To reduce generation of fume and fine powder so as to prevent an operator and circumference from being polluted by irradiating laser rays onto the surface of concrete to form a plurality of slits, and giving shearing force to them to break from the roots and breaking away them.
An optical fiber 2 is connected to a laser generator 1, and the other end part is arranged oppositely to the surface of a concrete 1. The other end part of the optical fiber 2 is fitted to a light converging device 4. The other end part of the optical fiber 2 is scanned longitudinally and laterally along the concrete face 3a, and the concrete surface layer part 3b is melted and evaporated to form a plurality of slits 5. A tool is pessed to the surface layer part 3b from the side to give shearing force, and the concrete is broken from the roots of the slits 5 and broken away. The diameter of the laser ray is set to be under 3 mm, the energy density is over 50000 wat/cm2, and it is iodine laser of wave length of 10.6 μm Nd:YAG, 1.315 μm. The depth of the slit 5 is set over 1.2 times the longest side of the outer circumferential side of the concrete part surrounded with the slits.
KAMATA HIROBUMI
ITO AKIRA
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