The effect of silica fume on the rheological properties of a cement–silica fume–high range water reducer–water mixture with ultra-low water binder ratio (CSHWM) was studied. The results indicate that the W/B ratio and silica fume content have different effects on the rheological parameters, including the yield stress, plastic viscosity, and hysteresis loop area. The shear-thickening influence of CSHWM decreased with the increased silica fume content. When the silica fume content increased from 0% to 35%, the mixture with W/B ratio of 0.19 and 0.23 changed from a dilatant fluid to a Newtonian fluid, and then to a pseudoplastic fluid. When the silica fume content was less than 15%, the yield stress was close to 0. With the increase of silica fume content, the yield stress increased rapidly. The plastic viscosity and hysteresis loop area decreased slightly with the addition of a small amount of silica fume, but increased significantly with the continuous increase of silica fume. Compared with the Bingham and modified Bingham models, the Herschel–Buckley model is more applicable for this CSHWM.
In addition to the water binder ratio, the production process, fiber, silica fume and admixture have a significant impact on the compressive strength of RPC. Several factors such as materials and production process affecting RPC compressive strength were studied by experiments. It exhibits that the reinforcement influence of steel fiber on RPC is affected by the strength of composite matrix. The higher the strength of composite matrix is, the better the effect of fiber reinforcement is. The compressive strength of RPC can be greatly improved by vacuum vibration forming. The water demand and activity of silica fume have significant influence on the compressive strength of RPC.
<p>Sintered NdFeB as a third-generation rare earth permanent magnet material, has been in rapid development since 1980’s due to its broad industrial applications and high electromagnetic performance. Sintered NdFeB metal materials can easily be oxidized, so future efforts to improve their antioxidative stability are required and the study of new manufacturing technology and new technology is necessary. At present, the traditional technology of sintering NdFeB is discussed, together with the processing technology of powder preparation, hydroforming and vacuum sintering. The article focuses on the milling and forming process, including the traditional ball mill to hydrogen explosion, air grinding powder, and dry magnetic field molding to wet pressure magnetic field oriented molding, to prevent the production process of oxidation, thereby enhancing the electromagnetic properties and their anti-corrosion antioxidant capacity. During the NdFeB sintering process, content of oxygen is regulated to control the phase change. As a result, electromagnetic properties of sintered NdFeB obtained a qualitative leap. </p>
The effect of polycarboxylate superplasticizer on the fluidity and rheology of cement - silica fume - water paste was investigated. The changes of dispersion degree, yield stress and plastic viscosity of paste with different superplasticizer content were analyzed. The results show that the rheological properties of paste with different superplasticizer content conform to Herschel-Bulkley model. The shear thinning of the slurry is manifested as a typical yielding pseudoplastic fluid characteristic. When the content of superplasticizer is less than 1.0%, the plastic viscosity and yield stress decrease and the fluidity increase with the increase of plasticizer content. When the content of superplasticizer is more than 1.0%, the yield stress decreases slightly and the plastic viscosity increases with the increase of plasticizer content. The fluidity decreases with the increase of yield stress, and there is a good correlation between them.
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