MICROSTRUCTURAL CHARACTERIZATION OF THE TRANSITION ZONE IN CEMENT SYSTEMS BY MEANS OF AC IMPEDANCE SPECTROSCOPY

The microstructure of the transition zone between aggregate and cement paste, and the effect of silica fume, slag , fly ash and latex (EVA) aggregate coatings were investigated by means of A.C. impedance measur ements. It has been demonstrated experimentally that the A.C. impedanc e technique has the potential to describe microstructural changes of t he cement-aggregate transition zone induced by surface modification of aggregate. Coatings of pozzolanic materials such as silica fume, slag , fly ash can increase the density of the transition zone. Latex coati ngs (eg. EVA) actually make the deposition of hydration products on th e aggregate surfaces more difficult and give rise to a more porous cem ent-aggregate interfacial zone.