Percorrer por autor "Dias-da-Costa, Daniel"
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- Effect of surface preparation and bonding agent on the concrete-to-concrete interface strengthPublication . Santos, Dinis S.; Santos, Pedro M.D.; Dias-da-Costa, DanielConcrete-to-concrete interfaces are present both in new and existing structures. Two distinctive situations can be identified: (1) placing hardened concrete against hardened concrete parts, such as the case of precast members for viaducts and bridge decks; and (2) placing fresh concrete against hardened concrete parts, such as the rehabilitation and strengthening of existing structures by concrete jacketing or concrete overlay, among other techniques, as well as the use of precast members placed on site to later receive a cast-in-place concrete layer. The bond strength of the concrete-to-concrete interface is influenced by several parameters but mainly by: (1) the surface preparation; (2) the use of bonding agents; (3) the compressive strength of the weakest concrete; (4) the moisture content of the substrate; (5) the curing conditions; (6) the stress state at the interface; (7) the presence of cracking; and (8) the amount of steel reinforcement crossing the interface, among others. This paper presents an experimental study conducted to assess the influence of the surface preparation and bonding agent on the bond strength of the concrete-to-concrete interface. The contribution of the substrate moisture is also addressed. Experimental results are discussed and conclusions drawn.
- A modified slant shear test designed to enforce adhesive failurePublication . Saldanha, Rui; Júlio, Eduardo; Dias-da-Costa, Daniel; Santos, PedroPresently, there are several tests available to evaluate the adhesion between concrete layers cast at different times. Among these, the Slant Shear Test (SST) has a wide spread use, mainly for being sensitive to the roughness of the interface surface, one of the most influencing parameters in this scope, but also because of the simplicity of the experimental setup. However, the major drawback of this test is the fact of being often obtained cohesive (monolithic) failures, therefore providing a lower bound of the interface strength, which is related with the concrete compressive strength. To definitely solve this issue, i.e., to enforce adhesive (interface debonding) failures in all situations, the 'Modified Slant Shear Test' (M-SST) was herein designed and developed. Both numerical and experimental tests have been conducted to validate this new method. All relevant conclusions are presented. In summary, it can be stated that the M-SST always enforces adhesive failure, therefore allowing to accurately assessing the adhesion of concrete-to-concrete interfaces.