Page 431 - New Trends in Eco efficient and Recycled Concrete

384 New Trends in Eco-efficient and Recycled Concrete

drying specimens. Zaharaki et al. (2016) studied powdered concrete collected from

demolished buildings in Crete. After 80 C curing for 24 h and aging at room tem-
perature for 7 days, 7.8 MPa was obtained in the compression test. Komnitsas
(2016) studied the co-valorisation of marine sediments and CDW through alkali-
activation by using KOH/sodium silicate as the activating solution. After curing at

80 C for 24 h, the concrete waste geopolymer yielded less than 10 MPa while one
of the sediments studied yielded close to 20 MPa. WC/sediment in 90:10 and 70:30
showed a compressive strength close to 15 MPa. Abandoned mortar powder was
achieved with Na 2 SiO 3 9H 2 O(Ma et al., 2011). 4 8 MPa was reached after 3 days

of curing; however, the compressive strength rate was very important from 7 to 28
days, and 23 31 MPa was obtained. These values were raised when 1:1
Na 2 SiO 3 9H 2 O/Na 2 SO 4 mix was used as an activator (up to 35 MPa).
Powdered waste brick and WC were blended for preparing new binding geopoly-
meric materials (Allahverdi and Kani, 2009): selected systems (waste brick/WC
from 100:0 to 40:60) were designed and prepared with different silica modulus,
water-to-dry binder ratio and Na 2 O percent concentration. Setting time and 28-day
compressive strength were measured. The final setting time was between 100 and
259 min and 16 19 MPa were achieved at 28 days for systems with WC in 50%
60% and 28 33 MPa for 20% 40%.
Yang et al. (2009a,b,c) studied the activation of concrete sludge. Low strength
geopolymers were synthetised and the addition of MK in 40% replacement let to
increase the compressive strength to 25 MPa and the addition of SF in 10%
improved the strength to 13 MPa (Yang et al., 2009c).
Lampris et al. (2009) used the silt from filter cake recovered from washing
aggregates in a concrete plant. Plain silt geopolymer, MK/silt and FA/silt geopoly-
mers were obtained by means sodium hydroxide/sodium silicate activators. 7-day
compressive strength of 18.7 MPa was obtained for plain silt system, and the
replacement of 20% of silt by MK or FA increased compressive strength to 30.5
and 21.9 MPa, respectively.
Mineral wools waste (rock wool, RW, and glass wool, GW) present many pro-
blems for recycling because of its fibrous nature and low density. Yliniemi et al.
(2016) pulverised both wools and activated them with sodium aluminate solutions.
RW contained CaO, SiO 2 , MgO and Al 2 O 3 as the main oxides, while GW contained
SiO 2 and Na 2 O as the main ones. Their median particle diameter was close to
7 μm. Curing the specimens at 50 C for 4 days and 24 days more at room tempera-

ture led to producing geopolymers with 30 MPa in compression for RW and
48 MPa for GW.

13.2.1.5 Industrial wastes
Cement clinker dust (CKD) is a problematic waste derived from the cement indus-
try which may cause some problems in clinkering kiln operations and cement per-
formance. CDW has to be discarded despite its hydraulic properties due to high
content of chlorine, sulphur and alkalis. Wang et al. (2004) analysed CKD/FA
blends activated with NaOH. 50%/50% CKD-FA system activated with 2% of