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Chemical Shrinkage

Chemical shrinkage, the volume reduction associated with the reaction between cement and water in hydrating cement paste, was assessed using the method described by Geiker,29 which is similar to that recently used by Tazawa et al.30 A known mass of cement paste (typically 10 g) was placed in the bottom of a small glass jar, with a diameter of 2.5 cm and a height of ~6 cm. After the cement paste was covered with ~1 mL of water, the remainder of the jar was filled with a hydraulic oil. The jar was then sealed with a rubber stopper encasing a pipette graduated in 0.01 mL increments. The jar was then placed in a constant-temperature water bath (T = 25ºC), and the oil level within the pipette was measured to the nearest 0.0025 mL over time, typically for a period of 28 d. A control sample using only cement powder and oil (no water) was used to correct for minor room-temperature fluctuations. By normalizing the change in volume by the mass of cement in the sample, the chemical shrinkage per gram of initial cement (mL/(g of cement)) could be determined. Based on the estimated uncertainty of the mass (0.02 g) and volume (0.00072 mL) measurements, the maximum expanded uncertainty 27 in the calculated chemical shrinkage was estimated to be 0.001 mL/(g of cement), assuming a coverage factor27 of 2. In all cases, two specimens were run for each w/c ratio and cement, with the average result being reported.