Applied Mechanics and Materials Vols. 438-439

Abstract: During the construction of concrete structure, laying controlled permeability formwork within the traditional formwork can effectively improve the durability of concrete for marine structures and prolong the working life of concrete structures. This paper discusses the working mechanism of controlled permeability formwork, introduces its development history and research status, summarizes the construction process and matters needing attention of controlled permeability formwork, and puts forward the problems remaining to be solved at present.

Abstract: Self-compacting concrete (SCC) refers to one kind of high-performance concrete which can fill formwork and condensed reinforced steel by the weight of concrete mixture without vibration. In this investigation, local raw materials from Shenzhen Jinqiang Concrete Co. Ltd were employed. Self-compacting concrete mixtures with targeted 3-day compressive strengths of 60MPa or 80MPa and required flow properties were evaluated. Moreover, the SCC was successfully applied in Shenzhen Mangrove Garden project.

Abstract: Regional confined concrete is a method which can strengthen constraint in the most needed position, it can make concrete, longitudinal reinforcement and transverse stirrup to form a more effective binding, and provide a stronger restraint in required regional giving full play the role of constraints. In the result analysis of the regional confined column specimen load test, we found that longitudinal reinforcement and stirrup strains have certain relationship. This article analyses the relationship between the two from the stirrup and longitudinal reinforcements strains in the contingency load, references are provided for the further development of regional confined concrete theory. Taking the two specimens as examples, the regression analysis was carried on between longitudinal reinforcement and stirrup strain, the relationship equation was obtained

Abstract: The corrosion rates of rebar HRB335 in 0.5%wt. NaCl solution and the tensile mechanical properties before and after corrosion of rebar were investigated. The results showed that, with increasing corrosion time from 30 days to 90 days, the corrosion rate of rebar HRB335 increases. With the increase of corrosion time (corrosion rate), the yield strength and tensile strength decrease, but the elongation decreases at first and then increases.

Abstract: Corrosion rate of steel bar in concrete plays an important role in load bearing-capacity evaluation, maintenance decision and residual life prediction of existing RC structures. A macro cell corrosion model was developed to investigate the influences of concrete resistivity on corrosion rate of steel bar in concrete based on the electrochemical principle and the Bulter-Volmer equation. Analysis results show that concrete resistivity has significant effect on corrosion rate of steel bar in concrete if the limit current density is relative large and the steel corrosion is under control of ion transportation. With the increase of relative humidity, the limit current density decreases obviously and the steel corrosion is influenced by both oxygen diffusion and concrete resistivity. However, if the concrete resistivity is relative small, steel corrosion will be under control of oxygen diffusion.

Abstract: The corrosion behavior of rebar HRB400 in 0.5 wt.%, 1.5 wt.% and 3.5 wt.% NaCl solutions was investigated by corrosion rate calculation and corrosion morphology observation. The results showed that, with the increase of corrosion time from 240h to 720h, the corrosion rate of rebar HRB400 in each NaCl solution increases. With the increase of NaCl solution concentration, the corrosion rate of rebar HRB400 increases. The corrosion morphologies show strong consistency with the test results of corrosion rate.

Abstract: The influence of different surface forms on GFRP reinforcement mainly manifest in bonding between reinforcement materials and concrete, especially when the GFRP bars are used in slope, the form of the surface of GFRP bar will affect reinforced materials torsion and shear properties directly. This article made some tensile tests on several different surface forms of GFRP reinforcement, and learned that the form of the surface wound of GFRP bar make the influence on tensile strength, ultimate elongation and modulus of elasticity. Test results show that the surface of the winding way will affect on the tensile strength, ultimate elongation and modulus of elasticity of GFRP bar.

Abstract: Different surface forms will have a huge impact on bond of GFRP rebar and concrete, and the ribs depth is the key factor that affects the bond with concrete, therefore, the surface forms and rib depth should be taken into account when GFRP bars are used as the structural reinforcement material. Based on two kinds of rib spacing and rib depth of GFRP reinforcement on tensile performance test, this article studies the different influence of ribs depth on the tensile properties and mechanism. Experimental results show that rib depth has distinctive impact for the GFRP tendons ultimate tensile strength, elastic modulus and ultimate elongation.

Abstract: The GFRP bar has good mechanical properties and durability, but it is hard to test the tensile strength of large diameter FRP bar. Its test method given by ACI is too conservative, especially for large diameter FRP bar, and the length of test specimen will be too long and beyond the range of most testing machine. This article tested the tensile strength of GFRP bar using new methods, meanwhile, analyzed its stress distribution along the length of the specimens. The test results show that the use of bond anchor with steel plug or internal thread to measure the tensile strength of GFRP bar is feasible, and it can reduce the free length and the anchor length of the specimens, thus simplifying the test method of the tensile strength of FRP bars.

Abstract: During the service of asphalt pavement, the aging makes asphalt binder become brittle, gradually lose flexibility and adhesion. All these result in the low-temperature properties of asphalt pavement to be poor. This paper conducts the rolling thin film oven test (RTFOT) and pressure aging vessel (PAV) test on base asphalt and rubber-modified asphalt respectively. The bending beam rheometer (BBR) test was conducted on original asphalts, rolling thin film oven test (RTFOT) residuals and RTFOT + pressure aging vessel (PAV) residuals of base asphalt and rubber-modified asphalt respectively. Results indicate that the low-temperature properties of all aged asphalts were declined. The attenuation of low-temperature properties of RTFOT + PAV residuals is larger than that of the RTFOT residuals. The attenuation of different types of asphalt is different. From the overall trend, effect of aging on the low-temperature properties of asphalt binder reduced as the test temperature reduction. The rubber-modified asphalt has superior low-temperature performance than that of base asphalt, and its low-temperature performance decreases more slowly than the base asphalt.