Ultrasonic Pulse Velocity Test on Concrete

An in-site, non-destructive ultrasonic pulse velocity test (UPV) checks the quality of concrete and natural rocks. During this test, measuring the speed of ultrasound pulses, which pass through a concrete structure or natural rock formation, assesses the strength and quality of concrete or rock. The experiment is done by applying an ultrasonic pulse in concrete to check and the pulse moment to pass the building. Higher speeds show excellent quality and material stability, while slower speeds can show concrete with many holes and voids.

Equipment for ultrasonic testing consists of a pulse generation system composed of a pulse electronic circuit as well as a mechanical pulse transducer with a frequency of oscillation of 40 kHz to 50 kHz and a signal processing circuit for transforming electronic pulses.

The Ultrasonic Pulse Velocity is used to:

1) Evaluate the quality and homogeneity of concrete materials

2) Predict the strength of concrete

3) Evaluate dynamic modulus of elasticity of concrete,

4) Estimate the depth of cracks in concrete.

5) Detect internal flaws, cracks, honeycombing, and poor patches.

The experiment can also be used to assess crack repair efficiency. Ultrasonic experiments are reflective and the structural and mechanical characteristics of the product should be determined by other exams such as damaging testing. In its most fundamental form, ultrasonic pulse speed testing is called time of flight. This relates to the time when an ultrasonic signal is reached through a strong medium from one transducer to the next. In this instance, the ultrasonic pulse is a p-wave. By dividing the gap between the transducer at the moment of entry, the ultrasonic wave speed (UPV) is calculated.

An electro-acoustic transducer produces the ultrasonic pulse. If the wave is induced from a transducer into the concrete, it is subjected to several reflections within the matrix at the limits of the various material stages. A complex stress wave system comprising longitudinal (compressive), shear (transverse), and Rayleigh waves is developed. The transducer detects the start and the fastest start of the longitudinal waves.

Because pulses ‘ speed is almost independent of their geometry and relies only on their elastic characteristics, the pulse speed method is the appropriate technique to investigate structural concrete. 

A relatively greater rate is achieved if the quality of concrete is excellent, in terms of density, homogeneity, and uniformity. The basic concept of evaluates concrete performance is. Lower speeds are achieved in case of poorer performance. When the concrete has a gap, a gap or a defect in the pulse’s transmission, the pulse strength is reduced and the discontinuity is passed, making the track longer. Lower speeds are therefore achieved.

The current pulse speed acquired mainly depends on the fabrics and mixing concrete ratios. Aggregate density and elasticity modulus also affect the pulse velocity considerably.

The apparatus for ultrasonic pulse velocity measurement shall consist of the following:

a) Electrical pulse generator,

b) Transducer – one pair,

c) Amplifier, and

d) Electronic timing device.

Any suitable type of transducer operating within the frequency Lange of 20 kHz to 150 kHz may be used. Piezoelectric and magnetostrictive types of transducers may be used, the latter being more suitable for the lower part of the frequency range.

Electronic timing device: 

The period can be measured between the pulse start produced by the transducer and the start of the transducer introduction. Two shapes can be made from an electronic timing apparatus, one using an interval timer with an immediate digital reading screen on which the guiding pulse curve in comparison to the appropriate time scale is shown; the other utilizes a timer for the interval. The interpretation of outcomes becomes more accurate if the two types of timing devices are possible.

Assembly performance: 

The device should have a precision of 1 % over a spectrum of 20 microseconds to 10 milliseconds to measure transit periods.

For this purpose, the overall performance needs to be controlled by creating readings on two standard samples of reference with accurate pulse transit moments. The two benchmarks (generally steel bars) are to be approximately 25 microseconds to 100 microseconds in pulse travel moments. The equipment provider shall be indicated to 0.2-microsecond precision.

To determine the zero for the device, a shorter reference specimen must be used and a longer specimen to monitor the exactness of the transit time measurement of the device. The measurement received should not vary by more than O.5 percent from the established value of the reference sample. An electronic arousal pulse should have an increased time of not more than one-quarter of its natural time applied to the transmitting transducer. To guarantee that the pulse starts sharply.

The pulse interval should be low enough to guarantee that reverberations in previous operating cycles do not interfere with the start of the received signal for the smaller concrete sample samples. The unit shall retain its efficiency across the supplier’s indicated spectrum of environmental temperature, moisture, and energy distribution voltage.

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