Various reducing agents such as ferrous sulphate heptahydrate (HH) and monohydrate (MH), solid lignin (SL), Na₂S₂O₄,
NaHSO₃, SnCl₂·2H₂O, N₂H₄·H₂O and FeS are used to reduce Cr(VI) contents of three types of cements under 2 mg/L,
as it is requested by European Parliament Standards. Optimum conversion temperature of HH to MH was found as 130°C,
for 20 min., by thermal analysis. Minimum amounts of various agents to be used as additives in cements to reduce Cr(VI)
contents under the standard value were determined. Minimum reducing agent amounts of SL, MH and their mixture of 1:3
mole fractions were found as 0.44 %, 0.14 %, 0.24 % by weight, respectively for Portland cement (CEM I 42.5 R), 0.40 %,
0.26 %, 0.24 % for Portland Pozzolanic cement (CEM II/A-P 42.5 N) and 0.16 %, 0.05 %, 0.04 % for Pozzolanic cement
(CEM IV/B (P) 32.5 N). Minimum amounts of other materials to reduce Cr(VI) content of three type cements under the
required value, were found as 0.24 %, 0.16 %, 0.0 9 % (N₂H₄·H₂O), 0.10 %, 0.07 %, 0.04 % (Na₂S₂O₄), 0.04 %, 0.025 %,
0.01 % (SnCl₂·2H₂O) and 0.28 %, 0.27 %, 0.12 % (NaHSO₃), respectively. It was found that SL, the MH and their mixture of
1:3 mole fractions can be used successfully as additives for reducing Cr(VI) contents of cement. There are two advantages
of this usage of MH. It converts Cr(VI) to Cr(III) and extends the shelf-life of cement. On the other hand, SL reduces Cr(VI)
and increases durability of cements by lowered water/cement ratio. |
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