طرح مخلوط بتن برای پاسخگویی به مقاومت و گرمای هیدراسیون
Abstract
1- Introduction
2- Current state of knowledge
3- Materials and methods
4- Results and discussion
5- Conclusion
References
Abstract
In the case of massive concrete structures, the heat generated by cement hydration may cause cracking due to thermal strains. The mix design of the concrete used for such structures has to take account of mechanical properties and generated temperatures. Using experimental design principles, the hydration heat and the development of compressive strength are measured in order to determine how the composition of concrete and the presence of SCM influence the characteristics of concrete and to create a mix design protocol. This protocol can help to determine which mix design minimizes the hydration temperature for a given compressive strength.
Introduction
In massive structures, the exothermy of the hydration reactions of cement and the thermo-hydro-mechanical behavior of early age concrete can lead, if strains are restrained, to the development of compressive and tensile stresses. If the tensile stresses exceed the tensile strength, cracking may occur, threatening the durability of the concrete. In order to prevent the risk of cracking as well as that of Delayed Ettringite Formation (DEF), sulfate resisting cement and the use of additions are recommended [1]. Mineral additions such as limestone, slag or fly ash can also be added to concrete to decrease the exothermy of hydration reactions and, in the case of slag and fly ash, protect against DEF. The aim of this research is to obtain a tool which optimizes concrete mix design while respecting classical specifications such as the compressive strength after 28 days and minimizing the temperature rise in massive structures. To do this, the impact of several parameters of cement (composition and fineness) and of concrete (type and percentage of additions, W/B ratio, chemical admixtures) on the rheology, hydration heat and mechanical strength of concrete have been studied by means of an experimental design. The influence of the different factors is analyzed and a concrete mix tool is proposed. Finally, this tool is applied to the case of massive concrete structures.