Effect of Modifications of Lignosulfonate on Adsorption on Cement and Fresh Concrete Properties

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Title: Effect of Modifications of Lignosulfonate on Adsorption on Cement and Fresh Concrete Properties

Author(s): K. Reknes and J. Gustafsson

Publication: Special Publication

Volume: 195

Issue:

Appears on pages(s): 127-142

Keywords: adsorption; concrete (fresh); rheology

Date: 7/1/2000

Abstract:
Lignosulfonate has a long history as plasticizers in concrete. This paper reports an investigation of the effect of ultrafiltration of lignosulphonate on rheological properties of concrete with two different modified lignosulfonates. It is shown how the modification also changes the adsorption of the lignosulfonate on the cement and the effect this has on the properties of the fresh concrete. The workability of the concrete is different for the lignosulfonates tested, however, true differences in workability are only observed by the applied rheological approach. The rheological measurements reveal differences in terms of plastic viscosity. Modifications of the lignosulfonate change the performance of the lignosulfonate as a plasticizing admixture. Increased molecular weight and purity of the lignosulfonate increase the plasticizing effect and also improve the ability of the lignosulfonate to reduce the viscosity of the concrete. The viscosity reduction is for a high molecular weight lignosulfonate efficient even at very low dosages. Increasing the molecular weight and purity of the lignosulfonate also reduce the concrete set retardation. High molecular weight lignosulfonate is because of the viscosity and yield value reduction an effective material for formulation of a plasticizing admixture.