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Ultrasonic Pulse Velocity

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  EXPT NO:……………………….   Date:…………………….  Name of the Experiment: ULTRASONIC PULSE VELOCITY Aim: To assess the quality of concrete by ultrasonic pulse velocity method as per IS: 13311 (Part 1) - 1992. Theory: The ultrasonic pulse is generated by an electro-acoustical transducer. When the pulse is induced into the concrete from a transducer, it undergoes multiple reflections at the boundaries of the differ material phases within the concrete.  A complex system of stress waves is developed which includes longitudinal ( compression), shear ( transverse ) and surface( Rayleigh ) waves. The receiving transducer detects the onset of the longitudinal waves, which is the fastest. Because the velocity of the pulses is almost independent of the geometry of the material through which they pass and depends only on its elastic properties, pulse velocity method is a convenient technique for investigating structural Concrete. It can be theoretically proved that pulse velocity in an elastic solid is: V =      Where E= Elastic modulus in MPa ρ =density in kg/m3  µ= Poissons ratio(0. The underlying principle of assessing the quality of concrete is that comparatively higher velocities are obtained when the quality of concrete in terms of density, homogeneity and uniformity is good. In case of poorer quality, lower velocities are obtained. If there is a crack, void or flaw inside the concrete which comes in the way of transmission of the pulses, the pulse strength is attenuated and it passes around the discontinuity, thereby making the path length longer. Consequently, lower velocities are obtained. The actual pulse velocity obtained depends primarily upon the materials and mix proportions of concrete. Density and modulus of elasticity of aggregate also significantly affect the pulse velocity. Apparatus: i.)   Ultrasonic Concrete Tester (UX 4600;Make:Roop Telsonic),ii.) 2 nos. Trasducers (Contact type) 50 mm dia, iii.) Standard reference Bar (Calibration time mentioned on bar); iv.) Probe Cables. v.) Grease as couplant   PROCEDURE: i)   Connect Transducer output & to receiver input respectively via cables. Switch on the instrument with on/off switch. Place transmitting and receiving Transducers across the reference block of 64.5 µ-s after applying suitable couplant i.e grease to ensure maximum contact between transducers and reference block. Try to adjust 64.5 µ-s with the help of zero control. Once the display starts exhibiting 64.5 µ-s it is understood that the instrument is dully calibrated. ii)   Once the instrument is calibrated we proceed on the actual job. The transducer may be arranged on the surface after applying grease same as before of the specimen to be tested, the transmission be either direct/indirect or semi direct as the case may be. Note the time in micro seconds as depicted in the display and the distance between transducers as the case may be. iii)   Thus Pulse Velocity is measured as =            Precaution: 1.   Donot touch the exposed end of cable connected to the transmitting connector. Always connect the transducers first and then switch on the instrument. 2.   Donot try to turn the instrument faced down. 3.   Donot put heavy objects on the instrument. 4.    Avoid dust deposited inside the instrument. 5.   Remove the grease and clean it after each exiperiment and store it in dry place. Observation. Sl no. Sample Path Length in mm Time recorded in µs Pulse velocity in km/s  Avg Remarks 1 7 days-150 mm concrete cube- Side 1 150 52.5 2.85 2.8 Below 3 km/s hence Conc. Quality is doubtful due to 7 day strength Side 2 150 54.5 2.75 Side 3 150 53.5 2.80 2 28days -150 mm 150 32.5 4.62 4.54 As it is greater than 4.5 km/s  concrete cube- Side 1 hence Conc. Quality is excellent Side 2 150 33.5 4.47 Side 3 150 33.0 4.54 Remarks: It is very evident that after 28 days cube strength (M25) is high as a result pulse velocity is also higher than 7 day strength. Thus Velocity increases when the cube has completely hardened. From the above mentioned formula dynamic elastic modulus can be calculated using poisons ratio=0.2 and density of concrete =2400 kg/m3 and recorded velocity of 4.54 km/s and found to be 44521 MPa which is within limit of E of concrete i.e 25000 to 45000 MPa CONCLUSION: The ultrasonic pulse velocity method could be used to establish: 1.   the homogeneity of the concrete, 2.   the presence of cracks, voids and other imperfections, 3.   changes in the structure of the concrete which may occur with time, 4.   the quality of the concrete in relation to standard requirements, 5.   the quality of one element of concrete in relation to another, and 6.   The values of dynamic elastic modulus of the concrete. Recommended values as per IS: 13311 (Part 1) - 1992.

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Jul 23, 2017

class 2

Jul 23, 2017
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