Advanced Materials Research Vols. 671-674

Abstract: The axial performance of CFRP is excellent, while the lateral compression strength and shear strength are low, thus they can’t be anchored by traditional anchors. A new type of adhesive anchor was designed and five experimental cables were fabricated and the static tests were carried out. In the tests, the tensile capacity, bond strength and pullout behavior of CFRP cables anchors filled with resin were discussed. The efficiency coefficients and the load-slip behaviors of the bond-type anchors and the uniformities of the stresses in the tendons were studied. Several conclusions are drawn which have become powerful evidences for using the bond-type anchors in the first cable stayed bridge with CFRP cables in China.

Abstract: 23,037 values of concrete compressive strength from construction sites were obtained from Beijing Building Construction Research Institute from 2009-2012 by standard cubes testing method. The mean values, standard deviations, coefficients of variations, maxima and minima were derived from the original strength values analyzed and compared with the data in 1989. The results make up for the lack in C25/C30 and the maxima/minima of every strength class of concrete of the former data. Both the coefficients of variations and mean values have increased in recent years. The log-normal distribution commonly used in concrete compressive strength statistics is not that suitable for strength modeling for it is unbounded. So a bounded normal distribution was given in this paper. By Geary's test, the goodness-of-fit of bounded normal distribution is better than log-normal distribution has been proved.

Abstract: Degradation mechanisms of GFRP bar in real concrete are still not clear to civil engineers due to limited field applications. To avoid unsafe design, in current design codes a material factor is used to assure long-term safety of GFRP RC structures. This paper presents an assessment of material factors for GFRP bar as specified in Canadian Design Codes by predicting GFRP long-term performance with monthly average temperatures from 14 weather reporting stations in Canada. Results showed that the material factor varies from 0.57 to 0.61 for an application with 100% RH exposure, while a factor of 0.75 could be adequate for cases with exposure RH ≤90%. Considering the annual relative humidity across Canada, conclusion could be made that current factors in Canadian codes could provide sufficient safety margin.

Abstract: With repeated action of freeze-thaw cycles, chloride ion diffusion characteristics changed obviously in concrete structure. In the study, the chloride ion diffusion coefficient and the surface chloride ion concentration were discussed especially with the trends. Based on these facts, the chloride diffusion model and the improved model of concrete was also discussed based on its time-dependent characteristics, which indicated that the freeze-thaw damage of concrete would have a greater impact to the chloride transport course in the concrete, and so on the service life of concrete structures would be affected.

Abstract: The real thermal parameters always have inevitable influence on the simulation results of the structure thermal field and stress field in the construction of mass concrete. A new measuring and calculation method for concrete thermal conductivity was put forward. Eight or six sensor points measuring method and calculation formula are present, and the latter is the simplification of the former. Comparing the real thermal conductivity with the calculation result by the new method, it can be seen that the thermal conductivity can be obtained within about 6 day’s age at site and with the accurate degree of 98%. The new method will provide an efficient way for the concrete structure researcher and designer.

Abstract: In view of the limitation of seismic damage model for concrete structures with recent methods, based on Drucker-Prager constitutive model, with the concept of damage surface, Mazars concrete damage equation obtained by uniaxial test was extended to the triaxial state. Material stiffness damage degradation impact on the yield process of concrete yield surface was considered. Given Druker-Prager constitutive model adapted to the low friction angle soft clay type, the yield parameters threshold of yield surface is low that does not meet the concrete reality, draw double-shear strength theory, the strain threshold of double shear strain yield equation has been adopted, Modified damage threshold of uniaxial test strain damage equation. This paper developed a simplified concrete damage constitutive model in FLAC3D environment. The model is simple and easy to practical engineering applications, and the model has a certain accuracy. Try to explore a new constitutive model of concrete.

Abstract: Through calculation and analysis on routine examination and neutralization of reinforced concrete chimney, the service life of concrete structure was evaluated only considering neutralization of concrete single factor. The results show that the neutralization of the reinforced concrete chimney was serious than that of other similar projects. The initiation time of reinforcement corrosion were 19.3a, cracking time of concrete cover were 27.35a.

Abstract: The deterioration of concrete under the acid rain and freeze-thaw co-existed environment was investigated in laboratory. The results show that the deterioration caused by acid rain attack is aggravated by freeze-thaw damage in north China and increases with the increase in acidity of acid rain solution and mechanical loading. The SEM results demonstrate that the aggravation results from the cooperation of freeze-thaw damage which accelerates the expansion of the micro-cracks of concrete so that the penetration of erosion media in acid rain solution into the internal pores of concrete is intensified.

Abstract: High frequency vibration was brought to two different air-entrained concrete. Pore structure analyzer of hardened concrete quantitatively described the influence of vibration to air content, air spacing coefficient and bubble size distribution. Meanwhile, the relationship between high frequency vibration and the ability of frost resistance was accurately determined through the testing freeze-thaw cycle. The results showed that: long time high frequency vibration would cause decline of frost resistance.

Abstract: A nanostructural layer was formed on the surface of 35CrMo steel rods rolled by cross-rolling. The layer microstructure is composed of nano-scale grains and some deformation grains, which contains compressive residual stress of -479Mpa. The surface roughness is decreased from Ra 2.1μm to Ra 0.14μm with improvement of the cylindricity and straightness. The rolling strengthenes the surface but has ignorable influence on the mechanical properties of the rods.