114. The value of colloidal silica for enhanced durability in high fluidity cement based mixes

Title: 114. The value of colloidal silica for enhanced durability in high fluidity cement based mixes
Author(s): I. Jansson, U. Skarp, C. Bigley
Paper category : conference
Book title: 5th International RILEM Symposium on Self-Compacting Concrete
Editor(s): G. De Schutter and V. Boel
Print-ISBN: 978-2-35158-047-9
e-ISBN: 978-2-35158-088-2
Publisher: RILEM Publications SARL
Publication year: 2007
Pages: 761 - 766
Total Pages: 6
Nb references: 4
Language: English

Abstract: This research focuses on the effect of adding small amounts of (nanometric) colloidal silica (CS) to highly fluidised Portland Cement mixes. The mixes discussed were designed to highlight the effects different sources of Portland cement would have in terms of yield values and plastic viscosity with time as a measurement of the stabilising effect of the CS addition.
CS dosages used were sufficient to eliminate all segregation and bleed characteristics. At these levels of addition, CS could be classified as an admixture to the definitions of EN480.
The mechanism we are proposing is that the addition of the CS to fluidised Portland cement systems results in the accelerated generation of and increased amount of C-S-H gel (Calcium Silicate Hydrate). This greater quantity of C-S-H gel thereby contributing to much greater stability in the fluid state and, with some cement sources, greater early strength.
CS nanoparticles preserve their integrity during the hydration processes. The silica particles behave as highly active nucleation sites for ions released from dissolving clinker phases. The significant rates of both Alite and Belite hydration brought about by CS addition suggest a rapid formation of C-S-H gel on the active CS surface.
The addition of polycarboxylate superplasticiser will generally retard the rate of formation of C-S-H gel from both the Alite and Belite phases. It is this effect that causes many of the fresh state stability problems that can (to a large extent) be overcome through the addition of small amounts of CS.

Online publication: 2009-06-16
Publication type : full_text
Public price (Euros): 0.00