FUNDAMENTAL STUDY ON ESTIMATION METHOD FOR SURFACE ROUGHNESS OF CONCRETE CANAL GENERATED THE EXPOSURE OF COARSE AGGREGATE

摘要

The surface of agricultural concrete canal was deteriorated by abrasion due to both water flow and sand in it. It is well known that progress mechanism of this type of abrasion starts from dissolution of cement paste, then coarse aggregates are exposing gradually. This phenomenon, exposure of coarse aggregate at the inner surface of canal, is considered to give bad affect to the hydraulic performance on transportation of planned flow as the increment of irregularity leads the loss of smoothness of concrete surface. However, the evaluation method of this deterioration has not established yet. In this study, evaluation indexes on deterioration degrees of irregular surface were studied using the numerical information gotten from concrete surface. In addition, the application limit of image analysis was examined when the roughness of concrete surface was evaluated using three-dimensional image processing. Porous concrete, its surface condition has enough roughness comparing with abraded surface of concrete canal, was applied for numerical expression of roughness of concrete surface on the assumption that the surface condition of porous concrete was similar to that of abraded concrete canal. Following three indexes concerned to roughness of concrete were focused in this study; arithmetical mean roughness “R_a”, maximum height “R_z” and Manning roughness coefficient which was used as an index of hydraulic performance. As a result, it was indicated that “R_z/D”, divided maximum height “R_z” with maximum size of coarse aggregate “D”, could be used as the index of deterioration degree if the coarse aggregate were falling off from concrete surface when the abrasion depth of concrete canal was progressing to “R_z”. Furthermore, it was clarified that analytical estimation of surface roughness using three-dimensional image processing was effective when focusing to the roughness coefficient. Therefore it was considered that hydraulic performance of concrete canal could be estimated simply using three-dimensional image processing.