The scanning electron microscope (SEM) proves to be ideally suited for studying the configuration, texture, and fabric of clay samples. Growth mechanics of crystalline units — interpenetration and interlocking of crystallites, crystal habits, twinning, helical growth, and topotaxis — also are uniquely revealed by the SEM. Authigenic kaolins make up the bulk of the examples because their larger crystallite size, better crystallinity, and open texture make them more suited to examination by the SEM than most other clay mineral types.

Scanning electron microscopy of clays and clay minerals

http://eprints.um.edu.my/8864/1/Improved_strength_and_reduced_permeability_of_stabilized_peat.pdf

Improved strength and reduced permeability of stabilized peat: Focus on application of kaolin as a pozzolanic additive

Berbuff, Nargus and Durr clay samples, commonly known as various grades of Swat china clay, were characterized and compared with imported English china clay. Dehydration of these clays occurred at ~90 to 150oC, followed by dehydroxylation at ~500 to 530oC. The formation of �-Al 2O3-type spinel phase or primary mullite began at ~990 to 1000oC. The major crystalline phases present in Durr and imported English china clay were kaolinite and illite. Additionally, trace amounts of quartz and muscovite were also identified in Durr clay. Berbuff and Nargus clay samples comprised kaolinite along with paragonite, clinochlore, montmorillonite, quartz and albite. Unlike Nargus, halloysite was also identified in Berbuff. Durr, Berbuff and Nargus contained ~28, ~27 and ~23 mass% kaolin respectively. The microstructure of English china clay comprised typical book- and flakelike kaolinite agglomerates and particles. Durr clay comprised mealy and hexagonalshaped kaolinite grains. Clinochlore and/or halloysite of tubular morphology were observed in the microstructure of Berbuff and Nargus. The chemistry, phase constitution and thermal behavior of these local clays were found close to those of high quality English

/pdf/phase-and-microstructural-characterization-of-kaolin-clays-3fgamk42m0.pdf

Phase and microstructural characterization of kaolin clays from north western pakistan

Nowadays the blended cements acquire the merit of high significance due to the thermal, energetic and ecological demands for ordinary Portland cement (PC) production. Metakaolin as a partial substitute of PC represents important pozzolana contributing to production of effective cement composites with high quality. Pozzolanic reaction of metakaolinite with PC in the presence of water is main reason of this statement. Comparison of three types of metakaolin sand (fineness below 60 μm) with different metakaolinite content (31–40 mass%) is presented in this study. The substitution of PC with metakaolin sand of the maximal metakaolinite content (40 mass%) leads to the highest compressive strengths of relevant composites. This is valid for composites with the highest substitution of PC by metakaolin sand in specimens (20 and 40 mass%). The best effectiveness of pozzolanic reaction is given especially by the highest consumption of portlandite which represents composite with the maximal metakaolinite content in metakaolin sand (40 mass%) and the higher substitution level of PC by metakaolin sand in specimens. This fact is connected with the improvement of pore structure parameters resulting in the pore structure refinement as well as permeability decreases. Both 29Si MAS NMR and 27Al MAS NMR spectra of metakaolin sands and respective composites confirm the most intense pozzolanic reaction in the case of metakaolin sand with the highest metakaolinite content (40 mass%). The results are properly supplemented by scanning electron microscopy (SEM) identifying the formed typical phases. The study has shown that metakaolin sand with reduced metakaolinite contents is also applicable as a pozzolanic addition to PC in the on-coming building practice.

Performance of composites with metakaolin-blended cements

Peat is formed by the degradation of plants and animals in the lack of oxygen and is widely known for its very weak geotechnical characteristics. This is the reason to be considered as an unsuitable foundation soil for construction activities. Several attempts have been made to characterize and stabilize peat soil to make construction viable. This study encapsulates an extensive literature review of the available published data for Atterberg limits, consolidation, and stabilization of peat soil using traditional additives, especially cement and lime. Moreover, peat formation and distribution around the world are also discussed. The analysis of the gathered data shows that peat soils having a high amount of fibers may suffer a large amount of secondary consolidation when the load is applied. Besides, the compressibility factors vary for Malaysian peat due to different water and organic contents. The improvement of peat soil is challenging and expensive, requiring an extra amount of stabilizer for the initiation of the stabilization process. However, the optimum and threshold stabilizer’s dosage for peat is also a challenging task to predict due to several factors affecting the stabilization process. Lastly, the study concludes with recommendations on the implication of the fall cone and thread rolling tests for the determination of Atterberg limits of fibrous peat, effective consolidometer for peat, and utilization of traditional additives for peat soil stabilization.

Physio-Chemical Properties, Consolidation, and Stabilization of Tropical Peat Soil Using Traditional Soil Additives — A State of the Art Literature Review

In order to provide a set of reference photographs to be used in identification studies, electron micrographs at relatively high magnification (40,000 to 132,000 diameters), together with some electron diffraction patterns, have been obtained of a group of (a) kaolinites, (b) halloysites, and (c) South Texas outcrop soil samples. Some of the kaolinites consist of well-formed hexagonal crystal plates with edges still sharp at a magnification of 132,000 diameters. Other kaolinites consist of irregular, relatively thin crystal sheets, which may be bent or folded. In one instance it has been possible to demonstrate that the average thickness of the sheets is only 10 A. At high magnification the halloysite clay minerals exhibit a structure consisting of rolled sheets, rather than hollow rods. In some cases, it is evident that several separate crystal sheets are coaxially rolled to form multiple concentric hollow tubes. In the South Texas outcrop samples, the morphology is very complex, as the samples do not consist of one uniform type of particle. Matted sheets composed of interlaced bundles of lath-like particles have been observed. These oriented particles exhibit typical “fiber” type electron diffraction patterns. Kikuchi lines were observed in a thin quartz crystal plate, examined for comparative purposes.

M. S. Taggart

Papers

Electron Micrographic Studies of Clays