Department of Mechanics: Seminar: Abstract Matschei

From thermodynamics to predictive engineering in cement and concrete

The use of thermodynamic methods in cement science was often doubted, as the cement-water system was considered to be too complex. However most of the people working in cement science or industry did or do still apply thermodynamics on a daily routine while frequently using Bogues equations to estimate the mass balance of cement clinkers based on a high temperature equilibrium of the quaternary system CaO-SiO2-Al2O3-Fe2O3. Others argued that cement hydration is a “non-equilibrium” process, which cannot be treated thermodynamically. Nevertheless Bogue showed already 80 years ago that metastable features can also be handled with thermodynamic approaches, provided sufficient knowledge is available.

In recent times thermodynamics was also applied to complex cement hydration processes. It was shown that cement hydration follows a consistent thermodynamic pathway which can be described with specific models to a relatively high degree of accuracy, provided that the necessary thermodynamic data are available. During the past 20 years the composition of cements changed significantly – blended cements dominate the markets in many countries. As a consequence engineers cannot rely anymore on experiences gained in the past, mainly from OPC systems. Generic tool kits e.g. thermodynamics coupled with focused experiments help to understand and predict the complex hydration behaviour of blended cements. An example relevant to blended cements will be discussed.

Finally I will show one example on applied thermodynamics which concerns the development of predictive tools for engineers to master complex challenges of the construction industry which is directly related to a very important thermodynamic property: Heat of hydration. Hydration reactions are very exothermic. As a consequence during hardening of massive concrete structures temperature induced stress strains due to heat gradients in concrete may appear and lead to cracking, etc. With help of a tool developed together with CTU Prague we are now able to better master temperature evolution in massive concrete elements and to optimize the choice of binder and the related mix design of concrete in order to minimize temperature-induced stresses in concrete.