Investigation of Reactive Electrokinetic Processes for Permeability Reduction in Hardened Cement Paste

239 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002.This work examined the feasibility of transporting chemical precursors into hardened cement paste pores using an electric field and causing them to undergo a chemical reaction that results in blocking the pores and reducing permeability. The chemical precursors, silicate and aluminate solutions and sols, were tested with simulated pore fluid solutions to assess production of precipitates within pores. Electrokinetic pore blocking processes were modeled using micropore filters. Permeability tests were used to study the effect of these processes on hardened cement pastes of high water/cement ratio and of both high and low alkali contents. Significant reductions in coefficients of permeability were observed in model filter systems. Similar results were obtained for hardened cement paste. In each case, it was seen that treatment particles entered pore systems and reacted with pore fluid constituents to produce precipitates. The coefficients of permeability for each of these systems were reduced by at least one order of magnitude. It was observed that the system impedance provided an indication of the permeability-reduction effectiveness of a given process. A transport model was developed to determine the viability of a given treatment candidate. This model predicted the extent of penetration achievable by a treatment as a function of competing transport processes (hydraulic pressure flow, electroosmosis, and ionic conduction). Model predictions correlated well with observed cement paste microstructures and permeability measurements. In addition to conducting hydraulic permeability tests, impedance measurements were also used to predict the viability of a given treatment process. An analytical model was developed to correlate impedance measurements to permeability measurements. This model was based on laminar Poiseuille flow mechanics and the definition of ohmic resistivity as applied to a parallel tube flow system. It was found that this model worked well in predicting changes in system permeability as a function of the observed change in system resistivity. The findings of this study indicate that reactive electrophoretic reduction of permeability can be achieved in hardened cement paste in the presence of an opposing hydraulic flow and that the potential influence of a treatment candidate can be predicted with the use of these physical and analytical models.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD