Estimation of the compressive strength of eco-concrete using ultrasonic testing with embedded piezoelectric transducers

In most concrete applications, setting and hardening of concrete are important parameters in assessing the period during which concrete is still workable and the time when the formwork can be removed. In particular, the estimation of the compressive strength allows to determine the time when the next phase of construction can be started and to make sure that the concrete has reached the desired performance. Conventional techniques for estimating the compressive strength are laboratory tests on cubic or cylindrical specimen cast at the same time as the element of concrete in the formwork. Even if such specimens are stored next to the formwork, the concrete is not exposed to the same humidity and temperature as the element in the formwork, which can result in a poor estimation of the compressive strength. An alternative is to embed sensors directly in the formwork in order to monitor the properties. Two commercial systems exist:  (i) the maturity method based on temperature measurements, and (ii) a method based on the measurement of electrical resistivity (http://www.consensor.nl). Both methods provide indirect measurement of the compressive strength based on calibration curves which need to be established through preliminary laboratory tests on cubic specimen, especially due to the growing use of specific cement compositions such as eco-binders.

 References

[1] Dumoulin C., Karaiskos G., Carette J., Staquet S. and Deraemaeker A.. Monitoring of the ultrasonic P-wave velocity in early-age concrete with embedded piezoelectric transducers. Smart Materials and Structures, 21(4), (2012)

Objectives of the master thesis

The main objective of the master thesis is to investigate an alternative approach based on ultrasonic testing of concrete in order to estimate the compressive strength. The method consists in sending and receiving waves inside the concrete. For this purpose, we are using piezoelectric transducers directly embedded inside the concrete, which are developed at ULB-BATir [1]. Such measurements do not provide the direct measure of the compressive strength, but allow to measure the wave propagation velocity which is directly related to the Young’s modulus. Well established relationships exist between the Young’s modulus and the compressive strength. These are mainly dependent on the aggregate size. In doing so, we aim to avoid the preliminary tests required for the maturity and the resistivity methods.

The work consists in developing experimental tests in which concrete cubes with embedded piezoelectric transducers will be produced. Classical compressive tests will be performed in order to measure directly the compressive strength, and ultrasonic tests will be performed on the same specimen. A critical comparison will be made between the results obtained with both approaches in order to assess the possibility to estimate the compressive strength using ultrasonic testing. In particular, the applicability of this method should be confirmed for concrete with specific cement compositions such as eco-concrete containing a high content in mineral additions, for which the relationships between the Young’s modulus and the compressive strength can be different than for ordinary concrete.

Arnaud Deraemaeker (aderaema@ulb.ac.be)

Co-Supervisor

 Stéphanie Staquet (sstaquet@ulb.ac.be)

Cédric Dumoulin (cedumoul@ulb.ac.be)

 Jérôme Carette (Jerome.Carette@ulb.ac.be)

English/French

Architectural Engineering/Civil Engineering/Mechanical Engineering

The student must have an interest in Structural Dynamics, wave propagation, Cementitious materials and Concrete behavior , basic programming skills in Matlab and an interest in experimental testing.