| 摘要 |
PROBLEM TO BE SOLVED: To provide crime preventive gravel having continuous void and high collapse strength so as to be hardly crushed even if trodden on and holding a high noise generating ability effective in crime prevention over a long period of time. SOLUTION: The crime preventive gravel comprises inorganic foamed grains manufactured using expanded shale and/or expanded clay as a raw material at least and baking at a baking temperature of 1,000-1,300°C, and the absolute dry density is 0.6-1.3 g/cm<SP>3</SP>. Further, the percentage of absolute volume is 65% or less, and grains with grain diameters less than 10 mm are 40 mass% or less. COPYRIGHT: (C)2010,JPO&INPIT
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