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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.

The investigation into the syntheses and the intercalations of LDHs is the focus of the work described in this thesis. An introduction to Layered Double Hydroxide (LDH) materials with an emphasis on the possible host lattices and to their applications is given in <strong>Chapter 1</strong>. The application of LDHs in cement including; history of cement, cement production process, and cement hydration is detailed. The synthesis of the Ga-doped Ca₂Al(OH)₆Cl•nH₂O LDHs (Ca₂Ga_xAl_(1–x)-Cl; where 0 < x < 1) via the co-precipitation method is reported in <strong>Chapter 2</strong>. The effect of doping Ga³⁺ on a parameter of Ca₂Ga_xAl_(1–x)-Cl was determined by using Vegard’s law and the correlation between a parameter and x value was derived. The intercalation of organic anions including; sodium styrene sulfonate, sodium butene dicarboxylate, sodium fumarate and ammonium poly(styrene sulfonate), in Ca₂Ga-Cl structure is described. The intercalation of lignosulfonate, naphthalene sulfonate and polycarboxylate into Ca₂Al(OH)₆NO₃·6H₂O (Ca₂Al-NO₃) is detailed in <strong>Chapter 3</strong>. The release behaviour for the LDHs and the kinetic modelling of the release are reported. The effects of these LDHs on cement hydration studied by using the in situ X-ray diffraction and the ultrasound shear-wave reflection are discussed. In <strong>Chapter 4</strong>, the synthesis of Ca₂Al(OH)₆NO₃·nH₂O via a non-ionic surfactant reverse microemulsion is reported. The effects of the amount and the solubility [Hydrophile-Lipophile Balance (HLB)] of non-ionic surfactant on the morphology and the size distribution of the LDHs are discussed. Two new nitrite intercalated Ca₂Al-LDHs [Ca₂Al(OH)₆NO₂·nH₂O] synthesised via both the co-precipitation and the reverse micro-emulsion method are detailed in <strong>Chapter 5</strong>. The hydration of Portland cement samples with additive nitrate- and nitrite-intercalated Ca₂Al-LDH made using co-precipitation is discussed. The synthesis of dispersed, uniform nanoplatelet [Ca₂Al(OH)₆DDS]•H₂O LDHs is reported in <strong>Chapter 6</strong>. The effects of the amount of the surfactant on the morphology and size distribution of the LDHs are described. The experimental procedures and characterising techniques employed in this study are listed in <strong>Chapter 7</strong>. Additional data are provided in the <strong>Appendices</strong>.