Crushed Quartz Research Articles

Mineral admixtures in mortars effect of type, amount and fineness of fine constituents on compressive strength

This work is the third part of an overall project the aim of which is the development of general mix design rules for concrete containing different kinds of mineral admixtures (also named mineral additions or mineral constituents). It deals with the compressive strength of mortars made with up to 75% of crushed quartz, limestone filler or fly ash of different fineness. The paper presents all the experimental results as a sort of database and emphasizes the effects on strength of the nature, amount and fineness of mineral admixtures. For short hydration times (1 to 2 days), the nature of mineral admixture is not a significant parameter, as mortars containing the same amount of different kinds of admixtures having equivalent fineness present similar strengths. For long hydration times (up to 6 months), the excess strength due to fly ash pozzolanic activity is quantified by the difference between the strengths of mortars containing the same proportions of inert and pozzolanic admixtures with the same fineness. In the case of inert mineral admixtures, the increase in strength with the fineness of mineral admixtures cannot be explained by the filler effect, but can be attributed to the physical effect of heterogeneous nucleation. In the next part of this work, these results will be used for the elaboration of an empirical model leading to the quantification of both physical and chemical effects. This model presents strong similarities with the previous model based on calorimetric results.

Production Technology for Copper‐ and Cobalt‐Blue Vitreous Materials from the New Kingdom Site of Amarna—A Reappraisal*

Previously published data on the chemical compositions and microstructures of copper‐ and cobalt‐blue frit, glass and faience from the New Kingdom site of Amarna in Egypt (Shortland 2000) are summarized. The data are then used to infer the raw materials and processes employed in the production of these vitreous materials. The results suggest that crushed quartz pebbles were the source of the quartz for all the materials, but that different sources of alkali, both natron and a range of plant ashes, were used in the production of each material. It seems probable that the cobalt‐rich alum colorant was pre‐treated before use by precipitating cobalt hydroxide from a solution of the alum by the addition of natron. It is further hypothesized that cobalt‐blue glass was produced by melting the cobalt‐blue frit together with additional plant ash and possibly quartz. Finally, it is suggested that, in glazing the cobalt‐blue Variant D faience first produced in the 18th Dynasty, the efflorescence or application method was selected according to object type.

Sources of non-glacial, loess-size quartz silt and the origins of “desert loess”

Descriptions of peridesertic loess deposits and possible non-glacial origins for silt size quartz are reviewed, including direct release from weathered bedrock. Results from salt and frost weathering experiments are presented and methods by which sufficient energy can be imparted to sand size grains to release silt-size fragments are identified. These fragments may then be entrained by aeolian or fluvial action. Results from fluvial comminution experiments indicate that high energy, mixed sediment fluvial systems may be very effective in generating quartz silt. Purely aeolian attrition is also seen as a major source of silt size and finer material. Results from aeolian abrasion experiments performed using crushed quartz sand are complemented by trials using sands from deeply weathered granite and Pannonian Sands from Hungary. Field and laboratory observations are therefore seen to argue for the existence of deposits that can be classified as ‘desert loess’.

Prediction of the settling velocity of irregularly shaped particles

This work presents a new empirical relationship between Reynolds number Re t and Archimedes number Ar. From this relationship it is possible to calculate the free settling (terminal) velocity of irregularly shaped (e.g. crushed) solids in water. Experimental terminal velocities for various size fractions from earlier works were correlated with the new equation. The data refer to crushed quartz and galena particles. The new relationship gives for a very wide range of Archimedes numbers (flow regimes) a good correlation between experimental and calculated terminal velocities. Comparisons with the Ganguly relationship also showed a good agreement for the prediction of the terminal velocities. The current work shows that the terminal velocities in water can be calculated with a single equation for various irregularly shaped solids and for various size fractions.

A transmission electron microscopy study of interfaces and matrix homogeneity in ultra-high-performance cement-based materials

Ultra-high-performance cement-based materials produced under different conditions have been characterized by transmission electron microscopy (TEM), scanning transmission electron Microscopy (STEM), high resolution transmission microscopy (HRTM) and chemical analysis. In addition to cement, these materials contain large amounts of crushed quartz and amorphous submicrometre silica. A post-set heat treatment was also applied in some cases. An abrasive thinning method combined with grazing angle ion etching allowed the preparation of 100 nm thick specimens with wide observation surface areas while avoiding any water or CO2 contact which may cause changes. Clinker, silica fume and crushed quartz reactivity as a function of the curing processes have been studied, as well as the interfacial zones with the hydrated matrices. The Ca/Si ratio spatial distribution in hydrated products has been analyzed and shown to undergo strong local fluctuations. Nevertheless, the composition fluctuations were less pronounced and the average Ca/Si ratio was lower than in silica-free cement paste. HRTM lattice imaging shows the coexistence of nanocrystalline phases and mesoscale ordered regions within an amorphous matrix. A d-spacings analysis of the nanocrystalline phase suggests a tobermorite-like structure for the calcium silicate hydrates, whereas the mesoscale order might reflect modulations in the water content.

Narrowing of ESR Spectra of the E? Center in Crushed Quartz by Thermal Annealing

The E' center formed by γ-irradiation in crushed quartz has a distribution in the value of the hyperfine fine structure (hfs) constant of 29 Si (nuclear spin: I = 1/2) and of the g-factor. The widths of both distributions decreased after annealing. The central line due to the E'center associated with 28 Si (I = 0) shows a clear narrowing as to allow the numerical simulation of the distribution of g-factor based on the following assumptions. One is that the distribution is composed of Gaussians with various line widths. The other is that the broader component has a small thermal activation energy. The simulated spectrum shows good agreement with the experimental one. The distribution of the g-factor can be explained with an inhomogeneous eigenvector of a singly occupied molecular orbital (SOMO).

Sand grain analysis—image processing, textural algorithms and neural nets

A quantitative method for characterising and classifying quartz grain form by mathematical analysis of surface texture is presented. Scanning electron images of quartz grains were ‘frame grabbed’ and converted to a digitised grey level image. Image enhancement, segmentation and histogram equalisation were applied to produce standardised images. Two major textural approaches were then applied. The Roberts gradient operator determined the degree of surface edgeness while calculation of spatial grey level dependence matrices allowed production of distribution maps of surface homogeneity, entropy and correlation. Textural parameters were obtained from samples of 0.5 mm quartz grains from three distinct populations: Desert quartz; Fire Island, New York, beach grains; and Brazilian crushed quartz. A comparative analysis using discriminant analysis and neural networks was undertaken to quantify the success in classifying the different populations. Both methods achieved excellent degree of quartz grain classification. However the use of neural networks provided a more robust method of analysis particularly when presented with incomplete data sets.

Comminution of geological samples using Syalon based milling vessels: comparison with established sample preparation methods

The productivity and reputation of analytical laboratories are in part underpinned by the standards of efficiency and quality applied when preparing samples for analysis. Sample milling vessels constructed from Syalon 101 (an aluminium–silicon–oxynitride alloy) have recently become available. This paper describes an assessment of their efficiency and contamination characteristics to assist the evaluation of Syalon as a possible alternative to agate for sample preparation prior to multi-element geochemical analysis. Samples of crushed quartz, quartz sand, garnet-bearing schist and marble were milled in Syalon vibrating-cup and planetary ball mill vessels to compare their comminuting efficiency with that of conventional hardened chromium steel and agate vessels. Contamination during milling was estimated by comparison with samples comminuted in agate vessels only, because metallic preparation equipment is known to introduce contaminants including Fe, Cr, W, Mn, Ni and Co to the sample. The comminuting efficiency of Syalon is superior to that of agate. Although some contamination does occur it may be less analytically critical than that derived from metallic comminution equipment.

Effects of UV Exposure on E' Centers Formed in Crushed Quartz Grains

Electron spin resonance (ESR) study of E' centers in crushed quartz (SiO2) indicated the formation of a new type of E' center by UV-irradiation. On the other hand, the concentration of E' centers formed by γ-irradiation in the crushed quartz is reduced by UV-irradiation. It was possible to distinguish between the three types of E' centers in crushed quartz (E' c: formed simply by crushing, E' UV: formed by crushing and UV-irradiation and E'γ: formed by crushing and γ-irradiation) using UV-irradiation. The distribution of the activation energy of the E' centers just after crushing was revealed by annealing experiments and computer simulation. The technique of characterization by UV-irradiation will be useful for evaluating the local strain in SiO2, especially in natural quartz.

Scaling Bacterial Filtration Rates in Different Sized Porous Media

Aquifer sediments contain a wide distribution of particle sizes, but only a single collector diameter ( d ) can be used in a filtration equation. To establish a method for selecting a characteristic d when media are composed of different sized particles, we measured bacterial retention in columns packed with either crushed quartz sand (separated into three different size ranges) or borosilicate glass beads. The best methods for choosing d were those that produced nearly constant collision efficiencies (α's). Characteristic diameters included: d10 (10% of all particles were smaller), d90 (90% of all particles were smaller), d a (arithmetic mean), and d g (geometric mean), where all diameters were calculated using number, area, and volume size distributions. Bacterial α's decreased in proportion to the distance traveled in the packed bed, and were scaled by the number of bacteria-sediment collisions using a dimensionless collision number (ξ). These comparisons indicated that characteristic diameters based on the smaller particles ( d a and d g using number distributions, and d10 using a volume distribution) most accurately described bacterial transport in the different-sized porous media.

Filtrate turbidity improvement of existing mono-media filters based on a pilot plant study

With the advancement of knowledge in drinking water and health impacts related to it, requirements for drinking water have progressively become more stringent. Removal of particulate matter causing turbidity has also been found to be an effective means for removal of microbial contaminants such as Giardia. The conventional treatment process most effective at removal of small particulates is filtration. Presented is a two-phase pilot-scale study used to select new filter media for the Rossdale Water Treatment Plant in Edmonton, Alberta. The study was necessitated by more stringent turbidity guidelines which existing filters would have difficulty achieving. The design and planning of the study had to consider constraints posed by upgrading of an existing filter facility which dictated the media depth and the allowable bed expansion during backwashing. Phase I involved a screening test of four types of media. Based on the phase I results, a crushed quartz and a dual-media consisting of anthracite and sand were selected for more detailed study in the second phase involving investigation of the effects of filtration rate (3.5–12.5 m/h). Filter performance was analyzed using different statistical methods. Factorial experimental concepts were used to study significant effects. Results from both phases indicated that crushed quartz consistently provided the best effluent quality, while the dual-media provided longer filter runs. Key words: water treatment, constant rate filtration, turbidity standards, filter media, crushed quartz, statistical analysis.

The use of Fourier descriptors in the classification of particle shape

ABSTRACTA new quantitative method for characterizing quartz grain shape is presented. The method employs a harmonic analysis based upon Fourier descriptors which is a distinct variation of the traditional and widely used Fourier series. Quartz grain images from a scanning electron microscope were ‘frame grabbed’and converted to a digitized grey‐level image. The image processing techniques of enhancement, segmentation and boundary tracking were applied to remove all features except the image boundary. This boundary was sampled at uniform intervals of are length and represented mathematically on the complex plane. In this way problems associated with the location of particle centroid and re‐entrant values were avoided. The resulting data was standardized relative to scale, rotation and starting position. Hence the discrete Fourier transform was applied using modern fast Fourier transform techniques and the modulus of the resulting harmonic amplitude used to characterize the grain shape. The technique was applied to a sample of 0–5‐m quartz grains from three distinct populations: desert quartz, beach grains (Fire Island, New York) and Brazilian crushed quartz. Whilst plots of average amplitude vs. harmonic number for each population appeared similar, discriminant analysis applied to each grain sample distinguished characteristic grain shape with an excellent degree of success. The problems of location of the centroid and re‐entrant values were eliminated. This allowed the technique to be applied to a much wider group of irregularly shaped sedimentary particles such as loess.

THE BEGINNINGS OF ISLAMIC STONEPASTE TECHNOLOGY

A multidisciplinary programme of research on Islamic pottery has been focused on questions of the dating, provenance and technology of Islamic pottery. One particular question has been the development of stonepaste, a material made primarily of crushed quartz with added frit-glass and clay. The combination of the different approaches of this study has revealed early foundations for the technology in ninth-century AD Iraq, apparently originating in the clay ceramic rather than the ‘Egyptian faience’ tradition. Subsequent and final practice developed in tenth- and eleventh-century AD Egypt. This technology becomes the primary body for all fine Islamic ceramics.

THE BEGINNINGS OF ISLAMIC STONEPASTE TECHNOLOGY*

A multidisciplinary programme of research on Islamic pottery has been focused on questions of the dating, provenance and technology of Islamic pottery. One particular question has been the development of stonepaste, a material made primarily of crushed quartz with added frit‐glass and clay. The combination of the different approaches of this study has revealed early foundations for the technology in ninth‐century AD Iraq, apparently originating in the clay ceramic rather than the ‘Egyptian faience’ tradition. Subsequent and final practice developed in tenth‐ and eleventh‐century AD Egypt. This technology becomes the primary body for all fine Islamic ceramics.

Glacially crushed quartz grains in loess as indicators of long‐distance transport from major European ice centers during the Pleistocene

Detailed mineralogical analysis of the fine and very fine sand fractions (63–250) in the Dreihausen Loess Sequence shows the presence of numerous glacially crushed grains, including a significant amout of quartz. Previous theories regarding the origin of loesses in central Germany held that all sediments were derived locally, following short‐distance transport from nearby sandstone outcrops. New data presented here show that many quartz and feldspar grains were glacially crushed, weathered, crushed again, transported, and emplaced by aeolian processes at Dreihausen. Crushing features observed are compatible with transport in both continental and alpine glaciers; some clasts show the effects of abrasion by both water and ice transport, while others are partly rounded presumably by fluvial and/or aeolian processes. Stronger palewind systems during the Pleistocene presumably contributed to the transport and emplacement of glacial grains from ice centers in both the Alps and the Baltic areas, and also possibly from the Rhine Basin.

Relative differences between glacially crushed quartz transported by mountain and continental ice; some examples from North America and East Africa; discussion and reply

Relative differences between glacially crushed quartz transported by mountain and continental ice; some examples from North America and East Africa; discussion and reply

Relative differences between glacially crushed quartz transported by mountain and continental ice; some examples from North America and East Africa

Relative differences between glacially crushed quartz transported by mountain and continental ice; some examples from North America and East Africa

The surface chemistry of crushed quartz dust in relation to its pathogenicity

The surface chemistry of finely divided quartz dust has been investigated from the standpoint of its fibrogenicity by EPR and adsorption calorimetry. Even after grinding in the atmosphere, quartz bears surface radicals, originating from homolytic cleavage of SiOSi bonds and subsequent reaction with atmospheric components. These radical sites, which readily react with both O 2 and H 2O, can be regarded as possible initiators of the macrophage-mediated reaction resulting in lung fibrosis. The heat of adsorption of water indicates the presence of ∼3 × 10 17 very strong sites (−Δ H≥180 kJ mol −1) on all quartz samples, but these are totally abseht in chemically prepared amorphous silicas. Mechanical cleavage of the covalent SiO bond, more than crystallinity, is suggested as the primary cause of SiO 2 toxicity.

Silicate nephrotoxicity in the experimental animal: the missing factor in analgesic nephropathy.

Three silicon-containing compounds (magnesium trisilicate BP, crushed quartz and crushed Arran granite) were added to the drinking water (250 mg/l) of three groups of male guinea pigs for four months. At autopsy all animals receiving magnesium trisilicate showed a focal tubulo-interstitial nephritis mainly affecting the distal nephron. Similar but less intense lesions were encountered in two animals receiving crushed quartz. No renal lesions were found in the control group or in animals receiving crushed Arran granite. The concentration of soluble silicates in drinking water, measured as elemental silicon (Si) by atomic absorption spectroscopy (AAS) was determined for twenty-eight locations in different regions of Britain. Following ingestion of magnesium trisilicate, significant increases in urinary excretion of Si were demonstrated in two healthy adults using atomic absorption spectroscopy.

Investigations of Dissolving Mechanically Processed Quartz Grains

AbstractThe dissolution of polycrystalline quartz strained by compression and shear or by impact crushing in 1‐N NaOH lead to different results. The defects of the impact crushed quartz grains, measured as crystallinity by X‐ray methods, are not preferentially concentrated in regions near the surface. It is assumed that in this case the corners and edges of the quartz grains are preferred centers of defects.