LD steel slags are industrial by-products resulting from steelmaking process in oxygen converters( Linz-Donawitz process).Contrarily to blast furnace slags, LD steel slags are generally not valuated in the materials used in civil engineering as preliminary attempts to use them in road construction sometimes led to serious damages. This is mainly due to a dimensional instability, which occurs with aging. Thus, LD steel slags have to be aged in order to be stabilised before potential use in this domain. However, the aging conditions vary and are more or less efficient. Moreover, the exact mechanisms leading to the expansion of LD steel slag grains are still subject to debate. The aim of this study is to undertake carefully chemical and mineralogical characterisations of LD steel slags in order to clearly identify the phases which could be responsible for their instability. Thus, LD steel slags that were not aged have been studied first. Chemical composition was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma-mass spectrometry (ICP-MS) and C-H-N-S analyses. Lime contents were determined by Leduc test, thermogravimetric analyses (TGA) and Bernard calcimeter analyses. Results showed that un-weathered LD steel slags contain essentially lime CaO although very small amounts of portlandite Ca(OH)z and calcite CaC03 can punctually be detected. A complete mineralogical characterisation was then made using X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) coupled with energy dispersive system (EDS) analyses. It was found that LD steel slags contain essentially calcium silicate phases having CaO/(SiO2+P2O5) ratios ranging from 2 to 3.2, dicalcium ferrites Ca2(Al,Ti,Fe)2O5 iron oxides (Fe,Mg,Mn,Ca)O and lime CaO present under two forms: some modules observed into the matrix and some micro-inclusions observed into certain silicate phases. Magnesia MgO was not detected. Concerning the calcium silicate phases, dicalcium silicate beta-Ca2SiO4 was clearly identified but higher CaO/(SiO2+P2O5 ratios are expected to be some mixtures of dicalcium silicate, lime micro-inclusions and may be tricalcium silicate Ca3SiO5. Thus, taking account of our results and the different hypotheses explaining the LD steel slags expansion, it appears that without the presence of magnesia, lime is expected to be the only phase responsible for LD steel slags instability. Moreover, we have pointed out that the size of the lime particles could have an influence on grains stability.
Chemical and mineralogical characterisations of LD steel slags
Zur chemischen und mineralogischen Charakteresierung von LD-Schlacken
2008
12 Seiten, 5 Bilder, 2 Tabellen, 15 Quellen
Aufsatz (Konferenz)
Englisch
Developing compact autoregressive characterisations of terrain topology profiles
Online Contents | 2012
|Developing compact autoregressive characterisations of terrain topology profiles
Kraftfahrwesen | 2012
|In situ mechanistic characterisations of granular pavement foundation layers
Online Contents | 2012
|