COMPARING THE INFLUENCE OF FLY ASH ON THE DURABILITY PROPERTIES OF PORTLAND CEMENT-BASED AND ALKALI ACTIVATED SLAG-BASED CONCRETES

Author(s): Provis, J. L., Bernal, S. A., Ismail, I., Nicolas, R. S., Brice, D. G., and van Deventer, J. S. J.
Paper category: Conference
Book title: XIII International Conference on Durability of Building Materials and Components - XIII DBMC
Editor(s): Marco Quattrone, Vanderley M. John
Print ISBN: none
e-ISBN: 978-2-35158-149-0
Publication year: 2015
Pages: 93-100
Total Pages: 8
Language: English

Abstract: Low calcium fly ash is widely used as a pozzolan in the production of Portland-blended cements and concretes, and also in production of alkali-activated materials, either as sole precursor or blended into slag-based concretes. Significant chemical and structural changes are induced through the addition of fly ash, as a low-calcium aluminosilicate source, to more calcium-rich binders. However, there has not previously been a detailed comparison of the role of fly ash in blending with each of these two types of calcium-rich cementing systems. Although appearing superficially similar in chemistry and gel nanostructure, the very different alkali levels present in the two types of binders have important implications for the reactivity of fly ash in each instance. This study reports the mechanical strength development, water absorption properties, and chloride permeability of Portland cement-based and alkaliactivated slag-based concretes with 25 wt.% fly ash inclusion in the binders, with mix designs tailored to give comparable 90-day strengths of 60±3 MPa. The incorporation of fly ash into Portland cement-based concrete is seen in general to enhance later-age properties, while the effects of its inclusion in alkali-activated slag concretes seem in several cases to be reversed. The reasons for this are related to the fact that there is not sufficient excess calcium in an alkali-activated slag to induce a pozzolanic-type reaction, and so the ongoing alkali-induced reaction of fly ash in an alkali-activated slag binder instead results in an alkali aluminosilicate gel which does not show the same influence on transport properties.

Online publication: 2015
Publication Type: full_text
Public price (Euros): 0.00