The Effect of Water, Nanoparticulate Silica and Dry Water on the Flow Properties of Cohesionless Sand

Abstract

Cement hydration within particle bed concrete 3D printing processes can be benefited by storing water in the otherwise dry aggregate bulk material. Additional water also has the advantage of acting as a source of passive cooling. However, even small amounts of liquid lead to detrimental effects on bulk properties, such as the flowability. For that reason, this study proposes implementing dry water (DW) in order to store large amounts of water in a bulk material of non-absorbent, coarse sand whilst maintaining its initial bulk properties. DW is essentially created by mixing water and hydrophobic fumed silica in a high shear process, leading to water droplets surrounded by a protective silica shell. Herein, several DW variants, distinguished by their deionised water to hydrophobic silica ratio, were mixed with non-absorbent, coarse sand particles. In addition, mixtures were produced to contain a specific overall water content of up to wH2O = 5% within the bulk material. It was shown that dry water can be used to incorporate large amounts of water into a granular bulk material and simultaneously preserve flow properties. The decisive factor is the proportion of hydrophobic silica for a given water content as the DW capsules may otherwise not endure mechanical stress during mixing. However, even minimal quantities of silica can prevent liquid capillary bridges from forming and, thus, inhibit bulk property degradation.