Large-scale Concrete Structures Research Articles

Analytical Calculation Model for Predicting Cracking Behavior of Reinforced Concrete Ties

This paper formulates an analytical calculation model for predicting the cracking behavior of reinforced concrete ties to provide more consistent crack width calculation methods for large-scale concrete structures in which large bar diameters and covers are used. The calculation model was derived based on the physical behavior of reinforced concrete ties reported from experiments and finite-element analyses in the literature. The derivations led to a second order differential equation for the slip that accounts for the three-dimensional effects of internal cracking by using a proper bond-slip law. The second order differential equation for the slip was solved completely analytically, resulting in a closed-form solution in the case of lightly loaded members and in a non-closed-form solution in the case of heavily loaded members. Finally, the paper provides a solution strategy to facilitate a practical and applicable method for predicting the complete cracking response. Comparison with experimental and finite-element results in the literature demonstrated the ability of the calculation model to predict crack widths and crack spacing consistently and on the conservative side regardless of the bar diameter and cover.

Automatic air-cooling system for early-age crack control in concrete

Early-age heat-induced cracking is a potentially fatal problem for critical concrete structures such as liquefied natural gas storage tanks. This paper reports on a novel automatic air-cooling system designed to solve the problem. The system was designed following a series of air-cooling experiments in China on concrete walls during the first 72 h after casting. An air velocity of approximately 12 m/s appears to provide effective cracking control for ambient air temperatures up to 30°C, while the optimal cooling segment length was found to be approximately 14 m. The paper aims to provide a reference for the application of air cooling for any large-scale concrete structures at risk of early-age cracking.

Damage Mechanism Evaluation of Large-Scale Concrete Structures Affected by Alkali-Silica Reaction Using Acoustic Emission

Alkali-silica reaction has caused damage to concrete structures, endangering structural serviceability and integrity. This is of concern in sensitive structures such as nuclear power plants. In this study, acoustic emission (AE) was employed as a structural health monitoring strategy in large-scale, reinforced concrete specimens affected by alkali-silica reaction with differing boundary conditions resembling the common conditions found in nuclear containments. An agglomerative hierarchical algorithm was utilized to classify the AE data based on energy-frequency based features. The AE signals were transferred into the frequency domain and the energies in several frequency bands were calculated and normalized to the total energy of signals. Principle component analysis was used to reduce feature redundancy. Then the selected principal components were considered as features in an input of the pattern recognition algorithm. The sensor located in the center of the confined specimen registered the largest portion of AE energy release, while in the unconfined specimen the energy is distributed more uniformly. This confirms the results of the volumetric strain, which shows that the expansion in the confined specimen is oriented along the thickness of the specimen.

Multiple crack evaluation on concrete using a line laser thermography scanning system

This paper proposes a line laser thermography scanning (LLTS) system for multiple crack evaluation on a concrete structure, as the core technology for unmanned aerial vehicle-mounted crack inspection. The LLTS system consists of a line shape continuous-wave laser source, an infrared (IR) camera, a control computer and a scanning jig. The line laser generates thermal waves on a target concrete structure, and the IR camera simultaneously measures the corresponding thermal responses. By spatially scanning the LLTS system along a target concrete structure, multiple cracks even in a large scale concrete structure can be effectively visualized and evaluated. Since raw IR data obtained by scanning the LLTS system, however, includes timely- and spatially-varying IR images due to the limited field of view (FOV) of the LLTS system, a novel time-spatial-integrated (TSI) coordinate transform algorithm is developed for precise crack evaluation in a static condition. The proposed system has the following technical advantages: (1) the thermal wave propagation is effectively induced on a concrete structure with low thermal conductivity of approximately 0.8 W/m K; (2) the limited FOV issues can be solved by the TSI coordinate transform; and (3) multiple cracks are able to be visualized and evaluated by normalizing the responses based on phase mapping and spatial derivative processes. The proposed LLTS system is experimentally validated using a concrete specimen with various cracks. The experimental results reveal that the LLTS system successfully visualizes and evaluates multiple cracks without false alarms.

RIKEN Accelerator-driven Compact Neutron Source, RANS (RIKEN Accelerator-driven compact Neutron Source) for Non-Destructive Test of Infrastructures

A compact neutron source by using a particle accelerator is a promising tool for actual material analysis, infrastructural diagnostics, nuclear detection, and medical treatment. We have been operating the neutron source RANS (RIKEN Accelerator-driven compact Neutron Source) with 7 MeV proton LINAC with a beryllium long-life target for 6 years. In recent years, imaging with fast and thermal neutrons, engineering diffraction for texture evolution estimation and austeninte volume fraction estimation for iron and steel, Prompt-Gamma neutron Analysis (PGA) are the major activities. The research and development results with RANS fast neutron back scattered imaging methods for large scale concrete structures revels that the requirement for the neutron yield is less than 1011 neutrons s‒1 especially for out-door type compact neutron source. RANS2 has been designed and developed with 2.49 MeV proton linac. RANS proves that compact neutron source is useful for neutron scattering analysis on-site with reasonable measurement time, and resolution.

A feasibility study on real-time evaluation of concrete surface crack repairing using embedded piezoceramic transducers

Surface cracking in large-scale concrete structures are inevitable, and some cracks shall be repaired to prevent further structural damages. Various methods of repairing surface cracks in concrete structures have been studied, however, evaluation of repairing of those cracks, especially through real time means, have not much been reported. In this paper, a feasibility study was performed on evaluation of repairing concrete surface crack in real-time using embedded piezoceramic-based transducers, called Smart Aggregates (SA). Using the active sensing approach, a pair of SAs in a concrete structure can communicate through generating and detecting stress wave. In the experimental study, three concrete beam specimens were investigated. In each specimen, four smart aggregates were embedded in the beam with two designed surface cracks. Subsequently, these two cracks were repaired by using mortar and Carbon Fiber Reinforced Polymer (CFRP) sheet. Due to interfacial properties among the three different interfacial conditions: the healthy concrete structure, the concrete structure with a crack, and the concrete structure with a repaired crack, the stress wave attenuation characteristics differ. The received signals of SAs among those three interfacial conditions were compared in time domain. In addition, a wavelet packet-based energy analysis was performed to quantitatively indicate the energy value of the received signal. Experimental results shows that the signal energy values computed by the wavelet packet-based energy analysis has potential to determine the crack occurrence in concrete structures and to help evaluate the repair effects.

Fast neutron transmission imaging of the interior of large-scale concrete structures using a newly developed pixel-type detector

Given the increased demand for nondestructive inspections of the insides of bulk concrete structures, in this paper, we propose a new transmission imaging system that uses fast neutrons via an accelerator-driven compact neutron source. A key component that we have developed is a pixel-type fast neutron detector that consists of a 4×4 array of plastic scintillators with semiconductor photon sensors. Using neutron transmission images obtained with this detector, we have successfully identified a steel bar, a void hole, and water with 300-mm-thick concrete blocks via a RIKEN Accelerator-driven compact Neutron Source (RANS).

Immobilizing bacteria in expanded perlite for the crack self-healing in concrete

Immobilization has been reported to be an efficient approach for bacteria-based self-healing concrete to maintain the high-efficiency mineral-forming capacity of incorporated bacteria over a period of time. However, the relatively high-cost, local unavailability, and low adsorption capacity of the current bacteria carriers make them impractical for potential implementation in large-scale concrete structures. In this study, the feasibility of expanded perlite (EP) as a novel bacteria carrier on quantifying cracks-healing in concrete via immobilization of Bacillus cohnii was demonstrated. The effects of two other self-healing techniques, i.e., direct introduction of bacteria and expanded clay (EC) immobilized bacteria, on the efficiency of crack-healing were also investigated. Experimental results showed that specimens incorporated with EP-immobilized bacteria exhibited the most efficient crack-healing after each healing time. The values of completely healed crack widths were up to 0.79mm after 28days of healing, which is larger than the value of 0.45mm for specimens incorporated with EC-immobilized bacteria. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) analysis confirmed that mineral precipitations on their crack surfaces are calcite crystals. The findings obtained in this study may provide a scientific basis for the potential implementation of expanded perlite, as a new microorganism carrier, in bacteria-based self-healing concrete.

Diffuse ultrasound monitoring of stress and damage development on large scale concrete structures

This paper describes the use of an ultrasonic imaging technique (Locadiff [1]) for the NDT&E of concrete structures. By combining coda wave interferometry and a sensitivity kernel for diffuse waves, Locadiff can monitor the elastic and structural properties of a heterogeneous material with a high sensitivity, and can map changes of these properties over time when a perturbation occurs in the bulk of the material. The applicability of the technique to life-size concrete structures is demonstrated through monitoring 2 reinforced concrete strutures [2-3]. Locadiff achieved to detect and locate the cracking zones in the core of concrete and monitor the internal stress level in both temporal and spatial domains by mapping the variation in velocity caused by the acoustoelastic effect. The mechanical behavior of the concrete structure is also studied using conventional techniques such as acoustic emission, vibrating wire extensometers, and digital image correlation. [1] E. Larose et al., “Locating a small change in a multiple scattering environment,” Appl. Phys. Lett. 96 (20), 204101 (2010). [2] Y. Zhang et al., “Diffuse ultrasound monitoring of stress and damage development on a 15-ton concrete beam,” J. Acoust. Soc. Am. 139 1691-1701 (2016). [3] Y. Zhang et al., “3D in-situ imaging of cracks in concrete using diffuse ultrasound,” Struct. Health Monitoring, under review (2017).

Enhanced lumped circuit model for smart nanocomposite cement-based sensors under dynamic compressive loading conditions

Smart composite nanostructured materials represent one of the fastest-growing areas of interest among scientists in recent years and, in particular, carbon nanotube (CNT) cement-based composites are attracting more and more attention. These composites exhibit self-sensing capabilities providing measurable variations of their electrical properties under the application of mechanical deformations. Together with this exceptional property, the similarity and compatibility between these composites and structural concrete suggest the possibility of developing distributed embedded strain-sensing systems with substantial improvements in the cost-effectiveness in applications to large-scale concrete structures. In order to design and optimize CNT reinforced cement based dynamic sensors, it is fundamental to develop theoretical models capable of simulating the relationship between dynamic mechanical strains and the effective electrical conductivity. This paper presents an electromechanical modeling of the Direct Current (DC) electrical resistance of CNT reinforced cement paste sensors based on a piezoelectric/piezoresistive lumped circuit. The model represents an enhanced version and a generalization of another model previously proposed by the authors. Previously published experimental results have been used as validation benchmark. In particular, experimental tests concerning the characterization of the step response under unloaded conditions, steady state response under harmonic loadings and sweep analyses are considered. The results demonstrate that the newly proposed model is superior in comparison to the previous one in reproducing the dynamic response of the sensors when subjected to harmonic mechanical loads. Overall, an excellent agreement between theoretical predictions and experimental results is achieved.

Micromechanics modeling of the uniaxial strain-sensing property of carbon nanotube cement-matrix composites for SHM applications

Recent advances in the field of Nanotechnology have made possible the development of new smart materials, among which Carbon NanoTube (CNT) cement-based composites are attracting an increasing attention. These composites exhibit strain-sensing capabilities providing measurable variations of their electrical properties under applied mechanical deformations. This unique property, together with the similarity between these composites and structural concrete, suggests the possibility of developing distributed strain-sensing systems with substantial improvements in the cost-effectiveness of large-scale concrete structures. In order to design and optimize self-sensing CNT-based composites, it is therefore essential to develop theoretical models capable of simulating the relationship between external mechanical strains and the effective electrical conductivity. This paper presents a micromechanics model to predict the piezoresistive properties of CNT cement-based nanocomposites, with the consideration of waviness and non-uniform distributions of nanoinclusions. The origin of the piezoresistive response is attributed to (i) strain-induced changes in the volume fraction, (ii) filler reorientation and, (iii) changes in the tunneling resistance. In order to count on an experimental basis to use as benchmark for validation, several nanocomposite cement-based specimens are manufactured and tested under uniaxial compression.

Numerical aspects of microplane constitutive models for concrete

This paper presents a comprehensive study on the numerical aspects of a class of microplane constitutive models for concrete, with emphasis on the most popular one, i.e., the model M4 developed by Bažant and co-workers. The effect of the computational procedures for the microplane shear stress components, the strain increment magnitude, the integration scheme and the loading direction on the model responses are investigated in detail. Several problems in the responses of the model, from the computational point of view, are detected and discussed. Some procedures to enhance the numerical performance of the model are then proposed. These include a removal of the tensile volumetric stress boundary in the original formulation, the introduction of a novel semi-explicit numerical algorithm for the microplane volumetric and deviatoric stresses, and a method to minimise the sensitivity of the model responses to the loading direction through a simple meshing-based integration scheme. Finally, some practical considerations for the choice of numerical integration scheme in the finite element calculations of large-scale concrete structures with the microplane model M4 are presented.

Parallel Dispersive FDTD Method Based on the Quadratic Complex Rational Function

Recently, the quadratic complex rational function (QCRF) function was proposed for accurate finite-difference time-domain (FDTD) dispersive modeling. First, this letter discusses two implementations of QCRF-FDTD to a zeroth-order temporal derivative term and it is observed that the numerical accuracy of the double averaging implementation is better than that of the direct implementation. Second, this work presents a fast QCRF-FDTD algorithm by employing a parallel processing algorithm. The proposed parallel QCRF-FDTD is validated in terms of the speedup fact and the computational accuracy. Finally, we analyze the shielding effectiveness of large-scale concrete structures by using our parallel QCRF-FDTD.

Damage based constitutive model for predicting the performance degradation of concrete

AN ANISOTROPIC ELASTIC-DAMAGE COUPLED CONSTITUTIVE MODEL FOR PLAIN CONCRETE IS DEVELOPED, WHICH DESCRIBES THE CONCRETE PERFORMANCE DEGRADATION. THE DAMAGE VARIABLE, RELATED TO THE SURFACE DENSITY OF MICRO-CRACKS AND MICRO-VOIDS, AND REPRESENTED BY A SECOND ORDER TENSOR, IS GOVERNED BY THE PRINCIPAL TENSION STRAIN COMPONENTS. FOR ADEQUATELY DESCRIBING THE PARTIAL CRACK OPENING/CLOSURE EFFECT UNDER TENSION AND COMPRESSION FOR CONCRETE, A NEW SUITABLE THERMODYNAMIC POTENTIAL IS PROPOSED TO EXPRESS THE STATE EQUATIONS FOR MODELING THE MECHANICAL BEHAVIORS. WITHIN THE FRAMEWORK OF THERMODYNAMIC POTENTIAL, CONCRETE STRAIN MECHANISMS ARE IDENTIFIED IN THE PROPOSED ANISOTROPIC DAMAGE MODEL WHILE EACH STATE VARIABLE IS PHYSICALLY EXPLAINED AND JUSTIFIED. THE STRAIN EQUIVALENCE HYPOTHESIS IS USED FOR DERIVING THE CONSTITUTIVE EQUATIONS, WHICH LEADS TO THE DEVELOPMENT OF A DECOUPLED ALGORITHM FOR EFFECTIVE STRESS COMPUTATION AND DAMAGE EVOLUTION. ADDITIONALLY, A DETAILED NUMERICAL ALGORITHM IS DESCRIBED AND THE SIMULATIONS ARE SHOWN FOR UNI-AXIAL COMPRESSION, TENSION AND MULTI-AXIAL LOADINGS. FOR VERIFYING THE NUMERICAL RESULTS, A SERIES OF EXPERIMENTS ON CONCRETE WERE CARRIED OUT. REASONABLY GOOD AGREEMENT BETWEEN EXPERIMENTAL RESULTS AND THE PREDICTED VALUES WAS OBSERVED. THE PROPOSED CONSTITUTIVE MODEL CAN BE USED TO ACCURATELY MODEL THE CONCRETE BEHAVIORS UNDER UNI-AXIAL COMPRESSION, TENSION AND MULTI-AXIAL LOADINGS. ADDITIONALLY, THE PRESENTED WORK IS EXPECTED TO BE VERY USEFUL IN THE NONLINEAR FINITE ELEMENT ANALYSIS OF LARGE-SCALE CONCRETE STRUCTURES.

캡슐형 슬러리 PCM을 혼입한 매스콘크리트의 수화열 평가 및 온도균열 FEM 해석에 관한 연구

The purpose of this study is to investigate the effect of capsulated slurry phase change material (PCM) on the thermal crack in mass concrete by experimental work and FEM analysis. In this study, three conditions of samples were prepared for evaluating the level of hydration heat, i.e., a material condition, a cement paste condition and a concrete condition. Also, a compressive strength test was conducted for FEM inverse analysis. Based on the results of the experiment, exothermic function coefficients of concrete with encapsulated slurry PCM were deducted by the inverse analysis. After that, they applied to FEM analysis of the mass scale concrete structures. From the results of this experiment, 31℃ capsulated slurry PCM had no super cooling phenomenon in the material condition. In the cement condition, hydration heat decreased by 34.61J when PCM of 1g was mixed. In the concrete condition, PCM of 6% was deducted as the best level in hydration heat absorption. In FEM inverse analysis, rate coefficient of reaction gradually decreased when PCM mixing ratio increased. But, temperature-rise coefficient increased when PCM mixing ratio exceeded 6%. For the inversed exothermic function coefficients applying to large scale concrete structures, a thermal cracking index increased by 0.05 when PCM of 1% was mixed.

Full-Field Deformation Measurement and Crack Mapping on Confined Masonry Walls Using Digital Image Correlation

The understanding of the load-resistance mechanisms and failure modes of large-scale concrete and masonry structures relies on accurate measurements of surface motions and deformations, and faithful crack maps. Measurements are typically taken using surface-mounted point-wise sensors (PWSs), and crack maps are hand-drawn based on visual inspection. It is impractical to obtain detailed displacement and deformation maps that describe the complex response of large structures based on PWS measurements. In addition, manual crack drawing is difficult, time-consuming, and prone to human errors, which makes it challenging to consistently produce faithful crack maps. This paper reports on a pilot study to test the use of three-dimensional digital image correlation (3D-DIC) as a non-contacting method to measure surface deformation fields on full-scale masonry walls, and produce detailed crack maps. Three confined masonry walls were tested under horizontal in-plane reverse-cycle loads. The specimens were designed to attain different levels of strength and deformability through different load-resistance mechanisms. Representative 3D-DIC measurements of drift, diagonal deformations, and interface slip between the reinforced concrete tie columns and the masonry infill were evaluated vis-a-vis benchmark PWS measurements, showing a comparable accuracy. Strain maps based on 3D-DIC measurements were enlisted to visualize the development of the fundamental strut-and-tie resisting mechanism in confined masonry walls subjected to horizontal in-plane loads, and illustrate practical structural analysis and design implications. More detailed crack maps compared with traditional hand-drawn maps were obtained based on 3D-DIC maximum principal strain contours.

A novel technique for acoustic emission monitoring in civil structures with global fiber optic sensors

The application of acoustic emission (AE)-based damage detection is gaining interest in the field of civil structural health monitoring. Damage progress can be detected and located in real time and the recorded AEs hold information on the fracture process which produced them. One of the drawbacks for on-site application in large-scale concrete and masonry structures is the relatively high attenuation of the ultrasonic signal, which limits the detection range of the AE sensors. Consequently, a large number of point sensors are required to cover a certain area. To tackle this issue, a global damage detection system, based on AE detection with a polarization-modulated, single mode fiber optic sensor (FOS), has been developed. The sensing principle, data acquisition and analysis in time and frequency domain are presented. During experimental investigations, this AE-FOS is applied for the first time as a global sensor for the detection of crack-induced AEs in a full-scale concrete beam. Damage progress is monitored during a cyclic four-point bending test and the AE activity, detected with the FOS, is related to the subsequent stages of damage progress in the concrete element. The results obtained with the AE-FOS are successfully linked to the mechanical behavior of the concrete beam and a qualitative correspondence is found with AE data obtained by a commercial system.

A Simulation Study of Fast Neutron Imaging for Large-scale Concrete Structures

The fast neutron imaging can be a powerful method for measuring the aging deterioration of the large-scale concrete structures, which is an urgent social problem in Japan. We discussed the preliminary design of the fast neutron source in the imaging system and confirmed its feature with the Monte Carlo simulation.

Condition assessment of PC tendon duct filling by elastic wave velocity mapping.

Imaging techniques are high in demand for modern nondestructive evaluation of large-scale concrete structures. The travel-time tomography (TTT) technique, which is based on the principle of mapping the change of propagation velocity of transient elastic waves in a measured object, has found increasing application for assessing in situ concrete structures. The primary aim of this technique is to detect defects that exist in a structure. The TTT technique can offer an effective means for assessing tendon duct filling of prestressed concrete (PC) elements. This study is aimed at clarifying some of the issues pertaining to the reliability of the technique for this purpose, such as sensor arrangement, model, meshing, type of tendon sheath, thickness of sheath, and material type as well as the scale of inhomogeneity. The work involved 2D simulations of wave motions, signal processing to extract travel time of waves, and tomography reconstruction computation for velocity mapping of defect in tendon duct.

An Assessment of Damage to Large-Scale Basement Slab Caused by Groundwater and Expansive Soil

Cracking damage is a common phenomenon in large-scale concrete structure. But for the underground structure it is not permitted because crack will cause heavily damage and other disasters. With the aid of finite element method for deformation and stress field simulation, a detailed study is carried out for a large area foundation slab of an underground parking lot. The foundation soil condition and the hydrogeological condition are the principal influence factors that result in the cracking problems. The simulation results illustrate that the combined effects of foundation settlement and larger groundwater pressure cause the foundation slab cracking and the existence of expansive soil indeed exacerbates the problem.