Thermal properties and modeling of aluminosilicate materials for low temperature bulk applications

摘要

This thesis concerns itself with the thermal properties of aluminosilicate materials such as cements, blended cements and clays and their application to the problem of radioactive waste encapsulation.;The objective of this thesis is to study the thermal properties (heat of hydration, thermal conductivity and diffusivity) of these materials and to determine their effect on the temperature in large monoliths and on the material itself. During the hydration process changes occur in the strength, microstructure and phase chemistry of cementitious materials. These changes are compounded by the exothermic nature of hydration which results in higher temperatures, in turn leading to accelerated reactions and possibly the formation of different hydration products.;In this thesis the hydration temperatures for the extreme conditions (adiabatic) were experimentally measured and compared to those predicted under real conditions. Such a simulation can be made by measuring the thermal properties and studying the temperature distribution predicted by a finite differences computer model.;Measurements of adiabatic temperature rise were made using a computer-controlled adiabatic calorimeter which was designed and developed for this thesis. Conditions very close to zero heat exchange with the environment were achieved. The existence of this method made it possible to actually observe the fact that cement hydration results in "boiling off" of the water in such conditions. A number of additives were tried to prevent this.;It was observed that waste or by-product materials such as blast furnace slag and fly ash could be used to dramatically reduce the temperature in large bodies. These materials also reacted extensively with the highly alkaline radioactive waste solution to form hydrogarnet and zeolitic material which had useful cementing properties.;The conclusion was reached that a selection of blends of aluminosilicate materials can be utilized for providing the proper thermal environment for long-term geological disposal of radioactive waste.