Page 412 - New Trends in Eco efficient and Recycled Concrete

Application of alkali-activated industrial waste 367

Figure 13.5 Compressive and flexural strengths (left) and bulk density and absorption
values (right) for fly ash/lead slag activated mixtures (Onisei et al., 2012).

setting time was less than 300 min and the heat of hydration was in the range
20 50 J/g, much less than that found for OPC (CEM I 42.5 N, 251.40 J/g). The
best strength performance, at 28 days for pastes, was found for 7% Na 2 O and 0.70
silica modulus, although the reached compressive strength was less than 15 MPa.
For mortars with 0.4 water:binder ratio, the reached strength in laboratory condi-
tions was 5.23 MPa and the strength increased to 20.15 MPa when the water:binder
ratio was reduced to 0.3. The behaviour of ferrochrome slag geopolymer under
sulphate attack was assessed (Karakoc et al., 2016). The concrete samples were
submerged in MgSO 4 solutions (3%, 5% and 7% in solution). In all cases, a
decrease of compressive strength with the curing time and with the magnesium salt
percentage was observed. The expansion process yielded a change in length, which
was significantly lower (less than 0.1%) than that observed for OPC concrete
(0.12% for 7% MgSO 4 ). The temperature behaviour of these concrete mixes was

tested (Tu ¨rkmen et al., 2016) and it was found that temperatures higher than 300 C
produced a decrease in the strength.
Silicomanganese slag is generated as a by-product in the synthesis of silicoman-
ganese alloy (used for steel industry). The process requires the carbothermic reduc-
tion in an electric arc furnace. SiMn slag consists of an amorphous mixture of SiO 2 ,
CaO, Al 2 O 3 and MgO. Kumar et al. (2013) ground SiMn slag by means ball (BM),
eccentric vibratory (VM) and attrition (AM) mills. The activation of this slag by
means 6 M NaOH solution produced C S H. The calorimetric study demonstrated
the higher reactivity of VM and AM samples because of their higher fineness. The
reactivity of SiMn slags was also assessed by compressive strength development.
While the BM sample yielded 24 MPa after 28 days, AM and VM samples gave 66
and 101 MPa, respectively. Navarro et al. (2017) determined that most silica in the
granulated slag was reactive (92.5%) with a mean particle diameter of 15.2 μm.
They studied, by using statistical experimental design methodology, the optimum
dosage in geopolymer preparation, varying the Na 2 O content in the range of 4%
6%, the silica modulus in the range of 0.75 1.25 and the solid:solution ratio in the
0.35 0.45 range. In Fig. 13.6, response curve surfaces for compressive strength are