RETROFITTING OF RC BEAMS WITH EXTERNALLY BONDED SIMCON LAMINATES
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This paper presents the results of experimental studies concerning the flexural strengthening of RC beams using externally bonded Slurry Infiltrated Mat CONcrete (SIMCON) laminates. A total of four reinforced concrete beams were cast and tested in the laboratory over an effective span of 3000 mm. Three beams were strengthened with bonded SIMCON laminate at the bottom under virgin condition and tested until failure; the remaining one beam was used as control specimen. Static responses of all the beams were evaluated in terms of strength, stiffness, ductility ratio, energy absorption capacity factor, compositeness between laminate and concrete, and the associated failure modes.
Comparison was made between the Control specimen and strengthened beam. The results show that the strengthened beams exhibit increased flexural strength, enhanced flexural stiffness, and composite action until failure.
The cost of civil infrastructure constitutes a major portion of the national wealth. The rapid deterioration of reinforced concrete structures has thus created an urgent need for the development cost-effective methods for repair, retrofit and new construction.
As the number of civil infrastructure systems increases worldwide, the number of deteriorated buildings and structures also increases. Complete replacement is likely to be an increasing financial burden and might certainly be a waste of natural resources if upgrading or strengthening is a viable alternative.
A new way of resolving this problem is to selectively use advanced composites such as High Performance Fiber Reinforced Cementitious Composites (HPFRCCs). With such materials repair, retrofit, and new construction approaches can be developed effectively.
The new approach called SIMCON produces concrete components with extremely high flexural strength, Since SIMCON is manufactured using pre-made continuous fiber mats, fiber placement is substantially simplified.
The only difference being that the fiber is placed in a mat rather than discrete fibers. The fiber volume percent for manganese carbon steel mats ranged from 1.2 to 3.6 percent. Fiber mat thickness ranges from 12 mm to 50 mm.
Preliminary experimental study was conducted to determine the optimum volume fraction(i.e volume of fibre). Laminates of size 125x25x500mm were cast with different volume fraction (Vf), say 4.0%, 4.5%, 5.0%, 5.5% & 6% . Among these combination the test results is found that Vf=5.5% gives better performance with regard to ultimate load and stiffness.
The fibers are arranged in such a way that 60% of fibers aligned in the longitudinal direction and the remaining 40% aligned in the inclined direction not exceeding 50degrees with the horizontal. Every mat has a 4 to 5 layers of fibers and each individual fibers are bonded with low viscosity epoxy resin. After spraying the resin the mat was held in position by compression machine under 50KN at 30min and then allowed for 24 hours air curing. Then the fiber mats were kept in the mould and were grouted.
The cement slurry was mixed in the following proportions with super plasticizer.
- Sand/Cement – 0.5
- Water/Cement ratio – 0.3
- Super plasticizers /Cement – 0.025
The purpose of using the admixture is to increase the workability and to reduce the water content.
Hand compaction and gravity feeding were used to produce thorough penetration of slurry into the preplaced steel fibers, then it is allowed for 28 days curing in water.
Total of 4 beams, 125x250x3200mm in size, were cast and tested in the laboratory over an effective span of 3000mm. Of the above four beams, one beam was used as control specimens(CB1), and three beams (RB1,RB2,&RB3) were strengthened with bonded SIMCON laminates at the bottom under virgin condition and tested until failure. The details of test beams are presented in Table 1.
Load, displacement and strains have been recorded for each specimen at the mid span of the beam.
Three numbers of SIMCON laminates of 25mm thick were used for externally strengthening the RC beams.
All the test beams were over designed for shear to avoid the undesirable brittle failure .
The SIMCON laminate thickness of 25mm and bond line thickness 2.0mm were kept constant for all the test specimens.
COMPARASION OF TEST RESULTS
1) SIMCON laminates properly bonded to the tension face of RC beams can enhance the flexural strength substantially. The strengthened beams exhibit an increase in flexural strength of 45.0% as compared to the Control beam(CB1)
2) At any given load level, the deflections are reduced significantly thereby increasing the stiffness for the strengthened beams.
3) All the beams strengthened with SIMCON laminates does not exhibit premature brittle failure.
4) A flexible epoxy system will ensure that the bond line does not break before failure and participate fully in the structural resistance of the strengthened beams.