MORTAR EXPANSIONS DUE TO DELAYED ETTRINGITE FORMATION - EFFECTS OF CURING PERIOD AND TEMPERATURE

The expansion behavior of 55 portland cements, utilizing mortar prisms (40x40x160 mm), is reported for a range of initial elevated temperature cures followed by storage under water at 20 degrees C. The relationship between expansion and curing condition is complex: increasing expansiveness accompanies higher curing temperatures and a minimum curing temperature for expansion is found to lie between 65 degrees C and 70 degrees C; greatly extended periods of elevated temperature curing result in much reduced expansions, suggesting that a progressive neutralization of the chemical components critical for expansion may be taking place during periods at elevated temperatures. The chemical composition of a cement is an important factor determining expansion behavior. Linear correlation coefficients between expansions after curing at 100 degrees C for 3 hours and chemical compositions show a number of chemical parameters to be significant, including %MgO and %SO3.