Investigating the Influence of Shell Material and Size of Capsules and Beads on Mortar Properties

Abstract

Durability is a key property of concrete, ensuring long‐term structural integrity and resistance to environmental exposure. A promising strategy to enhance durability is the incorporation of functionalized capsules that either enable self‐healing or reduce the ingress of harmful agents. As such capsules may remain dormant in the cementitious matrix over extended periods, they must not compromise workability or mechanical performance.

This study investigates the influence of particle size and shell material on fresh and hardened mortar properties using spherical single‐material particles and alginate‐based oil‐filled capsules as model systems. Foamed glass beads, polystyrene beads, and paraffin wax particles were incorporated into a reference mortar (w/c = 0.5) at constant volume fractions. Mechanical performance was evaluated by compressive and flexural strength tests, while workability was assessed using flow table tests. Particle distribution and particle–matrix interaction were analysed using optical microscopy.

Results indicate that particle dosages should generally not exceed 5 vol.%, with larger particles exerting a stronger influence on mechanical strength. Rougher particle surfaces exhibited improved bonding with the cement matrix. The findings provide a basis for the safe integration of encapsulated admixtures aimed at improving concrete durability.