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Title: Effect of humic acid and chloride salts on the behaviour of lime-stabilised organic clay
Author: Yunus, Nor Zurairahetty Mohd
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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The effectiveness of lime as a chemical additive for the stabilisation of organic clay is considered uncertain, especially in the long term. Humic acid is believed to be the main deleterious constituent of organic matter that renders lime stabilisation inefficient. Due to this circumstance, the influence of chloride salts to mitigate the adverse effect humic acid has on lime-stabilised clay was investigated experimentally. Artificial organic clay, prepared by mixing commercial kaolin and various amounts of humic acid (0.5%, 1.5% and 3.0%) was used in this study as untreated (organic) clay. A chemical binder, hydrated lime, was used in conjunction with the chloride salts (i.e. CaC/2 & NaCI). The properties of all the organic clay mixtures including the control specimens and the salt treated limestabilised mixtures were determined by Unconfined Compressive Strength (UCS), triaxial (CU & CD) and oedometer tests. The chemical reaction known to occur during a typical stabilisation process was evaluated using microstructure analysis (Scanning Electron Microscope & X-Ray Diffractometer). Curing periods of 7, 28 and 90 days were chosen as key pOints to monitor the evolution and the effect of the stabilisation process on lime-treated specimens and specimens to which the salts had been added. A testing programme, comprising three stages, was scheduled to achieve the overall objectives of this study. The influence of humic acid on untreated clay was investigated. Masking effects which occur due to the humic acid coating the clay minerals were first detected during Energy Dispersive X-ray (EDX) analysis of a representative specimen. In addition, the SEM analysis revealed cracks on the surface of an untreated specimen containing 1.5% humic acid. Furthermore a significant shear strength reduction was noticed for untreated clay specimens containing at least 1.5% humic acid. Although successful stabilisation of organic clay specimens with 5% lime (OlC) was achieved following a cure period of 7 days, the specimen's properties (i.e. shear strength and compressibility) progressively deteriorated as cure duration was prolonged. The abovementioned observation casts doubt over the long term stabilisation potential of lime and its practicability to solve engineering problems. It was observed that the development of lime-treated organic clay properties was most affected when it contained 1.5% humic acid. However by adding relatively small quantities of chloride salts (0.5% CaCI 2 & 0.5% NaCI), a significant improvement occurred as early as day 7 of curing. The enhancement of the properties of the lime-treated organic clay augmented with chloride salts continued in long term. The formation of cementitious products (CSH) was observed in SEM images and detected quantitatively through XRD analysis. Of the two types of salts considered in this study, CaCI 2 demonstrated more superior enhancing capability. The consistent and promising outcomes of this study suggest that the deleterious impact of lime as an organic clay stabiliser can be improved by the addition of chloride salts. Consequently, the findings obtained from this study could be considered in future practice standards with regards to the requirement of lime stabilisation, specifically for organic clay.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available