Page 409 - New Trends in Eco efficient and Recycled Concrete

364 New Trends in Eco-efficient and Recycled Concrete

in the presence of HMNS, sodium-alumina (magnesia) silicahydrate (NA (M)
SH), improves the thermal stability.
Nazer et al. (2016a) studied several copper slags from smelters which were land-
filled during the 19th century in Chile. They stated that slag had acidic behaviour,
with SiO 2 content in the range 38% 49%, Fe 2 O 3 in the range 18% 37% and
Al 2 O 3 in the range of 5% 9%. The partially amorphous character showed great
possibility for geopolymer synthesis. Two copper slags (CS) were used (Nazer
et al., 2016b) for preparing alkali-activated mortars which were designed with a
SiO 2 :Na 2 O molar ratio of 1.45 and water:CS ratio of 0.30. Compressive strength
development was measured at 20 C(7 90 days) and 65 C(3 7 days) curing tem-

peratures (Fig. 13.3). The authors concluded that the use of CS in alkali-activated
binders is an interesting way for solving the environmental concerns related to the
century-old landfilled waste in Chile.
Lump and granulated copper slags were tested as precursor material in AAMs
(Kuterasi´ nska and Kro ´l, 2015). Both slags contained high percentages of acidic oxi-
des (Fe 2 O 3 ,Al 2 O 3 and SiO 2 ) and CaO (12% for lump and 21% for granulated). The
main difference was their amorphous content, presenting 4.75% for lump and 98%
for granulated. Lump slags were activated by using five different activating solu-
tions, applying silica modulus in the 1 3 range.
The reached compressive strength after curing was under 2 MPa. However, gran-
ulated copper slag showed good behaviour when it was activated with silica modu-
2
lus solution in the range 1.75 2. Thus, for granulated slag with 3500 cm /g Blaine
2
fineness, 24.42 MPa was reached after 90 days of curing, while with 4000 cm /g
the compressive strength was 53.53 MPa when using 1.75 silica modulus. Short
curing times at 80 C (3 and 6 h) also yielded strength in the range of 40 60 MPa.

All these described results suggested the importance of the cooling treatment of the
melted slag and the key role that the amorphous content plays in reactivity
behaviour.

70 64 60 55 64 70
Compressive strength, MPa 50 14 44 40 38 50
60
60
40
40
30
30
20
20
10
0
0 8 9 10
7 28 90 3 7
CS_PN AA20 Curing time, days CS_PN AA65
CS_PQ AA20 CS_PQ AA65
Figure 13.3 Compressive strength development of mortars cured at 20 C (left) and 65 C

(right) for alkali activated ancient copper slags CS (from Puquios, PQ, and from Playa
Negra, PN) (Nazer et al., 2016b).