CEMENT--SET AT DIFFERENT TEMPERATURES.
568
The mean results of the compression tests shown in the preceding details are given in the table which next follows, after which may be found tables arranged for more definite purposes.
Referring to the latter, results are shown on specimens 1 month old, from each of the three groups, that is, those which were exposed to 0° F. temperature, while setting, and those which were kept at about 39° and 70° F., respectively.
This is followed by a similar table showing the strength on specimens when 3 months old. In the next three tables the one month and three months’ tests are arranged side by side for each respective group of different temperatures, and these are followed by two tables showing the strength of specimens which were exposed to zero temperature one month and three months, respectively, each followed by intervals at 70° F. of one day and seven days.
The next table introduced is a comparison of the results on specimens which were exposed to zero temperature one month or three months, followed by an interval at 70° F., with specimens which set in air, at the latter temperature only, an equal interval of time to which the former were exposed to 70° F.
A corresponding■ table comes next in which similar comparisons are made between specimens as above, excepting the lower temperature was in this instance 39° F. instead of zero.
The results were next arranged to show the gain in strength after exposure to zero temperature different intervals, followed by a given interval at 70° F. A corresponding table was arranged for those specimens which aged at 39° F., succeeded by the same interval as before at 70° F., and also another table showing the strength of specimens which set at 70° F. only, which were tested with intervals between the different ages equal to those of the preceding tables. Seven day intervals were taken, as far as possible.
A consolidated table follows showing the gain in strength for each of these groups in such tests as were directly comparable.
Finally a table is introduced in which the actual compressive strengths are shown on specimens exposed to zero temperature different intervals, succeeded by seven days or fourteen days at 70° F.
An examination of these tables shows that specimens exposed to zero temperature shortly after mixing do not display, when subsequently thawed, the strength of the other two groups, which is true whether the interval in the freezer was one month or three months. The mean strength of those which set three months in the freezer is above those which set only one month at zero, but the difference is small, insufficient to conclusively show whether a very slow acquisition of strength takes place during the interim, or whether a practical suspension of such action characterizes this period. Those which aged at 39° F. showed a more decided gain for each brand in the three months’ test over the one month, while those which set in air at 70° F. appeared to have acquired their maximum strength during the first month, the results on the three months’ tests showing a diminution in mean values.
That the interval of exposure to zero temperature is at least a period of decided retardation is shown by the rapid acquisition of strength upon removing the material from the influence of this low temperature and exposing it for an additional period in air at 70° F. Specimens one month in the freezer and one day at 70° F., or three months in the