MITIGATION OF DELAYED ETTRINGITE FORMATION USING CLASS F FLY ASH OR MIX WATER CONDITIONER | |
| Conference | 30th Our World in Concrete and Structures (OWICs) - 2005 |
| Authors | A M Amde*, University of Maryland, USA A Azzam, District Department of Transportation, USA R A Livingston, Federal Highway Administration, USA |
| Handle | 100030021 |
| Key Words | Ettringite, delayed ettringite formation, DEF, fly ash, mix water conditioner, concrete durability |
| Abstract | The effects on delayed ettringite formation (DEF) of partially replacing the Portland cement by different amounts Class F fly ash or using mix water conditioners (MWC) are discussed. Recent studies have shown that DEF may be associated with deterioration problems in concrete. Many countries have reported deterioration of concrete structures where the main cause of distress has been identified as DEF. The results presented in this paper are part of an on going comprehensive study on DEF that is being conducted at the University of Maryland in collaboration with the Federal Highway Administration. The study has involved numerous parameters. Quantitative X-ray diffraction (QXRD) and scanning electron microscope (SEM) equipped with a high-energy dispersive Xray analysis (EDAX) methods were used to identify materials in the cavities, transition zones and cracks to determine the mechanism of concrete failure. The X-ray computed tomography (CT) method was employed to reveal interior cracks. Heat cycles and other techniques were used to accelerate the test. The results showed formation of ettringite crystals in cavities, in the interface between aggregate and cement paste, etc. Partially replacing the Portland cement with Class F fly ash decreased the expansion, with specimens showing larger reductions as the percentage of fly ash increased. The SEM results correlated with the observed expansions. The effect of using MWC was found to be similar to using 10% fly ash with respect to expansion but not with respect to compressive strength. The short term and long term effects on compressive strength were also investigated. |
| Full Text |  100030021 |
| Link to this page | www.cipremier.com/100030021 |
