Hygrothermal analysis of mass concrete by derived finite element

摘要

The present thesis deals with problems regarding mass concrete, in which the temperatureudrises due to the heat of cement hydration during the curing phase. A rise of temperature inudconcrete may result in cracking of young concrete. In the first part of the thesis cementudcomposition and its influence on the released hydration heat is described. The hydrationudprocess is explained by its individual phases which occur during hardening of concrete. Twoudtypes of cement are presented, the CEM I 42,5 R and CEM III/B 32,5 N SR-LH. The hydrationudheat released by those two types of cement differs significantly. Also an analytical expressionudis given for evaluation of heat release of cement.udNext, the discretization of the problem and the derivation of the coupled equations is made foruda single finite element. The derived equations are used to form a system of linear algebraicudequations, which is needed for calculation of the temperature and moisture distribution. Alsoudthe derived equations are used to write a computer program in MATLAB environment. Theudprogram is used as a tool for numerical hygrothermal analysis of mass concrete.udThe last part of the thesis presents the results of three different. The purpose of the firstudanalysis is to investigate the influence of the coupling degree between heat and moistureudtransfer. While the results of non-coupled and semi-coupled models seem reliable, the resultsudof a fully-coupled model are not realistic and therefore are not used in further analyses. Theudsecond analysis confirmed there is not much influence of semi-coupling on temperature fields,udso the equations can be solved separately and still give useful results. The third analysis showsudthe necessity of low heat cement use in mass concrete structures.