Degree Name

Doctor of Philosophy


Department of Civil and Mining Engineering


This research is applicable to the solution of problems encountered in the application of Australian made BOS slag in engineering construction.

The general chemical and physical properties, in patticular F-CaO content variation and volume expansion, were investigated. The causes responsible for expansion of steel slag are analysed theoretically by the author in an attempt to clarify the causes of instability of steel slag. This thesis holds that, for cooled solid steel slag, from the point of view of utilization in general engineering construction, MgO and crystalline transformation of C2S do not contribute to the expansion for normal BOS slag. The dominant cause for expansion of steel slag is uncombined lime, i.e. F-CaO.

Calculations for determination of volume expansion and body force are developed. Several usability criteria, including use as road base materials, aggregates for cement concrete and component material of steel slag blended cement, are proposed. These criteria are dependent on F-CaO content, expansion properties (i.e. volume expansion and body force ) and the properties of the final composite or matrix material containing steel slag. The principles, test methods and theoretical basis of the quantitative critical criteria for steel slag use in engineering applications are presented.

In order to facilitate the use of steel slag in quasi-rigid matrix materials, such as for use as a road base material or in hot mix asphalt concrete, a theoretical calculation of volume expansion of steel slag has been developed based on F-CaO content which is the main compound contributing to the expansion of steel slag. Results based on this calculation are compared with the laboratory experimental results. It is shown that the critical value of F-CaO content in a given steel slag is consistent with, or close to, previously proposed empirical values. However, different critical values are necessary in different matrix materials with differing confining force (surcharge) for a given steel slag. A criterion based on experimental measurement and calculation is derived to determine the usability of a given steel slag according to its F-CaO content.

For use in rigid matrix materials, such as an aggregate in cement concrete, a theoretical acceptability criterion was derived based on a steel slag expansion. disruption model, the structural sensitivity of cement concrete and maximum tensile stress due to expansion stress. The equation demonstrates that if the bociy force conforms to the given equation, steel slag could be used in the matrix as coarse or fine aggregates.

For use as a dispersed media, such as an ingredient of blended cement, an allowable F-CaO content, independent of the grind ability of steel slag when interground with cement clinker, is suggested. The criterion given for this use shows that, provided the relative content of steel slag is controlled, slags with a high free calcium oxide content can be used as an ingredient of blended cement. These slags would not normally be suitable for other engineering applications.

Various properties, including expansion and stability of steel slag or matrices containing steel slag were investigated experimentally. The experimental investigations were undertaken with relation to the special concerns associated with the use of BOS slag in individual applications, such as grindability of steel slag in SSBC, volume expansion for road base, body force for use in concrete. It can be concluded that, provided the BOS slag conforms to a given criterion, the performance will be satisfactory.

Through these approaches, optimum use of steel slag may be achieved. This will lead to benefit in two aspects: (i) resulting in economic savings in construction by the use of industrial by-product materials and, (ii) substantial benefits to the environment by less depletion of the natural resources normally used as concrete aggregates and road base materials and a reduction in environmental pollution due to industrial by-products (waste) discarding. Both of these aspects will result in immense economic value and social value, with the additional benefit of being able to modify various engineering· properties of construction materials.