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Protective Systems for New Prestressed and Substructure Concrete
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1987-04-01
[PDF-4.15 MB]
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Edition:Final Report
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Abstract:A three-year corrosion research project on 11 corrosion protection systems was undertaken in two laboratory studies. A total of 124 reinforced concrete slabs were subjected to a 48-week cyclic wet and dry saltwater exposure in the first study. The second year-long study dealt with cyclic saltwater exposure on 19 full-size sections of reinforced concrete columns and beams and precast, prestressed piles and stay-in-place bridge deck panels. The slab tests evaluated concrete having w/c ratios of 0.51, 0.40, and 0.28 with clear cover of 1, 2, and 3 in. The reinforcing steels evaluated were normal gray bars, normal prestressing strands, galvanized bars, and fusion-bonded epoxy-coated bars and prestressing strands. A calcium nitrite corrosion-inhibiting admixture for fresh concrete was evaluated. A penetrating silane sealer and a methacrylate coasting system were evaluated as surface treatments for hardened concrete. The full-size member tests included most of the above materials in concrete at a constant w/c ration of .44, generally with 1-in. cover. A concrete containing a silica fume admixture was also evaluated in the full-size member tests. The full-size columns and beams were moist cured while the precast., prestressed piles and bridge deck panels were heat cured overnight at 130 to 140°F. Corrosion-related measurements included monitoring macrocell corrosion current and instant-off voltage between corroding and noncorroding reinforcement, half-cell potentials, chloride contents at the initiation of corrosion and at the conclusion of the test cycle, and measurement of the corroded areas on the reinforcement. The measured corrosion activity of these numerous specimens is presented and comparisons are made in their corrosion protection performance. Of particular significance were the beneficial influence of low w/c ratios and adequate concrete cover in reducing corrosion and chloride penetration. The silane sealer and the silica fume pozzalanic admixture concrete both dramatically reduced chloride penetration and the reinforcement did not develop corrosion. Epoxy-coated reinforcing bars and prestressing strands were not corroded in these tests, even though surrounding concrete had high chloride contents. Galvanized reinforcement embedded in conventional concrete and bare reinforcement embedded in concrete made with calcium nitrate corrosion inhibitor both developed a low level of corrosion when surrounding concrete had high chloride contents. Design considerations are suggested for these different corrosion protection materials to provide for greater corrosion protection for new cast-in-place reinforced concrete and precast, prestressed concrete bridge members.
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