Ultra Fast Hydration Opening New Application Fields

 
This paper investigates the kinetics of hydration provided by Ultra Fast Calcium Aluminates Cements (UF-CAC) and how this technology is able to bring very fast hardening and early mechanical strength properties. A comparison is proposed between the behaviour of standard Calcium Aluminate Cement (CAC) and UFCAC of compositions close to C12A7. Both technologies are compared following early strength development on applicative test. Hydration kinetics are characterised by exothermic profiles and microcalorimetry. Solid and liquid phase analyses have been performed in order to propose hydration mechanisms. It is shown that for the same chemical composition, UF-CAC is much more rapid than CAC. 1800 daN tensile load values are obtained on pull off test only one minute after setting time for UF-CAC compared to others materials where only a few daN can be measured at the same time. The hydration path, i.e. evolution of pore solution composition over time, shows a clear difference between CAC and UF-CAC despite the same chemical composition of the solid. CAC hydration is usually characterised by an increase in ionic concentration up to about 20 Mmol/l followed by a nucleation period and ending with the massive precipitation of hydrates. UF-CAC hydration is characterised by a higher C/A ratio of the solution leading to an instantaneous and continuous precipitation of C2AH8 which keeps the ionic concentration at a low level of about 5 Mmol/l.