Strengthening of an existing reinforced concrete structure

Experimental lab test:

4.1: Experimental introduction:

The main objective of this experiment is to study the effect of the different environments on FRP strengthening method behavior.

The experimental work consists of testing 16 beams of dimensions 100 mm X 100 mm X 500 mm. The beams were divided into four groups, group 1 consists of plain concrete strengthen with one strip of FRP, group 2 consists of steel reinforced beams, group 3 consists of steel reinforced beams strengthened with one strip of FRP, group 4 consists of steel reinforced beams strengthened with two strips of FRP (See Figure 4.1).

Figure 4.1: Beams with different reinforcements

All the beams were reinforced with the minimum reinforcement of one bar with 6mm diameter (1Φ6).

The main idea of our experimental tests was to make four samples of beams with four deferent reinforcement (plan concrete, steel reinforcement, steel and one strip FRP, and steel and two strips reinforcement) and to apply each kind sample to four different environments (control room temperature 26^oC (indoor), hot temperature 45^oC with Abu Dhabi humidity 100% (Hot 100% Humidity), hot temperature 50^oC with Al Ain summer 0% humidity (Hot 0% Humidity), and external exposed to the temperature ranged between   &   and the humidity ranged between    &   (outdoor). After 1000 hrs of applying the samples to the different environments, lab tests were done in order to determine the effect of these environments on the behavior of these beams.

4.2 Equipments:

• Digital balance.
• Molds of beams and cubes.
• Mixer.
• Vibrator.
• Hot water tank.
• Oven.
• Test machine.

4.3 Materials:

• Concrete mix: water, cement, sand, coarse and small aggregates.
• Plastic sheet.
• FRP strips.
• Strain gages.

4.4 Procedures:

The procedure of our experiment consists of 13 steps. First of all, steel bars and stirrups were cut and put in the molds. Second, strain gages were fixed in the steel reinforcement (See Figure 4.2).

Figure: 4.2: Beam Reinforcement with strain gages and wire

Third, the concrete ingredients were calculated and measured. Fourth, the concrete ingredients were mixed by using a big mixer. Fifth, the concrete was poured in the molds of beams and cubes (See Figure 4.3).

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Figure 4.3: Poring concrete in the beams molds.

Sixth, the concrete was vibrated and covered by plastic sheet (See Figure 4.4).

Figure 4.4: Vibrating concrete beams and cubes.

 Seventh, the concrete beams and cubes were removed from molds and cured in potable water for 14 days. Eighth, 3 cubes were tested after 7 days. Ninth, beams and cubes were exposed to air drying in laboratory. Tenth, FRP was applied and protected with layer of epoxy. Eleventh, beams were exposed to the different environments for 1000 hours. Twelfth, 3 cubes will be tested after 28 days. Finally, all beams will be tested after 1000 hours.

4.5 Results and discussion:

All the experimental results were recorded in tables 4.1 to 4.16 and figures 4.5 to 4.22 in appendix A. The conclusion table was determined in table  4.17.

Table 4.17: Results Conclusion for the sample tests

In table 4.18, the strengths of 3 cubes of concrete mix were at age 7 & 28 days were recorded.

Table 4.18: Cubes strengths

From table of results (table 4.17), the following could be noticed:

A-    Effect of Fiber Reinforcement Polymer (FRP) on strengthening the beams:

·        One FRP strip increased the beam's capacity by about 100% for all environments.

·        Two strips of FRP increased the beam's capacity by about 200% fr all environments.

·        All reinforced beams strengthen with FRP failed on de-bonding of the FRP at the end of strips due to the shear force at this location.

B-    Environmental effect on the beams:

·        The effect of environment on reinforced concrete beams with steel only is negligible. This is attributed to the embedded steel strength is not affected by the environment.

·        The environment affected the plain concrete with one strip of FRP; the hot and humid environment cured the concrete causing increase in the concrete strength which increases the shear capacity of the beam. The hot and dry environment reduced the concrete strength as well as the shear capacity.

·        The environment affected the reinforced concrete beams strengthen with FRP; the hot and humid environment cured the concrete causing increase in the concrete strength which increases the bond capacity between the FRP and the concrete. The hot and dry environment reduced the concrete strength as well as the bond capacity.

·        Although the FRP in the outdoor environment were subjected to the Ultra Violet during the 1000 hrs exposure, no reduction in the beam capacity was noticed.

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