Formation of nanocrystals of AFt phase during the reaction between alkali-free accelerators and hydrating cement: A key factor for sprayed concretes setting and hardening

Title: Formation of nanocrystals of AFt phase during the reaction between alkali-free accelerators and hydrating cement: A key factor for sprayed concretes setting and hardening
Author(s): Cristiano Maltese, Carlo Pistolesi, Anna Bravo, Tiziano Cerulli, Davide Salvioni
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: 329 - 338
Total Pages: 10
Nb references: 15
Language: English

Abstract: In the field of underground constructions, concrete is commonly sprayed on the rock wall, for preventing the section tendency to squeeze. Flash setting accelerators are indispensable for reaching this aim. Recently, a new class of setting admixtures has been discovered: the alkalifree accelerators. Today, several types of alkali-free accelerators are available on the market and they can affect the concrete properties in different manners. They are based on soluble aluminium sulphate complexes which, interacting with hydrating cement, give origin to nanocrystals of AFt phase.
In this paper the formation and the development of these phases have been studied in connection with their effects on the cementitious materials mechanical properties. Setting time and compressive strength development of three cement paste samples (without admixture and containing two flash setting alkali-free accelerators) have been determined. In order to understand the different mechanical properties of these systems, some morphological (ESEM-FEG), crystal-chemical (XRD), physical-chemical (hydration temperature profile) and chemical (ICP-AES) analyses have been carried out. The results showed that the morphology and the amount of nanocrystals, formed during the initial stages of cement hydration, influence the mechanical strength development.

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