International Concrete Abstracts Portal

The No. 1 ore dock at Great Lakes Steel Division's Zug Island facility was originally constructed in 1909. Damage caused by freeze-thaw cycling, abrasion wear, severe impact loadings, and reinforcing steel corrosion resulted in a need for repair and rehabilitation. Multiple Dynamics Corporation conducted extensive condition surveys and testing to develop repair strategies for this structure. The remaining service life was then predicted to assist in economic planning. This case history provides an excellent example of concrete performance in an aggressive environment.

During the 12 years since construction of the bridge, cracking and spalling have developed in the concrete superstructure, predominantly on the underside of the bridge deck in the area of expansion and construction joints. The evidence indicates the deterioration was initiated by leakage of expansion and construction joints, and that poor performance should be attributed to design and construction practices whose effectiveness falls short of the environmental demands. Moisture, deicing salts, and debris that spill through the joints had deteriorated concrete at an accelerated rate and penetrated to the reinforcing steel. The concrete breakdown caused by corrosion of reinforcing steel, as well as from freezing and thawing action, and the expansion resulting from alkali-aggregate reaction damaged the bearing areas of cantilever spans and adjacent parts of suspended slabs, and was a cause for concern for the bridge's structural integrity. The paper addresses the main factors involved in the initiation phase of the corrosion mechanism: carbonation, chloride diffusion, and water penetration into concrete. The selected materials and methods are discussed, as well as importance of compatibility of materials for durable repairs. The paper outlines a need to integrate knowledge and understanding of the mechanism of deterioration with concrete design, materials, and methods of repairs.

A characteristic example of reinforced concrete structural damage in an urban environment after 25 years' service is the east end of a stadium in Zagreb, Yugoslavia, for 11,000 spectators. This paper presents research works that served as a basis for the design of repairs to prolong the structure's service life. The damage is classified by types. The basic causes of the damage are explained with a detailed description of the influence of carbon dioxide from the air on the concrete. The repair design is described. The basic principle in repairing the upper and lower surface of the stand was that the materials and construction methods must be compatible with the existing concrete and also meet durability criteria. The repair design prescribes conditions for the materials, construction methods, and durability criteria. The paper presents preliminary investigations to select the optimum composition of a mortar that complies with the criteria required by the design. The influence of two polymer dispersions based on acryl and latex, as well as the influence of silica fume added to the mortar, are investigated. To repair the stand slab, the selected mortar applied was the cement mortar modified by added silica fume and superplasticizer to obtain a dense and compact composition and increased chemical resistance. The proposed solution for the lower surface was shotcrete improved by special admixtures. In designing the overlay, care was exercised that the additional load should not require strengthening of the stand structure. Acceptance of the repair work performed is outlined.

"A collection of 24 papers form an international panel of experts on topics ranging from fundamental laboratory studies of concrete durability to case histories of concrete rehabilitation. The volume is arranged in three parts. Part 1: covers the more fundamental aspects and laboratory investigations. Topics include freeze-thaw resistance, durability of high strength concrete, corrosion of reinforcing steel, air voids in concrete, and effects of high range water-reducers. Part 2: covers field studies where concrete is exposed to natural conditions. Topics include carbonation of concrete, deicer scaling resistance of roller compacted concrete pavements, performance in marine environments, and microbiologically-induced deterioration. Part 3: covers case histories of the performance and rehabilitation of concrete structures in severe service environments. The types of structures include cooling tower shells, precast prestressed concrete conveyor bridge, heavy duty dock, elevated road way, and a masonry structure under corrosive exposure." Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP122

Report presents the results of a multi-year laboratory exposure of more than 150 concrete samples to alternate immersion exposure in flowing sea water and flowing fresh water. Other exposure variables included loading, cracking, and electric currents. The validity of the controlled-exposure samples was determined by comparing the results with the results from selected samples removed from concrete structures throughout the United States. The results from a marine seawall are presented in this report and compared with previously reported results from marine masonry structures, highway bridges, and other structures.