Non-destructive non-invasive assessment of the development of alkali-silica reaction in concrete by spectral induced polarization: Evaluation of the complex electrical properties

Abstract

The distress caused by alkali-silica reaction (ASR) to concrete structures can occur long time after the reaction has been triggered. We propose to use spectral induced polarization (SIP) as a non-destructive method for early detection of ASR reaction before the damage is apparent. Our research deals with monitoring the difference between the electrical behaviour (phase lag, bulk resistivity, relaxation time, total chargeability) of non-reactive (NR) and reactive (RC) concrete samples affected by ASR. Laboratory measurements of complex resistivity were done in the frequency range 1.43 mHz-20 kHz. A Debye decomposition (DD) model was used to determine the DC bulk resistivity (ρ0), and the distribution of the chargeability as a function of the relaxation time. The total chargeability (Σm) and the mean relaxation time (τmean) were computed as DD parameters to characterize the ASR development. While ρ0 was strongly dependent on the electrical conductivity of the solution (water, NaOH) with a constant change with time, both concrete mixtures saturated with the same solution showed an increase ρ0 due to the development of the matrix skeleton over time. In this work, ρ0 did not play a significant role to characterize the ASR development. For the samples affected by ASR, a significant evolution of Σm and τmean was found compared to the non-affected mixtures (RC, NRC-H2O), specially over the low frequency range [1.48 mHz < f < 5.86 Hz]. The RC-NaOH samples displayed a strong linear correlation between normalized chargeabilty and imaginary conductivity. This observation could be associated with an increase in surface conductivity of the Stern layer at reactive grain surface or the evolution of specific surface area due to production of ASR silica gel, or both. Based on our conceptual electrochemical model of RTD presented in this work, an evolution of chargeability peak was observed at relatively long relaxation time τ>102 s that could be associated with the polarization of aggregates affected by ASR.