To preserve and extend the durable service life of existing deteriorating or otherwise structurally inadequate structures is an important problem currently facing the construction industry all over the world. Designing structures with adhesive bonded components is a relatively new concept to the construction industry [1]. The technology is, simple, cost-effective, and yet, a technically sound and reliable method which can enhance the performance of structures and extend the quality of their service life. The success of this patch bonding strengthening technique also depends on the type of epoxy used [2, 3]. Existence of crack between any bonding interface or crack of adhesive layer will reduce the effectiveness of strengthening function and cause premature failure of the composite system. Hence, from public safety concern, there is a crucial demand to develop some techniques which can be easily applied in the construction site to quantitatively evaluate the bonding condition between the steel plate and strengthened concrete structure. Furthermore, this technique can be used not only to evaluate the performance of the bonding condition after repair but also to ensure the fullness of adhesive injected into the gap between steel plate and concrete surface. So far from the literatures, it is hard to find any convenience and quantitative method which can detect the bonding condition between the steel plate and epoxy adhesive material at working field. Although, traditionally we can simply use a small hammer to impact the steel plate and listen the anomalous vibrating sound reflected the flaw area underneath the plate. Due to the large contrast of acoustic impedance between steel and epoxy materials also makes the measurement and detection of disbound condition using conventional ultrasonic method [4] as a tough problem.
In this paper, the bonding condition between the steel plate and concrete structure is investigated by using the impact echo method [5] and ultrasonic method both in time and frequency domains. A new mixed method is introduced to detect and display the debonding area between the epoxy bonded steel plate and concrete structure. A simple criteria is established based on the amplitudes of the multiple reflection echoes among layers of steel plate, adhesive and void. Test results show that this simple method can detect small debonding zone quite accurately and can be easily applied in field by engineers to ensure the safety and control the quality of strengthened concrete structures. REFERENCES
- A. Nanni, "Concrete Repair With Externally Bonded FRP Reinforcement", Concrete International, June 1995, pp. 22-26.
- R. Jones; R. N. Swamy and A. Charif, "Plate Separation and Anchorage of Reinforced Concrete Beams strengthened by Epoxy- Bonded Steel Plates, " The Structural Engineer, Vol. 66, No. 5/1 March, 1988, pp. 85-94.
- M. D. MacDonald and A. J. J. Calder, "Bonded Steel Plating for Strengthening Concrete Structures", International Journal of Adhesion and Adhesives, Vol. 2, No. 2, April 1982, pp. 119-127.
- J. Krautkramerand H. Krautkramer, "Ultrasonic testing of Materials", 3rd Ed., Spring-Verlag, New York, 1983.
- M. Sansalone and Y. Lin, "Detecting Delaminations in Concrete Slabs With or Without Overlays Using the Impact Echo Method, " ACI Materials Journal, pp. 175-184, 1989.
NDTnet
