The purpose of this paper is to demonstrate the influence porosity and fissuration exert on the physico-mechanical properties and durability of nine Portuguese ornamental granites with different petrographical and physical characteristics. Scanning electron microscopy (SEM) allows the type of cracks (intergranular, intragranular and transgranular) to be identified. A microfracture index was calculated based on the collected data. This index is called linear crack density (LCD) and is defined by the number of cracks per length unit. The results reveal that intragranular cracks are the most frequent and represent between 62.9% and 82.3% of all the cracks observed. A physical weathering classification system based on linear crack density values of the studied granites is presented. The voids included in these types of rocks are predominantly microfractures and correlate closely with open porosity and linear crack density. Uniaxial compressive strength and P-wave velocity (V P ) appear to decrease as linear crack density increases, albeit with low correlation coefficients. This may be due to the fact that linear crack density does not take into account possible preferential crack orientation and both properties are strongly dependent on this preferential orientation. Other textural characteristics, such as grain size and preferential orientation of certain minerals, may contribute to these low correlation coefficients. In ageing tests, the salt crystallization test demonstrated greater material loss in granites with higher linear crack densities and thermal shock testing proved that thermal cracks have a greater influence on V P in rocks with lower linear crack densities. In light of the ageing tests results, precaution is recommended when using granites with effective porosities greater than 3% as dimension stone out-of-doors in polluted continental or marine areas. D
Fecha recepción: 10/11/87 RESUMEN Se presenta la utilidad de la microscopía óptica de fluorescencia para el estudio textural del clinker de cemento Portland, especialmente su porosidad. Se comentan los fundamentos y modalidades de la técnica, y se describe el método recomendado de preparación de muestras. La utilización de la microscopía de fluorescencia permite un estudio más fácil de ia porosidad, obteniéndose imágenes muy apropiadas para su cuantificación mediante técnicas automatizadas. Además, las muestras para fluorescencia pueden ser estudiadas complementariamente por microscopía óptica de polarización por luz reflejada.
SUI\/IMARYThe application of fluorescence light microscopy in the textural study of Portland cement clinker, specially its porosity, is presented. Principles and types of the technique are comented and the suggested sample preparation method is described. The use of fluorescence microscopy allows an easier study of the clinker porosity, and very proper images for automated quantification can be obtained. Besides, the samples can also be observed by reflected-light polarizing microscopy.
INTRODUCCIÓNLa técnica microscópica más utilizada para el estudio del clinker de cemento Portland es la de polarización. No obstante, para el estudio de determinados aspectos pueden aplicarse otras técnicas más específicas, con las que se consigue una información más detallada. En concreto, la microscopía óptica de fluorescencia resulta especialmente indicada para la observación de la porosidad. La importancia de esta característica textural ha sido puesta de relieve por numerosos autores, como por ejemplo [1] y [2], puesto que puede obtenerse información muy útil, tanto sobre el proceso de fabricación del clinker, como sobre ciertas propiedades del mismo, especialmente su molturabilidad.La microscopía de fluorescencia ha sido utilizada en ocasiones por algunos autores para el estudio textural del hormigón [3], y del clinker de cemento Portland [4].
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