Hydration and durability of fast hardening binders incorporating supplementary cementitious materials

The use of supplementary cementitious materials (SCMs) is widely considered the most promis-ing approach to reduce CO2 emissions relative to cement production. SCMs are not commonly present in binders used for special applications. On the other hand, due to their low reactivity at early age, cements incorporating SCMs such as Limestone calcined clay cement (LC3) exhibit low early age strength when compared to PC. This could restrict their field of applications and therefore solutions have to be found.This thesis focused on two main axes: The first one is to lower the CO2 footprint of ternary blends composed of Portland cement (PC), calcium aluminate cement (CAC) and calcium sulfate (Cs) using calcined clay as clinker substitute. The hydration of simple systems composed of PC with an increas-ing amount of CAC and Cs with and without calcined clay from 3 hours up to 90 days of hydration helped to understand and identify the contribution of each component. The results showed that in-creasing the CAC and Cs content in a PC system with and without calcined clay led to an increase of the ettringite content and a decrease of the portlandite content due to the portlandite consumption to form ettringite. The C3S hydration was not delayed in presence of CAC and Cs. However, the pres-ence of CAC, Cs and calcined clay led to slightly lower degree of hydration especially at later ages. The hydration and strength of a more realistic system "a fixing mortar formulation" with and without calcined clay was investigated. Overall, results showed that calcined clay can replace Portland cement by up to 20% with acceptable strength results. The second aspect on which this thesis focused was the influence of incorporating CAC and Cs as limestone substitute in LC3. The effect of the C/A molar ratio of the used CAC and its content were the main parameters investigated. The incorporation of 10% (CAC, Cs) improved the strength com-pared to LC3 at all ages. The massive ettringite formation during the first hours of hydration explained the early age strength improvement. Results showed that the C3S hydration was hindered when the C/A ratio of the CAC is equal to 1.7. The calculation of saturation indices indicated that a super satu-ration with respect to portlandite is likely needed to trigger the C3S hydration. The high late age strength in LC3-CAC blends was explained by a high volume occupied by hydrates in comparison with LC3 blends. In terms of durability, the resistance to chloride ion penetration was investigated through the mini-migration method. LC3-CAC blends showed a better chloride resistance than LC3, which is mainly explained by the porosity refinement compared to PC, and the decrease of the total porosity in comparison with LC3. On the other hand, the natural carbonation study showed that LC3-CAC blends have a higher carbonation rate when compared to PC. Contrary to PC, accelerated car-bonation of LC3 and LC3-CAC blends resulted in a decrease of the strength. However, the strength of carbonated LC3-CAC specimens is still at least similar to the non-carbonated PC specimen.