CURB STONE, natural, border stone, curbstone (EN: border stone, curbstone; DE: naturlicher Randstein; FR: pierre de bordure; ES: piedra de borde; RU: бортовой камень) is the road construction product in the form of a bar, which has been made of rocks, which is purposed for the separation of carriageway of the streets from their sidewalks, of the roads from their roadsides, of footpaths from lawns within the parks, and so on.
They classify curb stones into the chopped stones, which are obtained with the help of the shock or thermal instrument, and into the sawn stones, which are obtained during the cutting of the stone block by string saws and diamond cutting discs. They manufacture curb stones of erupted, metamorphic, or sedimentary rocks, which have not been affected by weathering, and which are not having open cracks. The limit for compressive strength is at least 90 megapascals for erupted rocks, and at least 60 megapascals for metamorphic and sedimentary rocks. The frost resistance (in cycles of alternating freezing and thawing for the samples) is at least 100 for erupted rocks, at least 50 for metamorphic rocks, and at least 25 for sedimentary rocks. Within the USSR, according to the GOST standard, the sizes for the curb stones (millimetres) are: the length is 700-2000, the height is 200, 300, 400, 600, the width is 80, 100, 150, 180, and 200, the radius of curvature (for the curved curb stones) is 5000, 8000.
The curb stones must have machined surfaces with the dotted, thermal, or sawn textures: the upper horizontal face along the entire width, the visible part of the vertical face, the chamfer along the edge of the front face at the angle of 45 degrees, and also the strip with the width of 20 millimetres along the edges of the rear vertical and end faces. They do not subject remaining surfaces to texture processing. Within the modern production of the curb stones, the level of mechanization has been increased at the expense of the usage of installations for the thermal processing of the stone, of diamond-disc and boucharde machine tools; there is being introduced the automated continuous flow production. The curb stones, which have been made of the rocks, distinguish themselves with great durability and mechanical strength.
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