Civil Engineering Reference
In-Depth Information
Table 17.3
Pull-out test findings (20
¥
20
¥
20 cm moulds) (Fernández-Jiménez and
Palomo, 2009)
Sample
denomination
Bar diameter
(mm)
Maximum load
(Q = kN)
Maximum load
t
(MPa)
Cracked area
H-CE
H-CE
H-FA-N
H-FA-N
H-FA-N
H-FA-W
H-FA-W
H-FA-W
16
16
16
16
16
16
16
16
95.49
122.6
136.6
142.15
124.59
102.94
101.09
99.95
11.88
15.24
17.0
17.7
17.5
12.8
11.6
12.4
Pull-out
Pull-out
Specimen fails
Specimen fails
Bar fails
Specimen fails
Specimen fails
Specimen fails
H-CE, Portland cement concretes; H-FA-N, fly ash concretes alkali-activated with
NaO; H-FA-WN fly ash concretes alkali-activated with NaOH + Na
2
SiO
3
.
Alkali-activated fly ash concrete bonding properties differ depending
on the activator used, but in all cases the materials tested by these authors
exhibited higher than the minimum 9.70 n/mm² beam stress requirement
for 16 mm diameter bars laid down in the Spanish structural concrete code
(eHe). concretes activated with a naoH solution reached higher maximum
stress values than the materials containing soluble silica in the alkaline
activator. in this latter case, in one of the three specimens tested the steel
bar failed before the matrix cracked (Fig. 17.11(c)). This is an indication of
the excellent matrix/steel bonding attained in these systems.
Rheology
The rheological performance of portland cement pastes, mortars and concretes
is, even today, an area difficult to analyse, very likely because of the many
factors involved in cement blending, mixing and hydrating (presence of
admixtures, batching, etc.). Several papers have shown the utility of rheology
for monitoring fly ash or metakaolin alkaline cement paste setting (Palomo
et al.,
2005; criado et al.,
2009; Poulesquen et al.,
2011; van deventer et al.,
2011). By contrast, practically no data can be found on mortar or concrete
rheology in the literature.
In a study of rheology in alkali activated fly ash pastes, Palomo
et al.
(2005) and Fernández-Jiménez and Palomo (2011) found that, like hydrated
Portland cement pastes, the Bingham visco-plastic flow model fits their
behaviour fairly well. They also observed that the type of activator is the
most significant parameter in determining paste rheology.
criado et al. (2009) studied the effect of commercial admixtures commonly
used in Portland cement concrete manufacture, such as lignosulphonates,
melamines (first and second generation products) and polycarboxylates (latest
generation) on alkali-activated fly ash pastes. According to their findings,
