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SOME EXPERIMENTS ON THE FIRECRACKING OF TERRA COTTA 1
Author(s) -
Hill F. C.
Publication year - 1922
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1922.tb17411.x
Subject(s) - porosity , weathering , absorption of water , transverse plane , mineralogy , materials science , composite material , clay minerals , geology , geotechnical engineering , geochemistry , anatomy , medicine
Firecracking .—occurs on terra cotta under certain conditions and is characterized by the appearance of sharp, hair‐line cracks extending into the body. The experiments were made by firing large typical pieces of terra cotta made from various clays and grogs and cooling them at different rates. The tendency to firecrack was observed after weathering. The absorption, porosity and transverse strength of the various bodies were determined. Rate of Cooling .—All bodies similar to those used in practice showed a tendency to firecrack when cooled rapidly and all were free from cracks when cooled slowly. The rate of cooling has a much greater effect on the tendency to firecrack than the composition or physical properties of the body. Effect of Clay .—Three of the four sandy clays showed a decided tendency to firecrack, due to the difference in the expansion and contraction behavior of sand and clay in heating and cooling. The sandy clays showed more tendency to firecrack than the non‐sandy, vitrifying clays. The tendency of a clay to develop firecracks in a body depends to a very large extent upon the character of the clay itself, regardless of the impurities it contains. The presence of sandy material and the character of the clay appear to have a much greater effect on the tendency to firecrack than the absorption, porosity or transverse strength of the body. No relation was found to exist in these experiments between the porosity and transverse strength of a body and its tendency to firecrack. Effect of Grog .—The greatest tendency to firecrack was found on a body with all grog finer than 40‐mesh, but a body with all grog coarser than 40‐mesh did not appear to have much less tendency to firecrack than the average. Increase of grog reduced the tendency to firecrack. The kind or source of the grog used does not have as much effect on the tendency to frecrack as the size and amount. The kind of grog is of much less importance in this respect than the kind of clay.