Assessment of technological properties of calcareous and non-calcareous clays used for the brick-making industry of Zaragoza (Spain)
The granulometric, mineralogical, and geochemical features of two different types of clayey raw materials (carbonated clays, CC; and non-carbonated clays, NCC) used for the brickmaking industry near Zaragoza (Spain) have been studied. Their particle-size distribution suggests that they may be classified as silty clays and are suitable for use as thin-walled hollow bricks. For technological testing, prismatic bars obtained by extrusion under vacuum conditions from raw materials were fired from 800 to 1050 °C. Technological determinations, such as linear shrinkage, bulk density, hydric tests, and an accelerated decay test, indicate that both CC and NCC are suitable to be used as bricks for building, although bricks made of NCC would be of better quality. In addition, pore-size distribution suggests that the durability of the highest temperature fired products will be higher because of an increase both in the dominant pore access radius and in the percentage of larger pore sizes.
Ceramic applications of Middle Ordovician shales from central Spain
Abstract This paper describes the mineralogical and ceramic characteristics of three Ordovician shales from the Ciudad Real province (Central Spain). These materials are mainly composed of phyllosilicates (> 85%), quartz, K-feldspar, and hematite. Clay mineral assemblages include illite + kaolinite + paragonite ± chlorite, with traces of mixed-layered muscovite/paragonite. Chemical analyses indicate a Fe 2 O 3 content of less than 8%. Three different types of complementary raw materials (quartzitic sands, quartzo-feldspathic sands, and fly ash) have been used to improve the linear shrinkage and water absorption of clayey raw materials. Firing tests were performed maintaining the sample at T max for 2 h on both clay raw materials and improved clay samples and they indicate an optimal firing range between 1100–1150°C. Under these conditions linear shrinkage is less than 8% and water absorption is close to zero. The analytical results therefore indicate that these clays meet the firing specifications required by the ceramic industry for application in the manufacture of red stoneware tiles. Moreover, the addition of fly ash improves the ceramic properties of the clay materials and is an ecological application of an industrial waste.
Regional Appraisal of Clay Resources - A Challenge to the Clay Mineralogist
Abstract A regional approach to clay resource appraisal demands a ready means of identifying and assessing the basic characteristics of clays which promote their use as industrial raw materials. The principal features and commercial uses of clays in the United Kingdom are discussed in this context and proposals made for laboratory evaluation procedures to support a broad-based reconnaissance programme.