The article analyses the peculiarities of the combined effect on hydration process of the following pozzolanic additives: metakaolin waste (MW), material generated in the manufacture of expanded glass granules (GEG) and fluidized bed cracking catalyst waste (FCCW), as well as melamine-based superplasticizer (SP). Mixes with and without GEG containing two types of waste were tested. Peculiarities of hydration process were evaluated from the results of calorimetry, SEM and mechanical properties tests. The effect of pozzolanic additives and SP was analysed according to strength activity index (SAI). Test results revealed that synergistic effect of MW and FCCW was significant and practically relevant. These pozzolanic additives have a different effect on hydration process, yet when both waste materials are used together, it is possible to control the progress of hydration process. Besides, specimens with GEG and additive of both waste materials demonstrated the highest SAI index. The results of calorimetry tests of cement paste and plaster modified with plasticizer were different. Active metakaolin particles present on GEG surface significantly slow down the hydration process.