Interfacial bond properties for ECC overlay systems

[摘要] Bonded overlays are increasingly used in concrete and reinforced concrete repair and rehabilitation applications,despite the high probability of interfacial debonding. Reasons for such failures include inefficientsubstrate surface preparations, inappropriate overlay materials, poor curing conditions and time dependentinfluences.The introduction of engineered cement-based composite (ECC) as an overlay or repair material, doesnot only address durability aspects but also structural performance. The associated ductility of the materialinduces a high performance aspect where applied. It is crucial to execute reliable design methods,especially at interfacial level, in order to harness the ductility at hand. The fact of the matter is thatthrough identifying the required performance, one can engineer an optimal bond through implementationof reliable substrate surface preparation techniques (SSPT's).ECC is a material which exhibits ductile mechanical behaviour. The material matrix is reinforced withsynthetic fibres, in the case of this study, poly vinyl alcohol (PVA) fibres were used. The introduction offibres induces strain-hardening behaviour when in tension. Strain-hardening occurs from the first crackonwards and is accompanied by ductile behaviour, due to a multiple cracking phenomenon. Multiplecracking continues until the increased tensile load incurs localising of an existing crack.The literature study investigates bond properties and bond model parameter test methods. A review ofcomposite design, mainly concrete to concrete, in local and international codes discloses design specificationstowards calculating interfacial shear bonds. The interfacial transition zone (ITZ) between theaggregate and cement matrix of concrete is used to define the interfacial bond characteristics and processes.The next step is to investigate a variety of interfacial shear and tensile test methods, in order toimplement the most suitable tests.

[发布机构] Stellenbosch University