It is commonly accepted that the geopolymers are potential solutions as an alternative to conventional hydraulic binders. Geopolymers are produced from no-carbon reactants unlike Portland cement and require relatively little energy to be developed. These are inorganic binders from the alkali activation of aluminosilicates. To make a geopolymer as viable alternative and industrially interesting, several technological hurdles must be overcome in particular, their casting and the chemical mechanisms involved at very early age. Previous studies on the mechanisms of this reaction of geopolymerisation show the existence of a three phase's mechanism (dissolution - reorganization - polymerization). Our study focused on the mechanisms involved in fresh behavior and during setting of model metakaolin based geopolymers. For this, we have developed a combined approach between the rheological measurements and chemical measurements (liquid NMR) to respond to the complexity of the local chemical heterogeneity during geopolymerisation. In the first two parts of the thesis, we are interested in understanding the development of mechanical properties from mixing to setting of geopolymers. During the measurement of the elastic modulus' evolution, we also observe three phases, the first increase of elastic modulus during the first few hundred seconds, a plateau characteristic of a latency period followed by a second increase of elastic modulus after several hours. As a first step, we are interested in the first increase of modulus. It was established that the origin of this modulus was the formation of a first gel with a Si / Al ratio <4.5 localized at the grain boundaries of metakaolin. In a second step, we focused on the last increase of the elastic modulus. The origin is the formation of a second gel; the chemical composition is that of the final product that is to say the geopolymer with a Si / Al ratio ~ 2.Finally, in the third part, we have identified the major differences between geopolymer and Portland cement from a rheological point of view. These materials behave as Newtonian fluids. The interactions between the particles are dominated by hydrodynamic effects, which are mainly controlled by the high viscosity of the alkaline silicate solution and not the contribution of direct contacts between the grains of metakaolin
