Influence of grouting conditions on deterioration of post-tensioned prestressed concrete beams (original) (raw)

2006, Japan Concrete Institute

Abstract

Chloride-induced corrosions of a sheath and a prestressing tendon in post-tensioned prestressed concrete (PC) beams are investigated under different grouting conditions. Two series PC beams were tested by the electrically accelerated corrosion. The first series of accelerated corrosion tests were performed to determine the influence of grouted ratios in a curved sheath on the corrosion of the sheath and the prestressing tendon. In the second series of tests, the relationship between corrosion crack and expansive pressure surrounding the sheath and tendon during the corrosion process was clarified.

Figures (5)

approximately 60% of the tensile strength of the tendon. After stressing, the tendon was anchored through the steel plate using wedge-type anchorages at each end of the test beam. To prevent corrosion of the steel plate, the area extending 50 mm from each end of the test beam was coated with epoxy resin and a rubber pad was inserted between the steel plate and the beam. After the tendon was stressed and anchored, grout was injected into the sheath. Table 1 lists the details of test specimens and the experimental variables for all beams. To accelerate the corrosion, sodium chloride of 3 kg/m? was added to concrete used for all beams except beam AO. Beam AO was the control specimen of the Series A. The curved sheath of each beam of Series A was filled with different grouted ratios at the center section, as shown in Fig. 2, in order to clarify the influence of the grouting conditions on corrosion of the prestressing tendon. Other sections of the curved sheath were filled with full grouting. The grouted ratios at center section of the sheaths were varied corrosion process was investigated. The test variables were based on the grouting conditions of actual PC bridges. All of test beams were cast in a laboratory using high-early-strength Portland cement with a maximum aggregate size of 20 mm and a slump ranging from 100 to 140 mm. The design strength of concrete was specified as 40 MPa which is usually used for actual PC structures. Two types of sheaths were used in the test: curved for Series A, and straight for Series S. The prestressing tendon was of strand type with a diameter of 9.3 mm and designated as SWPR7A in Japan. Its tensile strength was 1720 MPa.

approximately 60% of the tensile strength of the tendon. After stressing, the tendon was anchored through the steel plate using wedge-type anchorages at each end of the test beam. To prevent corrosion of the steel plate, the area extending 50 mm from each end of the test beam was coated with epoxy resin and a rubber pad was inserted between the steel plate and the beam. After the tendon was stressed and anchored, grout was injected into the sheath. Table 1 lists the details of test specimens and the experimental variables for all beams. To accelerate the corrosion, sodium chloride of 3 kg/m? was added to concrete used for all beams except beam AO. Beam AO was the control specimen of the Series A. The curved sheath of each beam of Series A was filled with different grouted ratios at the center section, as shown in Fig. 2, in order to clarify the influence of the grouting conditions on corrosion of the prestressing tendon. Other sections of the curved sheath were filled with full grouting. The grouted ratios at center section of the sheaths were varied corrosion process was investigated. The test variables were based on the grouting conditions of actual PC bridges. All of test beams were cast in a laboratory using high-early-strength Portland cement with a maximum aggregate size of 20 mm and a slump ranging from 100 to 140 mm. The design strength of concrete was specified as 40 MPa which is usually used for actual PC structures. Two types of sheaths were used in the test: curved for Series A, and straight for Series S. The prestressing tendon was of strand type with a diameter of 9.3 mm and designated as SWPR7A in Japan. Its tensile strength was 1720 MPa.

Note: Symbols for specimen identification: P60 = fpe/fpu = 60%; fpe: effective prestress; fpu: ultimate tensile strength of tendons G0, G33, G50, G66, G100: grouted ratios of 0%, 33%, 50%, 66%, 100% respectively S: specimen with sheath only. T: snecimen with tendon onlv as 0% (beams Al, A4), 50% (beams A2, A5), and 100% (beams A3, A6). pe. -e -~:; as 0% (beams Al, A4), 50% (beams A2, A5), and 100% (beams A3, A6). the longitudinal bars and stirrups were coated with epoxy resin. For the beams S1 to S4, no steel tendon was provided since the purpose is to investigate the relationship between corrosion crack and expansive pressure due to corrosion of the sheath only. Desired depth of grout was varied as 0% (S1), 33% (S2), 66% (S3) and 100% (S4) to evaluate the influence of grouted ratios on the corrosion of sheath. For the beams $5 to S7, steel tendon with a diameter of 9.3 mm was provided. After casting, however, spiral steel sheath was removed from those beams so that only the tendon was used for the accelerated corrosion test. The Figure 3 show the configuration of test specimens of Series S. All the specimens were provided with 4-D3 (deformed bar of 3 mm in diameter) longitudinal bars and 3-D6 (deformed bar of 6 mm in diameter) stirrups. In this experiment, electrical-resistance strain gages with 2 mm length were used to measure strains of stirrups. The purpose is to investigate expansive pressure surrounding the sheath and steel tendon during the corrosion process. Locations of strain gages are shown in Fig. 4. To avoid the corrosion, Table 1 Details of specimens and test variables

Note: Symbols for specimen identification: P60 = fpe/fpu = 60%; fpe: effective prestress; fpu: ultimate tensile strength of tendons G0, G33, G50, G66, G100: grouted ratios of 0%, 33%, 50%, 66%, 100% respectively S: specimen with sheath only. T: snecimen with tendon onlv as 0% (beams Al, A4), 50% (beams A2, A5), and 100% (beams A3, A6). pe. -e -~:; as 0% (beams Al, A4), 50% (beams A2, A5), and 100% (beams A3, A6). the longitudinal bars and stirrups were coated with epoxy resin. For the beams S1 to S4, no steel tendon was provided since the purpose is to investigate the relationship between corrosion crack and expansive pressure due to corrosion of the sheath only. Desired depth of grout was varied as 0% (S1), 33% (S2), 66% (S3) and 100% (S4) to evaluate the influence of grouted ratios on the corrosion of sheath. For the beams $5 to S7, steel tendon with a diameter of 9.3 mm was provided. After casting, however, spiral steel sheath was removed from those beams so that only the tendon was used for the accelerated corrosion test. The Figure 3 show the configuration of test specimens of Series S. All the specimens were provided with 4-D3 (deformed bar of 3 mm in diameter) longitudinal bars and 3-D6 (deformed bar of 6 mm in diameter) stirrups. In this experiment, electrical-resistance strain gages with 2 mm length were used to measure strains of stirrups. The purpose is to investigate expansive pressure surrounding the sheath and steel tendon during the corrosion process. Locations of strain gages are shown in Fig. 4. To avoid the corrosion, Table 1 Details of specimens and test variables

Fig. 6 Typical crack pattern of Series A due to accelerated corrosion test

Fig. 6 Typical crack pattern of Series A due to accelerated corrosion test

Table 2 Results of loading test and weight loss of prestressing tendon (Series A)

Table 2 Results of loading test and weight loss of prestressing tendon (Series A)

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References (3)

  1. Schokker, A. J., Breen, J. E., and Kregeg M. E: Grouts for bonded post-tensioning in corrosive environments, ACI Material J., Vbl.98, No,4, 2001, pp.296-304
  2. Mutsuyoshi H: Present situation of durahility of post-tensioned PC bridges in Japan, Proceedings of Wbtkshop on Durability of Post-tensioning Tendons, fib, Belgium, 2001. pp. 75-88.
  3. Mutsuyoshi H, Hamada Yl Igo Yl Watanabe H.: Design concepts for durabie prestressed concrete structures in Japan, Proceedings of the Second VVbtkshep on C`Durability of Post-Tensioning