Infrastruct was requested by our Client to determine the in-situ quality of concrete in recently placed pad foundations using non-destructive techniques. We recommended the following combination of test systems:
- Proceq PUNDITLab+ UPV test system with 54kHz exponential transducers
- MIRA Pulse Echo tomograph using 48 pairs of dry contact transducers.
UPV Testing on the Pad Foundations
Ultrasonic Pulse Velocity measurements were carried out using the Proceq PUNDITLab+ equipment.
UPV testing on concrete elements is a recognised non-destructive evaluation method to qualitatively assess concrete integrity. The measurement of pulse velocity is frequently used to determine the in-situ uniformity of concrete, the presence of cracks or voids in concrete, crack depth estimation and to indicate changes in properties of the concrete with time.
The PUNDITLab+ UPV test system consists of an electric pulse generator, a pair of transducers, in this case 54kHz exponential transducers and an electronic timing device for measuring the time interval between the onset of a pulse generated at the transmitting transducer and its arrival at the receiving transducer.
The pulse cannot travel through air and measurements around voids/cracks/air filled anomalies in the concrete will increase the path length resulting in lower velocities and indicating a reduction in concrete quality.
Different configurations of the UPV test are possible but for the assessment of concrete quality in these pad foundations, the Infrastruct team used a linear array on a grid layout. Figure 1 below shows the linear array used on site and Photograph 1 shows the team on site measuring the UPV values for the in-situ concrete.
MIRA Pulse Echo Tomography
The pulse echo testing on the surface of the concrete pad foundations, as shown in Figure 2 below, was carried out using the Acoustic Control Systems A1040 MIRA ultrasonic low frequency tomograph. The MIRA test system is intended for inspection of concrete, reinforced concrete and a stone with one-sided access for the purpose of evaluation of consistency of construction, searching for foreign inclusions, cavities, voids, delaminations and cracks in concrete and measurements of concrete thickness.
The MIRA pulse echo test system utilises 45 transmitting and receiving transducer pair measurements in a short scan resulting in a 2-d depth profile of the concrete under test as shown in Figure 2. The dry point contact transducers provide the necessary consistency of impact and wave front penetration for diagnostics deep within the concrete element under test.
The MIRA measurements are taken by placing the transducers flush to the surface for a b-scan measurement, see Photograph 2 above. A b-scan is a 2-dimensional reconstruction of the concrete directly below where the scan is taken, see Figure 3 below. The MIRA system can also be used to create 3-d imaging of the concrete element under test and this can indicate the size and extent of located defects within the concrete.
The results of the UPV assessment and MIRA testing on the concrete pad foundations were recorded on-site by our Engineers and a comprehensive report, with interpretation, was prepared for our Client.
For more information on the UPV testing or pulse echo tomography, please contact Dr Thomas Callanan in Infrastruct Asset Management Services Limited.