Papers by Chao Jiang
Sustainability, 2020
This paper assessed the service life of RC bridges subjected to carbonation under a changing clim... more This paper assessed the service life of RC bridges subjected to carbonation under a changing climate based on time-dependent reliability analysis. First, a simplified carbonation model and the corresponding incremental method were briefly reviewed. Then, the fatigue damage prediction model and climate model were briefly introduced. Afterward, the Monte Carlo simulation-based time-dependent reliability analysis procedure for service life assessments was presented, which integrated the carbonation depth prediction model, fatigue damage prediction model and climate model. Based on the analysis procedure, a comprehensive case study was conducted to estimate the effects of climate change, fatigue damage, concrete cover thickness and concrete grade on the service life under different reliability levels. The case study showed that the service life under a reliability level of 2 is around half of that under the reliability level of 1. Under the reliability level of 1.5, the service life under RCP8.5 (a high emission scenario defined by Intergovernmental Panel on Climate Change) can be 28 years shorter than that under no climate changes. The service life at girder top undergoing compressive fatigue damage can be 49% shorter than that without fatigue damage and 25 years shorter than that at girder bottom undergoing tensile fatigue damage. The service life at girder top with a concrete cover thickness of 45 mm can reach 2.6 times that with a concrete cover thickness of 25 mm. The service life of C50 concrete can reach approximately 2-3 times that of C30 concrete. These findings inform civil engineers that for existing RC bridges, the effects of climate change and fatigue damage should be properly considered when the remaining service life of RC bridges is concerned. Moreover, for planned RC bridges, higher concrete grade and thicker concrete cover are two effective choices to achieve a longer service life.
Cement and Concrete Research, 2020
This paper models the instantaneous phase composition of cement pastes under elevated temperature... more This paper models the instantaneous phase composition of cement pastes under elevated temperatures (up to 1200 °C). First, a hydration model was introduced. Then kinetics models for dehydration of cement hydrates, including C-S-H, CH and aluminate hydrates, and evaporation of free water were proposed. Subsequently, based on the kinetics models, the thermal decomposition model for cement pastes was proposed, which could predict the solid phase, porosity and water compositions of cement pastes under arbitrary temperature history. The thermal decomposition model was then validated by multiple experiments. Finally, a parametric study was conducted to investigate the effects of heating rate on the instantaneous phase composition of cement pastes. It was found that the phase compositions of cement pastes at the same temperature differ greatly from one another among different heating rate cases. This demonstrates the needs to consider temperature histories when analyzing real-world concrete structures under fires.
Construction and Building Materials, 2018
This paper presents the theoretical modeling of carbonation in fatigue-damaged concrete. First, a... more This paper presents the theoretical modeling of carbonation in fatigue-damaged concrete. First, a residual strain-based effective carbon dioxide diffusion coefficient in fatigue-damaged concrete was proposed. Based on that, the general carbonation equations were established for concrete with uniform compres-sive, gradient compressive and gradient tensile damage patterns. Then a numerical program was written to solve the established partial differential carbonation equations. Subsequently, the numerical carbon-ation model was validated by comparing the predicted carbonation depths with experimental results. Finally, parametric studies were conducted on carbonation in commonly used concretes with various fatigue damage patterns, which separated the effects of residual strains and residual curvatures. The parametric studies showed that fatigue damage did not alter the widely accepted proportional relationships between carbonation depths and square roots of exposure durations. Moreover, the effects of exposure conditions on carbonation of concrete were far more influenced by residual strains than by residual curvatures.
Cement & Concrete Composites, 2018
This paper first introduced a numerical carbonation model (NCM) for fatigue-damaged concrete. The... more This paper first introduced a numerical carbonation model (NCM) for fatigue-damaged concrete. Then, based on the NCM, a simplified carbonation model (SCM) for fatigue-damaged concrete was established, comprised of a non-damaged concrete contribution term and a fatigue damage contribution term, through Monte Carlo simulations. Both the NCM and SCM were verified by experimental results reported in the literature. Subsequently, an incremental method was proposed to consider the time-variant fatigue damage and exposure conditions. Finally, a case study was conducted, which determined that cumulating fatigue damage could have a big influence on carbonation depth evolution. Meanwhile, differences in the cumulating fatigue damage could lead to noticeable differences in carbonation depth evolution among different points in the same concrete bridge. Moreover, drastic increases of CO 2 concentration and temperature could induce relationships of carbonation depths with square roots of service times to remarkably deviate from the proportional laws widely accepted under a time-invariant environment.
Construction and Building Materials, 2017
This paper studies the deformation evolution of concrete under high-cycle fatigue loads. First, u... more This paper studies the deformation evolution of concrete under high-cycle fatigue loads. First, uniaxial and eccentric compressive fatigue loads were exerted on prism concrete specimens to observe the mechanical properties of concrete under fatigue loading. Fatigue tests showed that elastic modulus does not always decrease, but strains always increase as loading cycles accumulate. Moreover, strains on the cross-section of each eccentrically fatigued specimen always maintain linear distributions. Based on these experimental findings, a simplified constitutive model for concrete under high-cycle fatigue loads was adopted; hence, a fatigue deformation prediction model was developed to analyze the strain and stress distributions on a cross-section under both cyclic axial forces and bending moments. The proposed model demonstrated its validity by predicting fatigue deformations in good agreement with experimental results. Finally, based on the new prediction model, a case study was conducted, which found that fatigue could pose a big influence on the long-term deformation of concrete bridges.
Cement and Concrete Research, 2017
This paper presents an experimental investigation on carbonation in fatigue-damaged concrete. Uni... more This paper presents an experimental investigation on carbonation in fatigue-damaged concrete. Uniaxial and eccentric fatigue loads were exerted on prism specimens to obtain concrete with uniform compressive, gradient compressive, and gradient tensile damage patterns. Carbonation tests were subsequently conducted on these fatigue-damaged concrete specimens. Fatigue tests showed that while elastic modulus decreased and residual strain increased with loading cycles, stresses redistributed in eccentrically fatigued specimens, but strains maintained linear distribution at all times. Carbonation tests showed that the widely accepted proportional relationships between carbonation depths and square roots of exposure durations also applied to carbonation in fatigue-damaged concrete. Also, carbonation rates evolved linearly with residual strains in concrete with low damage gradients, and a 75% increase could be observed at a residual strain of 0.002. In addition, fatigue damage with low gradients did not significantly sway the ways that relative humidity, temperature, and carbon dioxide concentration affected carbonation of concrete.
In the original paper, the simple power function used correlates carbonation rate with air permea... more In the original paper, the simple power function used correlates carbonation rate with air permeability in carbonated concrete rather than in non-carbonated concrete. However, the reported air permeability tests were conducted for non-carbonated concrete, which was not consistent with their theoretically-established function. This discussion modifies the original theoretical function through incorporation of a porosity-related term which connects air permeability in non-carbonated concrete with that in carbonated concrete. Consequently, a new analytical model to estimate carbonation resistance through air permeability in non-carbonated concrete is proposed and calibrated using experimental results reported in the original paper.
Residual strain was chosen as the damage index to identify fatigue damage states. We proposed a f... more Residual strain was chosen as the damage index to identify fatigue damage states. We proposed a formula to calculate CO 2 diffusivity in fatigue-damaged concrete beams. The general carbonation equation for fatigue-damaged concrete beams was established. The partial differential carbonation equation was solved through a Keller Box Scheme. A simplified carbonation model for fatigue-damaged concrete beams was proposed.
Conference Presentations by Chao Jiang
Concrete in realistic structures is constantly subjected to loading as well as carbon dioxide pen... more Concrete in realistic structures is constantly subjected to loading as well as carbon dioxide penetration. Previous experiments have testified the accelerating effect of tensile loading on concrete carbonation. However, present carbonation models that have considered tensile loading are regressed from their respective experiments and thus are limited to the specific experimental conditions. This paper proposes a carbonation model that factors in the effect of tensile loading based on 281 measurements of carbonation depths, which inherently considers a wide range of experimental conditions. First, a modified stress level is proposed to account for stress gradients in cross sections of concrete specimens. Then, a regressed linear expression between the carbonation depth amplification factor due to tensile loading and the modified stress level is established. Subsequently, through incorporating the linear expression into the simplified carbonation model proposed by Papadakis, a carbonation model that considers the effect of tensile loading is built. Finally, through comparison between the 281 experimental carbonation depths and model predictions, the proposed model is found to be acceptable.
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Papers by Chao Jiang
Conference Presentations by Chao Jiang