The effects of sodium lignosulfonate superplasticizer on the hydration of Portland cement Type V have been investigated by XRD and FTIR techniques.
The results of these studies indicate that the superplasticizer inhibits the hydration reaction as demonstrated by the reduced formation of Ca(OH)2 as well as a lower degree of polymerization of the silicate anions.
The hydration reaction seems to be controlled by dispersions of various charges present in hyperalkaline solution in cement paste.
The mechanism of inhibition is discussed and a ‘Charge Dispersed Tri-layer Model’ is proposed to explain the observed effects on the hydration reactions. According to this charge dispersal model, the Ca2+ ions from initial hydration reactions go into the solution to form a tightly-bound bi-layer of counterions with the negatively charged calcium-silica-hydrate surface.
Consequent to this intrinsic process, a tri-layer consisting of superplasticizer anions is immediately formed which inhibits further reactions. Possible consequences of the presence of superplasticizer on the solidification/stabilization of inorganic and organic pollutants by cementitious materials have also been discussed.
Modification of sodium lignosulfonate (SLS) via combined oxidation-sulfomethylation was employed to prepare concrete superplasticizer. It was found that the oxidation of SLS by peroxyacetic acid facilitated the subsequent sulfomethylation.
After modification, both the molecular weight and sulfo group content were significantly increased, and thus the performance of SLS as water reducer was improved. With the water to cement ratio at 0.4 and 0.3% (w/w) modified SLS, the fluidity of cement paste could reach 185 mm, which was 15% higher than that with unmodified SLS. It was also comparable to the performance of commercial naphthalene superplasticizer under the same conditions.
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