Advanced Materials Research Vols. 163-167

Abstract: The method of the second intrusion mercury in MIP was used to investigate the pore characteristics of hardened cement paste with w/c ratio 0.23, 0.35 and 0.53, respectively, in order to research the quantitative relationship between transport properties and pore characteristics in cement-based composite materials. The results show the second intrusion mercury could well determine the effective pore structure parameters, and effective porosity accounts for 25% to 50% of total porosity in cement paste. At the same time, the existence of the first and second peak in pore size distribution curves is confirmed by MIP, such as, the first peak in hardened cement paste with water to cement ratio 0.53 is very distinct, however, with the decrease of water to cement ratio, the first peak gradually disappears. The pore diameter corresponding to the first and second peak is critical pore diameter of capillary pore and gel pore, respectively.

Abstract: The reliability of the existing tunnel will decline gradually during service period due to various factors. This paper analyzes the structural reliability characteristics of the existing tunnel, the time-varying performance function of the reliability of the existing tunnel is proposed. The statistical value of lining action effect is calculated by using Monte Carlo Method combined with the finite element method .By analyzing the factors which influence the resistance degradation of tunnel lining, at the same time consider the time variability of the concrete strength deterioration and random changes of cross section size, the statistical parameters of each variable during follow-up service period is calculated by using Bayesian Method. The ultimate limit states equation of the concrete lining is established. The reliability index of the lining structures of an existing is calculated and the results show that the reliability decreases with the service time getting long.

Abstract: The effect of the load ratio, R, or the mean-stress on fatigue life has been recognized for more than a hundred years. In this paper we first describe a novel mechanics model for fatigue crak growth (FCG) under constant amplitude (CA) loading based on static fracture mechanics with thinking about the inertial effect coefficient and its impact to crack tip, and then discuss the relation between R-ratio and fatigue crak growth rate. Comparison of the present analysis with experimental data taken from the literature demonstrates that R-ratio has a greater impact to the fatigue crack propagation.

Abstract: The influencing information of structural resistance cannot be exactly inspected due to limitation of the experimental means, time and space. The study must be conducted by incomplete information and the uncertainty is enhanced. The uncertainty consists of fuzziness, randomness, and faultiness of knowledge. The faultiness of knowledge is the weak uncertainty, and can be incorporated into fuzziness and randomness. A novel probabilistic analysis method of corrosion-induced resistance degradation subject to fuzziness and randomness is developed in this paper. The reinforcing bar corrosion is induced by chloride ion attack in reinforced concrete (RC) bridge. The relationship between steel area corrosion rate and yield strength is presented based on the experimental investigation on mechanical property of corroded reinforcement. The fuzzy time-variant probabilistic analysis of resistance degradation is illustrated by an example problem of RC bridge beam. The result can be used to time-variant reliability-based evaluation for reinforced concrete.

Abstract: The permeability of chloride ion in concrete can be studied using the accelerated aging method in a short period, but the influence of loading characteristic on chloride ion permeability and diffusion coefficients is not considered generally. Three RC beam (120 mm×240 mm×2400 mm) specimens with different flexural loading state are exposed in an artificial corrosion container filled with salt-fog of 5.0 % sodium chloride for 40 days, the chloride ion concentration in different depths of compressive and tensile region are measured, diffusion coefficients of different region concrete are fitted on the basis of Fick’s second law, the effect of flexural loading on chloride ion concentration and diffusion coefficients of concrete are analyzed. The results show that the effect of the flexural load influences permeability of chloride ion and diffusion coefficients of concrete, content of chloride and diffusion coefficients of concrete are controlled by loading level, and the bending load is one of the important factors that can not be ignored in the study of concrete durability.

Abstract: Carbonation of cementitious materials results in a reduction of the pH value which makes the material less alkaline and leads to unsightly spalling on structures. In this paper, the experimental investigation on damping capacity of reinforced concrete materials and members with carbonization at different ages was carried out by the method of 3-point bending beam damping measurement and cantilever beam free vibration respectively. The experimental results show that loss tangent and loss modulus were all decreased by carbonization. It shows that the damping capacity is decreased by carbonation corrosions with the carbonation time increase. It is indicated that the effects of carbonation-induced corrosion on the damping capacity for engineering materials and structures are absolutely essential.

Abstract: In this paper, the lattice network model on mesoscale is established based on the random geometry meshing technique to investigate the chloride ingress into unsaturated concrete. Concrete is treated as a composite material with three phases, i.e., the coarse aggregates, the mortar, and the interface between them. The diffusivity for water and chloride in each phase of the mesoscopic structure of concrete is separately quantified by experimental data or through empirical assumption. The numerical predictions are compared with the available experimental measurements. The comparisons indicate that numerical predictions agree well with the test results.

Abstract: Blasting is a conventional technique for mining, but structures adjacent to open pit mines are often damaged by blasting vibration, therefore, durability and safety of these structures are affected. Damage characteristics of a three-floor frame structure on the top of an open pit mine under repeatedly blasting vibration is studied in this paper. The damage model of structural members is made based on the theory of damage mechanics of continuous medium, and an overall damage model of the structure is also established by the method of frequency. The results showed that the Young’s modulus, frequency of the structure decreased as increasing of the blasting times, the damage factors of structural members are bigger than that of the structure; the strength of the structure decreased greatly under repeatedly blasting vibration, the strength of the structure is low. The durability of structures is affected, but the structure will not collapse. The research is helpful for blasting control in open pit mines and design on structures adjacent to open pit mines.

Abstract: Strengthening concrete structure with E-glass fiber reinforced polymer (GFRP) is gaining more popularity, mainly due to their superior mechanical properties. However, there is insufficient information on environmental durability of glass fiber reinforced polymer, especially in harsh environmental conditions combined with sustained load. In this paper, the durability of an E-glass/ composite material under freeze-thaw cycle either in an unstressed state or loaded in about 30% of the initial ultimate load are investigated. The residual tensile properties of the GFRP are studied after coupled action of freeze-thaw cycle and sustained load. The results indicate that the single action of freeze-thaw cycle reduces the ultimate tensile strength and strain of the GFRP, and the coupled action of sustained load and freeze-thaw cycle further reduces the ultimate strength and strain of the GFRP.

Abstract: The cable is the main load-bearing component of suspension bridge and its safety assessment under extreme wind load is a key issue to the structure. Take a long-span suspension bridge in the East Sea China as an example, the standard of extreme wind load for structural safety evaluation is established; the wire’s strength model is established by the type I extreme value distribution; cable’s safety assessment function under wind load is established and the Monte Carlo method is used to get the cable’s reliability and reliable indicators. The bridge’s re-service term is taken for 90 years as an example, the results indicate that the wire’s serial effects can’t be ignored, the cable’s reliable indicator decreases as the number of broken wires increases in approximately the linear attenuation relations, the critical percentage of broken wires is about 10%.