Pyrogene nano-oxides in modern cement based composites

Title: Pyrogene nano-oxides in modern cement based composites
Author(s): Arjan Korpa, Reinhard Trettin
Paper category : conference
Book title: NICOM 2: 2nd International Symposium on Nanotechnology in Construction
Editor(s): Y. de Miguel, A. Porro and P.J.M. Bartos
Print-ISBN: 2-912143-87-X
e-ISBN: 2912143888
Publisher: RILEM Publications SARL
Publication year: 2006
Pages: 313 - 319
Total Pages: 7
Nb references: 3
Language: English

Abstract: We have tested various adapted synthetic colloidal nanosilica (aerosil®) supplied by Degussa, in modern concrete systems. Aerosil is an ideal pozzolanic material due to its very high purity (SiO2>99.8%), possibility of controlling the particles size, surface modification, and its very high reactivity attributed to its very small primary particle size (5-50nm).
A pozzolanic filler including here also silica fume (SF) offers the possibility to obtain superior concretes through these optimisations;
• chemical optimisation (pozzolanic reactions)
• physical optimisation (filling effect, packing density increase)
• bonding optimisation (very dense structure and interfacial transition zone, ITZ)
In the same way aerosil product offers;
• an increased pozzolanic reactivity because of the above mentioned reasons
• extends the packing possibility at the nanometer range, increasing in this way more the packing density
• and contributes of course to obtain a denser ITZ and a better bonding ability
These advantages make aerosil an ideal pozzolan for modern cement-based composites and its beneficial use is manifested at mechanical properties, porosity, durability and other important aspects. Aerosil in small quantities was used to partially replace the silica fume at RPC based mixture formulations, without fibres.
Due to this replacement, concrete specimens were obtained with mechanical properties that belong already to the ultra high performance concrete class (UHPC). The porosity and cumulative surface area comparison measurements for the hardened specimens cast by combining silica fume or other pozzolan fillers with aerosil® fumed silica show a denser structure and a shifting of porosity and pores refinement, which correlates very well with scanning electron microscopy (SEM) investigations. These results show a further structure densification at all levels and agree also with the mechanical property improvements.
An acceleration of the hydration reaction has been observed for the mixtures containing aerosil by comparing it with the hydration behaviour of various mixtures without aerosil. The rate of heat development measured by using isothermal conduction calorimetry is also lower and the induction period shorter (4-5h) in comparison to the normal RPC systems that are cast only with silica fume at around 25% (optimal content). Adequate nanosized fumed silica oxides (aerosil) used in optimized mixture formulations based on RPC systems can produce high and ultra high strength specimens with additional improvements.

Online publication: 2005-11-17
Publication type : full_text
Public price (Euros): 0.00