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.
This paper describes the relationship between the setting/hardening properties of cement paste and ultrasonic propagation characteristics from both a macroscopic and a microscopic point of view. The first experimental series was aimed at evaluating changes in the physical properties of high-early-strength cement paste. In the experiment, a single cylinder rotational viscometer was used for viscosity measurement. The second series of experiments was aimed at evaluating changes in the chemical properties of ultra-rapid-hardening cement paste. In the experiment, scanning electron microscopy (SEM) and powder X-ray diffraction analysis were done to investigate the generation of hydration products. As a result, it was confirmed that the maximum amplitude of the obtained waveform adequately reflects the changes in shear resistance of cement paste. On the other hand, change in ultrasonic wave velocity is well correlated with the formation of ettringite crystals as observed by SEM and powder X-ray diffraction analysis.
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. In this paper, 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.
Appropriate asset management 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.
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 inside a pan mixer to monitor moisture content of the concrete mixtures during mixing. The concrete 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 the concrete's 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 the concrete mixing process. 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.
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.
Steel-concrete composite slabs are a structurally efficient combination of constituents as they exploit the tensile resistance of the steel and compressive resistance of the concrete in an effective manner. Shear connection between the profiled steel sheet and concrete slab plays an important role in the design of these slabs. 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 slabs is proposed. This approach utilizes the results of the slip block test with a simple calculation model to obtain the moment of resistance based on the partial interaction method of composite slab governed by horizontal shear resistance. The results obtained using this approach are verified by comparison with the results based on the m-k test method.
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 five different steel fibre-reinforced concretes have been determined, using the wedge splitting test method (WST) and three-point bending tests (3PBT). Furthermore, for the WST method, two different specimen sizes have been investigated. Through inverse analyses, stress-crack opening (σ-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.
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 were 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.
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