actively provide the local excitation and simultaneously sense the structural dynamic response by using the electromechanical impedance (EMI) technique. The influences of mass variations of concrete structure and vibration condition on the EMI technique were investigated. The root-mean-square deviation (RMSD) index was used to evaluate the impedance spectra variation of the PZT sensor. The results show that the EMI technique is sensitive to the mass variation of the structure, and the EMI sensitivity shows the decreasing trend with increasing the distance between the PZT sensor and additive mass loadings on the concrete structure. The vibration condition is important for the accuracy of the EMI technique, which should be considered in the practical engineering application.

Preparation of hydrophobic organic-silicanano composites

ABSTRACT In this paper, we use silica nanoparticles modified by methacryloxy propyl trimethoxylsilane (KH570) as the core material, and employ polymers including hexafluorobutyl methacrylate (HFMA), dodecafluoroheptyl methacrylate (DFMA) and acrylic ester as the shell materials to prepare the hydrophobic inorganic–organic hybrid nanocomposites with a seed emulsion polymerization strategy. The size, morphologyandproperties of the core-shell structured nanoparticles are investigated by TEM and SEM. The results showthat the polymer nanocomposite has three concentric layers with silica nanoparticles in the center, acrylic polymer as the internal shell and fluorosilicone polymer as the outmost shell. By controlling the ratio of the silica nanoparticles and monomers, we can achieve each composite particle has the core-shell structure with silica nanoparticles as the core and the thin layer of fluorosilicone polymer as the shell. Compared with the traditional polymer film, the nanocomposite film shows a hydrophobic property with a contact angle of up to 100 degree. Therefore, it is feasible to prepare hydrophobic organic–inorganic nanocomposites using the method proposed here.

Bioinspired Design of Building Materials for Blast and Ballistic Protection

Nacre in abalone shell exhibits high toughness despite the brittle nature of its major constituent (i.e., aragonite). Its specific structure is a major contributor to the energy absorption capacity of nacre. This paper reviews the mechanisms behind the performance of nacre under shear, uniaxial tension, compression, and bending conditions. The remarkable combination of stiffness and toughness on nacre can motivate the development of bioinspired building materials for impact resistance applications, and the possible toughness designs of cement-based and clay-based composite materials with a layered and staggered structure were discussed.

Experimental Study and Analysis of the Structural Behavior of Steel-Concrete Composite Beam after Shear Connector Corrosion

Stud shear connector corrosion is an important factor for the durability degradation of steel-concrete composite structures. Stud shear connector corrosion in the natural environment is a slow process, so the shear capacity of deteriorated stud shear connector was studied by accelerate d deterioration using a galvanstatic method in this paper. Then, bending tests were conducted to study the structural behavior of steel-concrete composite beam after stud shear connector corrosion. Experimental results show that with the increase of conduction time, the corrosion rate of stud increases, the shear capacity of stud as well as the flexural capacity of steel-concrete composite beam decreases and the relative bond-slip between steel beam and concrete increases when loading. By the regression analysis of experimental results, formula was proposed to predict the shear capacity of studs after corrosion and the flexural capacity of deteriorated steel-concrete composite beam.

Research on Ingress of Chloride Ions in Concrete in an Artificial Simulation Environment

The time-varying of the diffusion coefficient and distribution of the chloride ion content in concrete was investigated in this paper. Based on the testing time and methods, the difference and the application range of the diffusion coefficient are discussed. In addition, the difference of the chloride ion ingress in concrete with various strength levels was also researched. Results showed that chloride diffusion in concrete can be described by Ficks diffusion law, and the fitting curve based on the annual diffusion coefficient was more suitable for describing the change. Generally speaking, the diffusion coefficient tends to stabilize the value when the testing time is more than a certain constant value.

Study on the Distribution of Coarse Aggregate in Concrete

The distribution of coarse aggregate in concrete at different depths from the surface layer was investigated. Based on the fractal theory, the fractal dimension model of the coarse aggregate in concrete was induced. Meantime, the cross-sectional area percentage of the coarse aggregate in concrete was calculated by sectioning method. The fractal dimension value was also indirectly estimated. The results indicate that there was certain change regularity of the coarse aggregate content in concrete, which presents a low percentage value in the surface region and a high percentage value at the depth. That may be caused by the effect of the size effect and boundary effect during the process of the production. In addition, the fractal dimension value of the coarse aggregate in concrete is about 1.35, which differs from the traditional Euclidean geometry. That may be due largely to the coarse aggregate in concrete with fractal character.

Convective Depth of the Chloride Ion in Concrete Surfaces

Based on the hypothesis of chloride ion concentration in concrete surfaces changing linearly, a convective depth model was established in this study. The rationality of the model was verified by experiment. In addition, a novel method for calculating the equivalent chloride ion content in the natural environment is proposed. The results showed that the diffusion of the chloride ion in concrete can be described by Ficks second law, and there was an exact convective depth value in a concrete surface. In general, the value of the convective depth is relative to the wetting-drying ratio of the environment and the permeability coefficient of the concrete. Compared with the water influence depth in concrete, the convective depth was shallow. Moreover, the equivalent chloride ion content in the environment was determined by the characteristics of the environment.

Chlorine Ion Content Distribution of Concrete Surfaces in a Natural Environment

Based on Ficks Law of Diffusion, this research created a correlation model between the chlorine ion content in concrete surfaces and the elevation and distance away from the ocean in a natural environment. The real-time monitoring data of concrete chloride erosion in a natural environment were used to validate the rationality of the proposed correlation model. In addition, the variations of the chloride diffusion coefficient in concrete and the maximum chlorine ion content in a concrete surface along an elevation were investigated. The results showed that the chlorine ion content in concrete in a natural environment significantly changed and correlated with the elevation and distance from the ocean. The variation of chloride ion content in concrete surfaces along an elevation can be characterized by an S curve, and the variation of chloride diffusion coefficient of concrete along an elevation had a Gaussian distribution.

Characterization and Application of Shear Thickening Fluids

The shear thickening phenomenon was explained in this paper. The characteristics of shear thickening fluids (STFs), including reversibility and liquid to solid transition at critical shear rate were presented. Also, the applications of STFs for protective clothing and equipment were discussed. Since little references can be found which concern the effect of interparticle forces like Van der Waals forces on the performance of cementitious materials subjected to impact loading, understanding the mechanism of STF and knowing how its structure affects the properties, behaviors, and resulting applications is expected to inspire potential designs for building cementitious materials.

Study on Chloride Ion Penetration for Concrete Structures in Zhunhai Area

The chloride concentration distribution is an efficient method of evaluating corrosion characteristics of concrete structures.A number of concrete samples at various positions were drilled in Zhuhai area and the free chloride concentration of concrete were determinated.Besides,the influences of elevations,distances from the sea and the local environment on chloride were analyzed.The value of chloride diffusion coefficient and surface chloride ion concentration along various elevation at the sea were calculated according to Ficks second law.The results show that chlorides erosion aciton tends to reduction with elevation and it is the most serious at an elevation of 1 meter for concrete by the sea.There is the large convective depth in alternate wetting-dry ares.Whereas it is just about 0.02%-0.05% on the road,at the distance of 15 kilometers from the seafront,which indicates that the father away from the seafront,the weaker chlorides erosion action becomes.