Abstract
Self-compacting concrete (SCC) should generally be placed continuously, but it is not uncommon for contractors to be forced to use interruptions in concrete works due to delivery delays. The multilayer casting of SCC can cause weak bond conditions in the contact area of subsequent layers. Methods of preventing cold joint or lift line formation for normal concretes are not suitable for self-compacting concretes. This article provides research on the effect of multilayer casting technology on the bond strength between two layers of SCC. Three technological variants of connecting successive layers of SCC mixture on beam elements were analyzed: The free flow of the mixture, dropping the mixture from a greater height, and mechanical disturbance of the first layer. Three delay times were applied: 30, 45, and 60 min between two layers of SCC. In general, the research revealed that, regardless of the multilayer casting variant, the bond strength between two layers decreased as the delay time was extended. The best performance and the lowest drop in bond strength were obtained for samples with a mechanically disturbed first layer, independent of the delay time. This method gave similar results to a reference element made without a break in concreting. It was also demonstrated that current recommendations and standard guidelines for multilayer casting appear to be insufficient for ensuring an adequate bond between layers.
Highlights
One of the most valued features of concrete is the possibility to form a complete structure from it—known as a monolithic reinforced concrete structure
The results enabled us us to to formulate recommendations for the multilayer casting of self-compacting concrete (SCC), in order to reduce the impact of formulate recommendations for the multilayer casting of SCC, in order to reduce the impact of delays delays between successive layers on the mechanical strength and durability of the beam-type structure
In the casecase of this variant, no significant loss loss of bond strength between successive layers was observed in the examined delay of bond strength between successive layers was observed in the examined delay time time range.range
Summary
One of the most valued features of concrete is the possibility to form a complete structure from it—known as a monolithic reinforced concrete structure. It is often not possible to perform all of the works at one time. Interruptions in concrete works can result in the formation of cold joints or lift lines between successive layers. As a result, this can lead to a deterioration of the strength properties of the hardened concrete, its durability, and the surface finish. Interruptions in concrete works, especially when combined with rapid workability loss of the mixture, results in visible marks in the contact areas and discoloration of the concrete surface [1]
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