Turbidity-based measurement of bleeding in fresh cement paste as affected by cellulose nanofibres

Abstract

This study examined bleeding in cement paste as affected by cellulose nanofibres prepared with varying the content of carboxyl groups that were grafted onto the fibre surface. Alongside the conventional ASTM test method, bleeding was further evaluated using a turbidity scanner. A linear correlation was obtained between the bleeding heights as found from the two techniques. The results demonstrate that adding cellulose nanofibre (CNF) significantly reduces the bleed-water volume. Besides, the layer of bleed water in mixtures containing the CNF was more turbid. Clearly, the water retention capacity of CNF hinders the cement grains from settling down and thereby the nanofibres obstruct the upward migration of free water. As well, the higher the carboxyl content, the higher the fibre dosage permissible. And, although it was independent of the amount of carboxyl groups, bleeding was progressively less with an increase in the nanofibre dosage. However, in the presence of a superplasticizer, the cellulose nanofibres were less effective in reducing the bleeding.