Dengwu Jiao

Magneto-rheological control enables real-time reversible regulation of fresh cementitious materials, yet sand typically restricts the mobility of magnetic particles (MPs). This study proposes a strategy to convert passive sand obstacles into active contributors in magneto-responsive mortars by anchoring the sand within MP structures. Mortars containing MPs of three sizes (D50 = 11, 20, and 95 μm, denoted as D11, D20, and D95) were systematically investigated under varying water-to-cement (w/c) ratios, sand-to-cement (s/c) ratios, and sand gradations. Results reveal that for D20 mortars at a w/c ratio of 0.45, increasing s/c ratio from 0.25 to 0.50 enhanced the yield stress response degree from 89.9% to 112.6% and penetration stress response intensity from 164.3% to 241.6%. At a w/c ratio of 0.45 and s/c ratio of 0.50, mortars with fine sand (≤ 0.16 mm) achieved nearly twice the penetration stress enhancement observed in mortars containing coarse sand (1.00-2.36 mm) after 20 minutes of magnetic treatment. SEM and X-CT observations provide microstructural evidence that fine sand can be incorporated into MP clusters, while the sand skeleton suppresses macroscopic MP migration. A theoretical model is further developed to correlate magnetic clamping force acting on individual sand particles with the magneto-induced structural build-up in mortars, successfully elucidating the underlying mechanisms and supporting the microstructural observations. Importantly, the compressive strength loss at 180 days after magnetic treatment remained below 2.5% relative to the non-magnetic field condition. This work challenges the conventional perception of sand in magneto-responsive mortars and offers a practical design strategy for active rheology control in mortar and even concrete scale.

This study investigates the influence of different dispersion methods of graphene nanoplatelets (GNPs) on the fluidity, mechanical, electrical, and microstructural properties of cement pastes with ultra-low water-to-binder (w/b) ratio of 0.18. Five dispersion strategies including ultrasonication (30 min and 60 min), mechanical stirring, and hybrid dispersion with silica fume (5% and 10%) were evaluated. Results reveal that extended ultrasonication for 60 min slightly reduced the initial fluidity but produced more stable time-dependent flow behavior due to the increased water adsorption on well-dispersed GNPs. Compared to the reference paste, the paste mixture after ultrasonication treatment for 60 min achieved the highest flexural and compressive strengths, as well as the most reduced electrical resistivity. This is possibly due to the fact that uniform GNP dispersion promotes crack bridging, nucleation of hydration products, and microstructural densification. Conversely, silica fume incorporation markedly improved early compressive strength through pozzolanic reactions and particle packing but significantly increased the electrical resistivity by disrupting conductive pathways. The findings highlight that dispersion efficiency is an important factor in maximizing the multifunctional potential of GNPs-containing cementitious composites, offering valuable insights for designing the next-generation high-performance self-sensing materials.

Magneto-rheology control, an advanced active rheology control (ARC) technique, is achieved by applying an external magnetic field to a cementitious mixture with responsive additives. It is a promising method to address the contradicting rheological requirements of cementitious materials during the placing process, enabling the development of smart and reliable concrete structures. This article reviews recent advances in magneto-rheology control for cementitious materials. The fundamental principles of magnetic particle movement and cluster formation in cementitious suspensions are first examined. Afterwards, the typical magneto-rheological responses and the key factors influencing the responsive behaviors are discussed. Finally, the potential applications and challenges of this technology in modern construction practices, including smart casting process, 3D/4D concrete printing, and the development of sustainable and multifunctional concrete, are provided.