Measuring early-age shrinkage of concrete incorporating shrinkage reducing admixtures using distributed fiber optic sensors

Hydration reactions of cement are exothermic and cause volume changes in concrete, resulting in early-age temperature and strain changes, which can result in concrete cracks and reduced mechanical strength and durability. This paper proposes to use distributed fiber optic sensors with fine gage pitch (0.65 mm) for measuring spatiotemporal distributions of early-age temperature and shrinkage of concrete incorporating shrinkage reducing admixtures. The development of bond between fiber optic sensor and concrete matrix for reliable strain transfer was quantified via pull-out tests to guide appropriate use of fiber optic sensors for measuring early-age shrinkage. The combined effect of temperature and shrinkage on strains in concrete was quantified to enable accurate interpretation of measurements. The results showed that distributed fiber optic sensors provided reliable measurements after concrete was cast for 12 hours. Compensating thermal effects enabled accurate measurements of shrinkage with a high coefficient of correlation (R² > 0.99).