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130 New Trends in Eco-efficient and Recycled Concrete

Table 5.7 Mineralogical composition of the SSA samples and estimated composition of
the amorphous phase

Mineral phase SSA1 SSA2 SSA3 SSA4
Anhydrite, CaSO 4 x x x
Quartz, SiO 2 xx xxx xxx xxx
2
Haematite Fe O 3 x x x x
Ettringite, Ca 6 Al 2 (SO 4 ) 3 (OH) 12 .26H 2 O X
Silicon carbide, SiC x x x x
x x x
Albite, NaAlSi 3 O 8
xx xx xx xx
Iron whitlockite, Ca 9 Fe(PO 4 ) 7
Cristobalite, SiO 2 x x
Tridymite, SiO 2 x x x

Chemical compound in amorphous phase
33 37 20 24
SiO 2
15 19 25 42
Al 2 O 3
15 5 15 8
Fe 2 O 3
16 15 22 17
P 2 O 5
CaO 15 14 10 3
x traces; xx minority compounds; xxx majority compounds. SSA, Sewage sludge ash.
Adapted from Dyer, T.D., Halliday, J.E., Dhir, R.K., 2011. Hydration chemistry of sewage sludge ash used as a
cement component. J. Mater. Civil Eng. 23 (5), 648 655. Available from: https://doi.org/10.1061/(ASCE)MT.1943-
5533.0000221.
finer than the mean values for the diameter and specific surface area found in the
2
literature [44 μm and a 450 (Blaine) or 15,000 (BET) m /g].
Donatello et al. (2010a,b) studied the effects of milling and acid washing on the
pozzolanic activity of SSA from the United Kingdom. The acid washing was made
to extract the phosphates from the ash. The chemical composition and physical
parameters are listed in Table 5.10.
In Fig. 5.4, the X-ray diffractogram of SSA before and after acid washing is
shown. It is observed that acid washing caused the complete dissolution of Ca and
P from whitlockite and precipitation of CaSO 4 .
Naamane et al. (2016) carried out studies about the influence of the incineration

temperature (300 800 C) of sludge on the characteristics of the ash, and the influ-
ence of these ashes obtained at different temperatures on cement-based materials.
The SSAs were characterised from chemical, physical and mineralogical points of
view. SS used in this investigation came from an industrial wastewater treatment
plant located in Fez (Morocco). The sludge samples were dried at 40 C, homoge-

nised, ground and sieved to a particle size smaller than 1 mm. Then, the dried SS
was calcined at different temperatures (300, 400, 500, 600, 700 and 800 C) during

50 min in an electrical muffle. Then, the sludge ash was cooled down to an ambient
temperature. The chemical composition of the ashes obtained at different tempera-
tures is shown in Table 5.11.