Volume 3, No. 3 Special section: NDT, Assessment and Monitoring of Concrete Structures edited by Prof. H. Mutsuyoshi Nondestructive Evaluation of Damaged Concrete due to Freezing and Thawing by Elastic-Wave Method (Invied Paper) Masayasu Ohtsu Journal of Advanced Concrete Technology, 3(3) 333-341, 2005 The damage of concrete subjected to freezing and thawing is normally evaluated with the resonance method, which estimates the elastic properties of concrete. This method is one of several nondestructive evaluation (NDE) techniques that use elastic-wave methods. The damage is evaluated based on resonant frequencies, which are related to the dynamic properties of concrete. Because resonance is closely associated with wave motions, the ultrasonic test (UT), which measures the velocity of wave propagation, is also available for NDE of damaged concrete. Another NDE technique using elastic-wave methods that can be applied to evaluate the damage of concrete is acoustic emission (AE) measurement. These three techniques are investigated and discussed for NDE of damaged concrete due to freezing and thawing. To theoretically clarify the dynamic behaviors of concrete specimens in the tests, numerical analysis of the three-dimensional boundary element method (BEM) were conducted. No difference between the dynamic modulus of elasticity and the static modulus was found to exist Compared with UT and AE, the heaviest damage was estimated by the resonance method in the freeze-thaw process. These results have to be carefully taken into account for NDE of damaged concrete. Nondestructive Evaluation of Setting and Hardening of Cement Paste Based on Ultrasonic Propagation Characteristics Toshiro Kamada, Shinya Uchida and Keitetsu Rokugo Journal of Advanced Concrete Technology, 3(3) 343-353, 2005 This paper describes the relationship between setting/hardening properties of cement paste and ultrasonic propagation characteristics from both macroscopic and microscopic point of view. Experiment I was aimed at evaluating changes in the physical properties of high-early-strength cement paste. In the experiment, a uni-cylinder rotational viscometer was used for viscosity measurement. Experiment II was aimed at evaluating changes in the chemical properties of ultra-rapid-hardening cement paste. In the experiment, scanning electron microscopy and powder X-ray diffraction analysis were done to investigate the generation of hydration products. As a result, ultrasonic propagation velocity and apparent viscosity measured with a rotational viscometer did not show good correlation. However, it was confirmed that maximum amplitude of received waveform adequately reflected changes in shear stress of cement paste. On the other hand, change in ultrasonic propagation velocity is well correlated with the formation of ettringite crystals as observed by SEM and powder X-ray diffraction analysis. The Use of Surface Waves to Estimate In-Place Strength of Concrete Gonzalo E. Gallo and John S. Popovics Journal of Advanced Concrete Technology, 3(3) 355-362, 2005 Non-destructive evaluation (NDE) techniques are needed to evaluate in-place strength of concrete in structures. Often mechanical wave propagation parameters are used to establish a correlation with strength. P-wave velocity measurements are most common for this purpose, but its application can be problematic. Here the utility of surface waves is investigated. Surface wave velocity and transmission (attenuation) properties are considered, where a self-compensating approach overcomes experimental difficulties usually experienced in transmission measurements. The testing configuration is described and the concept of the self-compensating approach introduced. Then a test series is described: surface wave velocity and wave transmission and P-wave through thickness velocity data are collected from concrete slabs of different strengths. Relations between concrete strength, wave velocity and surface wave transmission are established. Surface wave velocity and normalized surface wave velocity data correlate well with in-place strength. Transmission data also are sensitive to concrete strength but data variation must be improved. Proposal for Quantitative Evaluation Methodology of Inspection Value in Maintenance of Concrete Structures Based on Repair-Risk Yoshitaka Kato and Taketo Uomoto Journal of Advanced Concrete Technology, 3(3) 363-370, 2005 Appropriate asset management performance requires the accurate prediction of the future performance of a structure until the end of its life cycle. However, predictions of concrete structure deterioration are often executed with uncertain information since structure qualities may differ from design due to construction errors. A more accurate prediction can be obtained by inspecting the actual structure, but random inspections are not useful since the entire structure should be maintained. If the influence of inspection on the accuracy of prediction results can be quantitatively evaluated, then an efficient inspection plan that prioritizes structures can be developed. In this research, a repair-risk method is proposed to quantitatively evaluate the effect of inspection on the accuracy of predicted results. The repair-risk was calculated using the predicted results of concrete deterioration caused by corrosion-induced damage due to salt attack. The repair-risk method also considers the risk curve of the repair cost. Even when multiple structures are to be managed, an inspection plan (selecting inspection items, evaluating the effect of the inspection method, and selecting structures) can be designed using the proposed method. Use of a Moisture Sensor for Monitoring the Effect of Mixing Procedure on Uniformity of Concrete Mixtures Kejin Wang and Jiong Hu Journal of Advanced Concrete Technology, 3(3) 371-383, 2005 The present research is to explore a new approach to monitoring uniformity of concrete mixtures. A given concrete mix was subjected to three different mixing procedures. A moisture sensor was installed in a pan mixer to monitor moisture content of the concrete mixture during mixing. The mixtures were considered as uniformly mixed when stable moisture content was detected by the moisture sensor. The concrete workability and strength were then evaluated, and its microstructure (pore distributions and aggregate-paste interface) was examined. The preliminary results indicated that the moisture sensor provided reliable test results describing moisture distribution in concrete mixtures. The sensor readings well captured the subtle changes, such as the loading sequence of concrete materials, in concrete mixing process. Different mixing procedures required different mixing time for a given concrete mix to reach a stable moisture distribution. The material loading sequence, mixing time, and aggregate moisture condition had significant influences on the concrete workability, air void system, and strength. These research results provide researchers and engineers with insight into the control of concrete mixing quality and the optimization of mixing procedures in the lab and field. Mesoscopic Simulation of Failure of Mortar and Concrete by 3D RBSM Kohei Nagai, Yasuhiko Sato and Tamon Ueda Journal of Advanced Concrete Technology, 3(3) 385-402, 2005 Concrete is a heterogeneous material consisting of mortar and aggregate at the meso scale. Evaluation of the fracture process at this scale is useful to clarify the material characteristic of concrete. The authors have conducted meso scale analysis of concrete over a past few years by Rigid Body Spring Model (RBSM). In this study, three-dimensional analyses of mortar and concrete are carried out, which is necessary for the quantitative evaluation of concrete behavior especially in compression. Constitutive models at the meso scale are developed for the 3D RBSM analysis. Failure behaviors and strengths in compression and tension of mortar and concrete are predicted well by the analysis. In biaxial compression test of concrete, crack in normal direction to plane of specimen is simulated that cannot be presented by two-dimensional analysis. Simplified Design of Composite Slabs using Slip Block Test G.Mohan Ganesh, Akhil Upadhyay and Surendra K. Kaushik Journal of Advanced Concrete Technology, 3(3) 403-412, 2005 Steel-concrete composite slab is a structurally efficient combination of constituents as it exploits the tensile resistance of the steel and compressive resistance of the concrete in effective manner. In the design of these slabs, shear connection between the profiled steel sheet and concrete slab plays an important role. The verifications that are required for the design are long and complicated. Current design methods found in standards and guidelines rely on the results of costly and time-consuming large-scale laboratory tests. In this paper, a simplified approach for the design of composite slab is proposed. This approach utilizes the results of slipblock test with a simple calculation model to obtain the moment of resistance of composite slab governed by horizontal shear resistance. The results obtained using this approach is verified by comparison with the results based on m - k test method. Applications of Boundary Effect Model to Quasi-Brittle Fracture of Concrete and Rock Kai Duan and Xiaozhi Hu Journal of Advanced Concrete Technology, 3(3) 413-422, 2005 A recently-developed asymptotic boundary effect model for the quasi-brittle fracture of finite-sized fracture mechanics specimens is used to analyse the experimental results available in the literature. Three different experimental results are chosen in this study to cover various experiment designs, including geometrically similar specimens, specimens of identical size with different crack lengths and specimens of different configurations and geometries. It is shown that the size effect associated with quasi-brittle fracture, as reported in the literature, is in fact, due to the influence of specimen boundaries. The observed dependence of fracture behaviour on specimen size and crack length can be described by the same boundary effect model. The new asymptotic model is also compared with other size effect models dealing exclusively with geometrically similar specimens, and its distinct advantages over other models are discussed. Fracture Properties of FRC Determined through Inverse Analysis of Wedge Splitting and Three-Point Bending Tests Ingemar Löfgren, Henrik Stang and John Forbes Olesen Journal of Advanced Concrete Technology, 3(3) 423-434, 2005 Fracture properties of five different steel fibre-reinforced concretes have been determined, using the wedge splitting test method (WST) and the three-point bending tests (3PBT). Furthermore, for the WST method, two different specimen sizes have been investigated. Through inverse analyses, stress-crack opening ( -w) relationships have been determined for each mix and test method. Results from this investigation demonstrate the applicability of the WST method, show that inverse analysis can be used to determine stress-crack opening relationships, and the result demonstrate the effect of increased fibre content and the w/b-ratio. The major factor contributing to the differences in the determined stress-crack opening relationships is believed to be related to the variation in the number of fibres across the fracture plane. However, taking this into consideration, the inverse analyses indicate no systematic differences in the determined parameters between two WST specimen sizes, while the 3PBT seems to give slightly higher post-cracking stresses. Inventory Data and Case Studies for Environmental Performance Evaluation of Concrete Structure Construction Kenji Kawai, Takafumi Sugiyama, Koichi Kobayashi and Susumu Sano Journal of Advanced Concrete Technology, 3(3) 435-456, 2005 This paper aims to provide common basis for the estimation of emission inventory data necessary for the evaluation of environmental impact of a concrete structure through its life cycle. Intensive literature survey and hearing to the institutes concerned have been deliberately conducted to collect relevant data to concrete materials, other materials involved, construction, demolition, and disposal and recycling. Consequently emission inventory data of CO2, SOx, NOx, and particulate matter were able to be prepared in an objective way. In addition, fundamental inventory data of these emission gases and particulate matter were provided for various kinds of energy. Furthermore most commonly used machines, instruments and other equipments on concrete structure construction are presented and provided for their related inventory data. In this way, inventory data regarding 91 detail items in total was able to be provided. By using these inventory data, four case studies where environmental impact caused by the construction of concrete structures was considered as a performance parameter of the structures similarly to serviceability, safety, and durability of the structures were also investigated based on design methods proposed previously by the authors in order to confirm the applicability of these inventory data to environmental performance evaluation of concrete structures.