Testing and Specifying Electrochemical Properties of Expanded Shale, Clay and Slate Lightweight Aggregates

Electrochemical properties of earthen materials, including lightweight aggregates can be useful to assess the corrosivity and performance of metallic materials embedded within backfills. Electrical conductivity, the reciprocal of resistivity, relates to the transport of electrons during the corrosion process. Other chemical properties such as pH and ion contents interact with physical conditions like moisture content and gradation to influence the electrical conductivity. Sulfate and chloride contents are major performance measures in laboratory testing methods. These predictors are perceived as more accessible performance measures, but not necessarily more accurate, than direct assessment of corrosion like mass loss or instantaneous measures of corrosion potentials and corrosion using electrochemical measurement techniques. However, these measures do not address the full spectrum of material characteristics influencing corrosivity. This shortcoming is apparent for lightweight aggregates that exhibit different trends with respect to electrochemical properties compared to normal weight aggregates due to their characteristic porosity and moisture dynamics. Hence, application of ESCS lightweight aggregates requires modification of testing methods and specification of alternative thresholds for electrochemical properties, including electrical resistivity, pH, sulfate and chloride ion contents. This paper addresses such modifications using the outcomes of experimental investigations.