Chloride diffusion and pore structure in geopolymers

Author(s): I. Ismail, J.L. Provis, J.S.J. van Deventer, S. Hamdan
Paper category: Conference
Book title: 2nd International conference on Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. Van Breugel, Wei Sun, Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Pages: 1491- 1499
Total Pages: 8
Language: English

Abstract: 
Pore structure is the key factor that governs the mass transport of ions, fluids and gases in any concrete material, and thus directly relates to the behaviour of the material when exposed to aggressive environments. Chloride attack on reinforced concrete is a mechanism of deterioration which causes corrosion of steel reinforcement. However, detailed scientific and mechanistic information regarding the chloride resistance of alkali activated aluminosilicate materials, especially geopolymers synthesized from mixtures of fly ash and ground granulated blast furnace slag, is scarce. In this study, geopolymer mortars made from an alkali activated fly ash/slag system with varying water content were tested for non-steady state chloride migration using the standard NordTest 492 methodology. Mixtures of Australian class F fly ash and ground granulated blast furnace slag (GGBS) were activated by blending with water and solid sodium metasilicate. Water content was varied to produce a series of samples with water to binder ratios ranging from 0.40 to 0.60. Ordinary Portland cement (OPC) mortars with similar water to cement ratios were also prepared for direct comparison. Porosity and water absorption were measured, and correlated with the chloride diffusivity values. Although the porosity and water absorption of geopolymer are higher than the normal OPC mortars, chloride intrusion is lower in geopolymer system. This suggests that the differences in pore structure and gel chemistry between geopolymer and OPC system mean that the standard relationships between chloride penetration and porosity which apply to OPC systems cannot be directly applied to geopolymer binders. Scanning electron microscopy images with energy dispersive X-ray (EDX) analyzer and thermogravimetry analysis were performed at selected corroded sections of both sample types had shown some durability performance of geopolymer. In particular, geopolymers are seen to show higher resistance to chloride penetration than would be predicted based upon their high porosity.

Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00