Measuring the surface cohesion of calcium silicate hydrate

Calcium silicate hydrate (C-S-H) is the main binding phase of Portland cement concrete. Though C-S-H is known to be assembled from nanoscale features, there is little experimental study on how C-S-H nano solids interact with each other at the interface, which may hold the key to explain its macroscale strength, creep, and shrinkage behaviour. This work attempts to experimentally quantify the interactions between C-S-H solid surfaces using atomic force microscopy (AFM). We took a new approach to measure the surface adhesion under different relative humidity (R.H.) and calculate the Hamaker constant using an algorithm that eliminates the influence of surface roughness. The effect of chemical composition (e.g. Ca/Si ratio) and RH on surface forces, e.g. the van der Waals and capillary force, were systematically explored and compared with molecular calculation results. Our work provides an insight into the nexus of C-S-H chemistry – adhesion force – bulk mechanical properties.