# Accretion Dynamics on Wet Granular Materials

## TL;DR

This study investigates the growth dynamics of wet granular aggregates, revealing how capillary forces and liquid flow influence accretion, with a proposed model explaining the transition between viscous and capture regimes.

## Contribution

It provides the first detailed experimental analysis of accretion dynamics on wet granular materials and introduces a model linking growth regimes to hydrostatic depression.

## Key findings

- Growth is controlled by liquid fraction at the surface.
- Two regimes identified: viscous and capture.
- Model successfully explains the transition between regimes.

## Abstract

Wet granular aggregates are common precursors of construction materials, food, and health care products. The physical mechanisms involved in the mixing of dry grains with a wet substrate are not well understood and difficult to control. Here, we study experimentally the accretion of dry grains on a wet granular substrate by measuring the growth dynamics of the wet aggregate. We show that this aggregate is fully saturated and its cohesion is ensured by the capillary depression at the air-liquid interface. The growth dynamics is controlled by the liquid fraction at the surface of the aggregate and exhibits two regimes. In the viscous regime, the growth dynamics is limited by the capillary-driven flow of liquid through the granular packing to the surface of the aggregate. In the capture regime, the capture probability depends on the availability of the liquid at the saturated interface, which is controlled by the hydrostatic depression in the material. We propose a model that rationalizes our observations and captures both dynamics based on the evolution of the capture probability with the hydrostatic depression.