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Advanced investigation of ion diffusion on cementitious materials by using X-ray radiography

Parastegari, Niloofar
This dissertation discusses the concept of the diffusion coefficient (Dᵢ꜀) and its role in understanding and improving concrete durability. It presents a series of innovative approaches and findings, collectively advancing the knowledge of Dᵢ꜀ in concrete. The first research aspect introduces CHIP (Checking Ion Penetration), a novel application of dental X-ray technology. It refines Dᵢ꜀ measurement in concrete by combining measurements from multiple angles and correcting for X-ray beam hardening, resulting in a 20% increase in accuracy (as indicated by R square) and a remarkable 63% reduction in variability. The second phase offers an expedited Dic testing method that reduces the testing period to under 8 hours of ponding. This approach, using CHIP in an accelerated diffusion test, demonstrates strong correlations (R square equal to 0.96) with conventional diffusion measurements, regardless of age and mix design, potentially simplifying the use of diffusion coefficients in concrete specifications and performance-based designs. The third research focuses on the long-term evolution of Dᵢ꜀. It extends the measurement period to examine the change in Dᵢ꜀ of 17 fly ashes at 20% and 40% replacement levels from 45 to 1000 days. By employing a simplified predictive model based on bulk CaO, SiO₂ , and total equivalent alkalis (Na₂ Oeq) of the fly ash, this work offers an efficient tool for assessing the long-term diffusion coefficient in various fly ash replacement scenarios.