NON-DESTRUCTIVE EVALUATION OF INTERFACE FRACTURE BETWEEN MATRIX AND AGGREGATE

Preliminary investigations have clearly indicated that ultrasonic transmission technique is a suitable method for evaluating crack initiation and growth at the interface between matrix and aggregate in concrete under mechanical load. But since there is no unique coherence between alterations in the ITZ and ultrasonic wave propagation additional information from a direct measuring technique is necessary. This paper deals with a combined application of indirect ultrasonic transmission technique and a direct visualization method during compressive loading of “two-dimensional” model concrete, which represents real concrete in one plane. Specimens varying matrix and aggregate properties were subjected to alternately increased and decreased loading while ultrasonic transmission was observed. Furthermore, direct measurements have been carried out by applying an image correlation based visualization technique. With the help of this method, full field displacements of the specimen surface with accuracy at the micron range could be determined. Based on a correlation between frequency-dependent attenuation of ultrasound and alterations in the interface under defined levels of stress and furthermore in consideration of the theory of elastic wave propagation, a quantitative model could be derived, which describes the influence of interface fracture between matrix and aggregate on ultrasonic wave propagation.

• INTRODUCTION

• EXPERIMENTAL TECHNIQUES

• EXPERIMENTAL CONCEPTION AND INVESTIGATION

• RESULTS

• DISCUSSION

• CONCLUSION AND OUTLOOK

• REFERENCES