Abstract
Active rheology control, by means of pre-adding responsive additives and applying a trigger signal, is a potential approach to meet the contradicting requirements of concrete properties in different casting processes. In the present study, the possibilities of fly ash as responsive additive in magneto-rheology control of cementitious materials are examined from the viewpoint of early structural build-up of cement paste. Four different fly ashes with various particle sizes and magnetic properties are utilized. The magnetic properties of fly ash, characterized by saturation magnetization and magnetic fraction, are determined. Results reveal that the cement pastes containing fly ash exhibit apparent rheological response to an external magnetic field. The degree of the response depends on the magnetic properties and physical characteristics of the incorporated fly ash. Under the same volumetric replacement, the saturation magnetization of original fly ash is a useful parameter to describe the magneto-rheological effect of fly ash incorporated cement pastes. In comparison with the magneto-rheological response of cement paste with nano-Fe3O4 particles, the fly ash incorporated cement paste shows a longer period of dominating liquid-like properties. It is concluded that fly ash can be used as a responsive additive to improve the rheology of cement paste by applying magnetic field.
Highlights
Active rheology control is a ground-breaking approach to satisfy the contradicting requirements of rheological properties during the pumping and casting process for the same concrete mixture [1,2,3]
As magnetic fly ash exhibits a response to an external magnetic field, it could be used as a potential responsive additive in the concept of active rheology control of cementitious materials
The remnant magnetization, which is the magnetization left behind in a material after removal of the magnetic field, and the coercivity defined as the ability of a material withstanding a magnetic field without becoming demagnetized are recorded
Summary
Active rheology control is a ground-breaking approach to satisfy the contradicting requirements of rheological properties during the pumping and casting process for the same concrete mixture [1,2,3]. Due to the high costs, the extensive usage of ferromagnetic particles in engineering applications of cementitious materials is probably not the first option, especially for mortar and concrete In this case, traditional available mineral additives or waste materials with magnetic properties might provide better alternatives to achieve the magneto-rheology control of cementitious materials. The magnetic properties of fly ash have attracted some attention in cement and concrete materials. As magnetic fly ash exhibits a response to an external magnetic field, it could be used as a potential responsive additive in the concept of active rheology control of cementitious materials. The effect of external magnetic field on the early structural evolution of cement pastes with fly ash is investigated by using small amplitude oscillatory shear (SAOS) technique. Note that the origins of magnetic properties of fly ash, which have been clearly investigated by many researchers [20,21,22,24,30], are beyond the scope of this study
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