Investigations of the Pozzolanic Reaction of Silica Fume in Ultra High Performance Concrete (UHPC)

Title: Investigations of the Pozzolanic Reaction of Silica Fume in Ultra High Performance Concrete (UHPC)
Author(s): C. Pfeifer, B. Möser, C. Weber, J. Stark
Paper category : conference
Book title: International RILEM Conference on Material Science
Editor(s): W. Brameshuber
Print-ISBN: 978-2-35158-110-0
e-ISBN: 978-2-35158-111-7
Publisher: RILEM Publications SARL
Publication year: 2010
Pages: 287 - 298
Total Pages: 12
Nb references: 22
Language: English

Abstract: The aim of the study was to investigate the pozzolanic reaction of silica fume in Ultra-High Performance Concrete (UHPC). The silica fume content in investigated UHPC is 16 wt.-% based on cement. This is particularly necessary to fill the intergranular space and to achieve a high packing density. Additionally Calcium-Silicate-Hydrate phases are formed by the pozzolanic reaction.

Consumption of silica fume by pozzolanic reaction and degradation of calcium hydroxide were determined by the following three methods: silica fume content was quantified by selective acid solution process in depleted nitric acid solution, calcium hydroxide content was quantified by powder X-ray diffraction and differential thermal analysis. Furthermore the pozzolanic reaction of silica fume was imaged on fractured surfaces by high resolution Scanning Electron Microscopy by means of different imaging conditions (ESEM WET-mode at 90% relative humidity, high vacuum, low vacuum conditions using low voltage mode).

Results of the present study show that the pozzolanic reaction at low w/c ratio is significantly influenced by the storage conditions. After 56 days of hydration selective acid dissolution experiments reveal in samples with water storage a silica fume consumption of approximately 10 %. In contrast samples with heat treatment (90 °C/48h) show a highly pozzolanic reaction, approximately 49 % of silica fume has reacted. By means of high resolution Scanning Electron Microscopy (SEM) under low voltage conditions it is the first time possible to image the dissolution structures of silica fume particles caused by pozzolanic reaction in UHPC.
Calcium-Silicate-Hydrate phases create a very dense binder matrix close to silica fume particles.

Online publication: 2010-12-02
Publication type : full_text
Public price (Euros): 0.00