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.

Experimental study on dynamic angle of repose formation: Effect of granular type and water content

“…We observed the avalanche phenomenon as a result of water bridge formation. Hamilton et al [13] and Herminghaus [14] found that cohesive nature of water bridge influenced single particles so that particles did not flow independently and caused avalanche phenomenon.…”

Selective Paste Intrusion: Integration of Reinforcement by WAAM — Concept and Overview of the Current Research

“…Several patents report dry water as a suitable rapid cooling method for fire extinguishment or a retardant for certain reactions due to the release of the adsorbed water [23 -25]. By mixing dry water with aggregate particles, large amounts of water can be stored in the particle bed whilst maintaining its initial flow properties [26]. Consequently, suitable bulk properties can be ensured for a water-storing bulk material applied in SPI.…”

“…Produced variants were differentiated by their mass fraction of water at wH2O: 80%, 87%, 90%, and 95%. The mass fractions were chosen in accordance with [26].…”

“…Dry water with insufficient quantities of hydrophobic fumed silica creates aggregate mixtures with inadequate bulk properties for SPI (i.e, diminished bulk flow properties and irregular aggregate particle bed structure). Additional information about dry water and its properties is available in [26].…”

Integrating Wire Arc Additive Manufacturing into Selective Paste Intrusion for Reinforced Concrete Elements: Effect of Temperature on the Mechanical Performance

“…Passive cooling strategies, such as aggregate functionalizing have already been investigated [12,13]. But also increasing the protruding distance between the welding point and the particle bed surface [12].…”