Materials

The two cements selected for this study were issued as Cements 115 and 116 by the ASTM-sponsored Cement and Concrete Reference Laboratory (CCRL), located at the National Institute of Standards and Technology (NIST), as part of its proficiency sample program in January 1995. A sufficient supply of these cements stored in a double layer of plastic in cardboard boxes was obtained for the present studies. The chemical compositions of the two cements, as determined in the proficiency sample program, ²⁰ are given in Table 1 . Other results available in the CCRL summary report, ²⁰ obtained using the indicated standard test methods," include the initial and final times of set via the Vicat (ASTM C191*) and Gillmore (ASTM C266 *) needle methods, measured finenesses (ASTM C204* and C 115*), mortar cube compressive strengths (ASTM C109*), and heats of hydration at 7 and 28 d of age measured via the heat of solution method (ASTM C186*). The particle-size distributions for Cements 115 and 116 were measured at the University of Illinois using an X-ray sedigraph technique. The cumulative curves were discretized (binned) into 2 µm increments, resulting in the discrete distributions given in Table II, which were then used in the three-dimensional cement hydration model.

For the nonevaporable water content and chemical shrinkage determinations, cement pastes were prepared with w/c ratios of 0.30, 0.40, and 0.45. The cement powder and necessary mass of water were mixed together by kneading by hand in a sealed plastic bag for 2-3 min. For the studies of 15º and 35º C, a walk-in environmental chamber was used so that the mixing could be performed at the desired temperature, after the starting materials had equilibrated in the chamber overnight. After they were mixed, the samples were removed and stored in capped plastic vials and small glass jars for the nonevaporable water content and chemical shrinkage measurements, respectively. For the chemical shrinkage studies and all saturated hydration experiments, after the cement paste sample (typically 10-15 g) was placed in its container, ~1 mL of water was added on top )f the cement paste to maintain saturated conditions throughout the experiment. For the sealed hydration experiments, the plastic vials were capped with no addition of water. For the nonevaporable water content measurement, the samples were stored at the temperature of interest until being evaluated. Evaluations of nonevaporable water content usually were made after the following times of hydration: 8 h and 1, 2, 3, 7, 14, 28, 56, and 90 d.

*"Time of Setting of Hydraulic Cement by Vicat Needle," ASTM Designation C 191; "Calcium Sulfate in Hydrate Portland Cement Mortar," ASTM Designation C 266; "Fineness of Portland Cement by Air Permeability Apparatus," ASTM Designation C 204; "Fineness of Portland Cement by the Turbidimeter," ASTM Designation C 115; "Compressive Strength of Hydraulic Cement Mortars," ASTM Designation C 109; and "Heat of Hydration of Hydraulic Cement," ASTM Designation C 186. 1993 Book of ASTM Standards, Vol. 04.01. American Society for Testing and Materials, Philadelphia, PA.