Examination and evaluation of factors influencing the bond strength between old and new concrete

Title: Examination and evaluation of factors influencing the bond strength between old and new concrete
Author(s): Andreas Müller, Konrad Zilch
Paper category : conference
Book title: 2nd International RILEM Symposium on Advances in Concrete through Science and Engineering
Editor(s): J. Marchand, B. Bissonnette, R. Gagné, M. Jolin and F. Paradis
Print-ISBN: 2-35158-003-6
e-ISBN: 2351580028
Publisher: RILEM Publications SARL
Publication year: 2006
Nb references: 18
Language: English

Abstract: A good bond between old and new concrete is essential for the success of many structural repair and strengthening measures. Strength and durability of the bond depend on a variety of independent and interdependent factors. In order to achieve sufficient bond strength in a reliable manner, it is mandatory to take into account all decisive factors. Since questions concerning the evaluation of certain parameters, e.g. the surface roughness of the old concrete, have not been solved so far, an accurate “prediction” of the bond behaviour is hardly possible.
In order to gain a better understanding of factors influencing the bond strength, a research project based on a systematic experimental investigation was performed at the Technische Universität München in 2004/2005. Some of the main results are presented in this paper.
The investigated parameters consisted of the strength of the new and old concrete, the water content of the concrete substrate, the treatment and the roughness of the surface and the rheological properties of the new concrete at the time of its application. The concrete strength was varied from normal to high strength; the water content ranged from dry to wet; the surface of the concrete substrate was roughened by means of water jetting or sandblasting with different intensity; the flow ability of the new concrete was varied by adding different specific amounts of superplasticiser. Besides of vibrated concrete also self-compacting concrete was applied.
The bond strength was investigated by performing tensile splitting tests on cubes which were sawed out of small plates consisting of old and new concrete. By applying the splitting force in the plane of the interface between old and new concrete, failure was caused in the relevant area.
In sum, almost 500 tensile splitting tests on monolithic and bonded specimens were performed. The evaluation of the experiments clearly showed that the bond strength is significantly influenced by the surface roughness of the old concrete and the “wetting properties” of the new concrete. The findings of this research project could lead to a more realistic estimation of the bond strength and therefore to improvements of structural repair and strengthening measures.

Keywords: adhesion, bond strength, surface roughness, HPC, flow ability

Online publication: 2006-08-02
Classification: 3.3 Theme 3: Monitoring, Repair and Maintenance of Concrete Structures
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2351580028.102