Actions during service 159
A special case of sulfuric acid attack can be found in sewer systems,
involving the action of micro-organisms or bacteria. This is the so-called
biogenic sulfuric acid attack, which will be explained in Section 5.3.4.
Ammonium salts are also reported to be very aggressive. For ammonium
chloride and ammonium sulfate, the occurring chemical reactions are as
follows.
Ammonium chloride:
2 NH 4 Cl + Ca(OH) 2 → CaCl 2 + 2 H 2 O + 2 NH 3 ↑
(5.9)
2 NH 4 Cl + CaCO 3 → CaCl 2 + H 2 O + CO 2 + 2 NH 3 ↑
(5.10)
Ammonium sulfate:
(NH 4 ) 2 SO 4 + Ca(OH) 2 → CaSO 4 ∙2H 2 O + 2 NH 3 ↑
(5.11)
x (NH 4 ) 2 SO 4 + x H 2 O + x CaO∙SiO 2 ∙aq →
x CaSO 4 ∙2H 2 O +SiO 2 ∙aq + 2x NH 3 ↑
(5.12)
Upon the reaction with Ca(OH) 2 , gaseous ammonia, NH 3 , is formed,
which will escape from the concrete. The pH value of the system is reduced
and monosulfate as well as ettringite become unstable. In the case of ammonium sulfate, a reaction with the C-S-H phase also occurs, converting it
Figure 5.34 Sulfuric acid attack on a concrete wastewater tank in an industrial plant
(courtesy of SCICON Worldwide bvba).