Applied Mechanics and Materials Vols. 71-78

Abstract: In this experimental study, the setting agent Ca(OH)₂ used for activation of slag cement is used in the proportions of 0%, 2%, 4%, 6%, 8% and 10% by substitution method by mass of slag cement. The results indicated that the mineral activator has a significant effect on the flexural and compressive strengths. The optimum percentage of the mineral activator (hydrated lime) ranges between 2 to 4%. The activation of the slag cement by fine lime (calcium hydroxide) is a simple and economic method especially for cement containing not very reactive slag or low reactivity due to its low CaO/SiO₂.

Abstract: The purpose of this research is to investigate the influence of the freeze-thaw cycles on the flexural behavior of reinforced concrete members. The variation of the concrete stress-strain relationship due to frozen-thawed deterioration was considered. The temperature distribution was calculated based on the heat conduction theory, and the damaged region affected by freeze-thaw cycles was determined. By using Reponse-2000 program, the flexural behaviour of a reinforced concrete slab was analyzed and predicted. The analytical results show that with increase of number of freeze-thaw cycles, the yield moment, the ultimate moment and the curvature ductility decreased, while the relative depth of neutral axis and the midspan deflection increased.

Abstract: The adsorption of bisphenol-A (BPA) by hexadecyl trimethyl ammonium bromide (HDTMA) modified clinoptilolite was presented. In this paper, the equilibrium adsorption of BPA by HDTMA modified clinoptilolite was described by Freundlich isotherm with a correlation coefficient's square (R²) of 0.988. The kinetics of adsorption was defined by second-order kinetics with a rate constant (K_v) of 1.98 g/mg/h. The absorption rate was fast, and the liquid solid equilibrium was accomplished within 180 minutes. The effects of initial solution pH, and reaction temperatures had been estimated, showing that the adsorption was enhanced gradually by increasing pH value.

Abstract: In this paper, the tensile-compression prestressed concrete beam was researched, and gets deflection of the beam subjected to load. Then, the beam was analyzed by the finite element method of ANSYS software. The test and analysis results show that the beam has a good flexibility and the phenomenon of stress concentration were appeared in ends concrete of pre-compressed steel tube. The pre-compressed steel tube control stress is 0.5 times the nominal value of steel tube, the concrete pre-tensile stress can be obtained effectively by relaxes pre-compressed steel tube. This paper further optimizes the dosage of pre-tensile tendon (A_p), pre-compressed steel tube (A_T), tensile reinforcements (A_s)and compression reinforcements (A`_s).The results from example show that the concrete structure of tensile-compression prestressed can reduce the pressure area height of the beam effectively and solving conventional prestressed concrete structure excessive or cannot reinforcement in pressure area.

Abstract: According to the cycles of freezing and thawing frequently happened during early spring and late autumn in northeast china, this paper studies on the frost resistance of concrete using in highway pavement. Making experiments by adding flyash, silicon powder, air entraining and water reducing agent to normal concrete with different proportions and using flexure strength, compression strength and mass loss rate of concrete as evaluating indicators, a reasonable and economic concrete proportion is determined, which reaches high flexure strength and compression strength, good frost resistance. On the bases of the experimental results and economic analysis, it is shown that the concrete proportion can effectively enhance the frost resistance of concrete. Therefore, it has good use value and it is promising with a good prospect of application.

Abstract: In the mesoscale modeling, concrete is assumed consisting of three components, i.e., coarse aggregates, mortar matrix, and the interfacial transition zone (ITZ), each with different material behavior. The shape and the percentage of the coarse aggregate are the key factors in the mesoscale numerical simulation. The present paper investigates the effect of the coarse aggregate shape on the concrete behavior under high strain rate compression. Simplified methods are adopted to construct the aggregate distribution. Three different aggregate shapes, i.e., circular, oval and polygons, are generated to model the gravel and crushed stone aggregates, respectively. Using these different aggregate shapes, concrete specimens under high strain rate compression are modeled. Numerical results show that the aggregate shapes have a significant effect on the crack path, whereas little effect on the overall responses of the concrete specimen.

Abstract: Compare experiment analysis effect of material, slump, carbonation depth on green high performance concrete strength by rebound method, analysis under questions based on microstructure: (1)Basic reason for additives and admixtures etc. impact rebound testing; (2) Significant differences of pumping concrete and plastic concrete; (3) Concrete carbonation depth impact rebound value. Provide the method for improving testing accuracy of green high performance concrete strength testing by rebound method.

Abstract: In this paper, the influence of conventional triaxial compression on damage and chloride ion penetration of cement mortar are investigated. Conventional triaxial compression experiment was carried out with confining loading of 10Mpa. And the stress-strain curve was measured when axial stress was 50%, 80% and 100% of peak axial loading, and 80% axial loading post-maximum. Then the damaged cement mortars was stored in Qingdao sea water for 30 days, and the free chloride content as well as chloride diffusion coefficient of damaged mortars were quantitatively determined. The experimental results show that the cement mortar is compacted in the end, and shear damaged in the middle under conventional triaxial compression. Compared to cement mortar under uniaxial compression, its compressive strength and axial deformation increases by 1.94 times and 5.6 times when cement mortar under conventional triaxial compression. When the axial stress is less than 48% of peak axial loading, and the axial deformation is less than 0.63mm, the mortar is compacted and its relative dynamic elastic modulus increases with raising axial loading and deformation. The free chloride content in the pressure-bearing side is higher than that in the bottom side. And the free chloride content in the interior of mortar increases with raising axial loading. The chloride diffusion coefficient and axial loading are related in quadratic function. When the axial deformation of mortar is higher than 0.72mm and 1.57mm, the chloride diffusion coefficient of non-load mortar, is less than that of loaded mortar in the pressure-bearing side, and in the bottom side, respectively.

Abstract: Nitrogen doped TiO₂ (N/TiO₂) photocatalysts were prepared using a mechanochemica1 method with raw amorphous TiO₂ as precursors and various nitrogenous compounds doses (NH₄F, NH₄HCO₃, NH₃·H₂O, NH₄COOCH₃, and CH₄N₂O). The photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflection spectra (UV-Vis-DRS). Their photocatalytical activities were evaluated with the degradation of p-nitrophenol and methyl orange under UV or sunlight irradiation. The catalysts had a strong visible light absorption which corresponding to doped nitrogen and consequent oxygen deficient. Concentration of the nitrogen substances also affected the visible light adsorption of the TiO₂. The XPS results indicated the doped nitrogen in the TiO₂ may exist in the formation of O₂Ti−N−H and/or O₂Ti−N, nitrogen was in form of interstitial atom. The results of photocatalytic activity showed the visible light adsorption mechanisms, as the doped nitrogen species gave rise to a mid-gap level slightly above the top of the (O-2p) valence band, but not from the mixed band gap of the N-2p and O-2p electronic levels.

Abstract: This paper is focused on the method for improving capability of anti-sulfate corrosion of concrete. Based on the performance characteristics of mineral admixture, propose a method that mixing concrete with complex multi-mineral admixture to improve the effect of anti-sulfate corrosion. Finally, the ability of anti-sulfate corrosion and anti-dry-wet cycle, in different case, is studied and compared. The results show that concrete mixed with complex multi-mineral admixture is advantageous to improve the anti-sulfate corrosion effects of the concrete. The proportion of mineral admixtures has significant influence on the anti-sulfate corrosion effect. As the silica fume and slag content increased, the fly ash content decreased, the ability of anti-sulfate corrosion enhanced.