Effect of Functional Groups on the Performance of Lignosulfonates in Cement-Water Systems

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Title: Effect of Functional Groups on the Performance of Lignosulfonates in Cement-Water Systems

Author(s): J. Zhor

Publication: Special Publication

Volume: 239

Issue:

Appears on pages(s): 507-524

Keywords: air entrainment; cement paste; chemical analysis; dispersant; hydration; lignin and derivatives; molecular structure; plasticity; retardation; setting time; water-reducing admixture

Date: 10/1/2006

Abstract:
The relationship between the number of individual functional groups present in lignosulfonate molecular structures and the performance of lignosulfonates in fresh cement pastes was investigated. Lignosulfonate fractions from three different pulping processes (sulfite, sulfate and organosolv) were included in this study. The dispersing, set-retarding and air-entraining effects of these fractions in ordinary Portland cement pastes were studied. Elemental composition, methoxyl and sulfonate group contents were determined analytically. An algorithm was developed to generate model molecular structures representing individual lignosulfonate fractions. Each model structure was based on the results of the chemical analysis, the model structural segment typical of each particular lignin and additional literature data. The numbers of sulfonate, carboxyl, phenolic hydroxyl, aliphatic hydroxyl and methoxyl groups in each proposed molecular structure were determined. The numbers of C-C and C-O-C inter-unit bonds in each molecule were calculated as well. Correlations between selected functional group counts and the dispersing, set- retarding and air-entraining effects of lignosulfonates were determined. For the dispersing effect, methoxyl was the most positively correlated and carboxyl was the most negatively correlated group. Sulfonate had a very low correlation with the dispersing effect. For the set-retarding effect, the C-C inter-unit bond was the most positively correlated and sulfonate was the most negatively correlated. For the air-entraining effect, carboxyl was the most positively correlated and aliphatic hydroxyl was the most negatively correlated group. A low correlation was found between sulfonate and the air-entraining effect. The results are interpreted from the perspective of cement hydration processes and the implications on the understanding of lignosulfonate interactions with cement-water systems are discussed.