ULTRASONIC PULSE VELOCITY
Ultrasonic test on concrete is a recognized nondestructive test to asses the homogeneity and integrity of concrete. With this ultrasonic test on concrete, following can be assessed:1.Qualitative assessment of strength of concrete, its gradation in different locations of structural members and plotting the same.2.Any discontinuity in cross section like cracks, cover concrete delamination etc. 3.Depth of surface cracks.This test essentially consists of measuring travel time, T of ultrasonic pulse of 50 to 54 kHz, produced by an electroacoustical transducer, held in contact with one surface of the concrete member under test and receiving the same by a similar transducer in contact with the surface at the other end. With the path length L, (i.e. the distance between the two probes) and time of travel T, the pulse velocity (V=L/T) is calculated. Higher the elastic modulus, density and integrity of the concrete, higher is the pulse velocity.The ultrasonic pulse velocity depends on the density and elastic properties of the material being tested.

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Conclusion and Suggested Retrofitting Technique:

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Rehabilitation of RC Elements Concrete jacketing for the RC elements 1. Strengthening is to be done using micro concrete 2. Support the members which is contributing the load for the RC elements under rehabilitation.
Stages of repair Stage 1 .Remove the damaged concrete portions completely till the reinforcement is exposed from the member carefully with mechanical arrangements and hand chiselling. Clean the surface to remove loose dust/particles.
Stage 2 Anchoring shear connectors into existing RC elements .Shear connectors in the form of ‘L-shaped’ bars has to be anchored into the existing concrete to ensure integral action of the reinforced concrete jacket portion with the hardened core concrete of the existing elements. Drill holes not less than 75 mm depth (long) into the members from the surface (Perpendicular to the surface) taking care not to damage the existing steel reinforcements in the elements. The positioning of the holes has to be staggered along the perimeter and height of the elements. The vertical spacing of shear connectors should not be less than 300 mm for all the sides of the member. Clean the holes with a jet of compressed air and remove the loose dust particles thoroughly. Use chemical resin type capsules marketed by reputed firms (Lokfix S manufactured by M/s Fosroc Chemicals or equivalent) for anchoring/fixing dowel bars into the holes to serve as shear connectors.Adopt at least 10-mm dia. HSD bars as shear connectors for which 12-mm dia holes may be needed.  Provide additional reinforcement in case the existing rods have undergone 30% loss in diameter.  The additional reinforcement will be connected to the shear connectors already provided Stage 3 Application of anti-corrosive coating and providing Galvanic Protection .Clean the reinforcement and apply the anticorrosive coating like Nitozinc primer (manufactured by M/s Fosroc Chemicals or equivalent). Before the application of anticorrosive coating, provide the sacrificial Zinc anode as per the standard manufacturer’s specification. Product like Galvashield XPI can be used.
Stage 4 Provision of epoxy jointing compound .Prepare the elementss surface suitably using an epoxy based bond coat, so that the jacketed concrete may bond well with existing/old concrete. Manufacturer’s instructions/specifications are to be followed for the epoxy bond coat like Nitobond EP (manufactured by M/s Fosroc Chemicals or equivalent.
Stage 5 Provision of water tight shuttering .Suitable shuttering (leak proof) system has to be placed in position for the jacket portion of the members in stages and micro concrete as per specifications has to be placed into the form work of the jacket portion.  Care has to be taken so that the micro-concrete used does not flow out of the shuttering. 
Stage 6 .The preparation of the micro concrete (Rendroc RG manufactured by M/s Fosroc Chemicals or equivalent), placing, compaction and curing for the same should be as per manufacturers specification. The micro concrete used for jacketing should have a minimum characteristic compressive strength of 45 MPa at 28 days.
Stage 7 .After the concrete in the jacket portion of the elementss in the particular stage has attained its strength, the props placed for supporting the corresponding beams are to be removed.Traffic Analysis should be done