This article presents a study on the creep properties of limestone calcined clay cement. A series of paste samples using limestone and calcined clays as replacement materials were tested under basic compressive creep. The ternary mixes showed a lower creep compliance than the plain cement references, even when using low reactivity clays or lower replacement fraction. A finite element model was used to back calculate the visco-elastic properties of the C-S-H matrix and C-S-H gel. Whereas the elastic properties of C-S-H were found to be similar between LC3 and plain cement, the viscous behavior of C-S-H gel appeared to be noticeably different for LC3. The higher viscosity of C-S-H gel in LC3 could be attributed to a different chemical composition, a filler effect from the clayey particles or a combination of both.