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Abstract

This study examines the 28-day strength properties of concrete under shaking, such as from an earthquake, during its strength development period. With a concrete strength of 20.59 MPa (3,000 psi), groups of concrete cylinders were made and tested on a shaking table. The peak value of ground acceleration (PGA) level of the simulated earthquake and the cylinder age are the two variables considered. The test results are as follows. If the concrete is older than three days, the earthquake excitation will not significantly reduce its 28-day strength. At younger than two days, earthquake excitation will reduce the strength of the concrete. The largest reduction in strength was approximately 28%. The 28-day concrete strength was partially recovered up to 50% by appropriate curing, if the concrete suffers earthquake excitation within one day after placement. Additionally, earthquake excitation did not greatly affect the 28-day elastic modulus and the ultrasonic pulse velocity, when the concrete was properly cured.

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