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Application of alkali-activated industrial waste 371

Table 13.2 Chemical compositions of different red mud (RM) samples tested for
preparation of geopolymers

References SiO 2 Fe 2 O 3 Al 2 O 3 CaO SO 3 Na 2 O TiO 2
Geng et al. (2017) 12.83 33.39 20.26 0.87 0.60 10.85 7.53
Haijjaji et al. (2013) 5.54 51.8 18.8 3.27 11.2 6.84 0.23
Ke et al. (2015) 20.4 9.5 24.5 12.9 0.7 11.5 nd
Nie et al. (2016) 25.58 23.26 26.40 1.33 0.80 14.98 nd
Kaya and Soyer-Uzun 11.67 37.45 16.85 1.44 nd 10.55 nd
(2016)
Hairi et al. (2015) 10.52 38.92 22.12 1.36 0.59 6.82 7.61
Ye et al. (2014) 20.38 9.48 24.50 12.86 nd 11.46 2.92

was 40%. They found that with the addition of RM, the strength of geopolymers
decreased in a monotonous way and 40% of the replaced sample did not harden.
Authors proposed that iron species consumed hydroxyl anions for precipitating iron
hydroxide and reduced the alkalinity of the medium. In this way, the activation of
MK was strongly reduced.
Blast furnace (BFS) and RM blends were studied by Ye et al. (2014). The effect

of the calcination temperature of RM (200 1000 C) on the geopolymer properties
was assessed. The CaO/SiO 2 ratio was 0.71 and the SiO 2 /Al 2 O 3 was 3.27, and the

BFS/RM ratio was 1:1 by mass. The optimum calcination temperature was 800 C

(achieving 50 MPa after 28 days of curing). RM samples calcined under 700 Cor
up to 800 C and yielded less than 25 MPa in compressive strength. This behaviour

was attributed to the high solubility of silica and alumina achieved at 800 C. This

change in solubility could be attributed to the formation of new phases in calcined

RM when 800 C was reached. Also, these authors studied the influence of BFS/RM
ratio in the development of strength: they demonstrated that strength decreased with
the increasing of 800 C-calcined RM content and only 10% replacement of BFS by

RM gave similar mechanical behaviour than plain BFS in the alkali-activated
system.
Nie et al. (2016) studied 1:1 mixtures of RM with class C FA. They showed that
the alkalinity of RM was not enough for achieving the FA and an additional amount
of NaOH was required for getting good mechanical performance. It was concluded
that 2.5 M NaOH solution was required for optimum results (Fig. 13.8).
Silica content in the RM-geopolymer was increased by addition of RHA (He
et al., 2013). The RHA/RM 1:1 mixture yielded the best strength (20.46 MPa).
Also, they showed that low concentration of NaOH solution was required (2 M) and
grinding RHA enhanced the strength development. SF also was tested as co-
precursor in RM geopolymers (Hairi et al., 2015). High strength was observed for
RM/SF samples with SiO 2 /Al 2 O 3 5 3 and Na 2 O/Al 2 O 3 5 0.9 molar ratios:
44.33 MPa for raw RM and 58.13 MPa for 500 C-calcined RM.

Several studies have been carried out focusing on the preparation of one-part
RM-based geopolymer (Ke et al., 2015; Ye et al., 2016). Ke et al. (2015)