Aspects of Portland cement hydration studied using atomic force microscopy

Aspects of the mechanisms of hydration and microstructural evolution in Portland cement are still not fully understood. Atomic force microscopy (AFM) is in many ways a powerful tool for investigating changes in surface structure that accompany the hydration of Portland cement, especially because surfaces can be imaged under aqueous solutions at normal temperature, pressure and high magnification. We have investigated changes in the surface characteristics of sections of Portland cement clinker immersed initially in saturated calcium hydroxide solution which was then replaced by water, and in sucrose solution. In the case of the former, the observations are consistent with the early formation of a protective membrane and the subsequent growth of calcium silicate hydrate (CSH) structures by an osmotic process. The dissolution of the clinker in sucrose solution has also been directly observed. It is concluded that the use of AFM will help to resolve many questions relating to cement hydration.