Column wrapping with composite materials has become a routine retrofit measure for added confinement and /or strengthening of lap splices in existing deficient concrete columns in seismic areas. Experiences in the last seventeen years with fiber wraps that were utilized to fully encapsulate concrete columns in Chicago area have revealed unsatisfactory effects of freeze-thaw on the concrete and wrapping materials. The freeze-thaw effect has caused deterioration of the saturated concrete and the tearing of the fiber wraps in columns of a number of bridges. A proposed remedy to allow natural breathing of concrete and to eliminate the adverse effects of freeze-thaw on concrete columns in cold climates, is the use of intermittent fiber wraps instead of full encapsulation of concrete columns. To verify effectiveness of the intermittent confining wraps, a series of laboratory tests were performed on columns wrapped with 4" strips at 8" centers, placed along the test column. These tests showed results which were very close to those of the fully encapsulated column tests.

This article reviews 17 years experiences with freeze thaw effects on encapsulated concrete columns that is commonly performed for seismic retrofitting of concrete columns. Also, remedial measures to allow natural breathing of concrete and laboratory tests to substantiate the effectiveness of these measures are discussed.

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