Effect of Maximum Aggregate Size on Dynamic Compressive Strength of Concrete

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공과대학 건설환경공학부
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서울대학교 대학원
학위논문 (석사)-- 서울대학교 대학원 : 공과대학 건설환경공학부, 2018. 8. 조재열.
Structures under extreme events whose return period is significantly greater than design life such as impacts, explosions, collision, earthquake, tsunami, etc. undergo high deformation rate. In order to analyze and design the structures under extreme events, investigation into dynamic material properties is necessary for analysis accuracy and economic feasibility.

Concrete is rate dependent material which means the material properties are varied along strain rate. Especially, dynamic compressive strength of concrete increases as the strain rate increases, called as rate effect on compressive strength, which is should be considered to design the concrete structures. Dynamic increase factor (DIF), a ratio of dynamic compressive strength to static compressive strength, has been used for the consideration. Various DIFs has been suggested based on analytical, numerical and experimental studies. Split Hopkinson pressure bar (SHPB) is one of characterization tool for investigating DIF of various materials such as metals, polymers, rubbers, concrete-like materials, etc. at high strain rates based on one dimensional stress wave theory.

Meanwhile, concrete SHPB test has two issues associated with validity of the test results. First of all, due to both the absence of the standard test method and the difficulties of using SHPB with large diameter, only mortar or concrete specimens with much smaller maximum aggregate sizes were tested. However, results of the SHPB test for mortar or the small size concrete specimens are doubtful of validation since the coarse aggregate used in practice is much larger. Nevertheless, research about an effect of aggregate is insufficient. Only a few studies have investigated the influence of aggregate on rate effect such as volume fraction and size of aggregate. In the studies, however, also small size coarse aggregates have been used. Therefore, it is necessary to validate whether the results of the studies are applicable to the real concrete with much larger coarse aggregates.

In this study, mortar and concrete SHPB tests were conducted to investigate the effect of maximum coarse aggregate size on concrete dynamic compressive strength. Analysis of the test results was focused on two aspects. First, heterogeneity of the specimen induced by different maximum coarse aggregate size was investigated. Second, tendency of the DIF along with the maximum coarse aggregate size was evaluated. Consequently, a guidance of concrete SHPB test was suggested in consideration of heterogeneity and tendency of DIF.

Investigation of the effect of maximum coarse aggregate size on dynamic compressive strength of concrete conducted in this study can be used for establishment of standard test method of SHPB test to obtain DIF which is essential in designing and evaluating the concrete structures under extreme events. Furthermore, this study can be a cornerstone to activate the area of extreme performance evaluation system.

Keywords: dynamic increase factor, maximum coarse aggregate size, rate effect, split Hopkinson pressure bar, standard test method, concrete dynamic compressive strength, heterogeneity
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Civil & Environmental Engineering (건설환경공학부)Theses (Master's Degree_건설환경공학부)
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