3.コンクリートの打音と強度との関係について

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This paper is presented an experimental investigation of the relation between the concrete strength and the impulsive tone, which is produced when a concrete specimen is struck by a steel ball. It is intended that our study may contribute to the non-destructive testing of concrete strength. The test procedure is as follows: A specimen, 4×4×16cm, is suspended from a frame by a hinge with two pointed nails. And a steel ball, 40mmφ, is also hooked on a tip of a wooden arm which can be swung down from a certain height so as to make the ball to strike the specimen. The impulsive tone thus produced is received by a microphone and sent to a cathode-ray oscilloscope through an amplifier. The tone wave is recorded by a camera unit and the tone frequency is measured by a beat frequency oscillator. Among the several factors of tone special attension was paid to its frequency and its rate of damping. A total of over 1,000 specimens have been tested in order to compare the various results. These include i) cement-paste specimens, ii) cement-mortar specimens, and iii) concrete specimens which have each three kinds of water cement ratio. And each of the six kinds, of (ii) and (iii) specimens have three aggregate mixing proportions with different water cement ratios. The age of specimens covered from one day to 40 weeks. Immediately after the measuring of impulsive tone, each specimen was put to compression test. The summary of the results and conclusions is as follows: 1) A certain functional relation is observed to exist between the compressive strength and the frequency of the impulsive tone. 2) Generally, stronger specimens show higher frequency tone. 3) The relation mentioned in (2) depends largely upon the aggregate mixing proportion as well as water cement ratio. 4) At a given frequency, cement-paste specimens are stronger than mortar, and mortar than concrete. 5) When water cement ratio is defined, specimens having much aggregate show low compressive strength at the same frequency. 6) When aggregate mixing is defined, the decrease of water cement ratio in specimens results in lower compressive strength at the same frequency. 7) Formulas are representing these relations for concrete and cement-paste groups. for the group of concrete specimens [numerical formula] for the group of cement-paste specimens [numerical formula] F_c・・・compressive strength (kg/cm^2) f・・・frequency of tone 8) As for the rate of damping of tones, no clue relating to the strength of specimens are obtained, sofar as our present experiment is concerned.
社団法人日本建築学会の論文
1957-06-25

3.コンクリートの打音と強度との関係について

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