Requirements for permissible pauses of concreting during monolithic works

Introduction. The problem of “monolithicity” of structural concrete under construction has been and remains one of the most controversial in acceptance control in construction practice. The lack of clear criteria for assessing of cold joints presence arising during forced breaks in concreting, as well as differences in concreting conditions and properties of concrete mixtures, are among the main factors causing uncertainty in making a decision to reject the erected structure, or making a decision on the need for repair measures, or recognizing the erected structure complies with the project and does not requiring additional costs to ensure the design operational reliability. Lack of homogeneity of physical and mechanical properties of concrete separate parts of the monolithic structure creates stress-strain states of the power frame of the building that are not foreseen by the project and can provoke a threat to the safety of the structure, and lead to a reduction in the inter-repair service life of load-bearing structural elements.

Aim. The aim of the work is to clarify the conditions of cold joints occurrence when concreting depending on the technological properties of concrete mixtures and laying technology, to develop methods of their diagnosis, as well as the subsequent specification to define of the term “cold joint”, its characterization and formulation of proposals in order to make appropriate changes in regulatory documents.

Results. The results of the performed experiment do not support the requirement of the regulations to consider the boundary of the onset of setting as significant in terms of damage to the structure of concrete and the ability to have a noticeable effect on the drop in average strength due to the “loosening” of the “coarse aggregate – mortar” system. Despite the fact that in the series of such experiments it is required to consider more extended statistics, the obtained trends reduce the probability of identifying the beginning of setting as an indicative boundary of the rheological state, when the influence of vibration on reducing of concrete strength after its subsequent curing under favorable conditions becomes determinant.

Conclusions. The formulated and duplicating each other requirements of normative documents on the boundary condition of loss of conditional “continuity” of concrete properties in the body of the structure at simultaneous placement require revision and clarification based on the analysis of the previously performed and additionally conducted experimental studies.

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