Papers by Keyword: Autogenous Deformation

Abstract: The shrinkage of concrete is one of the main causes of cavity in concrete filled steel tube (CFST). In this paper, the effect of a kind of lab-made expansive agent on the deformation of CFST is studied. The laser displacement sensor combined with the round straight steel tube mould was adopted to test the deformation of concrete from the initial setting to 1 day after pouring, and the mechanical micrometer method was used to test deformation after 1 day in the laboratory. The full-scale model test was carried out to monitor the effect of expansive agent in CFST at the project site. The results show that, the addition of expansive agent produced significant expansion in the first 3 days, with the expansion basically compensating the autogenous shrinkage of the concrete; influenced by thermal deformation, the constraint action of steel tube to the core concrete in temperature rise stage was far greater than that in cooling stage. Compared with expansion produced in temperature rise stage, it is more important to produce expansion in cooling stage to solve the cavity problem of CFST.

Abstract: The temperature history of HPC remarkably affects their volume stability and mechanical properties, but no enough attention is pay to it in the literature. In this paper, for the purpose of clarifying the temperature effect of above-mentioned behaviors, a series of tests on autogenous deformation, compressive strength and elastic modulus of HPC are carried out. The outcome of research as follows: surrounding temperature intensely influences autogenous strain and mechanical indices; elevated temperature not only results in increased shrinkage strain, compressive strength and elastic modulus, but also accelerates their rates of development.

Abstract: Bedding cushion cracking in concrete dam is widespread, and has not been completely prevented [1,2]. There are many cracking causes of bedding cushion, including construction difficulty and structure requirements for concrete dam. Based on the method of FEM simulative calculation of temperature and stress fields of mass concrete using water cooling pipes, this paper makes relatively in-depth study on crack mechanism for concrete bedding cushion on rock. It is revealed that all three factors of uneven thickness of bedding cushion, thickness of new dam concrete placed on cushion after off period and foundation gallery upon bedding cushion have great influence on the tensile stress of bedding cushion and should be paid special attention during construction. The calculation results show that the tensile stress of thinner concrete cushion layer is much greater than the thicker one, and the thinner upon new concrete will also make greater tensile stress in cushion. As a result, both the thinner cushion layer and the cushion with thinner new concrete on it would have a bigger chance to crack than others. The mechanism is used to explain reasonably a dam crack in construction. Then some cracking prevention measures, which should have reference value for the construction of bedding cushion, are put forward in this paper.

Abstract: In order to establish a mathematic model of the autogenous deformation of concrete incorporating MgO as expansive agent, we study the characteristics of it. Based on the results of testing researches and testing data, we get a mathematic model, which can clearly reveal the characteristics of autogenous deformation of concrete incorporating MgO as expansive agent. Autogenous deformation of concrete incorporating MgO as expansive agent is steady, the expansion is not infinite and there is no retrogress. Age mainly influences the basic equation of autogenous deformation. The content of MgO (or fly ash) and temperature will magnify (or reduce) the deformation.