Potential and challenges in long-term monitoring of concrete carbonation using embedded-type optical sensors

This study explores the long-term viability of embedded optical sensors designed for nondestructive monitoring of carbonation and pH levels in concrete structures. The sensors, featuring a reactor with a phenolphthalein solution and optical fibers, were embedded at various depths within mortar specimens and monitored over 250 days under different curing, drying, and carbonation conditions. Key challenges were identified, including the fragility of the dialysis membrane and optical fibers during concrete pouring, as well as the rapid drying of the detection solution, which compromised sensor longevity. Additionally, phenolphthalein's color change behavior at high pH levels (>12.5) posed a limitation. Proposed improvements include using a gel-based indicator to reduce drying, enhancing physical protection for the sensor components, and exploring alternative pH indicators like thymolphthalein. These modifications aim to enhance the sensor's durability and reliability for long-term monitoring of carbonation and pH in concrete.