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DETERMINATION OF REACTIONS AND INTEGRITY OF CEMENT-MUDSTONE INTERFACES

Mendoza Ulloa, Jorge Arturo

[Thesis]. Manchester, UK: The University of Manchester; 2016.

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Abstract

This research examined the cement-rock/clay interface at an initial setting stage by undertaking a series of experiments involving setting of cement against clays and mudstone and examining the boundaries formed in terms of mineralogy, permeability and porosity. Reactions and integrity will be study within the context of the Deep Geological Repositories for Nuclear Waste.The experiments were undertaken in cement cores of around 2.5cm (for porosity and permeability). Polished thin sections were employed to analyse the interface and look at the reactions between cement and rock. The preparation of the samples is also described where some special moulds and methods were developed in order to make cement core samples that could be subject to permeability test. Environmental Electron Scanning Microscope and Electron Probe Micro Analysis were employed in the attempt to identify the interactions that took place in the interface between both materials (cement and rock). Petrophysical equipment such as permeameters and porosimeters were also employed to test cement cores and measure their flow properties. These equipment and methods are also described.Experiments ‘results indicated a clear Ca depletion zone near to the interface with the rock. This alteration was found only in common cement mixtures, whereas the specially designed mixtures did not show any alteration after 28 days of interactions with pore water. The usage of pore water is a difference with other researches since groundwater is mainly used. All of the cement samples investigated proved to have a very low permeability compared with the probable host rock for the repository. A particular result regarding the porosity of NRVB was found, where this cement shows a porosity of 44% and still keeps a very low value for permeability meanwhile other cements mixtures shows porosity of 10 to 20%.Cracking and shrinkage due to water loss was present in samples with high water-cement ratios. Therefore it was not possible to relate cement alteration with a change in porosity of permeability due to technical problems in the process of sample making (mostly cracking and shrinkage of cement samples). This was tried to be overcome by testing partially saturated samples (with pore water from curing) but results were not satisfactory due to lack of consistency.