Geopolymers (GPs), classified as polysilicate-aluminates, represent inorganic polymers or chemically bonded ceramics with diverse applications determined by the Si:Al atomic ratio, including: fire-resistant components, sealants, mortar for reinforcing beams and oil well plugging. The exploration of GPs under varying temperature and/or pressure conditions gained momentum post-2001. The addition of chamotte into GP formulation only occurred in 2014, followed by subsequent investigations into the impact of adding carbon nanotubes and nanoclay a year later. The primary objective of this thesis was to assess the compressive strength of plain potassium-based GP cured at temperatures and pressures of up to 200 degrees C and 70 MPa, respectively. This evaluation included comparative analysis with microstructural characterizations such as porosimetry and thermogravimetry. Initially, the study evaluated the reaction mechanisms of different GP formulations and determined the effects of alkali leaching on strength evolution under diverse curing conditions (dry and saturated). The results identified the K-waterglass composition with SiO2/K2O=1.53 and H2O/K2O=8.69 as presenting rapid strength gain, low leachability, and was thus selected. Curing temperature significantly impacted on the final properties, demonstrating a notable 144% improvement in compressive strength at 50 degrees C, and an additional 37 percent improvement at 50 degrees C under 20 MPa, attributed to enhanced microstructural densification. The thesis also explored the effect of adding micrometric (chamotte) and nanometric (nano-metakaolin, nanoclay and carbon nanotubes) particles under extreme curing conditions (150 degrees C and 40 MPa). Preliminary results indicated satisfactory dispersion of carbon nanotubes using a simple, low-energy technique. Individual additions contributed to GP performance improvement, yet hybrid additions surpassed any separate addition results, yielding a formulation with enhanced reactivity. Under 150 degrees C curing, GP with hybrid additions exhibited a remarkable 350 percent improvement in mechanical properties compared to plain GP. Under 40 MPa pressure, the mechanical performance was minimally affected by hybrid additions, confirming their efficacy in achieving the desired properties for high-temperature and pressure applications, including pore refinement, increased flexural strength, and reduced porosity.