Page 427 - New Trends in Eco efficient and Recycled Concrete

380 New Trends in Eco-efficient and Recycled Concrete

temperature. An addition of 2% Ca(OH) 2 was required for achieving setting, while
5% of this reagent induced a too-rapid setting. Compressive strengths in the range

of 25 30 MPa were reached for mortars cured at 65 C for 7 days (Reig et al.,
2013b).
Sanitary ceramic (CS) waste also has been activated in the preparation of geopo-
lymers (Reig et al., 2016b, 2018). This waste had (Reig et al., 2016b) a very low
CaO content (1.2%), with SiO 2 (66.0%) and Al 2 O 3 (23.6%) as the main oxides in
the composition. The activation also required the addition of Ca(OH) 2 in the range
of 4.5% 7.5% to yield good performance (compressive strength close to 20 MPa
after 7 days curing at 65 C). The effect of different calcium sources in the develop-

ment of CS alkali-activated systems was reported. OPC, CAC and Ca(OH) 2 were
used as calcium sources. Mortars were cured for 7 days at 65 C. When using Ca

(OH) 2 at 8%, the maximum strength was 43.59 MPa, for 10% OPC was 64.41 MPa
and for 20% CAC was 78.60 MPa.
Belmokhar et al. (2017) studied industrial sludge obtained from wastewater treat-
ment in the ceramic sanitary industry. This sludge was calcined at 800 C and the

resulting powder was tested as a precursor. The obtained strength was in the
40 55 MPa range when activated with NaOH/Na 2 SiO 3 and cured for 7 days at
room temperature.

13.2.1.3 Urban wastes

Two wastes will be discussed here: (1) the calcined water treatment sludge (usually
known as SSA) which is produced by calcining sludge at temperatures higher than

700 C (to remove organic matter); and (2) MSWI ashes, both bottom ash and FA.
Guo and Shi (2010) studied the geopolymerisation of FA and a water treatment

sludge calcined at 900 C. Replacement in the range 0% 50% was carried out and
the authors stated that 10% calcined sludge-containing system yielded the best per-
formance at 75 C curing temperature. The increase of calcining time from 1 to 3 h

worsened the compressive strength. Yagamuchi and Ikeda (2010) studied the behav-
iour of sewage sludge slag (SSS) by mixing it with FA and activated with sodium

silicate at 80 C.
The highest flexural strength was reached for the 25:75 SSS/FA mixture.
Waijarean et al. (2017) prepared 800 C calcined sewage sludge which was acti-

vated by means 10 M NaOH solution. The compressive strength was 11.2 MPa and
authors demonstrated that the presence of heavy metal hydroxides (Zn, Fe, Cr) dras-
tically reduced the mechanical performance. Calcined sewage sludge was blended
with RHA for obtaining different SiO 2 /Al 2 O 3 molar ratios (2, 3, 4 and 5)
(Waijarean et al., 2014). The NaOH-activated systems were cured at 30 C. The

presence of RHA improved the mechanical strength when the SiO 2 /Al 2 O 3 ratio was
2.0. The strength for non-containing RHA was 12 MPa after 60 days, while the
strength was raised to 18 MPa with RHA addition.
Binary MK-SSA mixtures were activated by Istuque et al. (2016). They demon-
strated that SSA was a good precursor for blending with MK up to 20% replace-
ment. The formation of zeolites with thermal curing was reduced for MK-SSA