Preparation and tests for workability, compressive and bond strength of ultra-fine slag based geopolymer as concrete repairing agent

•Prepared ultra-fine blast furnace slag based geopolymer for use as concrete repairing agent.•Workability, compressive and bond strength tests are conducted.•1day strength of geopolymer concrete is about 60% of 28days strength.•Addition of flyash and superplasticizer at low dosage level shows satisfactory results.•Bond of geopolymer concrete with rebar and old concrete shows promising results. In modern era, there is a need to develop sustainable concrete repairing material. This study aimed to develop ultra-fine blast furnace slag based geopolymer as concrete repairing agent. Sodium hydroxide activated geopolymer concrete mixes with various admixtures were prepared and tested to study fresh and hardened state properties including bond strength. The 1day strength of ultra-fine blast furnace slag based geopolymer concrete was found to be about 60% of that at 28days. Addition of flyash up to certain quantity level contributed towards achieving satisfactory workability, compressive and bond strength of the geopolymer concrete. Similar improvement in fresh and hardened state properties was also observed due to addition of superplasticizer at low dosage level. High alkali activator concentration led to loss of workability and strength of the geopolymer concrete.