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Application of alkali-activated industrial waste 401

Figure 13.30 Elemental compositions measured for gel regions in a 1:1 fly ash: blast furnace
slag binder activated by Na 2 SiO 3 solution, at ages of 28 days, 90 days, and 180 days. The
C A S H-type gel appears to become more homogeneous with longer-term curing, whereas
the N A S (H)-type gel remains more constant in composition (Ismail et al., 2014).

that their rheology is defined by two physical parameters: yield stress and plastic
viscosity.
τ 5 τ o 1 μ_ γ (13.1)

The AASc and AASm rheological behaviour are characterised according to two
different processes. The first, represented in Fig. 13.31A, is called a ‘loop test’.
This test is based on a linear increase of the shear stress, from minimum to maxi-
mum values and a return to the initial value. This cycle can be repeated several
times. Fig. 13.31B shows the behaviour of no-Newtonian systems (Leonelli and
Romagnoli, 2015).
One of the most relevant properties in rheological behaviour is the time-
dependence. A second test evaluates this property (Leonelli and Romagnoli, 2015).
The results obtained are shown in Fig. 13.32A.
During the test the sample is subjected to constant shear rates (or shear stress)
for a certain time. The second standard test, known as the steps procedure