Advanced Materials Research Vols. 163-167

Abstract: Based on fractal geometry theory and surface roughness characterization technology, this paper presents the fractal characterization of nonuniform corrosion degree of corroded reinforcing steel bars. The surface profile curves of different corroded reinforcing steel bars were obtained and their fractal dimensions were calculated in order to describe the fractal characteristics. As is shown by the results, the surface profile curves of rebar have statistical fractal feature. However, fractal dimension is not sensitive to small changes in profile curves. By combining fractal dimension D with scale parameter C, characteristic profile parameter r* is derived to characterize the surface profile of corroded reinforcing steel bars sensitively, which realized the unity of multi-scale similarity measurement and absolute measurement. The results of this analysis will become the basis for corrosion damage evolution of corroded reinforcing steel bars.

Abstract: The effect of mineral admixtures and air-entraining agent on freezing-thawing and de-icing salt resistance of concrete has been studied. Concrete specimens made with ordinary Portland cement or ordinary Portland cement incorporating fly ash with the replacement of 10% or 20%, or 0.7/10000 air-entraining agent and fly ash with the replacement of 20%, or ground blast furnace slag with the replacement of 15% or 30%, were made and exposed to 500 cycles of freeze-thaw and de-icing salt environment. Concrete properties including loss of mass, relative dynamic elastic modulus, compressive strength, flexural strength and chloride ion diffusion coefficient were measured. Phase composition of samples was determined by means of x-ray diffraction (XRD). Results indicate that concrete exposed to freeze-thaw and de-icing salt environment is subjected to both physical frost action and chemical corrosion. Incorporation of mineral admixtures and air-entraining agent possesses more effect on internal deterioration, mechanical properties and permeability of concrete than on the scaling of concrete.

Abstract: Stratified rock mass has been widely existing in geotechnical engineering. With obvious transversely isotropic characteristic, stability of stratified rock mass is not only related to strength of intact rock but also to the inclination and characteristic of structure plane. The parameters of the structure plane have great impact on the stability of stratified rock mass. For the stratified rock mass is no homogenous, the homogenous model is not suitable to describe the characteristic of stratified rock mass. Then building an appropriate becomes necessary. In the present paper, Ubiquitous-joint model is introduced to describe the characteristic of rock mass, and the strength reduction method based on the Ubiquitous-joint model is proposed, which then is used to calculate the safety factor of slope, while the relationships between safety factor, strength properties of structure plane are analyzed, whose results can give guidance for the real practice.

Abstract: The resistance of hydrated cement paste (HCP) to acid attack was investigated. Three groups of blended cementitious materials were designed, binary binder A (cement and slag), ternary binder B (cement, slag and silica fume), and quaternary binder C (polymer modified ternary binder). According to a series of designed experiments, acid resistance of HCP was tested by acid consumption, mass loss and corrosion depth of specimens. In the study, ternary binder B shows superior resistance to acid attack. The advantage of polymer modification is unobvious. Furthermore, the variability of acid corrosion depth d with time t was analyzed specially for the foundation of degradation model. Kinetics equation of acid corrosion was established in form of d=K•tn to predict HCP corrosion depth at specific age, which provides available references for durability analysis and engineering design of concrete structures.

Abstract: The reinforcement in concrete alters the pathway for chloride transporting and in turn causes the chloride concentration to accumulate faster near the reinforcement closest to the exposed surface. A mass conservation matrix equation under the non-stable diffusion based on the Fick’s second law was derived. Hereby, a numerical simulation method for predicting chloride concentration in concrete was established utilizing the compiled module based on FEA. The validity of the method was verified by the comparison with the analytical results. The proposed method has a wider applicability for predicting the service life of RC structures. And it can be applied flexibly to any complicated section shape of RC members with multi-boundary attacked by chloride and the reinforcement considered simultaneously.

Abstract: In order to evaluate and predict the behaviors of concrete structures under the environmental conditions, such as temperature, chloride invasion and earthquake effectively, a new experimental method is presented which can evaluate the field performance of reinforced concrete (RC) structures by measuring the structure in the artificial accelerated environment. The method establishes the similarity-relationship of performance changing between the field and the accelerated environmental conditions by contrasting and analyzing the behaviors changing under both environments, and realizes the effective and exact estimate to the field structures from the indoor accelerated experiments. It brings forward a new way of thinking to test the RC structures under the environmental conditions. We explain the implemental process of the design by taking the experimental design of multi-environment time similarity methodology on RC structures under the chloride invasion as an example.

Abstract: In this paper, the corrosion specimens are obtained by ways of constant temperature and humidity ,and the size of corrosion pits is detected by roughness tester. So surface characterization of steel corrosion is researched by fractal theory and it has been proved by structure function that it has the fractal character. It find that the fractal dimension is inherent and it will not change with the sample length. The result indicates that the fractal dimension is decreasing with the corrosion rate increasing. so it will help to solve the difficult of safety assessment for In-service steel structure.

Abstract: Based on time-dependent reliability theory, intermediate working state is considered, combining with current specifications, concrete filled steel tubular (CFST) arch bridge is discussed as a case, determination principle of three-stage mode is given. The direct correspondence from reliability indices to working states is made clear consequently. Introducing state variables, dynamic Monte-carlo method is presented. Basic formulas of failure probability and damage probability are derived by variable time increment method. The bridge is an CFST arch bridge with 83.6 meter-span, which operated for 10 years. According to test result, dynamic Monte-carlo method is used to estimate the reliability of this bridge. The analysis result shows that, in the tenth year, both damage reliability index and failure reliability index are above target reliability index. The example bridge is in safe working state at present. This conclusion is consistent with the facts.

Abstract: Durability and stress injury of concrete bridge were increasingly prominent on the bridge structure now, the use and safety performances of bridge have been significantly affected. "Applicable and durable configuration" can effectively solve these problems, "applicable and durable" include durability, mechanical properties, enforceability and economy. Impact factors of applicable and durable configuration structural include environmental, vehicle load and material. Combined with the meaning and impact factors of applicable and durable configuration, the proportion of main configurations in whole configurations of concrete bridge and the weight of various factors were identified, and the contents and methods of applicable and durable configuration were determined, which laid the foundation for study of applicable and durable configurations of concrete bridge.

Abstract: The diffusion performance of chloride ion in concrete under the coupling action of dynamic load and environment was researched by a new set of experimental system. The experiment are composed of study of saturated performance of concrete, diffusion performance of chloride ion with different water binder ratio and under coupling action of dynamic load and temperature. The results show that the transport mechanism of chloride ion in concrete accounted with diffusion theory due to the 99% of saturation degree of concrete; the diffusion coefficient of chloride ion is decreased with the increasing water binder ratio, but is increased with temperature increase; and the diffusion coefficient of chloride ion is changed with cycle number.