Microstructure of binder from the pozzolanic reaction between lime and siliceous fly ash, and the effect of limestone addition

Title: Microstructure of binder from the pozzolanic reaction between lime and siliceous fly ash, and the effect of limestone addition
Author(s): K. De Weerdt, H. Justnes
Paper category : conference
Book title: International Conference on Microstructure Related Durability of Cementitious Composites
Editor(s): W. Sun, K. van Breugel, C. Miao, G. Ye and H. Chen
Print-ISBN: 978-2-35158-065-3
e-ISBN: 978-2-35158-084-4
Publisher: RILEM Publications
Publication year: 2008
Pages: 107 - 116
Total Pages: 10
Nb references: 10
Language: English

Abstract: Currently, blended cements (CEM II) are the most commonly used cements in Europe.
Most blended cements are binary, composed of clinker and one supplementary cementitious material (SCM). The clinker replacement level in blended cements may be increased by combining different SCM’s. In this paper a preliminary study on the combination of fly ash (FA) and limestone and their interaction was conducted.
Cement-free pastes composed of lime/FA and lime/FA/limestone, respectively, were compared. Clinker was excluded to simplify the system. In stead an excess of calcium hydroxide (Ca(OH)2) and alkaline mixing water (i.e. pH 13.2 and K/Na = 2:1) was used to simulate the conditions in a hydrating cement paste.
The mixes were cured at 5, 20, 38 and 80°C, and the reactions were stopped after 1, 3, 7, 28 and 88 days of curing. The microstructure of the hardened binder was investigated by thermogravimetry (TG), X-ray-diffraction (XRD) and scanning electron microscopy (SEM).
The addition of limestone resulted in a slight increase in the amount of chemically bound water relative to the amount of FA. FA also appeared to bind more water than what was provided by calcium hydroxide. The XRD patterns confirmed an interaction between the limestone and the FA, which resulted in the formation of calcium carboaluminate hydrates. At higher temperatures (80°C) the calcium carboaluminate phase appeared to be unstable and other hydration phases (e.g. hydrogarnet type phases) were observed.

Online publication: 2009-06-09
Publication type : full_text
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