Bulk magnetic susceptibility measurements for determination of fly ash presence in concrete

Reproducible measurements of magnetic susceptibility χm of laboratory and field extracted concrete core samples were achieved with simple instrumentation. There was a nearly linear relationship between χm and the mass of fly ash per unit volume, or its volume fraction. The magnetic response of a given FA was not significantly affected by the process of curing and subsequent evolution of the concrete over two years, or by carbonation of the concrete. Field extracted concrete cores exhibited a wide range of χm values. The group of specimens with the highest values of χm also had the lowest chloride ion diffusivity, consistent with the presence of admixed FA. Conversely, specimens with nil magnetic response included those from concrete with the highest chloride diffusivity. The magnetic measurements provided reasonable order-of-magnitude indications of FA presence in field extracted cores. However, precise determination of FA content from magnetic measurements of field cores does not appear feasible in the absence of additional information.