Page 164 - New Trends in Eco efficient and Recycled Concrete

136 New Trends in Eco-efficient and Recycled Concrete

In the second article published, the authors compared the results obtained by
different pozzolans and diverse methods [strength activity index (SAI), Frattini test
and the saturated lime test] (Donatello et al., 2010b). The saturated lime method is
similar to the Frattini test, but in this test, the pozzolan is mixed with a saturated
lime solution. The amount of lime fixed is measured with the determination of the
residual dissolved calcium. The authors concluded that the SAI and Frattini test are
standardised methods with good correlation between them. The saturated lime test
did not have a good correlation with the other methods. The reactivity of SSA is
less than MK, pulverised FA and SF.
Dyer et al. (2011) studied pastes with SSA with XRD and showed the presence
of a poorly crystalline component with phosphorus. The compound was hydroxyap-
atite (Ca 5 (PO 4 ) 3 OH) and it was observed in the diffraction analysis together with
the AFm phases, portlandite and CSH gel. The presence of hydroxyapatite depends
on the source used. It is possible that the presence of this compound could be used
in waste solidification applications. In the same paper, the authors concluded that
the additional aluminium and iron in the ashes formed a greater quantity of AFm
phases. This statement was corroborated by the presence of a secondary peak in the
curves obtained by the isothermal conduction calorimetry (ICC) analysis.
The characterisation of pastes by TGA was employed by various authors. Yen
et al. (2012) studied the properties of binary and ternary mixtures. The replacement
of cement was 50% and 70% and the pozzolans employed were FA, GBS and SSA.
The peak of portlandite was less in the pastes with pozzolan. In the pastes with
SSA, a large amount of AFm phases were formed.
Baeza et al. (2014a) studied the percentage of fixed lime by TGA in pastes with
a 10% of substitution of cement by FA, RHA and SSA. They corroborated that the
most reactive pozzolan was RHA, and that at 28 days of curing, the percentage of
fixed lime was greater in the paste with SSA than in the paste with FA.
Wang et al. (2017) studied the influence of co-combustion of SS and rice husk
on the hydration properties. The ashes were burnt in two proportions. The ash
defined as H had 20% SS and 80% rice husk. The other proportion was 30% and
70%, respectively, and the ash was referred to as W. The heat flow curves show
that the presence of the ashes retarded the cement hydration with an induction
period higher than that for the control paste. However, in the final hours of the
experiment, an exothermic effect was observed as a consequence of the pozzolanic
reaction. The total hydration peak showed that the paste with the highest heat was
the paste with H. By means of the data obtained in the ICC experiment, the authors
proposed a hydration kinetic model. They concluded that the inclusion of ashes
inhibited the hydration process at the early ages, but the quantity of the hydrates
was higher due to the pozzolanic reaction.
Chen and Poon (2017a) studied the reactivity of SSA and FA using the Frattini
test, ICC and XRD analysis. In the case of SSA, the authors used two ashes, one
with a small mean particle diameter (the FSSA had a mean diameter of 6 μm). All
the ashes had pozzolanic behaviour from Frattini test results. In all the pastes stud-
ied through XRD, the major components were portlandite, ettringite, alite and
belite. In pastes that contained SSA or FSSA, a new crystalline compound, brushite