The experimental results which were carried out by different researchers on corrosion of RCC beam were validated in ABAQUS. A finite element (FE) model similar to experimental condition was generated in ABAQUS. The mo...The experimental results which were carried out by different researchers on corrosion of RCC beam were validated in ABAQUS. A finite element (FE) model similar to experimental condition was generated in ABAQUS. The model with different percentages of corrosion and with varying load conditions was also generated. The deflections of RCC beam for different corrosion percentages and for varying load conditions were then validated. The model is then used to explore the effects of bar radial expansion, due to formation of corrosion products, on the cracking of cover concrete. The predictions are compared with tests results from reinforced concrete accelerated corrosion specimens. The aim of the analytical investigation was to reveal the mechanism for the development of concrete cracking due to corrosion of reinforcement. Further the finite element model will be used to explain qualitatively the experimentally determined relationship between amount of corrosion for concrete cracking and ratio of concrete cover to bar diameter, as well as that between reinforcement bond strength and amount of corrosion.展开更多
The paper investigates the long-term seismic behaviour of an underground reinforced concrete(RC)metro tunnel in Santiago,Chile,considering the combined effects of chloride-induced corrosion and cumulative,low-amplitud...The paper investigates the long-term seismic behaviour of an underground reinforced concrete(RC)metro tunnel in Santiago,Chile,considering the combined effects of chloride-induced corrosion and cumulative,low-amplitude seismic shaking on the structure’s performance.The soil-tunnel response is evaluated with the aid of transient,nonlinear finite element analysis using a two-dimensional(2D)plane strain numerical model that adopts advanced nonlinear models for the simulation of soil and concrete plasticity and the dynamic stiffness behaviour.The effects of corrosion deterioration are demonstrated in terms of time-dependent loss of rebar area and cover concrete stiffness and strength.The study illustrates the influence of ageing and repeated seismic shaking on lining deformation,crack development,and the modal characteristics of the intact and degrading systems.The results indicate that multiple lowamplitude events drive the non-degrading RC tunnel beyond its elastic regime without significant structural response consequences.A noticeable impact of corrosion deterioration on the structure’s seismic performance is revealed,increasing with the number and intensity of earthquake events.Two different tunnel embedment depths are comparatively assessed.The analyses demonstrate larger coseismic section convergence in the case of the deeper tunnel,yet a less pronounced effect of ageing and successive seismic loading compared to the shallow section,which is evident in the RC lining cracks at the end of shaking.展开更多
We investigated the simulation of the cracking and ablation behavior of ferro-siliceous and siliceous nuclear sacrificial concretes. To this end, four type of sacrificial concretes were fabricated, i e, the ferro-sili...We investigated the simulation of the cracking and ablation behavior of ferro-siliceous and siliceous nuclear sacrificial concretes. To this end, four type of sacrificial concretes were fabricated, i e, the ferro-siliceous(F) and siliceous(S) plain concretes, and the polypropylene fiber reinforced concretes of the above two(FF, SF). The cracking and ablation behaviors of the sacrificial concretes were investigated by simulation tests, and the simulated elevated temperature was obtained by means of thermite powder. The number and the width of the cracks were compared and the pore size distribution of sacrificial concretes was measured. In addition, the interface and chemical composition of melt at different positions were analyzed, and the ablation depth of the sacrificial concrete crucibles was also measured. It was found that the siliceous concrete shows to be more prone to cracking than the ferro-siliceous concrete due to the higher content of fly ash and lower water to binder ratio; though the ablation depth of siliceous concrete is found to be slightly larger, no clear difference can be detected for the basemat ablation rate.展开更多
The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship betw...The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.展开更多
Self-deformation cracking is the cracking caused by thermal deformation, autogenous volume deformation or shrinkage deformation. In this paper, an extended finite element calculation method was deduced for concrete cr...Self-deformation cracking is the cracking caused by thermal deformation, autogenous volume deformation or shrinkage deformation. In this paper, an extended finite element calculation method was deduced for concrete crack propagation under a constant hydration and hardening condition during the construction period, and a corresponding programming code was developed. The experimental investigation shows that initial crack propagation caused by self-deformation loads can be analyzed by this program. This improved algorithm was a preliminary application of the XFEM to the problem of the concrete self-deformation cracking during the hydration and hardening period. However, room for improvement exists for this algorithm in terms of matching calculation programs with mass concrete temperature fields containing cooling pipes and the influence of creep or damage on crack propagation.展开更多
With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prev...With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prevention and repair of surface cracks,the reinforcement and grouting of structural cracks,and the design and construction of controlled cracks through the analysis of the causes and classification of concrete cracks.The methods and suggestions proposed in this paper are practical and can improve the quality and safety of buildings.展开更多
The assessment for bearing capacity of corroded RC members is one of the main component of durability study on RC structure. But few researches had been developed for the study of corroded RC eccentric especially litt...The assessment for bearing capacity of corroded RC members is one of the main component of durability study on RC structure. But few researches had been developed for the study of corroded RC eccentric especially little eccentric compressive members. By discussing the effect of factors, such as decrease of concrete strength in biaxial stress condition during pre-cracking stage and torsion buckling of local cracking concrete during post-cracking stage, on the bearing capacity of little eccentric RC members, the model of bearing capacity is established respectively, which the cracking damage coefficient of concrete k is suggested to be 0.15 in post-cracking stage. The experimental certification shows: model calculation fits well with experimental result, which proves the effectiveness of the model in this paper.展开更多
With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter o...With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.展开更多
In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete(PCC) and fly ash concrete(FAC), were tested wi...In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete(PCC) and fly ash concrete(FAC), were tested with various crack widths. Total 14 reinforced concrete(RC) beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing(RCT) method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors kf and kw can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.展开更多
The present paper concerns the fracture characteristics and ductility of cracked concrete beam externally bonded with carbon fiber-reinforced polymer (CFRP) sheet as well as the integration behaviors between CFRP/conc...The present paper concerns the fracture characteristics and ductility of cracked concrete beam externally bonded with carbon fiber-reinforced polymer (CFRP) sheet as well as the integration behaviors between CFRP/concrete interfacial debonding and concrete cracking.Three-point bending tests were carried out on the CFRP-strengthened cracked concrete beams with varying specimen depth and initial crack length.A straingauge method was developed to monitor the crack initiation and propagation in concrete,and the CFRP/concrete interfacial bonding behaviors,respectively.Clip gauges were used to measure crack mouth opening displacement (CMOD) and the deflection at midspan.Experimental results revealed that CFRP-strengthened specimen shows a higher load capacity under the same deformation level and a better inelastic deformation capacity compared with the unstrengthened one.For there are two manifest peak values in the obtained load versus displacement curve,the ductility of CFRP-strengthened concrete beams were investigated using index expressed as area ratio on the load versus displacement curve.The calculated results indicated that the contribution from CFRP sheet to the ductility improvement of specimen is notable when the deflection at midspan exceeded 10.5 times the first-crack deflection.展开更多
Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance meth...Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance methods, respectively. The results show the highest resistivity of C30 at the early stage until a point when C50 accelerated and overtook the others. It has been experimentally confirmed that the crossing point of C30 and C50 corresponds to the final setting time of C50. From resistivity derivative curve, four different stages were observed upon which the hydration process is classified; these are dissolution, induction, acceleration and deceleration periods. Consequently, restrained shrinkage crack and setting time results demonstrated that C50 set and cracked the earliest. The cracking time of all the samples occurred within a reasonable experimental period thus the novel plastic ring is a convenient method for predicting concrete's crack potential. The highest inflection time(t_i) obtained from resistivity curve and the final setting time(t_f) were used with crack time(t_c) in coming up with mathematical models for the prediction of concrete's cracking age for the range of concrete grade considered. Finally, an ANSYS numerical simulation supports the experimental findings in terms of the earliest crack age of C50 and the crack location.展开更多
Microbiologically⁃induced calcite⁃precipitation(MICP)has been increasingly studied in structural repair including self⁃healing and external applications.Among various MICP pathways,enzymatic urea hydrolysis is suggest...Microbiologically⁃induced calcite⁃precipitation(MICP)has been increasingly studied in structural repair including self⁃healing and external applications.Among various MICP pathways,enzymatic urea hydrolysis is suggested to be applied as external repair instead of self⁃healing.This study comprehensively characterised the enzymatic urea hydrolysis pathway in physical,impermeable,and mechanical rejuvenation of concrete cracks.The visual quality of repaired structures was presented,and the importance of humidity in the remediation of cracks was demonstrated.Moreover,this study investigated the differences in the effectiveness of repair between premixing bacteria with urea and without any premixing.With premixing,there was a concern that the accelerated reactions would precipitate calcite in the shallow spaces of the cracks and impede deeper healing.However,the observed results indicated that neither physical nor impermeable rejuvenation of concrete cracks repair would be detrimentally affected.The results obtained from this study will allow further development in commercialisation since the effectiveness of repair has been confirmed with an improvement in its efficiency.展开更多
To evaluate the effect of pulse parameters on the formation of electrodeposits in concrete cracks, five different types of pulse current were set up, and ZnSO_4 and MgSO_4 solutions were used as the electrolytes. The ...To evaluate the effect of pulse parameters on the formation of electrodeposits in concrete cracks, five different types of pulse current were set up, and ZnSO_4 and MgSO_4 solutions were used as the electrolytes. The rate of weight gain, rate of surface coating, rate of crack closure and crack filling depth were measured. Scanning electron microscopy was used to assess the morphology of the electrodeposits, and energy dispersive spectroscopy was used to analyze the mineral composition of the electrodeposits in the cracks. The experimental results demonstrate that, among five different pulse parameters, when T_(on)/T_(off)=0.8 ms/0.8 ms, the healing effect of electro-deposition is the best. The pulse mode hardly affects the mineral composition of the electrodeposits but changes the micromorphology. In addition, for both ZnSO_4 and MgSO_4 solutions, when T_(on)/T_(off)=0.8 ms/0.8 ms, the crystal structure of the electrodeposits is the most uniform and the densest.展开更多
To solve the problem that the digital image recognition accuracy of concrete structure cracks is not high under the condition of uneven ill umination and complex surface color of concrete structure,this paper has prop...To solve the problem that the digital image recognition accuracy of concrete structure cracks is not high under the condition of uneven ill umination and complex surface color of concrete structure,this paper has proposed a block segmentation method of maximum entropy threshold based on the digital image data obtained by the ACTIS automatic detection system.The steps in this research are as follows:1.The crack digital images of concrete specimens with typical fea-tures were collected by using the Actis system of KURABO Co,Ltd,of Japan in the concrete beam bending test.2.The images are segmented into blocks to dis-tinguish backgrounds of different grayscale.3.The max imum interclass average gray difference method is used to distinguish the sub-blocks and screen out the image blocks that need to be segmented.4.Segmentation is made to the image with 2D max imum entropy threshold segmentation method to obtain the binary image,and the target image can be obtained by screening the connected domain features of the binary image.Results have shown that compared with other algo-rithms,the proposed method can effectively decrease the image over-segmentation and under segmentation rates,highlight the characteristics of the target cracks,solve the problems of excessive difference between the identified length and actual length of cracks caused by background gray level change and uneven ilumnination,and effectively improve the recognition accuracy of bridge concrete cracks.展开更多
The early age performance of spread footing, especially the growth of cracks, is deeply influenced by the heat of hydration of cement. In this paper, 3D finite element method(FEM)models are set up to analyze the tempe...The early age performance of spread footing, especially the growth of cracks, is deeply influenced by the heat of hydration of cement. In this paper, 3D finite element method(FEM)models are set up to analyze the temperature distribution and thermal stresses of the spread footing during the first seven days after concrete placement. The mechanical properties of early age concrete are calculated, which are further used in the FEM models. The possibilities of crack growth are estimated by the method of crack index. The crack indexes of quite a number of points are very close to the allowable limit of 1.0 during the last three days. It is also indicated that the influence of foundation ring on the thermal stresses of concrete can be neglected.展开更多
In Greece extended cracking of twin-block concrete sleepers (ties) and fouling of the ballast-bed were observed with implied problems of gauge widening and deterioration of track's geometry. This led to a ten-year ...In Greece extended cracking of twin-block concrete sleepers (ties) and fouling of the ballast-bed were observed with implied problems of gauge widening and deterioration of track's geometry. This led to a ten-year investigation program, during which a new method was developed for the estimation of actions on track panel as well as of the pressures / stresses that develop under the seating surface of the sleeper on the ballast-bed. Results from the tests performed on the ballast used in the Greek network are also presented, conducted in laboratories in France, Austria, and Greece. The influence of the actions -static and mainly dynamic- on the track response and the stress and strain of the ballast-bed are also discussed as derived from the tests and theoretical analysis.展开更多
Liquid migrating into existing concrete cracks is a serious problem for the reliability of concrete structures and can sometimes induce full concrete structural failures.In this paper,the authors present recent resear...Liquid migrating into existing concrete cracks is a serious problem for the reliability of concrete structures and can sometimes induce full concrete structural failures.In this paper,the authors present recent research on water presence detection in concrete cracks using piezoceramic-based smart aggregate(SA)transducers.The active sensing approach,in which one piezoceramic transducer is used to generate stress waves and others are used to detect the stress wave responses,is adopted in this research.Cracks formed in concrete structures act as stress reliefs,which attenuate the energy of the signals received by the SAs.In case of a crack being filled with liquid,which changes the wave impedance,the piezoceramic transducers will report higher received energy levels.A wavelet packet-based approach is developed to provide calculated energy values of the received signal.These different values can help detect the liquid presence in a concrete crack.A concrete beam specimen with three embedded SAs was fabricated and tested.Experimental results verified that the SA-based active sensing approach can detect a concrete crack and further detect the liquid presence in the concrete crack.展开更多
A method of the fuzzy cross-correlation factor exponent in dynamics is researched and proposed to diagnose abnormality of cracks in the concrete dam. Moreover, the Logistic time series changing from period-doubling bi...A method of the fuzzy cross-correlation factor exponent in dynamics is researched and proposed to diagnose abnormality of cracks in the concrete dam. Moreover, the Logistic time series changing from period-doubling bifurcation to chaos is tested first using this method. Results indicate that it can distinguish inherent dynamics of time series and can detect mutations. Considering that cracks in the concrete dam constitute an open, dissipative and complex nonlinear dynamical system, a typical crack on the downstream face of a concrete gravity arch dam is analyzed with the proposed method. Two distinct mutations are discovered to indicate that the abnormality diagnosis of cracks in the concrete dam is achieved dynamically through this method. Furthermore, because it can be directly utilized in the measured crack opening displacement series to complete abnormality diagnosis, it has a good prospect for practical applications.展开更多
Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult ...Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult task.To address such inspection and maintenance issues,this study presents a computer-vision-guided semi-autonomous robotic system for identification and repair of concrete cracks,and humans can make repair plans for this system.Concrete cracks are characterized through computer vision,and a crack feature database is established.Furthermore,a trajectory generation and coordinate transformation method is designed to determine the robotic execution coordinates.In addition,a knowledge base repair method is examined to make appropriate decisions on repair technology for concrete cracks,and a robotic arm is designed for crack repair.Finally,simulations and experiments are conducted,proving the feasibility of the repair method proposed.The result of this study can potentially improve the performance of on-site automatic concrete crack repair,while addressing such issues as high accident rate,low efficiency,and big loss of skilled workers.展开更多
文摘The experimental results which were carried out by different researchers on corrosion of RCC beam were validated in ABAQUS. A finite element (FE) model similar to experimental condition was generated in ABAQUS. The model with different percentages of corrosion and with varying load conditions was also generated. The deflections of RCC beam for different corrosion percentages and for varying load conditions were then validated. The model is then used to explore the effects of bar radial expansion, due to formation of corrosion products, on the cracking of cover concrete. The predictions are compared with tests results from reinforced concrete accelerated corrosion specimens. The aim of the analytical investigation was to reveal the mechanism for the development of concrete cracking due to corrosion of reinforcement. Further the finite element model will be used to explain qualitatively the experimentally determined relationship between amount of corrosion for concrete cracking and ratio of concrete cover to bar diameter, as well as that between reinforcement bond strength and amount of corrosion.
基金supported by the Newton Fund:EPSRC,UK&CONICYT,Chile(EPSRC Grant No.EP/N03435X/1)the Extending Shaking Tunnel Vision project funded jointly by the Global Challenge Research Fund(GCRF)and the Higher Education Funding Council for England(HEFCE)under account number 95541229,both led by the University of Leeds.
文摘The paper investigates the long-term seismic behaviour of an underground reinforced concrete(RC)metro tunnel in Santiago,Chile,considering the combined effects of chloride-induced corrosion and cumulative,low-amplitude seismic shaking on the structure’s performance.The soil-tunnel response is evaluated with the aid of transient,nonlinear finite element analysis using a two-dimensional(2D)plane strain numerical model that adopts advanced nonlinear models for the simulation of soil and concrete plasticity and the dynamic stiffness behaviour.The effects of corrosion deterioration are demonstrated in terms of time-dependent loss of rebar area and cover concrete stiffness and strength.The study illustrates the influence of ageing and repeated seismic shaking on lining deformation,crack development,and the modal characteristics of the intact and degrading systems.The results indicate that multiple lowamplitude events drive the non-degrading RC tunnel beyond its elastic regime without significant structural response consequences.A noticeable impact of corrosion deterioration on the structure’s seismic performance is revealed,increasing with the number and intensity of earthquake events.Two different tunnel embedment depths are comparatively assessed.The analyses demonstrate larger coseismic section convergence in the case of the deeper tunnel,yet a less pronounced effect of ageing and successive seismic loading compared to the shallow section,which is evident in the RC lining cracks at the end of shaking.
基金Funded by National Natural Science Foundation of China(Nos.51378114 and 5161113020)National Basic Research Program of China(973 Program)(No.2015CB655105)
文摘We investigated the simulation of the cracking and ablation behavior of ferro-siliceous and siliceous nuclear sacrificial concretes. To this end, four type of sacrificial concretes were fabricated, i e, the ferro-siliceous(F) and siliceous(S) plain concretes, and the polypropylene fiber reinforced concretes of the above two(FF, SF). The cracking and ablation behaviors of the sacrificial concretes were investigated by simulation tests, and the simulated elevated temperature was obtained by means of thermite powder. The number and the width of the cracks were compared and the pore size distribution of sacrificial concretes was measured. In addition, the interface and chemical composition of melt at different positions were analyzed, and the ablation depth of the sacrificial concrete crucibles was also measured. It was found that the siliceous concrete shows to be more prone to cracking than the ferro-siliceous concrete due to the higher content of fly ash and lower water to binder ratio; though the ablation depth of siliceous concrete is found to be slightly larger, no clear difference can be detected for the basemat ablation rate.
基金Project(51078090)supported by the National Natural Science Foundation of China
文摘The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.
基金Funded by the National Natural Science Foundation of China(Nos.51409264,51509020,51209219)Zhejiang Provincial Natural Science Foundation(No.LQ15E090003)
文摘Self-deformation cracking is the cracking caused by thermal deformation, autogenous volume deformation or shrinkage deformation. In this paper, an extended finite element calculation method was deduced for concrete crack propagation under a constant hydration and hardening condition during the construction period, and a corresponding programming code was developed. The experimental investigation shows that initial crack propagation caused by self-deformation loads can be analyzed by this program. This improved algorithm was a preliminary application of the XFEM to the problem of the concrete self-deformation cracking during the hydration and hardening period. However, room for improvement exists for this algorithm in terms of matching calculation programs with mass concrete temperature fields containing cooling pipes and the influence of creep or damage on crack propagation.
文摘With the continuous development of civil engineering,concrete crack treatment technology has become an important research field.This paper proposes treatment techniques for different types of cracks,including the prevention and repair of surface cracks,the reinforcement and grouting of structural cracks,and the design and construction of controlled cracks through the analysis of the causes and classification of concrete cracks.The methods and suggestions proposed in this paper are practical and can improve the quality and safety of buildings.
基金Funded by the National Natural Science Foundation of China (No. 50278039 and 50538070)
文摘The assessment for bearing capacity of corroded RC members is one of the main component of durability study on RC structure. But few researches had been developed for the study of corroded RC eccentric especially little eccentric compressive members. By discussing the effect of factors, such as decrease of concrete strength in biaxial stress condition during pre-cracking stage and torsion buckling of local cracking concrete during post-cracking stage, on the bearing capacity of little eccentric RC members, the model of bearing capacity is established respectively, which the cracking damage coefficient of concrete k is suggested to be 0.15 in post-cracking stage. The experimental certification shows: model calculation fits well with experimental result, which proves the effectiveness of the model in this paper.
基金National Natural Science Foundation of China (No.50679009)Foundations for Young Teachers in Dalian University of Technology(No.893219)
文摘With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project.
基金Projects(50908103,51278230,51378241)supported by the National Natural Science Foundation of ChinaProject(2012M511215)supported by China Postdoctoral Science Foundation+2 种基金Project(11JDG132)supported by the High-grade Talent Program of Jiangsu University,ChinaProject(2011CEM010)supported by State Key Laboratory Foundation of High Performance Civil Engineering Material,ChinaProject(20123227110006)supported by Doctoral Foundation of Ministry of Education of China
文摘In order to examine the effect of load-induced transverse cracks on the chloride penetration in flexural concrete beams, two different concretes, Portland cement concrete(PCC) and fly ash concrete(FAC), were tested with various crack widths. Total 14 reinforced concrete(RC) beams, ten of which were self-anchored in a three-point bending mode, were immersed into a 5% NaCl solution with the condition of dry-wet cycles. Then, the free chloride ion contents were determined by rapid chloride testing(RCT) method. Based on the proposed analytical models of chloride penetration in sound and cracked concrete subjected to dry-wet cycles, the apparent chloride diffusion coefficient and chloride diffusivity of concrete were discussed. It can be found that the performance of chloride diffusivity in both concretes will be improved with the increase of crack width, and that the influence of convection action will also be augmented. Based on the two samples obtained in sound concrete after 15 and 30 cycles, the time-exponent, m, for chloride diffusion coefficient was determined to be 0.58, 0.42, 0.62 and 0.77 for PCC1, PCC2, FAC1 and FAC2 specimens, respectively. Finally, two influencing factors of fly ash content and crack width on chloride diffusivity were obtained by regression analysis of test data, and it can be seen that factors kf and kw can be expressed with quadratic polynomial functions of fly ash content, f, and crack width, w, respectively.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50578025)the National Key Project of Science and Technology (Grant No. 2006BAJ03A03-09)
文摘The present paper concerns the fracture characteristics and ductility of cracked concrete beam externally bonded with carbon fiber-reinforced polymer (CFRP) sheet as well as the integration behaviors between CFRP/concrete interfacial debonding and concrete cracking.Three-point bending tests were carried out on the CFRP-strengthened cracked concrete beams with varying specimen depth and initial crack length.A straingauge method was developed to monitor the crack initiation and propagation in concrete,and the CFRP/concrete interfacial bonding behaviors,respectively.Clip gauges were used to measure crack mouth opening displacement (CMOD) and the deflection at midspan.Experimental results revealed that CFRP-strengthened specimen shows a higher load capacity under the same deformation level and a better inelastic deformation capacity compared with the unstrengthened one.For there are two manifest peak values in the obtained load versus displacement curve,the ductility of CFRP-strengthened concrete beams were investigated using index expressed as area ratio on the load versus displacement curve.The calculated results indicated that the contribution from CFRP sheet to the ductility improvement of specimen is notable when the deflection at midspan exceeded 10.5 times the first-crack deflection.
基金Funded by National Natural Science Foundation of China(Nos.51478200 and 51178202)
文摘Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance methods, respectively. The results show the highest resistivity of C30 at the early stage until a point when C50 accelerated and overtook the others. It has been experimentally confirmed that the crossing point of C30 and C50 corresponds to the final setting time of C50. From resistivity derivative curve, four different stages were observed upon which the hydration process is classified; these are dissolution, induction, acceleration and deceleration periods. Consequently, restrained shrinkage crack and setting time results demonstrated that C50 set and cracked the earliest. The cracking time of all the samples occurred within a reasonable experimental period thus the novel plastic ring is a convenient method for predicting concrete's crack potential. The highest inflection time(t_i) obtained from resistivity curve and the final setting time(t_f) were used with crack time(t_c) in coming up with mathematical models for the prediction of concrete's cracking age for the range of concrete grade considered. Finally, an ANSYS numerical simulation supports the experimental findings in terms of the earliest crack age of C50 and the crack location.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51278157).
文摘Microbiologically⁃induced calcite⁃precipitation(MICP)has been increasingly studied in structural repair including self⁃healing and external applications.Among various MICP pathways,enzymatic urea hydrolysis is suggested to be applied as external repair instead of self⁃healing.This study comprehensively characterised the enzymatic urea hydrolysis pathway in physical,impermeable,and mechanical rejuvenation of concrete cracks.The visual quality of repaired structures was presented,and the importance of humidity in the remediation of cracks was demonstrated.Moreover,this study investigated the differences in the effectiveness of repair between premixing bacteria with urea and without any premixing.With premixing,there was a concern that the accelerated reactions would precipitate calcite in the shallow spaces of the cracks and impede deeper healing.However,the observed results indicated that neither physical nor impermeable rejuvenation of concrete cracks repair would be detrimentally affected.The results obtained from this study will allow further development in commercialisation since the effectiveness of repair has been confirmed with an improvement in its efficiency.
基金the National Natural Science Foundation(Nos.51479051,51778209,51609075,and 51508158)the Fundamental Research Funds for the Central Universities(2016B08414)the National Key R&D Program of China(Nos.2016YFC0401610 and2016YFC0401804)
文摘To evaluate the effect of pulse parameters on the formation of electrodeposits in concrete cracks, five different types of pulse current were set up, and ZnSO_4 and MgSO_4 solutions were used as the electrolytes. The rate of weight gain, rate of surface coating, rate of crack closure and crack filling depth were measured. Scanning electron microscopy was used to assess the morphology of the electrodeposits, and energy dispersive spectroscopy was used to analyze the mineral composition of the electrodeposits in the cracks. The experimental results demonstrate that, among five different pulse parameters, when T_(on)/T_(off)=0.8 ms/0.8 ms, the healing effect of electro-deposition is the best. The pulse mode hardly affects the mineral composition of the electrodeposits but changes the micromorphology. In addition, for both ZnSO_4 and MgSO_4 solutions, when T_(on)/T_(off)=0.8 ms/0.8 ms, the crystal structure of the electrodeposits is the most uniform and the densest.
文摘To solve the problem that the digital image recognition accuracy of concrete structure cracks is not high under the condition of uneven ill umination and complex surface color of concrete structure,this paper has proposed a block segmentation method of maximum entropy threshold based on the digital image data obtained by the ACTIS automatic detection system.The steps in this research are as follows:1.The crack digital images of concrete specimens with typical fea-tures were collected by using the Actis system of KURABO Co,Ltd,of Japan in the concrete beam bending test.2.The images are segmented into blocks to dis-tinguish backgrounds of different grayscale.3.The max imum interclass average gray difference method is used to distinguish the sub-blocks and screen out the image blocks that need to be segmented.4.Segmentation is made to the image with 2D max imum entropy threshold segmentation method to obtain the binary image,and the target image can be obtained by screening the connected domain features of the binary image.Results have shown that compared with other algo-rithms,the proposed method can effectively decrease the image over-segmentation and under segmentation rates,highlight the characteristics of the target cracks,solve the problems of excessive difference between the identified length and actual length of cracks caused by background gray level change and uneven ilumnination,and effectively improve the recognition accuracy of bridge concrete cracks.
基金Supported by the National Natural Science Foundation of China(No.51379142)International Science and Technology Cooperation Program of China(No.2012DFA70490)Tianjin Municipal Natural Science Foundation(No.13JCQNJC06900)
文摘The early age performance of spread footing, especially the growth of cracks, is deeply influenced by the heat of hydration of cement. In this paper, 3D finite element method(FEM)models are set up to analyze the temperature distribution and thermal stresses of the spread footing during the first seven days after concrete placement. The mechanical properties of early age concrete are calculated, which are further used in the FEM models. The possibilities of crack growth are estimated by the method of crack index. The crack indexes of quite a number of points are very close to the allowable limit of 1.0 during the last three days. It is also indicated that the influence of foundation ring on the thermal stresses of concrete can be neglected.
文摘In Greece extended cracking of twin-block concrete sleepers (ties) and fouling of the ballast-bed were observed with implied problems of gauge widening and deterioration of track's geometry. This led to a ten-year investigation program, during which a new method was developed for the estimation of actions on track panel as well as of the pressures / stresses that develop under the seating surface of the sleeper on the ballast-bed. Results from the tests performed on the ballast used in the Greek network are also presented, conducted in laboratories in France, Austria, and Greece. The influence of the actions -static and mainly dynamic- on the track response and the stress and strain of the ballast-bed are also discussed as derived from the tests and theoretical analysis.
基金partially supported by the Science Fund for Creative Research Groups under Grant No.[51121005]a research project under Grant No.[51278084]from the National Science Foundation of China.
文摘Liquid migrating into existing concrete cracks is a serious problem for the reliability of concrete structures and can sometimes induce full concrete structural failures.In this paper,the authors present recent research on water presence detection in concrete cracks using piezoceramic-based smart aggregate(SA)transducers.The active sensing approach,in which one piezoceramic transducer is used to generate stress waves and others are used to detect the stress wave responses,is adopted in this research.Cracks formed in concrete structures act as stress reliefs,which attenuate the energy of the signals received by the SAs.In case of a crack being filled with liquid,which changes the wave impedance,the piezoceramic transducers will report higher received energy levels.A wavelet packet-based approach is developed to provide calculated energy values of the received signal.These different values can help detect the liquid presence in a concrete crack.A concrete beam specimen with three embedded SAs was fabricated and tested.Experimental results verified that the SA-based active sensing approach can detect a concrete crack and further detect the liquid presence in the concrete crack.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51079046, 50909041, 50809025, 50879024)the National Science and Technology Support Plan (Grant Nos. 2008BAB29B03, 2008BAB29B06)+7 种基金the Special Fund of State Key Laboratory of China (Grant Nos. 2009586012, 2010585212)the Fundamental Research Funds for the Central Universities (Grant Nos. 2009B08514, 2010B20414, 2010B14114)China Hydropower Engineering Consulting Group Co. Science and Technology Support Project (Grant No. CHC-KJ-2007-02)Jiangsu Province "333 High-Level Personnel Training Project" (Grant No. 2017-B08037)the Natural Science Foundation of Hohai University (Grant No. 2008426811)Graduate Innovation Program of Universities in Jiangsu Province (Grant No. CX09B_163Z)the Science Foundation for The Excellent Youth Scholars of Ministry of Education of China (Grant No. 20070294023)Dominant Discipline Construction Program Funded Projects of Universities in Jiangsu Province
文摘A method of the fuzzy cross-correlation factor exponent in dynamics is researched and proposed to diagnose abnormality of cracks in the concrete dam. Moreover, the Logistic time series changing from period-doubling bifurcation to chaos is tested first using this method. Results indicate that it can distinguish inherent dynamics of time series and can detect mutations. Considering that cracks in the concrete dam constitute an open, dissipative and complex nonlinear dynamical system, a typical crack on the downstream face of a concrete gravity arch dam is analyzed with the proposed method. Two distinct mutations are discovered to indicate that the abnormality diagnosis of cracks in the concrete dam is achieved dynamically through this method. Furthermore, because it can be directly utilized in the measured crack opening displacement series to complete abnormality diagnosis, it has a good prospect for practical applications.
基金supported by the National Natural Science Foundation of China (Grants nos.71732001 and 71821001)the major science and technology project in Hubei Province,China:Key Technologies and Applications of Intelligent Construction (2020ACA006).
文摘Engineering inspection and maintenance technologies play an important role in safety,operation,maintenance and management of buildings.In project construction control,supervision of engineering quality is a difficult task.To address such inspection and maintenance issues,this study presents a computer-vision-guided semi-autonomous robotic system for identification and repair of concrete cracks,and humans can make repair plans for this system.Concrete cracks are characterized through computer vision,and a crack feature database is established.Furthermore,a trajectory generation and coordinate transformation method is designed to determine the robotic execution coordinates.In addition,a knowledge base repair method is examined to make appropriate decisions on repair technology for concrete cracks,and a robotic arm is designed for crack repair.Finally,simulations and experiments are conducted,proving the feasibility of the repair method proposed.The result of this study can potentially improve the performance of on-site automatic concrete crack repair,while addressing such issues as high accident rate,low efficiency,and big loss of skilled workers.