The use of synthetic red gypsum as a construction material

Abstract

Huntsman Tioxide produce a co-product "red gypsum" (red due to iron content) as a filter cake during the neutralisation of sulphuric acids at the end of the Titanium Oxide production process. Globally, Huntsman produce 925000 tonnes per year of red gypsum. The majority of the material goes to landfill, the rising cost of which has made it essential to find alternative uses. At present cementitious binders are used extensively in the construction industry, principally in concretes but also in applications like ground improvement. In these applications the cost of the binder, typically Portland cement, makes up a considerable percentage of the overall cost of the technique. In addition to the financial cost there is also the environmental cost of quarrying and processing of materials to produce Portland cements. Gypsum based industrial bi-products have been identified as alternative sources of cement (Beretka et al, 1996). Using these materials has two advantages: they have little or no production cost; and the re-use of such material would negate the need for expensive disposal. This thesis describes a programme of laboratory testing and field trials to investigate the potential of using synthetic red gypsum as a construction material. The main applications investigated were deep dry mix soil improvement and the production of paving blocks. Laboratory trials investigated the properties of red gypsum on its own and when mixed with Pulverised Fuel Ash, Ground Granulated Blast Furnace Slag, Lime and steel slag at a range of water contents. An assessment of samples was made on the basis of Unconfined Compressive Strength at 28 days curing. It was found that a red gypsum: Ground Granulated Blast Furnace Slag mix achieved the highest unconfined compressive strengths (up to 39 MPa) and was selected for further investigation as a binder. This binder was then mixed with a range of soils in the laboratory, it was found that red gypsum based binders can perform as well as Portland cement as a soil mixing binder, and that concrete blocks can be produced with strengths approaching that of equivalent Portland cement mixes. A field trial was also conducted in which red gypsum binders to investigate whether the binder would work in situ. It was found that the red gypsum binder performed adequately to pass standard engineering specifications for soil mixing. The thesis concludes that there are several potential applications for the use of red gypsum in the construction industry but that further work is required before it can be used commercially.