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Embedding magnetic particles into cement paste produces a smart material in which the rheological properties of the resultant paste can be actively controlled through the use of magnetorheological (MR) principles. This research investigates the rheological behavior of cement-based MR pastes with and without air entrainment to gain a better understanding of the effects of air-entrained bubbles on MR cement pastes. Such information would be critical for the use of such MR pastes in three-dimensional (3-D) concrete printing applications. It is revealed that the incorporation of entrained air increases the MR response, and this effect is related to the bubble-bridge effect.
Keywords: air-entraining agent (AEA); magnetorheological (MR) paste; rheology; small-amplitude oscillatory shear (SAOS); smart material; storage modulus.
(ProQuest: ... denotes formulae omited.)
INTRODUCTION
Concrete is one of the primary construction materials. One of the great advantages of concrete is that it undergoes a fluid-solid transition, and thus, while it is in its fluid-like state, it can be cast into various configurations. However, one challenge with concrete is that conventional concrete construction demands significant labor for formwork and reinforcement positioning, especially when the design is unique. As such, cost increases for structures and buildings with unique configurations, which makes design professionals hesitant to create unique configurations (Bos et al. 2016).
With the advent of the digital era and the union between additive manufacturing (AM) and digital design, three-dimensional (3-D)-printcd concrete (3DPC) has emerged. Possible benefits of 3DPC include labor savings, reduced consumption of raw materials, reduced construction time, and increased integration of topological design optimization practices. However, 3DPC also faces some challenges and limitations, one of which is having consistent, robust, and proper control of the rheological behavior of the mixtures throughout the entire printing process. To address this primary challenge, a method was proposed to achieve "active control" of cementitious slurries through the use of a magnetorheological (MR) fluid (Nair 2013; Nair and Ferron 2014). Traditional MR fluids show a reversible and very fast transition from a liquid to a nearly solid state under the presence of external magnetic fields. Previous work has shown that embedding cement paste with micrometer-sized magnetic particles, such as carbonyl iron particles (CIPs), allows real-time control over stiffening and setting behavior by varying the magnitude of the magnetic field strength...