Civil Engineering Reference
In-Depth Information
10.3-10.5, which were insufficient for full steel passivation. However, the
same authors prepared blended BCSAF (with 15 wt% of oPC) which showed
comparable steel protection to pure oPC. In any case, the studied BCSAF
clinkers were far from optimized with Al
2
o
3
contents close to 7.3 wt% and
so, C
4
A
3
S contents as low as 5-7 wt%.
Pore solution data for aBCSAF cements has been reported (G. S. li et al.,
2007). However, these data were determined at a very high W/C ratio, 20.
Elemental concentration evolutions within the first 24 hours were reported
(Al, Ca, S and na + K) but pH values were not given. Passivation studies of
aBCSAF mortars are lacking, but the high reactivity of belite may slightly
increase the pH of the free water which is key for its technological success.
Much more research is needed concerning the alkalinity of aBCSAF mortars
and their potential for steel passivation.
18.5 Durability of calcium sulfoaluminate
concretes
Properly produced mortars and concretes from yeelimite-containing cements
are durable binders. However, depending in the environment in which these
mortars or concretes are serving, degradation processes should be taken into
account. degradation may occur through a variety of chemical processes,
i.e. carbonation, sulfate attack or chlorine diffusion. All these effects need
ion diffusion through porous microstructure. The CSA or BCSAF cement
hydration process consumes the available water in a short time, which stops
the evolution of total porosity. Moreover, the large amount of hydration
products generated at very early stages decreases the interior pore space
(Bernardo et al., 2006; García-Maté et al., 2012), consequently, resistance to
diffusion is enhanced. A durability study with two commercial CSA cements
(W/C mass ratio of 0.56) was reported and the characterization techniques
included carbonation (and accelerated carbonation), sulfate resistance, chloride
ingress, in addition of compressive strength and expansion (Quillin, 2001).
These concretes showed excellent sulfate resistance and slightly higher
carbonation rates than oPC concretes.
Atmospheric carbon dioxide is able to react with hydration products by
dissolution in the pore solution of the pastes, and so increasing Co
3
2-
ion
concentration. This phenomenon will cause three effects: (i) lowering of
pH value, (ii) precipitation of CaCo
3
by the reaction of carbonate ions with
Ca
2+
ions and (iii) possible deterioration of ettringite. As mentioned before,
porosity (or W/C ratio) determines the degree of resistance to carbonation.
Zhang and Glasser (2005) reported a study about two Chinese concretes:
(i) a normal strength concrete sample from a crane column made during the
cold winter of 1982 with hot mix water with W/C = 0.55-0.60 and by adding
1 wt% of nano
2
as anti-freeze; and (ii) a high-strength concrete sample
