The Use of Secondary Gypsum to Make a Controlled Low Strength Material

Abstract

This paper reports on the use of secondary minerals to make Controlled Low Strength Materials for trench or mine backfill. The mixes used red titanogypsum which is a by-product of titanium dioxide pigment production. A number of other secondary minerals were considered for mixing with the gypsum and steel slag from the basic oxygen process was found to be most successful. An optimised mix was developed and a site trial was carried out. The results showed a good performance but the failure of one test sample during curing showed that the material may not be suitable for other The environmental advantages of reducing the use of cement in concrete are well known but the use of waste min- erals to replace it may lead to a reduction in strength. This paper reports on the use of waste minerals to produce a con- trolled low-strength material (CLSM) for which the reduced strength is not a problem. The principal waste material used was waste Red gypsum. This material is a by-product of titanium dioxide production using the sulphate process. It contains too many impurities to be used in cement or plas- terboard production. The study includes a review of the literature on CLSM and its properties. Different materials are then discussed for mixing with the red gypsum to make it set. The most promis- ing of these was Basic Oxygen Slag (BOS) from steel pro- duction. No materials with an existing market value were considered so Ground Granulated Blastfurnace Slag was not tested. The paper then describes laboratory trials of different mixtures. These started with numerous cup mixes followed by more detailed analysis of the more successful ones. Fi- nally just one mix was selected and a subsequent site trial was carried out.