Development and Validation of Steel-Reinforced Polymer (SRP) for Strengthening of Transportation Infrastructures

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Student Involvement

Project Objective

To investigate and validate by mean of laboratory and in-situ load testing, the mechanical properties and behavior of steel reinforced polymers (SRP) as external reinforcement for upgrade of concrete structures, intending to maintain and improve on the performance and installation advantages of FRP systems, while significantly reducing their cost.

Steel Cord with Filaments Wrapped by One Filament

Cords Held Together by Polyester and Copper Knits

Project Abstract

In the last decades, fiber reinforced polymer (FRP) composites have been effectively used as external reinforcement for the upgrade of concrete structures. Bonded FRP essentially works as reinforcement to provide additional tensile strength to reinforced and prestressed concrete (RC and PC) members. The proposed innovation intends to maintain and improve on the performance and installation advantages of
FRP systems, while significantly reducing their cost. This new material is composed of a unidirectional tape of continuously scrim bonded high-strength steel cords impregnated in polymeric resin, and is defined as steel reinforced polymer (HardwireTM SRP).

The use of cord, and specifically steel cord, over other fibers as a primary reinforcement is attractive in several areas. No special resin system is required for use with cord reinforcement, as is required for glass or carbon fibers. Carbon fibers require the use of epoxy resins to achieve the full properties of the fibers. Due to the coarse macrostructure of the cord reinforcement, cementitious grouts can also be used for impregnation. This coarse macrostructure, as compared to the extremely fine diameter of glass or even finer diameter of carbon or aramid fiber, greatly enhances the processability of steel cord reinforced composites. Steel cord reinforced composites should be faster to wet out or can be wet out in extremely thick sections, as compared to traditional fiber composites. The use of a steel based composite material will allow to increase the ductile behavior of the structural element strengthened, while with FRP materials this was not possible due to the completely elastic behavior of these materials with no yielding point. Finally by using cementitious grout to impregnate the steel cord mesh it will be possible to create a composite material that will be fire resistant as compared to the ones realized with epoxy resins and with either carbon or glass fibers that are not.

The research project to be undertaken is based around the three following research phases:

1. Material characterization.
2. Laboratory tests on RC slabs
3. In-Situ field tests.

Material Characterization

The characterization of the new composite material will be conducted by:

• Evaluation of material constants
• Comparison of experimental results with predictions obtained by micromechanical theory
• Evaluation of flexural properties

Once the new composite is characterized, the workability of impregnation of the mesh and the bonding properties to concrete will be investigated in order to have a complete understanding before laboratory and in-situ application.

Laboratory Tests on RC Slabs

The objectives of the laboratory experimental program are the following:

• Assessing the performance of externally bonded SRP as a technique for the upgrade of RC members;
• Comparing the performance of epoxy versus cementitious resin to bond SRP to concrete;
• Exploring the advantages of the SRP technique that could allow nailing the laminate to the RC support;
• Comparing the performance of SRP versus FRP strengthened slabs;
• Evaluating the influence of SRP properties on the post-peak behavior as compared to FRP (displacement control tests will be performed); and
• Analyzing the influence of the SRP reinforcement on crack pattern, crack width and spacing.

In order to achieve these goals, ten reinforced concrete (RC) slabs 12 feet long and internally reinforced with conventional steel grade 60 will be tested in four point bending test as reported in the figures below:

Cross Section Detail of Reinforcement

Test Set-Up

The following specimens will be tested under the test set-up previously shown:

• One virgin slab (V);
• Three SRP-strengthened slabs using epoxy resin as matrix: one with a single ply of SRP and a width (w) of the ply equal to w=8 in. (i.e., E18); another with 2 plies and w=4 in. (i.e., E24); and a third strengthened using 2 plies, w= 4 in., and mechanical anchors at the two laminate ends (E24N);
• Three SRP-strengthened slabs using cementitious paste (Specimens C18, C24 and C24N) following the test matrix of the previous ones bonded with epoxy resin, plus a fourth slab with 1 ply and w=4 in. (C14); and
• Two slabs strengthened with carbon fiber CFRP (F1 and F2) in order to compare the results obtained in the previous tests.

The test matrix is summarized in the following table:

In-Situ Field Tests

SRP composite materials will also be tested in two different field tests on concrete structures that are scheduled for demolition.

In the first case, the structure is a one-way reinforced concrete (RC) deck supported by steel columns located in St.Louis, Missouri. A total of four continuous beams specimens will be available to be tested within the deck of the garage, by saw-cutting the deck (full depth) along carefully defined lines.

Top Slab View

Bottom Slab View

The test matrix and test set-up to be followed in this field testing program will be according to the following drawings:

Test Set-up

Test Matrix

Strengthening Scheme

The following specimens will be tested in the experimental program:

• R1: control specimen with no strengthening;
• R2: specimen strengthened with CRP laminates in the positive moment region only;
• R3: specimen strengthened with CFRP laminates in both in the positive and negative moment regions; and
• R4: specimen strengthened with SRP laminates in the negative moment region and CFRP laminates in the positive moment region.

In the second case, the structure is yet a parking garage but built with Double-T prestressed (PC) beams simply supported by concrete reverse T-beams and columns, located in Bloomington, Indiana. A total of three beams specimens will be available to be tested within the garage, by saw-cutting any continuity between two adjacent beams and by testing each beam in a simple supported configuration with a single point load at mid span through each web of the Double-T.

Top View of Parking Garage

Bottom View of Double-T PC Beams

The test matrix and test set-up to be followed in this field testing program will be according to the following drawings:

Test Set-up

Test Matrix

The following specimens will be tested in the experimental program:

• D1: control specimen with no strengthening;
• D2: specimen strengthened with 1ply of SRP composite material using epoxy resins; and
• D3: specimen strengthened with 2 plies of SRP composite material using epoxy resins and in shear that will result as an anchoring device for the flexural plies.

Anticipated Benefits

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Milestones

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Transportation Research Board Keywords