Designing Sprayable EGC from Constructability to Mechanical Performance (2025-07)¶

The characteristics of engineered geopolymer composite (EGC), e.g. high early strength and exceptional ductility, have made it a promising material for construction, structural strengthening and repair. If EGC can be sprayed in the same way as shotcrete or engineered cementitious composite (ECC), and given its fast-setting behavior, construction efficiency can be further enhanced which is useful in scenarios with urgent demand. However, the high viscosity and weak workability retention of EGC make it difficult to apply through spray technology. To achieve this, the tailored constructability and mechanical properties of EGC must be studied to ensure both construction efficiency and quality control. In this study, by carefully considering construction demands, spray technology and workability of EGC, the design strategies to optimize equipment, balance workability range and control workability retention were developed. The constructability of sprayable EGC was optimized through extensive laboratory iterations. The vertical build-up thickness of sprayed EGC was up to 6 cm with excellent placement performance. Subsequently, the compressive, tensile and flexural properties of sprayed EGC were analyzed. Results revealed that the compressive strength and failure mode of sprayed EGC were direction-dependent. While exhibiting lower compressive strength compared to cast-in-situ counterparts, sprayed EGC demonstrated superior strain-hardening, flexural strength and ductility. Furthermore, sufficient bond strength between sprayed EGC and existing concrete validates its effectiveness for structural repair and strengthening.