Roofing Slate Research Articles

Unfired clay masonry bricks incorporating slate waste

This paper discusses the potential of using slate waste generated from roofing slate production in the UK in the manufacture of unfired clay masonry bricks. Ground granulated blast-furnace slag activated by lime and Portland cement were used to stabilise Lower Oxford Clay incorporating slate waste in the preparation of laboratory cylindrical test specimens. The specimens were moist cured at room temperature (20±2°C) for between 3 and 90 days before testing for compressive strength. The drying and linear expansion behaviours of the test samples were assessed by means of moisture content measurement (at the age of testing) and linear expansion measurement after soaking the samples in deionised water. The strength of the cement-activated blended mixture was lower than that of the lime-activated mixtures. An environmental comparison of the unfired clay masonry bricks with mainstream construction (fired) bricks shows that the unfired clay bricks have good environmental characteristics over a range of important criteria. These results suggest that there is potential for using activated slag mixtures in the manufacture of bricks for low-cost environmentally friendly housing and energy-efficient masonry wall construction within the UK.

Applications of slate waste material in the UK

The potential of using slate waste generated from roofing slate production in the UK in various applications is reviewed and the environmental impact of the stockpile of slate waste is also assessed. The findings suggest that there is potential for using slate waste in many situations, including engineering applications. In order to reduce the environmental impact arising from the quarrying of conventional construction materials, the abundance of slate waste in Wales in particular and the UK in general could be exploited. With associated economic advantages despite reported transportation difficulties, utilisation of this waste stream for most practical and low- to medium-strength engineering applications is feasible and would maximise the use of surplus regional and national industrial wastes and minimise the environmental impact of their disposal.

Optical microscope and SEM evaluation of roofing slate fissility and durability

The fissility and durability of representative samples of commercial roofing slates from ten deposits in the NW of Spain have been evaluated using transmitted and reflectedlight optical microscopy, scanning electron microscopy, chemical testing and geomechanical procedures. The dominant sulphides in the different slate samples are pyrite and pyrrhotite, the weathering potential of which can be highly variable. The dominant carbonate mineral is ankerite, which explains the low reactivity of these slates in acidic media. The minimum commercial plate thickness varies between 3.5 and 5 mm, depending on the microtexture of the rock. The methodology used in this paper is proposed in order to eliminate the subjectivity of input data that are used in current methods of evaluation and modelling of slate deposits, thus producing an improvement in the profitability of mining operations and a reduction in waste materials.

Passivation techniques to prevent corrosion of iron sulphides in roofing slates

The aim of the present study was to evaluate the efficacy of different methods of sulphide microencapsulation in terms of inhibiting sulphide oxidation in roofing slate. For this, a preliminary test was carried out with ground pyrite and the methods that provided the best results were applied to samples of roofing slate. Protection against oxidation was measured by the amount of iron released after enforced oxidation with H 2O 2 in the tests with pyrite, and by thermal cycle alteration, SO 2 and saline spray tests (EN 12326-2:2000 and EN 14147:2004) in the tests with the slate samples. The results indicate that treatments with potassium phosphate and potassium silicate, proposed for controlling acid mine drainage, were the most effective at protecting pyrite against oxidation, and that these methods are also effective when applied to slate.

Protocol for assessing the effectiveness of protective coatings for roofing slate

Spain is a world-wide leader in roofing slate production, quarriying more than 600,000 tons of slate of great quality and generating around 300 euros million in sales each year. However, an enormous quantity of slate plates is considered as a low quality product or discarded every year as waste. The application of protective products on roofing slate tiles helps to commercialise slate with higher oxidation rates, reducing wastes and environmental problems. The present protocol serves to evaluate the new protective products that are now used by slate producers. A combination of three technological tests is proposed here, along with a visual questionnaire to grant quality indices. Each test is oriented to clarify critical properties for the future use of the roofing slate, as follows: (i) Thermal cycles were used to determine the oxidation rate of iron sulphides; (ii) Slate behaviour in acid urban atmospheres was interpreted by exposition of slate tiles to SO2 gas; (iii) Effectiveness of the protective layer under saline corrosion and solar radiation was obtained by exposition to saline fog and UV-irradiation. Physico-chemical tests have been performed in the Technological Centre of the Slate (Orense, Spain) whereas the chemical-structural characterizations of natural, impregnated and altered slate plates were carried out by X-ray diffraction and optical and electronic microscopy in the University of Santiago de Compostela (NW Spain). The quantitative analyses of the alteration grades have been determined using a freeware program (IMAGEJ) on the scanned images of roofing slate tiles. The protocol here presented has been experienced with the more important protective slate products nowadays, i.e., siloxanes, organic resins and polyurethanes.

Characterization of slate processing fines according to parameters of relevance for mine spoil reclamation

Slate processing fines (SPF) are mineral wastes produced during the preparation of roofing slate. Slate is extracted in open-cast quarries, that often result in disturbed sites and wastes that are thrown into dumps which are inhospitable to vegetation due to their poor water holding capacity and limited capability to supply nutrients. Covering the slate dumps with a layer of fine materials is expected to help reduce their adverse properties, thus facilitating a reclamation process. Revegetation success will depend on a number of factors such as the physical condition of the restructured soil, its nutrient content, the presence or absence of toxic materials and the selection of the plants best suited to the prevailing conditions. In this work the main physical, chemical and biological properties of the SPF have been determined, emphasizing those which will influence the successful establishment of vegetation. Since the electrical conductivity and pH of the SPF are in the range which is tolerable by plants, and the quantities of heavy metals are under the thresholds of toxicity, they could be used for this purpose but, due to the lack of nutrients and biological activity, and adverse physical condition, some organic amendment will be necessary for successful reclamation.

Artificial Roofing Slates and Shingles

Abstract Early in the 1980s, manufacturers started to respond to the market desires for a Class A fire-rated steep-sloped roofing material. Other manufacturers sought slate-like roofs that were lower in cost than natural slate. Both groups tried a variety of materials and cellulose fibers including fibers recovered from newsprint, bundles of wood, and more fibrous or shredded wood to reinforce portland cement matrixes. Previously, asbestos fiber was used with cement to form very durable asbestos-cement shingles, sidings, and sheets. Many manufacturers felt they could replace asbestos with other materials and did so offering performance warranties of 25 to 50 years duration. The authors have investigated and tested eleven of these artificial shakes and slates manufactured by nine manufacturers. Hundreds of roofs have been examined in more than 20 states. Some products failed before the installation was completed. Few survived past their tenth year of exposure. None of the artificial shakes and slates investigated are currently manufactured in the United States. We provide data that were generated by our laboratory tests on thousands of specimens made by nine manufacturers (A through I), identify the reinforcements present, list some of the critical properties such as flexural strength, deflection at break, and water absorption, and the specific failure modes for each product. The principal recommendation to avoid failures of this kind is to use products that have a substantial history of effective performance in the environment to which they will be used. Proceed into a market place cautiously when formulation changes are made to products with successful track records.

Application of Bayesian networks to the evaluation of roofing slate quality

We present the results of an application of Bayesian networks to the evaluation of the quality of roofing slate. Using data from borehole samples of a slate deposit, two networks constructed with different levels of expert knowledge input were evaluated for their capacities for inference and prediction of the quality of slate for roofing. It can be concluded from the results that Bayesian networks are an extremely useful automated tool for evaluating the quality of a resource such as slate for the following reasons: they allow final quality to be assessed immediately and in probabilistic terms with a tolerable degree of uncertainty; they enable the probability of obtaining different final qualities to be estimated when new data is introduced into the network; they speed up the evaluation process by simulating and optimising the work of the expert (during field data collection and borehole description) in identifying the parameters with the greatest influence on final quality; and finally, they have a satisfactory capacity for prediction.

TL/OSL properties of natural schist for archaeological dating and retrospective dosimetry

Schist, a metamorphic rock composed largely of quartz and muscovite, has been used as a building stone through the centuries in many parts of the world. In ancient Greece, it was used in buildings and monuments (Knossos, Karthaia, etc). Basic TL and OSL properties of schist are studied in the present work to evaluate its potential use in archaeological dating and retrospective dosimetry. In particular, the optical stability, as well as the linearity of the TL and OSL signal were investigated for samples of natural schist obtained from a roofing slate. The results indicate that both signals are rapidly bleached when the sample is exposed to sunlight. An exposure of 1 min reduces the TL signal by 93%, the IRSL signal by 99% and the post-IR BSL signal by 90%. The dose response was found to be linear for a radiation dose at least up to 75 Gy for the TL and the IR OSL signal and at least up to 25 Gy for the post-IR BSL signal.

Organic Matter in Black Slate Shows Oxidative Degradation Within Only a Few Decades

Abstract Low-grade metamorphic black slates were examined for the impact of oxidative weathering after exposure to the atmosphere for well-constrained time periods. Measurements of organic carbon were carried out on roofing slates and alum slate mining waste, and were compared against data obtained from freshly mined material. The results show that the organic-carbon content of roofing slates decreased from initially 0.73–1.7 wt.% to 0.51, 0.42, and 0.50 wt.% after 90, 94, and 100 years, respectively. The organic-carbon content of alum slate mining waste decreased from > 7.5 wt.% at the base (5 m below surface) to < 1 wt.% at the top of a dump during an exposure time of 53 years. The thermal maturity of this black slate organic matter is of anthracite stage. The degradation of organic matter is controlled exclusively by its accessibility within the exposed rock. After intense weathering, different black slate types (alum slate, roof slate) show similar amounts (less than 1 wt.%) of a poorly accessible OM fraction. The results demonstrate that oxidative weathering of organic matter in black slates is a fast process. A substantial decrease of organic matter occurs within only some decades to a century, rather than over geological time spans.

European testing of roofing slate

This paper evaluates the newly introduced European roofing slate standard specification and test methods (BS EN 12326), including comments on the published acceptance criteria. The standard represents a major change from the previous long-established and limited-in-scope British Standard (BS 680-2), with a change of ethos from pass/fail criteria to mainly a means of determining the minimum required thickness of the slate. The European standard overall is judged to be better suited to the modern roofing slate sector, where a wide range of products from diverse countries is now commercially available.

Assessing the viability of underground slate mining by combining an expert system with a GIS

The slate sector in Galicia (NW Spain) is facing a growing crisis resulting from the gradual increase in the exploitation ratios for open quarries and increasingly stringent environmental restrictions. Given that good geotechnical quality reduces the costs of any underground mining operation, and — for slate and other ornamental rock — conditions the possibility of extracting blocks of a size acceptable to roofing slate transformation and finishing plants, we created a geotechnical quality index, aimed specifically at analysing slate masses, that applied techniques from the machine learning field (Support Vector Machines). This geotechnical quality index, together with the factors that affect underground mining operations, was integrated in a Geographical Information System, which would enable all relevant information on a slate mass to be viewed and analysed simultaneously.

Ceramic foams manufacturing from slate wastes

The objective of the present work is the recovery of slate wastes into a raw material for the ceramic industry. Foams are obtained without any addition of foaming agent thanks to the transformation of component present on the slate during heating. A glass base material with a closed porosity, gray color and density value around to 0,3g/cm 3 has been obtained. Raw material is the slate waste as slurry, after cutting roofing slates. After drying, the slate powders were die pressed to achieve green samples, which were sintered in N 2 -5%H 2 atmosphere at different temperatures, as well as in air as reference material at 1150°C. Dilatometer behavior was studied on die pressed slate powders under both atmospheres as well as X-Ray diffraction in order to determine the crystalline phases on sintered materials. Sintered density decreases as temperature increases under non-oxidant atmosphere, which leads to decrease the mechanical properties with the temperature when the foam structure is developed (over 1075°C on N 2 -5%H 2 atmosphere).

A not so clean slate

PurposeThis is an initial attempt to classify natural roofing slate quality using the new European Standard BS EN 12326 and suggest how such classification may be employed to predict in‐service performance and identify potentially problematic materials.Design/methodology/approachA wide range of natural roofing slates has been subjected to the new standard testing regime and additional tests carried out. Experience of known in‐service performance and previous test results have also been taken into consideration.FindingsAn initial classification of natural roofing slate quality has been proposed with the flexural strength, water absorption, potential for oxidation and carbonate content considered to be the key components.Research limitations/implicationsThere is considerable scope for refinement of the proposed classification by investigating the performance of the wide range of other natural roofing slates available and taking the results into consideration. Predicted in‐service performance is based on practical experience and can be considered only a general guide.Practical implicationsBy classifying natural roofing slate quality users will be able to make better informed purchasing decisions based on cost versus quality. Slate producers, especially those with higher quality slates, will also be able to market their materials accordingly with less chance of losing out to lower quality, potentially problematic materials that still conform to the new standard.Originality/valueThe concept of a quality classification for natural roofing slate is not new, but this has been omitted during the creation of the new standard. The proposed classification is broader and probably better defined than those in existence elsewhere or previously used within the European Union member states.

Modelling of flow rate in a photovoltaic-driven roof slate-based solar ventilation air preheating system

This paper describes the modelling of flow rate in a photovoltaic (PV) driven, roof slate based solar system for preheating ventilation air in cold climates. The system consists of a photovoltaic driven, attic mounted fan, which draws air through the spaces between the warm slates and delivers it through a metallic flexible duct into a house. A model for predicting the flow rate of air as a function of irradiance and ambient temperature is developed based on the measured performance of the different components of the system. Considering all experimental sources of error, the model predicts the flow rate of air with a maximum error of 12%. The model is validated for different combinations of components in a roof section constructed at Napier University in Edinburgh. The predicted flow rates are within 10% of the measured values. The model is extended so that it can be applied for different locations and different roof tilts and orientations. A future paper will make use of the model developed herein for system optimisation based on maximum monthly volume of preheated ventilation air delivered. The model will also be used to investigate the effectiveness of PV driven, roof slate based systems as solar air heaters.

Caracterización del comportamiento elástico de materiales pizarrosos del Sinclinal de Truchas mediante ultrasonidos

Truchas Syncline slates has been exploited since the second half of the last century to perform roof slate, as the main industrial application which implies an important economic profit to the mine companies working in this area. Petrographic studies from visu to microscopic scale, added to the physical property determinations report a better reological knowledge of this rocks. Ultrasonic measurements led us establish rock elastic constants, by a non destructive method, and it would inform about rock behaviour during exploitation works in slate quarries. Planar fabric and inclination of the cleavage planes are the main parameters involved in the propagation of the ultrasonic waves including lithologic changes. Maximum values obtained from the ultrasonic propagation are reached when foliation appears at 90o (waves travel along foliation planes) and minimum when waves travel at 0o, perpendicular way at foliation plane. Linear correlation has been obtanined to the main elastic constant from slates but not to Poisson relation.

Quantitative mineralogical analysis of Spanish roofing slates using the Rietveld method and X-ray powder diffraction data

The relative proportions of the minerals in a series of slates from the Iberian Massif in northwestern Spain, quarried and used for roofing purposes, have been evaluated using X-ray powder diffraction and the Rietveld-based SIROQUANT data processing system. Information on the chemical composition of the chlorite, mica and feldspar in the slates was obtained separately from electron microprobe studies, and was used in conjunction with the mineral proportions to calculate an inferred chemical composition for each sample from the quantitative XRD data. The inferred compositions were then compared to the actual chemical compositions of the respective slate samples, obtained by X-ray fluorescence spectrometry, to evaluate the consistency between the XRD results and independent chemical analysis data. A high level of consistency was observed between the element oxide percentages inferred from the XRD study and the equivalent oxide proportions determined by direct chemical analysis. The comparison suggests that Rietveld-based interpretation of X-ray powder diffraction data provides results that are consistent with other compositional parameters. Although no particular relationships were observed among the individual mineral percentages in the slates of the sample suite, a well-defined inverse relationship was found between the percentages of quartz plus feldspar on the one hand and the percentages of mica plus chlorite on the other. This may reflect variations in the relative proportions of coarse- and fine-grained sediment in the original parent materials that formed the slate deposits. Resumen Se han calculado las proporciones relativas de los diferentes minerales de las pizarras de techar explotadas en el Macizo Iberico del noroeste de Espana. Para ello, datos obtenidos por difraccion de rayos X sobre muestras de polvo de pizarra han sido procesados utilizando el sistema SIROQUANT, basado en la tecnica de Rietveld. A partir de estudios de microsonda electronica se determino la composicion quĺmica de cloritas, micas y feldespatos de las pizarras, lo que junto con las proporciones minerales obtenidas a partir de los datos de DRX, permitio inferir una composicion quĺmica para cada muestra de pizarra. Estas composiciones inferidas fueron entonces comparadas con composiciones quĺmicas de las respectivas muestras de pizarra, obtenidas mediante fluorescencia de rayos X, evaluandose la coherencia entre los resultados de las dos tecnicas empleadas. Un alto nivel de coherencia fue observado entre los porcentajes de oxidos de cada elemento inferidos a partir del estudio de DRX y las proporciones de oxido equivalentes determinadas por FRX. La comparacion sugiere que la interpretacion de la DRX basada en la tecnica de Rietveld aporta resultados que son coherentes con otros parametros composicionales. Aunque no se observaron relaciones entre porcentajes de minerales individuales en las pizarras muestreadas, se encontro una relacion inversa bien definida entre los porcentajes de cuarzo mas feldespato y los porcentajes de mica mas clorita, lo que se interpreta como una herencia de las proporciones relativas de limo y arcilla en los sedimentos a partir de los que se formaron las pizarras.

Recovered slate waste as raw material for manufacturing sintered structural tiles

Since roofing slate exploitations generate large quantities of slag from the quarry and mud from the cutting tools, special efforts are needed to avoid associated environmental hazards, such as floods and the unsightliness of slag-heaps. Recovering this mud and slag as raw material for manufacturing sintered structural parts could be a response to the demand. This study, which includes a characterisation of the material and an evaluation of the final properties, examines the raw material and its behaviour during compaction to determine whether it is suitable for processing by powder technology. A mineralogical characterisation by chemical analysis and X-ray diffraction, together with a thermal analysis, provided the data of the sintering process. The properties of the sintered samples were checked by: density, dimensional change, volume loss, mass decrement, three-point bending strength, water absorption and permeability, and wear behaviour trying to guarantee their behaviour.

Digital model of corrected accumulated flow for peak discharge data acquisition and drainage system design

The design of a drainage system for a roofing slate quarry was implemented by the enhancement of discharge peak estimation, and the uncertainty inevitably associated with the engineering model was reduced. The development of a topographical, geological, and vegetation cover database developed from a Geographical Information System (GIS) allowed for the definition of the drainage network for a hydraulic system, along with the calculation of the runoff coefficient. This is applied to the digital model of accumulated flow (DMF) as a weight correction coefficient, using a matrix-based model at 5×5 m resolution. The new digital model of corrected accumulated flow (DMCF) is the result of combining the thematic maps with the map of slope <3%, which was previously created from the slope model. It is demonstrated that this new model allows to apply the “Rational Method” on cartographic units defined by the GIS. The DMCF is compared with other traditional applications of the Rational Method based on the calculation of the discharge peak considering: (1) the drainage basin as a single watershed or (2) defining an average runoff coefficient in each sub-watershed. Both approaches have bigger discharge peaks than those obtained by the DMCF since the slope, lithology, and vegetation cover have average values, and the runoff coefficient is poorly defined, increasing the uncertainty in the discharge peak.

Monitoring results of two examples of building integrated PV (BIPV) systems in the UK

This paper presents monitoring results of two examples of building integrated PV system investigated at the School of the Built Environment, University of Nottingham in the UK. One of the systems is installed on an educational building, and consists of a thin film PV façade appropriate for commercial or office suites. The other system is installed on a detached house, and uses crystalline PV roof slates, appropriate for domestic buildings. As the two buildings are significantly different in size, construction and occupancy, the design and selection of the PV system for each was also different. The monitoring investigation has assisted identification of shortfalls in performance and possible explanations have been suggested. The results presented in this paper provide information on the design process, and highlight similarities and differences in the design, installation, performance and economics of the two systems.