ABSTRACT

To explain the above mentioned phenomenon, the following test was carried out. Approximately 550 cm3

of mixing water of mixtures P, U30 and U50, was poured on the pan in the laboratory at temperature of 20 ± 1◦C and relative humidity of 60 ± 5%. Mass of the water was measured every day. As can be seen in Figure 8, at the age of 7 days, plain water in mixture P completely evaporated, while only water evaporated from the urea solution mixtures U30 and U50 and urea remained on the pan in crystal form. It can be explained by the fact that Henry’s constant (The ratio of equilibrium vapor pressure of the pure component to the mole fraction of component) of urea is so small (4.4 × 10−8 atmm3/mol) that urea is nonvolatile. Thus, even if the concrete containing urea is exposed to the atmosphere, only water evaporates from the concrete and urea does not. Therefore, both drying shrinkage strain and mass reduction of the concrete containing urea are much smaller compared with plain concrete.