Chloride transport in fly ash and glass powder modified concretes - Influence of test methods on microstructure

This paper discusses the influence of rapid chloride transport test methods on the microstructure and the measured chloride penetration resistance of concretes containing fly ash or fine glass powder as partial cement replacement materials. Rapid chloride permeability (RCP), non-steady-state migration (NSSM), and steady state conduction (SSC) tests are performed on plain and modified concretes. The glass powder modified concretes demonstrate similar or lower RCP values as compared to the fly ash modified concretes of the same cement replacement level whereas the steady state conductivities are lower for the fly ash modified mixtures. The NSSM coefficients are lower for the fly ash modified concretes even when the initial conductivities are similar to those of plain or glass powder modified concretes. Chloride binding under the conditions of NSSM test, that influence the microstructure and the transport parameter, is quantified using thermal analysis and XRD patterns as well as an electrical circuit model for the impedance response. The resistance of connected pores (R_c) extracted from the model adequately captures the changes in microstructure with time and with chloride transport. The changes in R_c between the start and finish of the NSSM test also indicate microstructural alteration in fly ash modified concretes.