Formation of a Protective Layer During the Hydration of Cement

Abstract

The mechanism for the slow rate of reaction between portland cement and water during the early stage is not well understood, but it probably is controlled by either the rate that the reactants diffuse through a barrier that surrounds the unreacted cement grains or by the rate that nuclei of the stable product form and grow or by both rates. New evidence using environmental scanning electron microscopy is presented about the structure of a layer that forms around the particles of cement. Preliminary observations that relate mixing to the structure of the layer are also presented. [

Rheology of Fresh Cement and Concrete

“…the breakdown of skin linkage is irreversible. This model is consistent with both the instantaneous formation of a protective layer on cement [15], and the notion of links or junctions between particles [10,13]. …”

“…A microstructural model for breakdown [14] was followed by experimental confirmation [15] and an eventual model for the yield stress of suspensions, including cement pastes [16].…”

“…Tricalcium silicate reacts over a few days and dicalcium silicate reacts slowly (over several months) and both contribute to strength development. The hydration of cement proceeds in four stages [39,40]: (i) An initial rapid reaction between the anhydrous minerals and water, dissolving calcium and hydroxyl ions from the surface and leading to the formation of a gelatinous, poorly crystalline skin over the particles, which probably consists of mixed calcium silicate hydrate and calcium sulfoaluminate, and which is visible within a few seconds and fully formed in a few minutes [15,41];…”

The role of the environmental scanning electron microscope in the investigation of cement‐based materials

“…A similar layer which developed within 30 min was also observed in C 3 S by Bergstrom and Jennings (1992). Further research into this topic showed that the layer forming on the surface of the cement grains was thicker and more continuous than that forming on the C 3 S particles (Sujata and Jennings 1992). More recently, Meredith et al (1995) have shown that, in portland cement, an irregular and discontinuous layer appears on the C 3 S particles as early as 1 min after hydration, form-…”

New approach to assess build-up of cement-based suspensions

“…rigidity) on the degree of hydration may be related to the precipitation of hydration products, such as CSH at the pseudo-contact points between particles [8,41,42]. Indeed, during cement hydration, calcium and hydroxyl ions dissolve from the anhydrous cement and lead to the formation of a gelatinous, poorly crystalline skin over the particles [43,44]. The precipitated CSH contributes in turning the soft colloidal interactions to a more rigid ones [9,25].…”