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Sewage sludge ash 125

As a pozzolanic addition in mortars and concrete with Portland cement (PC).
For the manufacture of light aggregates.
In the manufacture of bricks and ceramic materials.
For the manufacture of PC clinker.
As a source of phosphorus extraction for organic amendment.
This chapter will deal briefly with some of the characteristics of these ashes,
focusing mainly on its uses, such as pozzolanic addition.
Tay (1987) used a SSA as a filler in concrete. The sludge was collected in the
Jurong sewage treatment (Singapore) and was incinerated in the furnace with tem-

peratures above 550 C. The chemical composition is summarised in Table 5.2. The
3
3
specific gravity of the SSA was 2.81 g/cm , the loose bulk density 1345 kg/m and
the pH 9.0.
In 1996 2003, Monzo ´ et al. (1996, 1999a, 2003) studied the physico-chemical
characteristics of a SSA from the Pinedo sewage wastewater treatment plant
(Spain). In this plant, part of the SS was incinerated at a maximum temperature of
800 C, in a silica sand fluidised bed reactor. The ash was collected by means of

electrostatic precipitators. The researchers separated the original SSA in several
sized fractions by sieving ( . 80 μm SSAC, between 80 and 40 μm SSAM, and
between 40 and 20 μm, SSAF). In Fig. 5.2, the particle size grading parameters are
shown and in Table 5.3, the chemical compositions of the original ash and the
sieved fractions are summarised. The increase of SO 3 content and irregular content
of SiO 2 is shown in the fractions. In this case, the critical parameter was the SO 3
content. The authors, in a later publication (Monzo ´ et al., 1999a), studied the influ-
ence of this parameter, using different types of cement with different C 3 A contents.
Paya ´ et al. (2002) also used this ash to compare the pozzolanic activity of the
original SSA (with a particle mean diameter of 30.70 μm) with other pozzolans as a
silica fume (SF), spent fluidised bed catalyst and rice husk ash (RHA). Finally,
Monzo ´ et al. (2003), studied the influence of the different size fractions of the ash
in the mortars with different substitutions of cement by these fractions.
Later, this original Spanish ash was used in corrosion studies (Garcı ´a-Alcocel
et al., 2006) or for analysis of mixtures with different types of cements (Cyr et al.,
2007). It was also characterised by X-ray diffraction where the crystalline phases
found were γ-anhydrite, quartz, magnetite, calcite and hydroxyapatite. Also, the
minor phases detected were corundum, gypsum and lime. SSA particles had a mean
3
diameter value of 33 μm and the specific gravity was 2.62 g/cm . The high-water

Table 5.2 Chemical composition of sewage sludge ash (g/kg)

Si S Fe Al Ca Zn Cu
102.8 80.8 80.6 50.3 29.2 26.8 18.8
Cr Na Pb Ni Mn K Mg
3.0 2.5 2.5 1.3 1.1 6.1 7.9
Adapted from Tay, J.-H., 1987. Sludge ash as filler for Portland cement concrete. J. Environ. Eng. 113 (2),
345 351. Available from: https://doi.org/10.1061/(ASCE)0733-9372(1987)113:2(345).