Utilising crumb rubber from waste tyres to replace silica sand in engineered geopolymer composites (EGC) can reduce the environmental impact caused by landfilling and burning the tyres as well as that induced by exhausting the natural resources. This paper presents a systematic study on the effect of partially replacing silica sand with crumb rubber (10–40 %) on the engineering properties of EGC, with special focus on deflection-hardening behaviour. Results indicate that the workability, density, ultrasonic pulse velocity, drying shrinkage resistance, and compressive and flexural strengths of EGC drop with the increasing crumb rubber content. Regardless of crumb rubber content, all studied EGC mixes exhibit pronounced deflection-hardening and multiple cracking characteristics. Replacing 10 % of silica sand with crumb rubber can lead to acceptable compressive and flexural strengths of EGC. The crack width of EGC containing crumb rubber after flexural loading ranges from around 39 µm to 68 µm, which is lower than that of EGC with silica sand only. The presence of crumb rubber can lead to more PVA fibres pulled out and the rubber at the cracking interface may contribute to restraining the crack growth, which is conducive to improving the flexural toughness of EGC and reducing crack width.