Evaluation of Elastic Anisotropic Relations for Plain Concrete Using Ultrasound and Impact Acoustic Tests

Abstract

Concrete is considered an isotropic material for structural analysis and design purposes. However, during concrete placement and compaction, segregation and bleeding may occur. A water film is deposited around larger aggregate particles, especially on the bottom surface. This effect was already identified in the literature as a cause of anisotropy in compression strength, but there is no evidence of anisotropy of concrete in terms of elastic constants. In this paper, impact acoustics and ultrasound measurements were used to measure dynamic elastic properties in prismatic specimens (125×125×400 mm). The specimens were produced with two directions of concrete placement and compaction: longitudinal and transversal. Three concrete batches were produced with high, medium, and low percentages of cement. Five identical specimens were produced for each combination of concrete mix and direction of concrete placement. A pattern of anisotropy was identified for all specimens through natural frequencies of the specimens and measured ultrasonic wave velocities. Although this effect is small, it could be clearly identified by impact acoustics and ultrasonic tests.