Open Access

Mechanically triggered core-shell materials for sprayed mortar: design, preparation, and performance

Zhitian Xie¹, Yanzhen Xiao², Xiaokai Niu¹, Wei Song¹, Xinru Sun², Xiao Liu^2,*, Shicheng Liu¹, Yanxi Li², Ziming Wang², Suping Cui²
1Beijing Key Laboratory of Underground Engineering Construction Prediction & Precaution, Beijing Municipal Engineering Research Institute, Beijing, 100037, China
2State Key Laboratory of Materials Low-Carbon Recycling, College of Materials Science and Engineering, Beijing University of Technology, Beijing, 100124, China
* Corresponding Author: Xiao Liu. Email:

ZKG International https://doi.org/10.32604/zkg.2026.075210

Received 27 October 2025; Accepted 29 December 2025; Published online 14 January 2026

Abstract

Sprayed concrete is widely used in tunnel support and structural repair, but the direct addition of conventional viscosity-modifying agents often causes pipeline blockage and competitive adsorption with polycarboxylate superplasticizers, which leads to poor workability and high rebound rates. To overcome these practical problems, this study designs a mechanically triggered core–shell HPMC-40000 thickening agent (HPMC @ SiO₂-TA) that can increase the instantaneous viscosity of mortar only when the material impacts the sprayed surface. The improvement effect of HPMC @ SiO₂-TA on the performance of sprayed mortar was evaluated by apparent viscosity property, mechanical properties, bounce rate tests. The experimental results indicated that HPMC @ SiO₂-TA exhibited thixotropic characteristics under external force and synergistic rapid hardening effects. When the dosage of HPMC @ SiO₂-TA was 0.05%, the 2-h bonding strength reached 0.053 MPa, which was 130.43% higher than that of the blank group. When the dosage of HPMC @ SiO₂-TA was 0.07%, the rebound rate of the released core material after spraying could be reduced to 7.95%, which was 35.15% lower than that of the control group. This study aims to provide a new material that mitigates the increase in viscosity and loss of elasticity in sprayed mortar, thereby effectively lowering the rebound rate of sprayed concrete mortar. These results demonstrate that the mechanically triggered HPMC @ SiO₂-TA is an effective thickening agent for low-rebound sprayed mortar and provide a promising strategy for designing smart admixtures for shotcrete applications.

---

Keywords

Core-shell material; mechanical trigger; cohesiveness; sprayed mortar; rebound rate

---