ABSTRACT
Radical Concrete Technology. Edited by R K Dhir and P C Hewlett. Published in 1996 by E & FN Spon, 2-6 Boundary Row, London SE1 8HN, UK. ISBN 0 419 21480 1. ABSTRACT. The greatest stability of properties is found in expansive cements made on the basis of calcium aluminate sulphate and/or the formation of ettringite. The factors influencing the properties of ettringite-forming expansive cements are represented in a phenomenological model. The factors influencing the properties and the process of expansion are analysed. By controlling the process of hydration during the hardening of the expansive cement the linear change of length may be kept within the range of 0.1 to 200mm/m and the properties of concrete and reinforced concrete structures may be improved. Expansive cements which are produced by mixing commercial portland cement with an expansive component offer considerable technological advantages and possibilities of further development. Keywords: expansive cements, controllable formation of structures, ettringite, pH-value, pore structure, durability Dr Igor Chartschenko is Ass. Prof, of the Institute of Building Materials at the University of Architecture and Building in Weimar, Federal Republic of Germany. Professor Dr Joachim Stark is director of the Institute of Building Materials at the University of Architecture and Building in Weimar, Federal Republic of Germany
PHENOMENOLOGICAL MODEL OF EXPANSIVE CEMENTS Practical experience shows that the greatest stability of properties is found in expansive cements made on the basis of calcium aluminate sulphate and/or the formation of ettringite. The properties, i.e. first of all the process of expansion, which may be represented in the form of a tree (“expansive cement tree”) (fig. 1), depend on “external” and “internal” factors of influence. By the influence of these factors on the mechanism of ettringite formation, on the morphology of ettringite phase, on the amount of ettringite phase formed, on the kinetics of ettringite formation and on the properties of the portland cement matrix, which is called the fifth root of the expansive cement tree, the process of the formation of microstructure during the hardening of expansive cement can be controlled. The “external” factors of influence are temperature (sun), moisture (rain or drying-out) and the extent of impediment to the expansion process.
