ADSORPTION STUDIES OF LIGNOSULPHONATES ON CEMENT AND CEMENT MODEL COMPOUNDS

Abstract

Lignosulphonates are important plasticizers for concrete. To learn more about their interactions with the cement adsorption isotherms were obtained for a high molecular weight lignosulphonate. The chemical reactivity of cement makes it impossible to obtain true isotherms. The different minerals present also have different adsorption characterstics. To overcome these problems several model systems, e.g., dicalcium/tricalcium silicate mixtures, tricalcium aluminate/tetracalcium aluminate ferrite, tricalcium aluminate, alumina, ferric oxide, magnesium oxide, calcium silicate, and kaolin were also investigated. In addition, Standard Portland Cement and White Aalborg Cement were used. All model systems were investigated at high pH, and moderate to high ionic strength to simulate the situation in pore water. The lignosulphonates show adsorption isotherms that match the expected isotherms for polyions. The high molecular weight fraction of the lignosulphonates are preferably adsorbed. The di- and trivalent cations present interact with the lignosulphonates and this interaction is important for the adsorption. The interaction with multivalent ions renders the lignosulphonate more hydrophobic