•The pozzolanic reaction of CBP contributes to the compressive strength of mortars.•Hydration products of blended pastes contain CH, C-S-H, C-A-H and C-A-S-H gels.•The pozzolanic reaction of CBP mainly occurs between 60 days to 90 days. Recycled clay brick powder (CBP) from waste clay bricks was utilized as a supplementary cementitious material to partially replace cement to prepare cement pastes or mortars. The compressive strength, hydration products and microstructure of these blended samples under different curing time were investigated to explore the pozzolanic reaction of CBP. The results showed that the compressive strength of mortars contained CBP decreased gradually with the replacement level of CBP increasing at early age. However, the compressive strength of blended mortars developed gradually at later curing time and the mortar contained 20% achieved the highest compressive strength of 62.2 MPa at 90 days. The XRD results demonstrated that the addition of CBP resulted in the formation of C-A-H gel in blended pastes after 28 days. SEM pictures also found that the microstructure of blended pastes became more compact with curing time increasing, and SEM-EDS demonstrated that C-A-S-H gel was produced in blended pastes. Finally, it could be concluded that C-A-H and C-A-S-H gel were produced due to the pozzolanic reaction of CBP and the microstructure of specimens with CBP became more compact, which lead to compressive strength of blended specimens increasing gradually.