Differences in chemical and mineralogical properties of power generation waste result in variability of mechanical properties of solidified hydraulic composite mixtures. Conditions of curing: temperature and humidity also influence strongly mechanical properties of solidified hydraulic composite mixtures. The paper presents comparison of uniaxial compressive strength of composite mixtures prepared with use of selected power generation waste and cement, cured in water and air-conditioned environments. Composition and description of tested mixtures have been shown in Table 1. Compressive strength of mixtures type GPŻ after 28 days of cure time in air-conditioned environment (KK) range from 15 to 22 MPa (Fig.1) and from 8 to 15 MPa (Fig.2) in case of mixtures cured in water environment (W), relatively to amount of cement, which was in range from 5 to 20%. Compressive strength of mixtures type GP after 28 days of cure time in air-conditioned environment (KK) range from 0,8 to 14,5 MPa (Fig. 3) and from 1,4 to 10 MPa (Fig. 4) in case of mixtures cured in water environment (W), relatively to amount of cement, which was also in range from 5 to 20%. Ratios of Rc (28 days) obtained in analyzed environments for type GPŻ mixtures are from the range from 1,81 to 1,46, with amplitudes of their changes from 2,00 to 0,22 and decrease with amount of cement (Fig. 5). Average value of Rc (28 days) ratio obtained in analyzed environments for GP type mixtures with 10 to 20% addition of cement equals 1,56 and 0,59 with 5% cement addition respectively. Amplitude of Rc ratios differences in analyzed cure time for all GP type mixtures equals round 0,55 (Fig.6). Selective Rc ratios for considered material groups in each cure environment are not constant and depend on cure time in first place, and also on percentage of cement, especially in materials of type GPŻ. Ratios of Rc for GPŻ type materials with 10 to 20% addition of cement after 28 days cure time in air-conditioned environment range from 2,9 to 1,3 (Fig. 7) and from 2,6 to 1,7 in case of water environment (Fig. 8). Rc ratio for materials from compared material groups containing 5% of cement after 28 days cure time equals round 18 in case air-conditioned environment (Fig. 7) and round 6 in case of water environment (Fig. 8). Selective Rc ratios for considered material groups in each cure environment are not constant and depend in first place on type of waste used in mixture and cure time, and also on percentage of cement, especially in materials of type GPŻ.