The Friedel's salt (Fs) is often formed when reinforced concrete is attacked by chlorides from marine environmental and/or thaw salts. In this investigation, a semi-quantitative analysis and study of the Fs (2h range = 11.16-11.34°) in the solid phase of the Frattini test was made by XRD analysis. For this purpose, two Portland cements (PC) P1 (14% C 3 A) and PY6 (<1% C 3 A), six pozzolans (M0 and M1, metakaolins, C and A, natural pozzolans, D, diatomite, and SF, silica fume) and 12 blended cements or POZC 70/30, except for SF 80/20, were used. The liquid phase of the Frattini test was 3.75% NaCl solution. Other complementary determinations were some specific chemical analysis and physic and mechanical properties of some cement tested. The experimental results have demonstrated that:
- All the pozzolans exhibited different pozzolanic activity depending on the mineralogical composition of the Portland cement with which they were tested, although such differences were attributable more to their Al 2 O rÀ 3 (%) content than to their SiO rÀ 2 (%) content for the case of the pozzolans A, C, M1 and M0 specially. Thus, M0, M1, C and A pozzolans mainly, tend to sustain [OH À ] content and react readily with Ca 2+ . On the contrary, for the SF and D pozzolans was due to their SiO rÀ 2 (%) content only, which react with both, Ca 2+ and OH À ions, in the same way. But despite what the physical state of D pozzolan is like SF, vitreous mainly and its SiO rÀ 2 content as well (practically), the size and shape of their respective particles (''frustules'' for D, empty, perforated sheaths) are totally different, and as a consequence, their respective behaviour in the Frattini test has been different as well. 2. In this investigation, the Friedel's salt (Fs) owns its formation to two different origins: the C 3 A of PC and to the reactive alumina, Al 2 O rÀ 3 , of pozzolans which reaction with chloride ions, pointing the latter as a preferential (see point 3); but it is also possible C 4 AF reactivity involved at later ages. 3. The role of the reactive alumina, Al 2 O rÀ 3 , and reactive silica, SiO rÀ 2 , (vitreous and/or amorphous fractions of the pozzolanic additions) during the Friedel's salt formation has been specified and, as a result, the formation rate of Fs from Al 2 O rÀ 3 of pozzolan turns out to be notably higher than the formation rate of Fs from C 3 A of PC. For this reason, both have been termed rapid forming Fs or Fs-rf and slow forming Fs or Fs-lf, respectively, but in any case, topochemical mechanism with prior dissolution must be preponderant over through-solution mechanism. 4. The Friedel's salt formation in all the PC/pozzolan blends have coincided quantitatively in the vast majority of the cases with the respective reactive alumina, Al 2 O rÀ 3 (%), content of each pozzolan. The number of these coincidences was greater for the PY6 blends, due to its C 3 A practical absence in these samples, since its presence in the P1 blends can stimulate directly, non-directly, but above all, indirectly the chemical reaction of the C 3 A hydration with NaCl solutions (3.75% and 3.00% in this study) and influence like that in the velocity of the compound formation: Fs. 5. The physical state of the reactive alumina, Al 2 O rÀ 3 , in C natural pozzolan must be more amorphous than vitreous, resembling metakaolin more than fly ash. That notwithstanding, pozzolan composition must have conditioned the water/cementitious material ratios obtained for their respective P1 and