Simultaneous Measurement of Deformation and Temperature of High-Strength Concrete at very Early Age to Determine the Initial and the Finial Setting Time

[[abstract]]The interior shrinkage deformation and temperature change of high-strength concrete (HSC) at very early age, i.e., the first 24h from casting, and up to an age of 72h was investigated experimentally using optic fibre sensors (SOFO) and thermally sensitive resistors. The initial and the final setting times of HSC were also investigated. Results show that two turning points (Ⅰ and Ⅱ) on the development curve of deformation, both represent the onsets of the variation of rigidity in fresh HSC, can be recognized as the initial and the final setting times, which are evaluated around 4.5h to 5.7h and 9.0h to 11.8h, respectively. Also, the higher the fly-ash or silica fume replacement ratio, the longer the setting times. The setting times of HSC evaluated from the curve of temperature development are quite close to those measured from the deformation curve. In addition, the HSC setting times determined by penetration resistance method (ASTM C403) demonstrate unusually large values. This method is therefore not advised to be used to measure the setting times of HSC