Title: Hindered Calcium Hydroxide Nucleation and Growth as Mechanism Responsible for Tricalcium Silicate Retardation in Presence of Sucrose

Author(s): Patrick Juilland and Emmanuel Gallucci

Publication: Symposium Paper

Volume: 329

Issue:

Appears on pages(s): 143-154

Keywords: retardation; sucrose; hydration; nucleation and growth; dissolution; calcium hydroxide; C-S-H; tricalcium silicate

DOI: 10.14359/51711210

Date: 9/24/2018

Abstract:

Among retarding molecules, sucrose is known since decades as probably one of the most powerful retarder of Portland cement hydration. Despite numerous studies, the underlying mechanism for this retardation remains highly speculative since unequivocal experiments are still lacking. Which process or which phase is affected and what is the nature of the interaction between sucrose and cement phases remain some of the unanswered questions. The present study lets aside the influence of sucrose on the aluminate phases and focuses on tricalcium silicate since it dominates the kinetics of hydration at early age.

The impact of sucrose on the independent basic hydration mechanisms was evaluated on the dissolution of alite (impure tricalcium silicate) by means of topological experiments and on the nucleation of its hydrates, i.e. C-S-H and calcium hydroxide, using potentiometric experiments at different pH.

Pure dissolution seems poorly affected by sucrose, if not at all, indicating that there is potentially no interaction between alite and sucrose.

The nucleation and growth of C-S-H, studied through precipitation experiments in diluted suspension showed to be affected to a very limited extent and only at high pH.

On the other hand, both the nucleation and growth of CH revealed to be extremely sensitive by the presence of sucrose, even at relatively low dosages, and at all studied pH.

Adsorption experiments on the various phases supported those observations. Thermogravimetric analysis of hydrated alite pastes further confirmed that sucrose effectively prevents the growth of calcium hydroxide and that the onset for the acceleration is subjected to this condition.

In light of those results a novel mechanism of retardation is proposed for sucrose and its implications regarding early age hydration processes are discussed.