Measurement of the E-modulus of cement pastes and mortars since casting, using a vibration based technique

The use of ambient vibration tests to characterize the evolution of the E-modulus of cement pastes and mortars during hydration, and immediately after casting, is addressed in this article. The methodology consists of using 550 mm long hollow acrylic tubes, with an internal diameter of 16 mm, as a formwork for the cementitious material under study (cement paste or mortar). Along hydration the hardening material together with the external tube will endure a composite behaviour; through clamping of one extremity of the resulting composite element and leaving the other extremity free, a 450 mm long cantilever is then obtained. By continuously monitoring the accelerations at the free end of this cantilever, and using an ambient vibration technique, the first resonant frequency of vibration can be identified, which allows to determine the growth of the instantaneous E-modulus of the cementitious material, and therefore to trace its evolution during hydration. A detailed description of the experimental setup and test procedures is presented first, and afterwards some exploratory experiments performed with cement pastes are commented, illustrating the capabilities of this novel method, as well as its robustness.Fundação para a Ciência e a Tecnologia (FCT

A Laser Interferometric Method for Small- and Finite-Amplitude Ultrasonic Waves’ Detection in Transparent Media

The acousto-optic interaction affords a convenient way of optically probing ultrasonic waves in medical diagnosis and nondestructive evaluation. The effects of ultrasonic waves on the light transmitting through transparent media arise from the refractive index variations produced by ultrasonic waves. The index variations may be detected by optical deflection, diffraction or interference methods [1–4]. In Raman-Nath regime, the acoustic waves act as a moving phase grating and diffract the light into different orders. Schlieren visualisation derived from this mechanism has been extensively used to ultrasonic measurements in liquids. In solid media, the acousto-optic effects become more complicated because of the induced optical birefringence. The usual photoelastic method consists in detecting the change in the polarization state of the light caused by ultrasonic waves [5]. Both of the methods are only amplitude-sensitive to ultrasonic waves.</p

How to monitor the modulus of elasticity of concrete, automatically since the earliest age ?

Monitoring the evolution of an early age set of parameters on concrete is necessary to predict the early age behaviour of structures. The difficulty lies in the fact that this monitoring must be automatic because the concrete hardening process takes place over a long period after the casting. This paper presents a new methodology and an apparatus, specifically designed at IFSTTAR, to monitor the hardening process of a concrete. Mainly, the Young's modulus can be monitored in compression. Measurements start soon after having cast the concrete and the sample temperature is completely controlled so that the concrete maturity is well mastered. The performances of this apparatus, obtained on an ordinary concrete, are compared to more classical measurements using an extensometer mounted on the sample just after the setting time and to ultrasonic measurements. In these cases, the temperatures were not controlled and results have to be expressed in equivalent time. A comparison with another method developed and used at ULB by using the same concrete, in the frame of a joined cooperation between our two laboratories is achieved. This test set up is based on the so called Temperature Stress Testing Machine (TSTM). This device has been specifically designed with a control of the concrete maturity by the use of a dummy specimen only submitted to free deformations (thermal, shrinkage). The TSTM allows compressive and tensile testing starting just after the setting time. In addition, concrete properties, such as compressive and tensile strength, have been characterized at early age. These values have been used for the design of the loading histories applied in the automatic tests. The heat released by the cement hydration has also been measured in order to express the results on a maturity scale. © 2013 RILEM.SCOPUS: ar.jinfo:eu-repo/semantics/publishe