Modelling of temperature, moisture and stresses in young concrete
Abstract (Summary)The present study consists of three areas, namely modelling of- (1) temperature, (2) moisture state, and (3) stresses in young concrete. The derivation of models, examination of material data, and development of computer programs have progressed differently in these areas. The first area, modelling of temperatures, is the most comprehensive and complete, since it has been researched more extensively than the other areas. On the other hand, the way of modelling stresses in this study is purely theoretical and has not been tested against empirical data, but gives some guidelines for future applications. Finally, the modelling of moisture state is somewhere in between the other two areas. The results can be applied to different fields of concreting, such as estimation of form stripping times, estimation of necessary measures to be taken in winter concreting, study of drying shrinkage cracking, and study of stresses due to varying temperatures in early age concretes. The aim of this report is not to discuss applications, but to give the background and material data used in the models for calculating the temperature, moisture state, and stresses in young concrete. It is shown that temperature can be modelled to within an accuracy of 1 to 2°C which is acceptable for most applications. However, it is essential to have good knowledge of both material data and environmental conditions. For the study of moisture states, a consistent model for the description of desorption and absorption isotherms has been developed. The treatment of both desorption and absorption isotherms in the same theoretical framework makes it possible to introduce scanning curves between these limit curves for subsequent drying and wetting. The effects of alkali have been modelled as an alkali equilibrium isotherm estimated from the known amounts of sodium and potassium oxides in the cement. The alkali influenced curve can be combined with any description of the isotherms with respect to the physically bound water. The need for considering the effects of alkali for higher humidities has been shown in moisture calculations.
School:Luleå tekniska universitet
Source Type:Doctoral Dissertation
Date of Publication:01/01/1994