title: On the Relation of Setting and Early-Age Strength Development to Porosity and Hydration in Cement-Based Materials.
abstract: Previous research has demonstrated a linear relationship between compressive strength (mortar cubes and concrete cylinders) and cumulative heat release normalized per unit volume of (mixing) water for a wide variety of cement-based mixtures at ages of 1 d and beyond. This paper utilizes concurrent ultrasonic reflection and calorimetry measurements to further explore this relationship from the time of specimen casting to 3 d. The ultrasonic measurements permit a continuous evaluation of thickening, setting, and strength development during this time period for comparison with the ongoing chemical reactions, as characterized by isothermal calorimetry measurements. Initially, the ultrasonic strength-heat release relation depends strongly on water-to-cement ratio, as well as admixture additions, with no universal behavior. Still, each individual strength-heat release curve is consistent with a percolation-based view of the cement setting process. However, beyond about 8 h for the systems investigated in the present study, the various strength-heat release curves merge towards a single relationship that broadly characterizes the development of strength as a function of heat released (fractional space filled), demonstrating that mortar and/or concrete strength at early ages can be effectively monitored using either ultrasonic or calorimetry measurements on small paste or mortar specimens.
authors.affiliation: Sika Technology AG, Tüffenwies 16, 8048 Zürich SWITZERLAND, lootens.didier@ch.sika.com.
authors.forename: Didier
authors.initials: D
authors.lastname: Lootens
authors.affiliation: Engineering Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8615, Gaithersburg, MD 20899-8615, , dale.bentz@nist.gov.
authors.forename: Dale P
authors.initials: DP
authors.lastname: Bentz
keywords: Calorimetry; hydration; percolation; porosity; setting; strength; ultrasonic reflection