Key Engineering Materials Vol. 848

Abstract: The search of ornamental rocks cutting technology to meet the market and efficiently together economic, environmental and safety parameters is increasingly requested in the mineral sector. This study tried to compare two cutting technologies with respect to their technical-operational aspects: diamond wire and water jet. The methodology used consists of a bibliographical research raising data of both technologies and organizing them in graphs and tables for the best comparison. The diamond wire offers significant economic advantages over water jet, which limits the use thereof. Regarding the environmental aspects, the two techniques proved to be equivalent, with optimum performance in this parameter. The water jet has advantage in safety factor in relation to the diamond wire, due to its ability to cut by computerized system.

Abstract: Research and development related to the processing of recycled materials has grown progressively in recent times, as scientists endeavour to integrate sustainability criteria, depletion of natural resources, reducing the energy of technological processes involving extraction and processing of raw materials, etc. When it comes to processing slate, industries have to pass over several steps ranging from the extraction of rock blocks until the final products consisting of plates, leaving behind a considerable amount of waste in the form of a mud composed mainly of water, lubricants and crushed rock. This waste with no defined destination accumulates in yards, reservoirs and streams, affecting the environment. Slate powder has great prospects for recovery, recycling and further applications once it has chemical composition and components similar to raw materials used in ceramic and building construction industries. Therefore, a complete characterization of this powder is important and here we present some results of XRD, SEM, EDS, G3 morphology and thermal analysis of slate powder samples from the southeastern state of Minas Gerais in Brazil.

Abstract: The dimension stone wrapping process is a method used before the sawing of the block which aims to enhance the integrity of the rock, thus ensuring that fractured or altered blocks remain intact while they are handling and splitting into slabs. This method increases safety and allows the processing of many materials once not commercialized. Nevertheless, the epoxy resin used in the process comes from a non-renewable resource and contains toxic substances on its composition. Therefore, in order to increase the eco-efficiency in the sector of dimension stones, a comparison of the epoxy resin with an ecological and non-toxic resin based on the castor oil, was carried out aiming to know the resulting tensile strength in the contact of the polymer with the stone surface. Two types of rocks were tested, a silicate and a carbonate one. The results indicated that the castor oil resin performed a higher tensile strength regarding carbonate rocks, suggesting that the castor oil resin could replace the epoxy resin when applied to this rock group, providing an environmental advantage and a global marketing differential.

Abstract: The dimension stone polishing consists of eliminating the surface roughness of the slabs with the use of fickerts. The main tools used for this activity are composed of epoxy resin, derived from petroleum, which contains chemical elements with harmful potential to the environment and human health. To overcome this problem, it is necessary to develop new technologies with the lowest environmental impact in the life cycle, from the raw material acquisition to the waste disposal. This study aims to contribute to the improvement of an ecological fickert developed by the Centre for Mineral Technology (CETEM). The fickerts presented here are composed of castor oil resin, silicon carbide and silica from rice hull ash. Two different compositional formulas were used for the preparation of the pieces that were tested in an industrial polishing machine. The results showed that the formula with higher percentage of fillers showed better performance, expressed by the relation between the loss of mass of the pieces and the increase of gloss on the surface of the slab. Other particularities of the product, as the high abrasion resistance of the matrix that reduced the cutting function, could be solved by choosing a filler with a lower hardness. This fact allows to infer that this line of research presents great potential of applicability in the dimension stones market.

Abstract: The presence of pores, cracks and microcracks in marble is one of the main features that govern the processes of decay of this stone material and, although marble is characterised by a modest porosity, there is a clear correlation between the presence and movement of fluids, and the phenomena of alteration. Through the study of porosity, it is possible to better understand the phenomena of alteration and degradation in order to obtain useful information, not only in the field of modern building, but also for the protection and recovery of historical and artistic heritage goods. This study was conducted through the characterisation of parameters directly related with the degree of alteration of the materials: water absorption at atmospheric pressure (EN 13755), open porosity (EN 1936), flexural strength (EN 12372) and bowing (EN 16306 par. 8.2). The physical and mechanical measurements have been compared with the Total Optical Porosity method (TOP) and the Adjacent Grain Analysis (AGA) index (a suggested method to evaluate the marbles’ tendency to bow, in EN 16306 annex C); two different methodologies both based on image analysis. The purpose of this study is to demonstrate the effectiveness, for the assessment of marble durability, of the two techniques of microscopic image analysis, the first correlating to the grain shape and the second to the open porosity index. This was done by comparing the microscopic image analysis results with the physical and mechanical properties, both after artificial ageing and after ten years of natural ageing. The results obtained with the TOP method seem to represent the tendency to decay better than the AGA index. The comparison of image analysis of the thin sections, in different portions of the marble specimens, shows the development of degradation due to atmospheric agents, from the surface to the inside, of naturally aged specimens, confirming recent studies made on different marbles.

Abstract: The term “roofing slate” comprises all natural rocks that can be used for roofing. Some of the characteristics that define their performance as construction materials are water absorption, bending strength, mineral composition, and aesthetics. From a sustainability point of view, roofing slates also have the largest life expectancy and lowest carbon emissions of all covering materials. This work reviews the constructive characteristics of roofing slates, from technical data provided by producers from all over the world. These data, supported by the petrological characterization of several roofing slate samples, are used to propose a general classification for this special type of rock. Thus, roofing slates are sorted in twelve lithotypes, depending of their petrographical characteristics, defined by the color. The resulting classification is named International Roofing Slate Classification (IRSC), formally defined in this paper.

Abstract: Six Portuguese magmatic ornamental stones were submitted to Soxhlet experiments during 10,000 hours (approximately 416 days) in order to evaluate how the rain water affects the rock behavior as a dimension stone. Macroscopic alterations were observed in the rock fragments and chemical analysis of leaching water solutions revealed how major elements were mobilized from rock-forming minerals allowing to compare weathering susceptibilities between different natural stones.

Abstract: The processing stages of the dimension stones industry uses inputs mainly from petroleum-derived chemicals that can cause damages to the environment and to the human health. Therefore, there is a need to develop more ecological and sustainable technologies aiming to replace the conventional inputs by less aggressive ones. From this, ecological fickerts made from polyurethane castor oil resin (Ricinus communis L.), silicon carbide (SiC), silica from rice hull ash (RHA) and synthetic diamonds were developed in order to compare them with the epoxy resin fickerts currently used in industry. For such, each half of a Brazilian granite slab was polished using each different type of fickerts and the gloss measures results were compared. It was found that the side of the slab polished using the ecological fickerts presented brightness values about 10 Gloss Units (GU) greater than the other side polished with the conventional abrasives. In addition, the ecological fickerts presented lower wear values, and consequently lower mass loss compared to the conventional ones. These results indicate that the ecological fickerts are a good alternative to the dimension stones polishing, even considering sustainability aspects and more eco-efficiency inputs materials.

Abstract: Cabeça Veada is the name of a relatively small exploitation cluster for ornamental limestones occupying an area of 98 ha in the Portuguese Natural Park of Serra de Aire e Candeeiros, which is also a Natura 2000 Network protected area. Supported by comprehensive geological, mining and environmental studies, a specific methodology was developed in order to address the compatibility between the long term sustainability of this industry with the preservation of existing protected natural values. The obtained land use map should allow the Cabeça Veada mineral resources to be adequately included in the municipal land use planning process.