Ebook: Construction Materials and Structures
Nganga, G. Construction and Building Materials. Nilsson, L. Esbo, Finland: Nordtest. Raath, B. Materials and Structures , Ronny, R. Simons, B. Concrete International, 26 4 : Streicher, P. Tang, L. Taylor, P. Thomas, M. Hossack, A. Torrent, R. Tuutti, K. Van der Lee, J. Walraven, J.
Reservation of rights for exclusive use No. User Username Password Remember me. Register with this site Forgot your password? Article Tools Print this article. Indexing metadata. They observed that the use of magnetized water in concrete resulted in a very significant increase in concrete strength, probably due to the higher surface area of magnetized water. Su and Wu [ 37 ] also observed a strength increase when using magnetized water in mortar and concrete containing fly ash.
Nevertheless, the use of magnetized water is still open to significant debate, as it is not clear how water could maintain its magnetization long enough after removal of the magnetic field. It has to be further studied whether the reported improvement of properties really is the effect of previous magnetization of water, or rather the effect of other experimental influences that have not been clearly identified. Soto-Bernal et al. They concluded that more CSH is produced, with denser morphology and reduced porosity.
It is conjectured that the magnetic field is influencing the hydration process by means of a restructuration process at molecular scale, resulting in microstructural improvement and increased mechanical performance. The application of magnetic fields to control rheology of cementitious materials containing magnetic particles in real time has been studied by Nair and Ferron [ 39 ].
They considered two types of carbonyl iron powder, added to Portland cement paste water cement ratio 0. Magnetic field with strengths up to 1. It is experimentally shown that the rheological behaviour of the paste containing magnetic particles can be actively altered by applying the magnetic field. The effect is depending on the field strength as well as on the dosage of magnetic particles. On the other hand, the authors conclude that the magnetic field does not seem to have a noticeable effect on the morphology and formation of early age hydration product, and does not influence the final compressive strength.
This seems to be in contradiction with the previously mentioned conclusions obtained by Soto-Bernal et al. Disregarding the discussion on the effect of magnetic field on hydration, the research of Nair and Ferron [ 39 ] is a major step forward towards active rheology control of cementitious materials. Abavisani et al. They conclude that the application of a magnetic field on the fresh steel chip-reinforced concrete facilitates the compaction process, and leads to an increased compressive strength depending on the test direction.
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Particularly interesting with regard to rheology control is their observation that the vibration of the steel chips in the alternating magnetic field can be considered as a way to obtain self - compactor elements for concrete. The same group of authors further studied the effect of alternating magnetic fields and alternating current on the behaviour of reinforced concrete columns [ 41 ], considering magnetic fields up to 0.
The alternating magnetic field facilitated the compaction of the fresh concrete in the reinforced columns due to the triggered vibration of the reinforcing bars. Applying the magnetic field on the hardened concrete seems to lead to contradictory results, with sometimes an increase [ 40 ] and sometimes a decrease [ 41 ] in performance.
The authors state that the application of magneto-electric fields can be the basis for real - time compressive behaviour controlling of reinforced concrete elements, even enabling a control of failure mode. However, their claims are based on contradictory results, and are not fundamentally supported by a clear mechanism explaining the potential influence of the electro- magnetic field on the material and structural properties.
While the principle of active control of concrete properties by magnetic signals has been set forward, it is not fully clear which mechanism could be the basis for the explanation of the reported effect of magnetization on hydration and microstructure development. This will need further research attention, with more rigorous test protocols in order to fully exclude potential influences of other parameters.
On the other hand, it seems clear that mixed-in magnetic particles or magnetizable materials like steel chips as well as preplaced steel rebars are responding to the magnetic signal, with effects on rheology, compactability and even mechanical performance. This opens a window for new developments and applications, possibly involving new types of magnetizable materials [ 42 ] or new fields of application like on-demand healing [ 43 , 44 ].
In some applications, the effect of the magnetic field is triggering its response via another physical mechanism like micro- vibration making the link with Sect. An electric control signal AC current has been mentioned in previous paragraph, where it was combined with the research on the magnetic control of the mechanical performance of hardened reinforced concrete columns. Other literature results are available on the application of electric fields on fresh or hardening concrete.
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As an example, Kovtun et al. The current serves as an indirect way of heating, while the higher temperature achieved is leading to the accelerated hardening of the material. In their research, Kovtun et al. While the external signal is electric, the physically controlling mechanisms behind the accelerated hardening is the thermal energy. Nevertheless, the response of the alkali activated material to the electric trigger is depending on the activator used, through its influence on the resistivity of the concrete.
A similar principle has been followed by Zhang et al.
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The electric field only serves as a practical means to control the temperature in the cementitious material, depending on its resistivity. A more innovative application of an electrical field can be found in the papers of Goudjil et al. The applied electric signal triggers a response in the material, resulting in a reduced adhesion between the hardening concrete and the formwork panel.
The induced electro-osmotic effect is thus facilitating the formwork release once the concrete has sufficient strength to be self-supporting. In this way, the application of demoulding oils can be avoided. Inspired by this electrically controlled formwork removal technique, Choi et al.
In a first pilot test, they externally applied an electromagnetic field around steel pumping pipes in order to polarize the material near the pipe surface and improve the formation of the lubrication layer.
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Although the electromagnetic field applied by Choi et al. They merely relied on the response of the classical constituents present in the concrete. Although they mentioned the increased mobility of magnetized water and the results of the pilot test were positive, the fundamental physico-chemical mechanisms behind the success of this technique need further study and elucidation.
Understanding this in detail might open the door to the development of new materials that could be mixed-in, strengthening its response triggered by the polarization signal and potentially enabling to better control the response to an intended level. Another example of electric intervention is the technique of cathodic protection by means of applied current in view of protecting an existing structure from reinforcement corrosion [ 51 ].
This technique is becoming more and more popular in concrete practice, and is a nice illustration of currently available active control mechanisms. The fundamental principle of its functioning can be understood by considering a Pourbaix diagram, explaining passive and active states of reinforcing steel in concrete [ 52 ]. As an extension of electric signals, microwaves can also be mentioned in this overview. A dielectric material placed in a high frequency electric field will heat up due to internal friction, as the induced vibration of the dipolar molecules is hindered by molecular attraction forces.
As already reported by Xuequan et al. However, an additional effect seems to be the desiccation of free water prior to setting, resulting in decreased porosity. In other fields, functional materials get a lot of research attention. For a multitude of potential applications, controllable materials are developed, responding to specific trigger signals, and resulting in an aimed-for effect. In this section, an non-exhaustive overview is given of some applications, type of materials, type of signals and type of responses. Some specific attention is given to different options to control rheology.
The applications and control methods used in other fields can be inspiring in view of reaching active control of properties of concrete. A major field of research studying stimuli-responsive materials is given by drug delivery on demand [ 55 — 63 ].
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