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Evaluation of Slag


Evaluation of Slag containing fill

TRS has very extensive experience of evaluating fill which may consist of or contain, various iron and steel industry slags.

The main purpose of evaluating fill is to identify any potentially volumetrically unstable constituents. Such materials may contain a variety of slags including:

  • Blast furnace slags - Fresh make is almost certainly volumetrically stable, but when weathered may sometimes contain residual pockets of unstable material.
  • Basic steel making slags - commonly contain constituents likely to give rise to volumetric instability at an unpredictable future date.
  • Acid steel making slags - these are almost invariably stable.

The most abundant are blast furnace slags, followed by basic steel making slags. Nowadays, acid slags are relatively uncommon and, when encountered, are usually present as only a small proportion of the fill.

 
Three phased approach to analysis
Phase 1
Petrology
  • By optical microscopy or X-ray diffraction

It is most important to identify the main constituents of the fill before embarking on any accelerated expansion tests. Failure to do so may give rise to misleading expansion results. The most effective means of determining the fills constituents is by mineralogical analysis.

Phase 1 may be carried out using either optical microscopy or X-ray diffraction. Commonly, TRS would recommend microscopy for mixed fill but the decision is best left to TRS after visual inspection of the material.

The results from Phase 1 determine the analyses necessary in Phase 2.

Phase 2

This phase comprises a variable suite of tests, including chemical and thermo-chemical analyses. The purpose is to identify constituents associated with past expansion and potential future volumetric instability. When both blast furnace and steelmaking slag are identified in phase 1, both groups of Phase 2 tests are necessary.

Blast Furnace Slag
  • Water soluble sulphate
  • Acid soluble sulphate
  • Total sulphur
  • Thermal analysis
Basic Steel Slag
 
  • Free lime (Ca0)
  • Free magnesia (Mg0)
  • Thermal analysis
Acid Steel Slag
  • No further testing
Slag Mixture
  • Water soluble sulphate
  • Acid soluble sulphate
  • Total sulphur
  • Free lime (Ca0)
  • Free magnesia (Mg0)
  • Thermal analysis

Phase 3

TRS accelerated expansion test

The TRS accelerated expansion test is a direct method of identifying potentially volumetrically unstable slags. The TRS test is unique in being appropriate to both blastfurnace and steelmaking slag and is the product of over a decade of development at Thomas Research Services. As already indicated, phases 1 and 2 should be carried out first if misleading results are to be avoided.
 

Evaluation of Results and Reports

Evaluation of the results from the three phases described is a specialist task. TRS are research consultants and not just a test house. Detailed advice can be given before an investigation commences and TRS provide a fully interpretative reporting service.

It is possible to carry out all 3 phases of work simultaneously, obviously significantly reducing the timescales involved. However, this may prove to be a more costly route, for example, if not all of the procedures were necessary.