Site: Hiyoshigura Viaduct
East Kanto Expressway
Kasumi, Chiba, Japan
Date Visited: October 1996
Owner: Japan Highway Corporation
Contact: M. Uemura, General Manager, Tonen Corporation
M. Saito, Deputy Manager, Tonen Corporation
Summary: Bridge deck strengthening with tow sheet (March 1993).

ACTIVITIES OF INTEREST

As part of a demonstration and monitoring project, a portion of a bridge deck on the Hiyoshigura Viaduct (Figs. B.102 and B.103) was strengthened through the application of two layers of FTS-C1-30 carbon tow sheet with FR-E3PW epoxy. The retrofit was aimed at upgrading the load capacity of the deck slab from TL20 to TL25 level.


Fig. B.102. Dimensions and geometrical details.


Fig. B.103. Overall view of the viaduct.

The area to be strengthened was first sand blasted, after which the cracked condition of the existing slab was clearly visible (Fig. B.104). Putty was then applied to the surface to fill the large cracks and voids.


Fig. B.104. Condition of slab showing cracking.

A primer coat was applied followed by the application of tow sheet in two layers (Fig. B.105), one in the direction transverse to the deck and the second along the longitudinal direction. The composite was formed using the wet layup process, employing two crews of three people each for a period of one week. Close-ups of the application area can be seen in Figures B.106 and B.107.


Fig. B.105. Application of tow sheet.


Fig. B.106. Close-up of the retrofitted area.


Fig. B.107. Overall view of the retrofitted section.

The FTS-C1-30 tow sheet consists of PAN-based carbon fiber in unidirectional form with a fiber density of 1.82 g/cm3 and an areal weight of 300 g/m2. The design thickness of the layer when it is dry is 0.165 mm, compared to 0.6 mm for the impregnated ply. The tow sheet has a specified tensile strength of 35,500 kg/cm2, a tensile modulus of 2.35 x 106 kg/cm2 and an ultimate elongation of 1.5%. The FR-E3PW epoxy has a specific gelation time of 10 hours under ambient conditions. Representative quantities of materials used per square meter of area are given in Table B.13.

Table B.13
Allocation of FTS-C1-30 Tow Sheet per Square Meter of Surface Area

Item

Description

Quantity

Putty

Epoxy based filler to fill large gaps, voids, cracks on the concrete surface

1.5 kg/m2

Primer

Epoxy resin of similar form to resin system used as surface treatment on concrete to promote adhesion

0.25 - 0.4 kg/m2

Tow Sheet

Reinforcement in sheet form

1.15 kg/m2

Resin System

Epoxy based resin for impregnation of tow sheet

0.8 kg/m2


Fig. B.108. Schematic showing approach for measurement of strains in reinforcing bars.

Based on measurements prior to the strengthening, the stress levels in the distribution bars were estimated to be about 40% higher than allowable levels for a T25 load. After the application of the tow sheet, stress levels in the main reinforcements were estimated to be reduced by 12% and those in the distribution bars by 26%, bringing them to safe levels. Overall slab deflection after the strengthening procedure was seen to reduce by 15 to 18% under static loads, and by 16 to 19% under dynamic loads (speed of 40 km/h).

Monitoring was undertaken at distinct intervals to assess degradation, moisture entrapment and corrosion of steel (due to the presence of carbon fiber in the vicinity of steel girders, although a clear separation was ensured through the use of a thick resin barrier). No effects have been noticed to date.


Fig. B.109. Measurement of strains at the tow sheet level.


Published: October 1998; WTEC Hyper-Librarian