Nondestructive detection and characterization of carbonation in concrete

Abstract

Exposure of concrete to the environment leads to changes in composition, microstructure, and properties; these effects often start from the surface of a concrete structure. A specific, widespread environmental effect is carbonation, where carbon dioxide penetrates the surface of concrete and reacts with calcium hydroxide that is a product of Portland cement hydration in concrete. Carbonation is of interest not only because it can lead to the initiation of reinforcement corrosion, but also carbon is increasingly used during curing to alter the surface properties of cement-based materials as a method to »sink» carbon in cement-based materials. Nonlinear Rayleigh surface wave measurements are performed on uncarbonated and carbonated concrete samples to assess any mechanical changes induced by carbonation, In order to minimize the effects of contact conditions, the generated signals are detected by a noncontact air-coupled transducer (100 kHz) at locations along the propagation axis. The nonlinearity parameter, β is used to quantitatively characterize the degree of carbonation. To more accurately analyze the data, corrections are made for the effects of attenuation and diffraction. A comparison between the carbonated and uncarbonated samples demonstrates that pores and micro-cracks are affected by the carbonation product and these significantly change the measured nonlinearity parameter. © 2014 AIP Publishing LLC.