Fine-Grained Concrete with Nanodispersed Silica Additive

The effect of the modifying nanodispersed silica (NS) additive, obtained by the polycondensation method, on the properties of fine-grained concrete (FGC) is studied. It is revealed that the dependence of the NS-additive particle size on its age is extreme. The maximum number of particles of up to 100 nm in the additive is observed at the age of 10 days, and then their number decreases. However, it affects the FGC strength little even after 30 days of the additive storage. It is established that the NS-additive could be most effectively used with 0.23% of an active silica concentration and pH 4.1 in combination with S-3. At that, the porosity declines from 17.5 to 12.9% and the pore diameter diminishes from 3.171 to 0.689 μm. It leads to an increase in the compressive strength by 2 times and a decrease in water absorption by 1.6 times as compared to the control composition without additives. An increase in the frost resistance of the modified fine-grained concrete to F250 is recorded; it occurs due to a decrease in porosity at portlandite binding with amorphous silica additives into low-basic calcium hydrosilicates.

Properties of Composite Gypsum Binders Depending on Multicomponent Mineral Additives

This article considers the possibility of increasing the effectiveness of composite gypsum binders (CGB) by controlling the processes of structure formation as a result of using new types of multicomponent mineral additives that are significantly different from the traditionally used quartz raw materials:- waste of wet magnetic separation of ferrous quartzites (WMS waste,) of polymineral composition with quartzy of varying degrees of crystallinity, nanodispersed silica and chalk powder. We have studied the cause-effect relationship between the change in the ratio of binding and mineral additives of various compositions, which determines the conditions for the formation of technological and strength characteristics of the projected composite materials with specified performance properties. We have established the presence of regularities in the changes in the properties of CGB, the composition of the hardening products and the microstructure depending on the type and content of gypsum binders of β-and α-modifications, portland cement, multicomponent finely-dispersed mineral additives, the regularity consists in the binding of portlandite, which is released upon portland cement hydration, by the amorphous phase of earth siliconas a part ofnanodispersed powder and chalcedony variety of quartz waste of wet magnetic separation of ferruginous quartzites. This provides a reduction in the basicity of the solidifying system, the intensification of crystal formation, and the formation of newgrowths with a high content of tobormorite-low-basic calcium hydrosilicates that compact the microstructure of the hardening matrix and, as a result, increase the water resistance and stability. It is noted that this mechanism of hydration of CGB minimizes inner stresses and volume deformations, therefore the number of microcracks decreases, which leads to an increase in its efficiency in comparison with the traditionally used gypsum binder and that differs from the traditional portland cement by a fast strength generation.

Influence of Nanodispersed Silica on the Physical and Mechanical Properties of Refractory Ceramics

In this paper the contribution of heterocoagulation of silica sols on powder materials to the formation of nanostructured forms of silicon oxide is presented. To a greater extent heterocoagulation is more appeared on the advanced surfaces of refractory particles and clay, and to a lesser extent on the particles of alumina and silica oxide, the surfaces of which contained significantly fewer active centers. Silica sols have positive effect on drying and firing modes of ceramic materials. It was established that the application of silica sol as binder in the preparation of aluminum silicate ceramics allows to reduce the firing temperature to 150-200oC with a simultaneous increasing of strength characteristics.