[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The International Society for Rock Mechanics has so far developed two standard methods for the determination of static fracture toughness of rock. They used three different core-based specimens and tests were to be performed on a typical laboratory compression or tension load frame. Another method to determine the mode I fracture toughness of rock using semi-circular bend specimen is herein presented. The specimen is semi-circular in shape and made from typical cores taken from the rock with any relative material directions noted. The specimens are tested in three-point bending using a laboratory compression test instrument. The failure load along with its dimensions is used to determine the fracture toughness. Most sedimentary rocks which are layered in structure may exhibit fracture properties that depend on the orientation and therefore measurements in more than one material direction may be necessary. The fracture toughness measurements are expected to yield a size-independent material property if certain minimum specimen size requirements are satisfied.

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ISRM-Suggested Method for Determining the Mode I Static Fracture Toughness Using Semi-Circular Bend Specimen

A disk-shaped compact tension (DC(T)) test has been developed as a practical method for obtaining the fracture energy of asphalt concrete. The main purpose of the development of this specimen geometry is the ability to test cylindrical cores obtained from in-place asphalt concrete pavements or gyratory-compacted specimens fabricated during the mixture design process. A suitable specimen geometry was developed using the ASTM E399 standard for compact tension testing of metals as a starting point. After finalizing the specimen geometry, a typical asphalt concrete surface mixture was tested at various temperatures and loading rates to evaluate the proposed DC(T) configuration. The variability of the fracture energy obtained from the DC(T) geometry was found to be comparable with the variability associated with other fracture tests for asphalt concrete. The ability of the test to detect changes in the fracture energy with the various testing conditions (temperature and loading rate) was the benchmark for determining the potential of using the DC(T) geometry. The test has the capability to capture the transition of asphalt concrete from a brittle material at low temperatures to a more ductile material at higher temperatures. Because testing was conducted on ungrooved specimens, special care was taken to quantify deviations of the crack path from the pure mode I crack path. An analysis of variance of test data revealed that the prototype DC(T) can detect statistical differences in fracture energy resulting for tests conducted across a useful range of test temperatures and loading rates. This specific analysis also indicated that fracture energy is not correlated to crack deviation angle. This paper also provides an overview of ongoing work integrating experimental results and observations with numerical analysis by means of a cohesive zone model tailored for asphalt concrete fracture behavior.

Disk-shaped Compact Tension Test for Asphalt Concrete Fracture

This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length.

Using Semi Circular Bending Test to Evaluate Low Temperature Fracture Resistance for Asphalt Concrete

In recent years the transportation materials research community has focused a great deal of attention on the development of testing and analysis methods to shed light on fracture development in asphalt pavements. Recently it has been shown that crack initiation and propagation in asphalt materials can be realistically modeled with cutting-edge computational fracture mechanics tools. However, much more progress is needed toward the development of practical laboratory fracture tests to support these new modeling approaches. The goal of this paper is twofold: (a) to present a disk-shaped compact tension [DC(T)] test, which appears to be a practical method for determining low-temperature fracture properties of cylindrically shaped asphalt concrete test specimens, and (b) to illustrate how the DC(T) test can be used to obtain fracture properties of asphalt concrete specimens obtained from field cores following dynamic modulus and creep compliance tests performed on the same specimens. Testing four mixtures wit...

Investigation of the Fracture Resistance of Hot-Mix Asphalt Concrete Using a Disk-Shaped Compact Tension Test

A rapid and simple test that can be performed on easy to prepare specimens, which gives decisive answers on the material characteristics needed for pavement design, and which can also be used for quality control and quality assurance purposes, is a test that pavement engineers are looking for. The question is, however, "does such a simple test exist?" Unfortunately the answer seems to be "no". A simple test like, e.g., the Marshall test doesn't fulfill all these requirements and is therefore abandoned in many countries. Developments in the field of performance related and performance based specifications have resulted in a search for more appropriate "fundamental" tests like, e.g., a triaxial test. The problem with many of these tests, however, is that they lack simplicity and that specimens cannot easily be obtained from the pavement. Furthermore the need to do repeated load testing complicates the applicability of such tests. In the Netherlands as well as in some other countries, like, e.g., South Africa, the possibilities of the so-called semi-circular bending test are therefore investigated since it is believed that this test is a simple tool to obtain information on the modulus and the tensile characteristics of asphalt mixtures. In this paper this test is described and it is shown to what extent this test is indeed the simple test that fulfills all the requirements mentioned above.

Semi-circular bending test; simple but useful?

An extensive experimental and analytical investigation is being currently carried out on the mechanisms leading to the initiation and propagation of fatigue damage in the top layers of asphalt concrete pavements when subjected to various types of loading. One of the major goals of the investigation is the development and finite element implementation of a triaxial, strain rate sensitive, history and temperature dependent constitutive model for asphalt concrete under arbitrary states of stress. Because of the hierarchical formulation of the model, the analyst can activate, at will, those features of the model which he considers relevant to his specific interests. Explicit procedures are suggested for the experimental determination of the parameters. As a minimum, only uniaxial test results are needed for determination of the basic parameters. An actual example of such a procedure is presented. In its current, prototype formulation, the model has been implemented in the finite element code CAPA-3D. Results of the utilization of CAPA-3D for the investigation of the dynamic non-linear response of asphalt concrete pavements are reviewed in the last part of this contribution.

Finite element simulation of damage development in asphalt concrete pavements

Aging during construction and in-service substantially changes the chemical composition and physical properties of bitumen thereof influences the performance of asphalt pavements. The modification of bitumen by crumb rubber modifier (CRM) significantly increases the complexity of the aging mechanism and is expected to improve the aging resistance of bitumen. This study aims to investigate the effects of laboratory short-term and long-term aging on the chemistry and rheology of crumb rubber modified bitumen (CRMB). Neat bitumen and CRMB with four different CRM contents were studied. Fourier transform infrared spectroscopy and dynamic shear rheometer were employed to measure the change in the chemical composition and rheological properties of binders at different aging states. Bitumen hardening, which was rheologically revealed by the frequency sweep and multiple creep recovery test results, was also reflected in the growth of carbonyl and sulfoxide functional groups. In addition, the aliphaticity and aromaticity indices of binders before and after aging were also investigated. CRMB binders showed improved aging resistance compared to neat bitumen as reflected by the decreased carbonyl and sulfoxide indices as well as the lower change in rheological parameters. Higher resistance against aging was achieved when increasing the CRM content. The results also highlight the correlation between chemistry and rheology of bitumen. Among six selected mechanical parameters of binder, the non-recoverable creep compliance and percent recovery show better correlations with the combined chemical aging index (sum of carbonyl and sulfoxide indices) than the parameters derived from the linear viscoelastic region.

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Effect of laboratory aging on chemistry and rheology of crumb rubber modified bitumen

Warm mix asphalt (WMA) technology has been increasingly utilised in rubberised asphalt pavements to reduce the production and compaction temperatures and the incidental fumes and odours. This study...

https://tandfonline.com/doi/pdf/10.1080/14680629.2018.1561380

Sandra Erkens

Papers

Semi-circular bending test; simple but useful?

Finite element simulation of damage development in asphalt concrete pavements

Effect of laboratory aging on chemistry and rheology of crumb rubber modified bitumen

Asphalt-rubber interaction and performance evaluation of rubberised asphalt binders containing non-foaming warm-mix additives

Evaluation of epoxy modification in bitumen