Crystal growth of Friedel's salt originated from pozzolan and Portland cement

Abstract

In the present paper, the Equilibrium Crystal Growth theory is applied to describe Friedel's salt (Fs) formation from two different routes C 3 A phase of Portland cement (PC) and Al 2 O 3 r-(reactive alumina) of pozzolans. Both of the reaction courses are contrasted and the role of reactive components (with an emphasis on Al 2 O 3 r-particularly) is discussed in detail.The experimental part consisted in PC blends elaboration with different natural and artificial pozzolans, (metakaolin, natural pozzolans, diatomite, silica fume), which were after subjected to chloride attack (3.75% NaCl). For this purpose, two Portland cements of different chemical composition from the C 3 A content point of view, have been selected. The samples have been analyzed by XRD and SEM techniques, as well as by selected Cement Chemistry standard methods.The applied methodology has permitted to opine about the kinetics aspect involved and their direct relation to the physical aspect of the originated crystals. The results show a significant difference in morphology of the Friedel's salt in function of its origin (Figure 1), which is directly related to its formation rate.The importance of reactive alumina, Al 2 O 3 r-, component of pozzolans is once again exhibited because of its contribution to the direct, non-direct, but above all, indirect stimulation of the C 3 A phase saline hydration (or non-saline) from the fraction of OPC with which it was mixed, due to its high, fast and early pozzolanic activity and, for this reason precisely, it is found more specific than generic, intensifying at the same time the Friedel's salt formation from the OPC origin. In contrast, the also high, fast and early pozzolanic activity of reactive silica, SiO 2 r-, of pozzolans for the same results is not specific at all, on the contrary, it is unspecific, or perhaps more precisely, insufficiently specific for the same purpose than [1] J. Garrido, "Forma y estructura de los cristales", Editorial Alhambra, S.A.