Maintenance and preservation of concrete structures. Report 2, Repair of erosion-damaged structures
McDonald, J. E. (James E.)
Technical reportAbstract: Investigation of maintenance and preservation problems associated with Civil Works concrete structures was initiated in February 1977 at the U. S. Army Engineer Waterways Experiment Station (WES). The primary objectives of the initial phase of this investigation were to (a) identify and evaluate various abrasion- erosion- resistant materials for repairing and improving the durability of concrete stilling basin slabs, (b) develop optimum techniques for repair and rehabilitation of stilling basins, and (c) develop guidance for designing stilling basin exit configurations to avoid entrapping abrasive materials within the basin. A survey of Corps Divisions and District offices identified 52 structures that have experienced concrete damage due to erosion. Depths of erosion ranged from a few inches to approximately 10 ft. In general, this erosion damage resulted from the abrasive effects of waterborne rocks and other debris being circulated over the concrete surface during construction and operation of the structure. A variety of materials including armored concrete, conventional concrete, epoxy resins, fiber-reinforced concrete, and polymer-impregnated concrete were used with varying degrees of success in the 31 repairs reported. The degree of success generally was inversely proportional to the degree of exposure to those conditions conducive to erosion damage. These materials have been used with various construction procedures, including dewatering and underwater repairs. It appears that given appropriate flow conditions in the presence of debris, all of the materials are susceptible to some degree of erosion. No one material demonstrated a consistently superior performance advantage over alternate materials. Pending the results of additional laboratory tests and field inspections to evaluate repairs, it is recommended that conventional concrete of the lowest practical water- cement ratio containing the hardest coarse aggregate economically available should be used for repair and in new construction of structures subjected to abrasion erosion damage. Improvements in materials should reduce the rate of concrete damage due to erosion, but will not solve the problem. Until the adverse hydraulic conditions that caused the original damage are minimized or eliminated, it will be extremely difficult for any of the materials currently being used in repair to perform in the desired manner. Prior to major repairs, model studies of the existing stilling basin and exit channel should be conducted to verify the cause(s) of erosion damage and to evaluate the effectiveness of various modifications in eliminating undesirable hydraulic conditions. In existing structures, releases should be controlled so as to avoid discharge conditions where flow separation and eddy action are prevalent. Substantial discharges that can create a good hydraulic jump without causing eddy action should be released periodically in an attempt to flush debris from the stilling basin. Guidance as to discharge and tailwater relations required for flushing must be developed through model/prototype tests. Periodic inspections should be required to determine the presence of debris in the stilling basin and the extent of erosion. Note: This is extremely large. Please allow additional minutes for downloading.
Concrete Laboratory (U.S.)Engineer Research and Development Center (U.S.)
Concrete erosion; Concrete slabs; Concrete structures; Erosion resistance (Concrete); Stilling basins
Technical report (U.S. Army Engineer Waterways Experiment Station) ; C-78-4 rept.2.
Approved for public release; distribution is unlimited.
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