Mechano-chemical interface processes with application to rock weathering

Abstract

The object of this thesis is to study the coupling of chemical and physical processes during rock weathering. Stresses which are produced due to chemical reactions can lead to fracture propagation which in turn increases the transport of reactants and the reactive surface area, and this coupling can therefore control overall rate of weathering. It is shown that weathering induced expansion can drive a hierarchical fracture process where originally intact rock is broken into progressively smaller blocks. Studies are also made on the micrometer scale in order to gain a more fundamental understanding both of fracture propagation and reaction induced stresses. It was found experimentally that the local chemistry has a profound effect on the velocity of fracture propagation in single crystals of calcite when stresses are applied slowly. This is related to the interaction between the mineral surface and water. Experiments on the so-called force of crystallisation showed that the process in which a crystal growing from a supersaturated solution can push on a neighbouring wall is more complex than previously assumed. This has implications for the understanding of how stresses evolve when crystals grow in a porous material.