International Concrete Abstracts Portal

The effect of FRP material properties on the long-term deflection of concrete beams reinforced with FRP rods was investigated by the experiment of 17 beams reinforced by nine types of FRP rods and a beam reinforced by steel bars. Test results showed that the flexural stiffness of a cracked beam decreased rapidly with a reduction in tensile stiffness of the reinforcing rods. Compared to the short-term deflection of beams, the long-term deflection of the FRP reinforced concrete beams at one week after loading increased on average by 17 percent, and 57 percent at 10 months. The material properties of FRP rods had a great effect on the long-term deflection of beams. The long-term deflection increase of beams with GFRP was the smallest among all of the tested beams, and oppositely, the deflection increase of beams with AFRP was greater than the average. The rate of increase in deflection of the beams reinforced with braided rods was about 10 percent smaller than that of beams with spiral rods. Contrasting, the rate of deflection increase of beams with ribbed rods was about 10 percent greater than that of beams with spiral rods.

A study was undertaken to examine the general behaviour of reinforced concrete beams confined with carbon-fibre-reinforced polymer (CFRP) laminates subjected to accelerated rebar corrosion. Eight small-scale RC beam specimens, 1200 mm long with cross-sectional area of 100 mm by 150 mm, were constructed. Five specimens were strengthened with CFRP laminates using three different strengthening schemes. The tensile reinforcement, 2-10M bars, of six specimens was corroded to 10% mass loss by means of an impressed current. Strain gauges were placed on the CFRP laminates to monitor and quantify tensile strains induced by the corrosion process. The CFRP laminates successfully confined the corrosion cracking, and total expansion of the laminate exhibited a fairly linear and continuous increase throughout the corrosion process.

Strength and stiffness properties of Glass Fiber Reinforced Plastic (GFRP) bars under various conditioning schemes with and without the application of sustained loads are described in this paper. Alkaline conditioning was more detrimental to the strength of GFRP bars as compared to salt conditioning. Increasing temperatures and stress resulted in a corresponding decrease in the strength of GFRP bars. Based on accelerated test results calibrated with respect to naturally aged results it is safe to conclude that the service life of the FRP bars with durable low viscosity urethane modified vinylester resin is about 60 years as a minimum with 20% sustained stress on the bar. Concrete cover protection on the GFRP bars enhanced the service life up to an additional 60 years.

New repair and maintenance technique for existing reinforced concrete structures has been developed as a result of a marriage of corrosion prevention and carbon fiber reinforced polymer (CFRP) installation techniques. Rebar corrosion prevention is basically provided by penetrating liquid and/or mortar, while mechanical degradation is compensated by CFRP. CFRP can also provide an effective protective layer for subsequent corrosive agent penetration. The technique can overcome various drawbacks of the current repair techniques by minimizing repair time and unnecessary chipping of damaged concrete, and protect degrading concrete structures. Such excellent performances have been proven by a series of experiments. Steel rebar embedded in a concrete block brushed with lithium nitrite-based penetrating corrosion inhibitor has been proven rust-free for years. The tensile strength of CFRP sheet have been proven unchanged after the exposure of 10,000 hours of accelerated weathering conditions. The CFRP sheet has also been proven impermeable to salt ion and water by experiments. Both shear and tensile strengths of concrete columns, damaged by salt penetration and then repaired with this new technique, have been proven equal or greater than the original strengths of control column. The performance of this technique has also been granted an official “Examination and Certification of Building Preservation & Maintenance Techniques” by the authorized organizations of the Ministry of Construction, Japan in July, 1998.

Experimental behavior of prestressed concrete beams strengthened with carbon sheets and the analytical predictions are reported. Two sets of beams made with normal strength (35 MPa, 5 ksi) and high strength (70 MPa, 10 ksi) concrete were strengthened with two and three layers of carbon sheet reinforcement. The beams were instrumented to measure deflection, and strains in composite, concrete, prestressed steel, and nonprestressed steel, and tested to failure using third point loading over a simply supported span of 3 m(10 ft). The results indicate that prestressed concrete beams can be effectively strengthened using high strength composites. As compared to reinforced concrete beams strengthened with carbon sheets, the loss of ductility was minimal for prestressed concrete beams. A strength increase of 86% was obtained for 3 layers, and the decrease in failure deflection was less than 10%. The authors believe that the stress-strain behavior of a prestressing strand, which has a continuous strain hardening with no yield plateau, is the main reason for this different behavior. The strength capacities can be predicted with good accuracy.