Cement-based stabilisation/solidification of oil and salt contaminated materials

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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- Oil spills, leakage and other releases of products from the petroleum industry are a source of contamination and are recognised as a major environmental concern. Managing these wastes becomes one of the pressing needs confronting the petroleum industry. Current treatment technologies are either cost prohibitive and/or the treated products have to be sent to land fill without any potential end-use, thereby rendering these solutions unsustainable. Cement-based stabilisation/solidification is an emerging technology; however there is limited knowledge about how oil contamination impacts the reuse of the resulting cementitious material. The objective of this research is to firstly, understand the impact of incorporated petroleum based oily materials and production water (saline water) generated from petroleum processes on the cement solidification process and secondly, to establish its effect on the properties of the resultant mortar. This knowledge is needed to determine the appropriate end-use of these materials. Isothermal and semi-adiabatic calorimetry was used to study changes to cement reaction due to oil and salt amendmates. Increased oil content in mortar led to increased reaction inhibition (lower peaks) and delayed reaction. Depending upon the type of oil, there were changes to the hydration of various hydration phases (C₃S, C₃A and C₂S). As a result, there were changes to the compressive strength and setting time. Incorporating saline water with mortar accelerated the reactions. Consequently, high early heat of hydration resulted in reduced setting time and high early strength compared with control. The degree of impact depended on the type of salt ions and additional levels in water. The substitution of sand with synthetic drill cuttings (SDC) in mortar mixes can increase and accelerate the hydration reaction. However, it is found to reduce the compressive strengths of mortar. This could be attributed mainly to the contrasting impacts between the ingredients of SDC. This study utilised cement-based mortars containing oily materials. Up to 10 % of the fine aggregates mass were found to decrease the mortar compressive strength by almost 64 ± 11 %. However, the mixes exhibited different results in compressive strength based on the oil type used. Incorporating saline water enhanced the strength development at the early stage but reduced the strength at the later stage by up to 38%. However, the level of strength reduction was based on the type and addition of the level of salt ions in the water. Additionally, the compressive strength of the mortar containing a higher content of SDC (25%) significantly reduced by up to 50% at 28 days in comparison to the control mix. However, since the compressive strength covered a wide range of values, various feasible end-use scenarios for petroleum contaminated mortar exist. These results indicate that cement-based solidification/stabilisation can be an effective technology for this kind of undesirable waste. The leachability data showed that although the chemical oxygen demand (from encapsulated oil) from 28-day mortar had increased with the increased oil content or SDC substitution, the performance of all mortar mixes had successfully immobilised the oil content to be landfilled. By contrast, others displayed their suitability to be used in the construction industry subject to particular acceptance criteria. Furthermore, although there was variability in the 28-day leachate conductivity from mortar mixes incorporating saline water, oily materials or synthetic drill cuttings, it was not significantly different from the control. This suggests that the dissolved salt ions were successfully trapped within the solid matrix and that the Portland cement (PC) had good binding ability.
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