Civil Engineering Reference
In-Depth Information
metakaolin (Zhang and Malhotra, 1995; Kim et al., 2007; Vejmelková et
al., 2010), when pozzolans are used in limited amounts (e.g. 10% for silica
fume). High-volume fly ash (> 40%) concrete can also be resistant to internal
cracking, on condition that the w/b is lower than 0.35 (Langan et al., 1990;
Langley et al., 1989).
Surface scaling
is much more dependent on the type and content of
pozzolan, and also on the curing time. The scaling resistance is usually
reduced when SCMs are used (Fig. 8.9 right). All SCMs are concerned:
fly ash (Gebler and Klieger, 1986b; Pigeon et al., 1996; Zhang et al., 1998;
Boyd and Hooton, 2007), GGBS (Stark and Ludwig, 1997; Saric-Coric and
Aitcin, 2003; Boyd and Hooton, 2007; Battaglia et al., 2010), silica fume
(Sabir, 1997) and metakaolin (Zhang and Malhotra, 1995; Vejmelková et al.,
2010). A few authors believe that the decrease in de-icer scaling resistance
is related to carbonation of the surface layer of the concrete, which produces
metastable calcium carbonates soluble in NaCl (Stark and Ludwig, 1997;
Battaglia et al., 2010).
Nevertheless, a few exceptions have been found, for instance for fly ash
up to 30-50% (Bilodeau et al., 1991; Naik et al., 1995a) or silica fume at
10% and low w/b (Bilodeau and Carette, 1989; Hammer and Sellevold,
1990). It should be noted that a difference is sometimes observed in field
cured specimens since GGBS concrete, for instance, can perform relatively
well up to 25-35% of GGBS (Boyd and Hooton, 2007; Bouzoubaa et al.,
2008).
8.3.4 Mechanical stresses: wear of concrete surfaces
Mechanical damage such as wear of concrete can mainly be caused by impact,
abrasion, erosion or cavitation. These effects concern the surface of the
concrete and are due to attrition by sliding, rolling, scraping or percussion.
Wear of concrete surfaces can occur on concrete pavements such as roads
and industrial floors, for instance, when mechanical stresses locally exceed
the strength of concrete. It can be initiated in the hydrated cement paste,
in the aggregates or in the paste-aggregate interface by aggregate pull
out. It has been pointed out that the wear resistance of concrete depends
on the strength and hardness characteristics of the concrete constituents,
including paste-aggregate bond strength. These characteristics are themselves
influenced by several factors such as the water-cement ratio, the type and
grading of aggregates, the presence of SCMs, air-entrainment, the finished
surface condition and the duration of curing (Hilsdorf, 1995; Neville, 1995;
Lawrence, 1998).
The behaviour of SCMs regarding abrasion resistance is strongly correlated
to the compressive strength of the concrete, as shown in Fig. 8.10. This figure
summarizes several relative results (81) taken from the literature for fly ash
