Role of the filler on Portland cement hydration at early ages

Comportamiento de los cementos Pórtland con puzolanas silícicas frente al ataque del yeso, determinado mediante el Método ASTM C 452-68

“…In any case, either all the POZC-Z pozzolan are store in a curing tank of water at (23 ± 1.7) ºC for 14 days, before the sulphate attack, like the Le Chatelier-Ansttet test (6,15,22,34) points out, or none does not, like the ASTM C 452-68 (1) points out. However, a perspective of some POZC-Z pozzolan storing in a curing tank of saturated limewater at (23 ± 1.7) ºC during several days (different (33), como es también lógico, dando por resultado final mayor expansión, y pudiendo ser, además, precursora de la formación ulterior de thaumasita a edades avanzadas (34)), pero sin olvidar tampoco la vía no-directa (33) de estimulación de la hidratación (selenitosa, en esta caso también), sin más, del C 3 S y el C 2 S del CP. Por esta razón, no tiene por qué extrañar que ningún cemento tipo CEM II/A-L, II/B-L, II/A-LL, II/B-LL, II/A-M ni II/B-M de la Instrucción RC-08 (35), ni de la nueva norma EN 197-1 (36), haya sido considerado RS.…”

“…The despair behavior exhibited by the SF specimens, from the age of 7 days up to 28 days, or Eq. [1], could be justified by stimulation of hydration, by direct and non-direct way (18,22,25,33) especially, since the SF (vitreous microspheres, principally) should have exerted its influence over the PC fraction, with which it was mixed in each POZC-SF, and particularly, over its C 3 A content (stimulation by indirect way (18,25), the SF should have exerted it also, since it has met the Frattini test requirements (41) at the very 1 day-age, that is to say, 7 or 14 days before the standard age (35), and particularly, at 16 hours of the beginning of selenitous hydration (22), that is why its action would have been overlapped by both direct and nondirect stimulations effects), not in vain, its humidity adsorption finished clearly being the highest from the other three Z pozzolans at the age of 28 days (Table 6); although the humidity adsorption for N pozzolan was major up to the age of 21 days, it is also true that this supremacy should have been provoked by its ≈ 20.3�% of calcite filler, and not so much by its another fraction of ≈ 79.66% of diatomite� since the humidity adsorption of D po��olan� with its ≈ 99% of diatomite (vitreous frustules, spongy and empty, of major size than, also vitreous, microspheres of the SF), was, on the contrary, the lowest from the others. It must to be emphasized here that calcite filler Examinando en segundo lugar, las curvas de sus co-• rrespondientes PUZC con puzolana Z a la edad de 7 días, se puede observar que sea cual fuere el máximo valor de Vcl 7d que se considere, dicho valor ha sido siempre menor que el correspondiente valor de Vcl 7d que se habría alcanzado considerando la puzolana Z como un "inerte RS ".…”

“…Puesto que, como es sabido, el árido calizo, fino y grueso, facilita a la par que aumenta el ataque de los sulfatos al hormigón, y el filler calizo también lo facilita como el propio (26,(30)(31)(32). Tanto por vía directa (33), en su doble vertiente: estimulación de la hidratación selenitosa, en este caso, del C 3 A del CPO, por el agua de amasado que los humedeció inicialmente, y formación adicional con dicho C 3 A de tri-, mono-y/o hemi-carboaluminato de calcio hidratado, como por vía indirecta, pero esta vez, sin actividad puzolánica alguna de por medio, lógicamente (formación preferente de mono-carboaluminato de calcio hidratado en detrimento de Fase AFm que se transforma en ett-lf in ett-lf (33), resulting finally in greater expansion, as logical as well; in addition, it may also be a precursor to thaumasite formation at advanced ages (34), but also not forgetting the non-direct sulphatic hydration stimulation (33) (26) state as a conclusion that "This test method procedure, ASTM C 452-68, may not be an appropriate tool for determination of sulphate resistance of blended cements, since sulfate exposure occurs before the pozzolanic effect", since whether this affirmation was supposedly true, it had also been applicable for the ASTM C 1012 method. The reason for such a supposition is that, except the pozzolans SF and MK, which fulfill the Frattini test already at 2 days age (18,22,23,25), and inclusively at 1 day age (25), many natural and artificial pozzolans (fly ash included) need at least 28 days (14,(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46) in order to develop the mayor part of their whole pozzolanic activity (14)(15)(16)(17)(18).…”

“…Because of the results and the conclusions obtained by these authors (26), achieved in base of the following cementitious materials: 1 SRPC, 1 OPC and its 2 POZC with FA+NP (BC1 and BC2) and 1 POZC with NP (BC3), which have been submitted to the both ASTM C 452 (1) and C 1012 (27) methods, these final statements might be debatable only when calcareous fine aggregate instead of the siliceous and graduated one of the ASTM C 778-92a type (28) would have been used, which is mandatory for these two methods. Since the calcareous aggregate, both fine and coarse and their respective filler, facilitates and increases the sulphate attack to concrete, even when the applied cement is SRPC (26,(30)(31)(32), by means of both direct way (33) (in its double aspect: sulphatic hydration stimulation of the C 3 A present in OPC, in this case, by the mixing water that moistens the surface of their particles during initial mixing, and additional calcium tri-mono-and/or hemi-carboaluminate hydrated formation from C 3 A origin of OPC), and indirect way (33), but this time, with no pozzolanic activity, logically (preferential formation of calcium mono-carboaluminate hydrated instead of AFm phase which is transformed ett-vlf (o de origen el C 4 AF del mismo CPO en las mismas circunstancias), debe de ser lógicamente más bien independiente que inter-dependiente o combinada (16)(17)(18).…”

Ataque de matrizes cimentícias por sulfato de sódio:adições minerais como agentes mitigadores

“…As adições minerais, independentemente do tipo (inertes, cimentantes ou pozolânicas), exercem efeito físico sobre a cinética de hidratação do cimento, pelos efeitos de diluição e de nucleação heterogênea [18][19][20], enquanto as adições ativas (cimentantes e pozolânicas), além do efeito físico, exercem efeito químico, com formação de C-S-H SECUNDÁRIO . As diferentes microestruturas hidratadas formadas quando da presença de adições minerais comportam-se distintamente frente à ação de agentes deletérios.…”