IMF2017

Cementing materials have been widely used throughout the history of humanity. In ancient Egypt stone blocks were fixed together with sand and burnt gypsum. The Romans discovered that opus caementicium could be made by mixing volcanic ashes from Pozzuoli village near Vesuvius with burnt lime and were using on a large scale in ancient constructions. Beside of its long history and common applications, cement presents also an attractive material for science. In this report, we present the results of magnetometric and dielectric measurements of dry and hydrated cements and mortars. In dry cements, the main magnetic phase is C₄AF (in cement chemistry notation) brownmillerite with formula Ca₂Al_2-xFe_xO₅ and intriguing physical properties depending on iron content. Ca₂Fe₂O₅ oxide (x=2) is known as a good ionic conductor in which O^2- ions can easily migrate along FeO₄ tetrahedral layers. It exhibits also pronounced magnetoresistance effect and belongs to G-type canted antiferromagnets with the Néel temperature T_N ≈ 770 K. For x < 1.5 this ferrite undergoes a phase transition to noncentrosymmetric Ibm2 structure and begins exhibit ferroelectric properties with strong magnetoelectric coupling and spin flop transitions. During the hydration reaction, C₄AF phase transforms and the properties of cement or mortar are dominated by magnetic nanoparticles of ferrith i.e. the ferrimagnetic phase of ferrihydrite 5Fe₂O₃·9H₂O. The evolution of magnetic moment of metastable ferrith and ferrihydrite phases allows investigating a progress of hydration reaction in cement.