Investigation by atomic force microscopy of forces at the origin of cementcohesion

In cement paste, the cohesion results of the interactions between calcium s ilicate hydrate (CSH) surfaces in an interstitial ionic solution. (N, V, T) Monte Carlo simulations show that the interactions are due to the ion corr elation forces influenced by the surface charge density, the ionic concentr ation and the ion valence. This paper deals with the direct measurement in solutions by atomic force microscopy (AFM) of the forces and the interactio n ranges between a probe and an atomically smooth substrate covered by CSH nanoparticles. Different electrolytic solutions (Ca(OH)(2), CaCl2. NaCl. Na OH) have been used in order to determine influent parameters permitting to identify the nature of acting forces. Investigations have been rendered pos sible by selecting appropriate experimental setup and solutions. The select ed probe and substrate on which CSH nanoparticles have previously grown are neutral regarding the reactivity during experiments permitting the exchang e of solutions. Results show that a force originates from electrostatic nat ure and differs from Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Agreem ent is found between experiments and (N,V,T) Monte Carlo simulations of ion ic correlation forces. These forces are at the origin of the cohesion of ce ment paste. (C) 2001 Elsevier Science B.V. All rights reserved.