Page 411 - New Trends in Eco efficient and Recycled Concrete

366 New Trends in Eco-efficient and Recycled Concrete

Table 13.1 Chemical compositions for several reported ferronickel slags
Reference SiO 2 FeO Al 2 O 3 CaO MgO Cr 2 O 3

Komnitsas et al. (2007) 32.74 38.8 8.32 3.73 2.76 3.07
Maragkos et al. (2009) 40.29 37.69 10.11 3.65 5.43 2.58
Sakkas et al. (2014) 41.14 34.74 13.79 0.71 3.59 5.41

geopolymers having low strength, the stability under distilled water and seawater
was observed. Also, good durability was found in freeze thawing cycles. However,
strength loss was detected when samples were under acid attack.
Furthermore, the use of KOH as activating reagent (Komnistas et al., 2009)
showed that resistance was increased when the samples were cured at 60 80 C,

reaching 30 40 MPa. The addition of sodium silicate to the activating solution, led
to an increase of up to 50 MPa for some dosages. It was suggested that the larger
1
size of K favours the formation of stronger silicate/aluminate oligomers.
Maragkos et al. (2009) studied the effect of the S/L ratio and concentration of
sodium and silica in the activating solution for the activation of ferronickel slag
on the compressive strength, density and water absorption. They optimised these
parameters and found that the highest strength (120 MPa) and the lowest water
absorption (0.7%) were achieved for S/L ratio equal to 5.4 g/mL and a silica mod-
ulus of 4/7.
Another geopolymer based on FeNi slags was used for fire protection (Sakkas
et al., 2014). The synthetised geopolymer with a mixture of slag and alumina pre-
sented a thermal conductivity of 0.16 W/m/K with a compressive strength of
8.7 MPa. For geopolymer prepared without alumina, the strength was slightly high-
er (11 15 MPa) and its thermal conductivity was 0.27 W/m/K. The behaviour of
both systems was suitable for two different thermal loading curves (ISO-834
and RWS).
Primary lead slag is a by-product from the synthesis of metallic lead from
sulphide-based compound by pyro metallurgical process. The main oxides of the
slag were silica and iron oxide as reported by Onisei et al. (2012), 21.56% and
31.57%, respectively. Also, significant amounts of Na 2 O (13.02%) and PbO
(12.28%) were contained. Several crystalline phases were found in the slag:
litharge, wustite and magnetite, among others. Different FA/slag blends were tested
in compressive and flexural behaviour. Fig. 13.5 shows these strengths, bulk density
and water absorption. In general, the sample containing 70% lead slag presented
very good performance.
Synthesis of metallic chrome requires the thermal treatment of chromite ore by
means the reduction with silicon or aluminium. Karakoc et al. (2014) studied the
reactivity of ferrochrome slag by activation with NaOH/Na 2 SiO 3 . Slag had high
percentages of silica (33.80%), alumina (25.48%) and magnesia (35.88%). They
studied selected mixtures with three different silica modulus (0.50, 0.60 and 0.70)
and four different Na 2 O contents (4%, 7%, 10% and 12%). Slag contained forsterite
(Mg 2 SiO 4 ) and spinel (MgAl 2 O 4 ) as main crystalline phases. In general, final