Physical and Mechanical Response of the Cementation of Aluminosilicate Seals

Stanford University, Stanford CA

Investigators

Abstract

For decades, geophysicists studying faults and earthquakes have focused on how rocks weaken or break in response to forces within the Earth. Another question we need to ask is, how do rocks restrengthen, for instance, between earthquakes? One process that makes rocks stronger is cementation. That is, groundwater passing through small pores and cracks in rocks may deposit minerals which act like glue or cement, strengthening the rock. Dr. Vanorio and her group will conduct laboratory studies to investigate in detail just how cements form, and how much they strengthen rocks under a variety of thermal and chemical conditions. In addition to helping scientists understand how faulted rocks rebuild their strength between earthquakes, Dr. Vanorio's research can also help engineers design materials that can maintain their strength under harsh chemical conditions over long periods of time. Because cementation fills small voids in rock and makes them more impervious to fluid flow, her research will also help engineers to design geothermal systems or select suitable sealed reservoirs for storing greenhouse gases. Active faults of the Earth's crust function as large-scale kiln factories — they mechanically pulverize aluminosilicate rocks to the micron or finer scale, and internally channel heat that treats and primes the fault gouge for fluid-mediated chemical reactions, eventually leading to cementation. Geophysical data shows that repeated failures and strength recovery of the Earth’s crust — a process known as fault healing, is a relatively fast process. In this project, the PI intends to advance knowledge on the natural cementation (i.e., frictional healing) of geological seals by studying Earth’s chemical synthesis of aluminosilicates exposed to two natural processes: CO2-induced carbonation and alkaline hydrothermal treatment. To understand how the physical and mechanical properties of rock materials measured at the macro scale connect to the underlying structure, the PI plans to study the micro- and nano-scale structures of the formed cementitious phases and how they influence strength and mode of failure as well as the acoustic signature of the loss of seal integrity (crack propagation and fracturing). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.