Phosphonates

The ability of phosphonates to retard cement setting is attributed to the lengthening of the induction period, without slowing down the time it takes for setting to occur (once the acceleratory period has begun). The mechanism by which phosphonates inhibit cement hydration consists of two steps. First dissolution, whereby calcium is extracted from the surface of the cement grains exposing the aluminum rich surface to enhanced (catalyzes) hydration and ettringite formation. Second, precipitation wherby the Ca-phosphonate material binds to the surface of the cement grains, inhibiting further hydration by acting as a diffusion barrier to water as well as a nucleation inhibitor. Bisley supplies a range of phosphonates taliored for specific applications.