On Probability Distribution of Chloride Diffusion Coefficient for Recycled Aggregate Concrete

Jingwei Ying,Jianzhuang Xiao,Qiujiang Meng 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.1

In predicating the probability distribution of chloride diffusion coefficient of recycled aggregate concrete (DRAC), the morphological characteristics of three phases, i.e., the old attached mortar, the natural aggregate and the new mortar, should all be taken into account. The present paper attempts to develop a probability density evolution method (PDEM) to achieve this. After verifying the derived PDEM results with experimental results, the effects of old attached mortar to the DRAC are examined in a quantitative manner. It is found that (1) the variation of the attached mortar content is much sensitive to DRAC; (2) given the probability distribution of the content and chloride diffusion coefficient of old mortar, the probability distribution of DRAC can be analysed based on the PDEM; and (3) the critical chloride diffusion coefficient at a certain assurance rate can be obtained by the PDEM. The analysis results of this investigation will be valuable to the durability design for RAC.

Seismic Analysis on Recycled Aggregate Concrete Frame Considering Strain Rate Effect

Changqing Wang,Jianzhuang Xiao,Zhenping Sun 한국콘크리트학회 2016 International Journal of Concrete Structures and M Vol.10 No.3

The nonlinear behaviors of recycled aggregate concrete (RAC) frame structure are investigated by numerical simulation method with 3-D finite fiber elements. The dynamic characteristics and the seismic performance of the RAC frame structure are analyzed and validated with the shaking table test results. Specifically, the natural frequency and the typical responses (e.g., storey deformation, capacity curve, etc.) from Model 1 (exclusion of strain rate effect) and Model 2 (inclusion of strain rate effect) are analyzed and compared. It is revealed that Model 2 is more likely to provide a better match between the numerical simulation and the shaking table test as key attributes of seismic behaviors of the frame structure are captured by this model. For the purpose to examine how seismic behaviors of the RAC frame structure vary under different strain rates in a real seismic situation, a numerical simulation is performed by varying the strain rate. The storey displacement response and the base shear for the RAC frame structure under different strain rates are investigated and analyzed. It is implied that the structural behavior of the RAC frame structure is significantly influenced by the strain rate effect. On one hand, the storey displacements vary slightly in the trend of decreasing with the increasing strain rate. On the other hand, the base shear of the RAC frame structure under dynamic loading conditions increases with gradually increasing amplitude of the strain rate.

Analysis on the dynamic characteristics of RAC frame structures

Changqing Wang,Jianzhuang Xiao 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.4

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

Seismic Analysis on Recycled Aggregate Concrete Frame Considering Strain Rate Effect

Wang, Changqing,Xiao, Jianzhuang,Sun, Zhenping Korea Concrete Institute 2016 International Journal of Concrete Structures and M Vol.10 No.3

The nonlinear behaviors of recycled aggregate concrete (RAC) frame structure are investigated by numerical simulation method with 3-D finite fiber elements. The dynamic characteristics and the seismic performance of the RAC frame structure are analyzed and validated with the shaking table test results. Specifically, the natural frequency and the typical responses (e.g., storey deformation, capacity curve, etc.) from Model 1 (exclusion of strain rate effect) and Model 2 (inclusion of strain rate effect) are analyzed and compared. It is revealed that Model 2 is more likely to provide a better match between the numerical simulation and the shaking table test as key attributes of seismic behaviors of the frame structure are captured by this model. For the purpose to examine how seismic behaviors of the RAC frame structure vary under different strain rates in a real seismic situation, a numerical simulation is performed by varying the strain rate. The storey displacement response and the base shear for the RAC frame structure under different strain rates are investigated and analyzed. It is implied that the structural behavior of the RAC frame structure is significantly influenced by the strain rate effect. On one hand, the storey displacements vary slightly in the trend of decreasing with the increasing strain rate. On the other hand, the base shear of the RAC frame structure under dynamic loading conditions increases with gradually increasing amplitude of the strain rate.

Simulation study on dynamic response of precast frames made of recycled aggregate concrete

ThiLoan Pham,Jianzhuang Xiao,Tao Ding 사단법인 한국계산역학회 2015 Computers and Concrete, An International Journal Vol.16 No.4

3-dimentional precast recycled aggregate concrete (RAC) finite element models were developed by means of the platform OpenSees to implement sophisticated nonlinear model subjected to seismic loads. Efforts were devoted to the dynamic responses (including dynamic characteristics, acceleration amplifications, displacements, story drifts) and capacity curve. In addition, this study extended the prediction on dynamic response of precast RAC model by parametric study of material properties that represent the replacement percentage of recycled coarse aggregate (RCA). Principles and assumptions that represent characteristics of precast structure and influence of the interface between head of column and cast-in-place (CIP) joint on the stiffness of the joints was put forward and validated by test results. The comparison between simulated and tested results of the precast RAC frame shows a good correlation with most of the relative errors about 25% in general. Therefore, the adopted assumptions and the platform OpenSees are a viable approach to simulate the dynamic response of precast frames made of RAC.

Analysis of the dynamic confining effect of CRAC short column under monotonic loadings

Changqing Wang,Jianzhuang Xiao 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.3

Based on the dynamic tests of recycled aggregate concrete (RAC) short columns confined by the hoop reinforcement, the dynamic failure mechanism and the mechanical parameters related to the constitutive relation of confined recycled aggregate concrete (CRAC) were investigated thoroughly. The fracturing sections were relatively flat and smooth at higher strain rates rather than those at a quasi-static strain rate. With the increasing stirrup volume ratio, the crack mode is transited from splitting crack to slipping crack constrained with large transverse confinement. The compressive peak stress, peak strain, and ultimate strain increase with the increase of stirrup volume ratio, as well as the increasing strain rate. The dynamic confining increase factors of the compressive peak stress, peak strain, and ultimate strain increase by about 33%, 39%, and 103% when the volume ratio of hoop reinforcement is increased from 0 to 2%, but decrease by about 3.7%, 4.2%, and 9.1% when the stirrup spacing is increased from 20mm to 60mm, respectively. This sentence is rephrased as follows: When the stirrup volume ratios are up to 0.675%, and 2%, the contributions of the hoop confinement effect to the dynamic confining increase factors of the compressive peak strain and the compressive peak stress are greater than those of the strain rate effect, respectively. The dynamic confining increase factor (DCIF) models of the compressive peak stress, peak strain, and ultimate strain of CRAC are proposed in the paper. Through the confinement of the hoop reinforcement, the ductility of RAC, which is generally slightly lower than that of NAC, is significantly improved.

Electrochemical and microscopic analysis on corrosion behavior of steel bars in slag/fly ash-cement paste subjected to seawater attack

Zou Shuai,Zuo Xiao-Nao,Li Xinagnan,Xiao Jianzhuang 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.2

A series of corrosion experiments of cement paste-steel bar specimens with different contents of slag and fly ash were performed to investigate the influence of slag/fly ash on the corrosion behavior of steel bars in concrete under seawater. In this investigation, the corrosion behavior of specimen was electrochemically monitored by open-circuit potential (OCP), Tafel polarization (TP) and electrochemical impedance spectra (EIS). Meanwhile, SEM/EDS and XRD were applied to microscopically analyze the microstructure deterioration of materials. Results showed that, replacing cement with slag/fly ash caused a decrease in Ca(OH)2 as well as an increase in C-S-H gel and Friedel's salt in concrete, which can improve the chloride-solidification ability and slow down the chloride diffusion in concrete by both physical adsorption and chemical binding, and thereafter promoting the corrosion resistance of steel bars in concrete in marine environment. Compared to slag, the equal replacing content of fly ash can contribute to a better improving effect on the corrosion resistance of reinforced concrete in marine environment. In this study, a replacement of cement by 20% slag+20% fly ash led to an optimum improving effect on its corrosion resistance. In addition, the results also indicate that the corrosion of reinforced concrete caused by seawater attack does not occur at a uniform rate, but it can firstly maintain a long-term uncorroded state, and then develops rapidly after pitting corrosion occurs.