Early-age monitoring of fresh cementitious material by acoustic emission

Concrete properties are mainly affected by the fresh state since it has a significant impact on the long-term concrete performance. In this study, acoustic emission (AE) was applied to monitor the behavior of fresh cement paste. AE is based on the detection of high-frequency elastic waves originating from different material sources. This highly sensitive technique provides data that contribute to a deeper understanding of the different ongoing processes for fresh concrete, as the possible AE sources are many. Characterization of each different source type is difficult and therefore, a combined methodology of AE, capillary pressure in the matrix and specimen deformation was applied to monitor the fresh cement paste

Monitoring early-age acoustic emission of cement paste and fly ash paste

In this study, a combined approach of several monitoring techniques was applied to allow correlations between the AE activity and related processes such as shrinkage and settlement evolution, capillary pressure and temperature development in fresh cementitious media. AE parameters related to frequency, energy, and cumulative activity which exhibit sensitivity to the particle size distribution of cement paste are compared with inert fly ash (FA) leading to isolation of the mechanical sources from the chemical ones. Characterization of the origin of different processes occurring in cement paste during hydration is complex. Although acoustic emission (AE) monitoring has been used before, a qualitative relation between the microstructural formation or other early-age processes and the number or parameters of AE signals has not been established. The high sensitivity of AE enables the recording of elastic waves within the cementitious material, allowing the detection of even low-intensity activities

Application of digital image correlation to cement paste

In this paper digital image correlation (DIC) has been applied to study the deformation process of cementitious material at very early age. After mixing of cement-based materials, the cement hydration process begins. Consequently, the ongoing Chemical reactions result in a 3D deformation process (shrinkage). The mechanism affecting the very early age hydration as well as specifically the deformation behavior of cementitious materials is a challenging topic. In view of that, it is essential to determine the significant effect of concrete hardening process on the deformation progression at different stages. The technique of DIC is highly sensitive and allows for the first time in literature an accurate and non-contact optical monitoring of the shrinkage of fresh cementitious material. The displacement of the surface is measured by correlating the different digital images taken at different ages after mixing of the material. The system enables a 3D observation that allows a deeper understanding of the deformation progression. The surface displacement determined by DIC-software (Vic-Snap 2010) is compared to the displacement measured by Linear variable differential transformer (LVDT) sensors for calibration purposes. DIC system realizes a more precise method avoiding the effect of self-weight of the traditional sensor. The purpose of this work is to check the sensitivity as well as the effectiveness of DIC technique, to characterize and better understand the 3D deformation process of fresh cementitious materials

Monitoring Acoustic Emission of Fresh Cement Paste

High strength and durability are the key factors determining the quality of concrete. To achieve the required properties, concrete mix design, and early age hydration, are the main factors affecting the performance of concrete. It is essential to monitor fresh concrete continuously through non-destructive techniques at the moment of mixing. In this study, acoustic emission (AE) has been applied to allow a continuous monitoring of the fresh cement paste. This non-destructive inspection allows the estimation of concrete properties by capturing elastic waves that are nucleated and propagate in the cement past. Moreover, ultrasonic pulse velocity (UPV), capillary pressure and heat evolution monitoring has been applied on cement paste to study the process of hydration mechanism. This study aims to check the sensitivity and effectiveness of AE technique to characterize the ongoing processes in fresh cementitious material and the possibility to contribute to a better monitoring of the process as an additional tool

Monitoring the hydration of cementitious material by acoustic emission

Studying the mechanisms affecting the very early age hydration as well as the microstructure of cementitious materials is essential to improve concrete performance. Consequently, it is necessary to monitor and onderstand the early age hydration process. In this work, continuous acoustic emission (AE), ultrasonic pulse velocity (UPV), and capillary pressure monitoring has been applied on Consolidated and non-consolidated cement paste to study the process of hydration mechanism as well as the formation of the microstructure. Preliminary experiments have presented a large rate of AE activities in the fresh state. Ultrasonic tests exhibited an increase of pulse velocity during hydration while capillary pressure and heat evolution were also monitored. The purpose of this study is to verify the sensitivity of AE to follow the ongoing processes in fresh cementitious material and the possibility to contribute to a better monitoring of the process as an additional tooi

Monitoring fresh cementitious material by digital image correlation (DIC)

Concrete undergoes strong displacements due to different processes at very early state, like shrinkage. This early state of concrete affects the long-term concrete performance. The concrete deformation cannot be directly attributed to a single process, due to the complexity of different processes such as, evaporation, water migration, settlement, formation of hydrates, shrinkage, early age cracking. Monitoring concrete properties at a very fresh state is essential to understand the different ongoing processes. Digital image correlation (DIC) has proven very useful as an optical and contactless method for surface monitoring of several materials. In the present paper the displacement distribution of fresh cementitious material from plastic state up to hardened state is studied by means of DIC. Moreover, an innovative technique of speckle pattern creation is presented, since creation of a pattern on fresh (and hence viscous) cementitious materials is not straightforward. The specimen surface is covered with a speckle pattern that deforms together with the specimen. The principle of DIC realizes a 3D continuous monitoring by recording the images at different time steps and comparing it to the reference or undeformed image. The experimental results confirmed the effectiveness and correctness of the new technique giving a global overview much more representative than point measurements with traditional displacement meters

Study on mechanical acoustic emission sources in fresh concrete

Acoustic emission testing has proven very useful as a non-invasive monitoring method for several material processes. Recently several studies have emerged related to fresh concrete monitoring, as AE has the sensitivity to record waves from many different processes, even though no external load is applied to the specimens. Due to the complexity of the activity including among others formation of hydrates, settlement, water migration, early age cracking, the accumulated AE cannot be easily explained. In the present paper, two mechanisms of mechanical origin (aggregate and bubble movement through the paste) are isolated and the characteristics of their emissions are studied. Experimental results are complemented with numerical simulations to enhance the understanding due to the complexity of the wave propagation problem. (C) 2017 Politechnika Wroclawska. Published by Elsevier Sp. z o.o. All rights reserved

Fresh concrete monitoring by NDT techniques

The most reliable examination for concrete is mechanical testing (usually compression) after hardening. However, ensuring the quality of fresh concrete before hardening, substantially reduces the possibility of performance at standards lowerthan designed. Curing of conventional cementitious material is complicated and becomes even more complicated considering the new generation of additives like super absorbent polymers and nano-reinforcement which may strongly modify cement behaviour. In order to obtain better control on the process from very early age, this study describes a combined approach of several monitoring techniques. Acoustic emission (AE) is applied to record the sources occurring during the first hours when concrete is still in liquid form and later when hardening takes place when shrinkage cracking occurs. In addition, pressure sensors register the development of capillary pressure in the matrix and indicate the moment of air entry into the System, which is the precursor of cracking. Settlement and shrinkage, measured both non-contact by Digital Image Correlation (DIC) and conventionally, as well as temperature shed light into the complex processes occurring into fresh concrete and help to verify the sources of AE. Among other, mechanical sources like aggregate impacts due to gravity and air bubbles release are isolated and tested in a dedicated experiment showing that these produce recordable AE despite the viscous nature of paste. The final aim is to develop a methodology to assess the quality of the fresh concrete from an early age, to possibly project to the final mechanical properties and to ensure a proper service life

Full-field settlement measurement at fresh cementitious material by digital image correlation

Monitoring concrete properties at a very fresh state is essential to understand the different ongoing processes. Concrete undergoes strong displacements due to different processes such as, evaporation, water migration, settlement, formation of hydrates, shrinkage, early age cracking. This early state of concrete affects the long-term concrete performance. In the present paper the displacement distribution of fresh cementitious material from plastic state up to hardened state is studied by means of the optical and contactless method of DIC. The principle of DIC realizes a full-field 3D continuous monitoring of the surface displacement. An innovative technique of speckle pattern creation allows monitoring the surface displacement few minutes after casting of cement paste and mortar. The experimental results confirmed the effectiveness and correctness of the new technique giving a global overview much more representative than point measurements with traditional displacement meters