# Low-Temperature Self-Healing Cement Mortar Enabled by Novel Composite Microcapsules: Performance, Mechanism, and Optimization

## TL;DR

A new type of self-healing cement mortar was developed to work effectively in cold environments by using composite microcapsules that enable crack healing and strength recovery.

## Contribution

The novel composite microcapsules with ethyl cellulose shell and dual-core content enable self-healing performance in low-temperature conditions.

## Key findings

- The optimal formulation achieved a crack surface healing ratio of up to 44.1% at −20 °C.
- Compressive strength recovery reached up to 6.0% under the same low-temperature conditions.
- The healing mechanism involves calcium carbonate, C–S–H gel, and anorthite within a polymerized epoxy network.

## Abstract

While self-healing concrete shows promise for infrastructure repair, its effectiveness is significantly compromised in low-temperature environments because of slowed reaction kinetics and the embrittlement of capsule shells. To address this limitation, novel composite microcapsules featuring an ethyl cellulose shell and a dual-core comprising expansive cement and epoxy resin were developed. These microcapsules were fabricated using a physical spheronization-coating method and subsequently incorporated into cement mortar. Response surface methodology was employed to identify the optimal system, which balances self-healing performance with the retention of mechanical properties: a microcapsule content of 3% (by mass of cement) and a particle size range of 1.4 to 1.7 mm. Under conditions of −20 °C, the optimal formulation achieved a crack surface healing ratio of up to 44.1% and a compressive strength recovery of up to 6.0%. Microstructural and spectroscopic analyses (SEM-EDS, XRD) revealed a synergistic healing mechanism. This mechanism involves the formation of calcium carbonate, C–S–H gel, and anorthite, all cohesively bonded within a polymerized epoxy network. This work establishes a functional material strategy for enabling autonomous crack repair in concrete structures subjected to cold climates. In such environments, even marginal strength recovery, when coupled with effective crack sealing, can significantly enhance structural durability.