2010 Project Progress Report
Program Name: Innovative Bonding and Fibers for
Strengthening Concrete Structures
Program Manager / PI: Dr. Sami Rizkalla
Company / Sponsor: Nippon Steel Company Co., Ltd, Fyfe Co.
LLC, Grancrete Inc., Freyssinet, Inc.
Project Number: NCSU-3
Overview: This research investigates the use of several innovative strengthening systems consisting of
different types of fiber reinforced polymer materials in combination with different adhesive materials,
for strengthening and repair of civil engineering infrastructure. The study combines three inter-related
projects under the umbrella of innovative materials for strengthening of concrete structures.
Experimental Plan: The first project has a total of four phases. The first phase is designed to explore
effective strengthening systems for flexural strengthening of reinforced concrete structures. The
second phase will explore effective flexural strengthening of infill masonry structures. The third phase
will explore the fundamental characteristics of the selected systems based on the findings of the first
two phases. The fourth phase will focus on developing design guidelines for the proposed strengthening
system.
For the first phase, a total of 20 reinforced concrete slab specimens are used to evaluate the proposed
fiber/adhesive strengthening system. The slabs are 2 ft wide by 11 ft long by 6 inches deep. The slabs
are strengthened flexuraly using various fiber/adhesive systems in order to study several parameters,
including fiber type, adhesive type, and fiber reinforcement ratio. The slabs are tested in a four-point
bending configuration to determine the flexural response, including the increase of the load-carrying
capacity and ductility provided by the various strengthening systems.
The testing of the second project will follow ICC Acceptance Criteria (AC 125) for a CFRP strengthening
system. The phases for the acceptance are: material properties and flexure and shear strengthening of
slabs, beams, and columns. For the material testing phase, the physical and mechanical properties of
the fiber are investigated. The tensile properties, creep (tensile), glass transition temperature, void
content, coefficient of thermal expansion, and interlaminar shear strength of the fiber will be
determined under various environmental exposures. The second phase consists of strengthened
reinforced concrete beams and slabs tested in flexure to determine the effectiveness of the various
systems. Both low and high concrete strength and various strengthening ratios will be used to capture a
wide range of behavior. The flexure and shear specimens will be tested in a four-point bending
configuration to determining the response of the system. Reinforced concrete columns will be
considered in the third phase to explore the systems effectiveness to strengthen the system under
compression.
Goals and Motivation: The primary objective for these experimental programs is to determine the
effectiveness of different fiber strand sheets with different adhesive systems for the repair and
strengthening of reinforced concrete structures including slabs, beams, and columns.
Previously Reported Findings: N/A
Budget Update: $125,000
Findings Since Last Report: The preliminary findings of the project indicate the following: All types of
fibers that were tested were adequate to increase load capacity. Fibers with high tensile strength and
modulus increased the load capacity but decreased the ductility. Test results indicated that fiber grids
with smaller spacing may cause localized debonding. For the bonding material, the epoxy had a slightly
higher load capacity than the Grancrete. On the other hand, Grancrete had a slightly higher deflection
and ductility and it formed well distributed flexural cracks along the slab. The epoxy caused the fibers to
rupture at a single crack. The fiber reinforcement ratio parameter yielded interesting results. The
higher reinforcement ratio increases the flexural capacity but decreases the ductility of the reinforced
slabs. Further tests are needed to fully explore this parameter.
Potential Member Company Benefits:
1. Evaluate the effectiveness of two different cementitious materials as alternative adhesives for fiber
strengthening of reinforced concrete structures.
2. Evaluate the effectiveness of carbon fiber strands with different reinforcement ratios.
3. Increase confidence in the use of Grancrete as an adhesive for strengthening reinforced concrete
structures.
4. Explore the effectiveness of two adhesives proposed with enhanced resistance for elevated
temperatures.
5. Evaluate the physical and mechanical properties of a new carbon fiber strengthening system.
6. Provide a strengthening system to the industry that has been approved with ICC Accreditation (AC
125).
7. This project can provide alternative strengthening systems that can be easily used and provide
industry with more options to select for strengthening reinforced concrete structures.
Next Steps:
1. Complete experimental program
2. Analyze experimental results
3. Introduce analytical model to be calibrated by experimental program