Masonry Magazine November 1965 Page. 9
Want To S-T-R-E-T-C-H Your Construction Seasons?
Here's How
COLD AND HOT
WEATHER
ASPECTS OF MORTAR
Shuldes
Bad weather means shrinking profits for the contractor unless he has the technical knowledge to operate under unfavorable conditions. MCAA members were fortunate in hearing Robert W. Shuldes at the All-Weather Conference held in Chicago, Oct. 15. A recognized authority in his field, Mr. Shuldes is a civil engineer with the Portland Cement Association. He has written many technical publications for PCA including the Trowel Talk series. At present, he is serving on two technical committees for the American Concrete Institute. MASONRY readers have an opportunity to study Mr. Shuldes Oct. 15th talk which is reprinted here.
The fact that the Mason Contractors Association of America has selected October 15 for the date of their All-Weather Masonry Conference is quite significant when we consider the fact that gardeners in this area regard October 15 to be the average date of the first killing frost. This is an indication that winter will soon be upon us and with it will come the necessity for modifying methods of construction to protect fresh masonry.
In cold weather a phenomena occurs that influences the hydration of portland cement. Portland cement, of course, is the binding agent in our mortar. Portland cement does not harden when it dries, but it hardens when it goes through a chemical reaction called hydration. Hydration is dependent upon three factors. They are:
1. Time
2. Favorable Temperature
3. Presence of H2O
The first point, time, of course, is necessary since hydration is not an instantaneous process. It does require a certain amount of time.
The second point, temperature, is the point that concerns us the most in our discussion today. This chemical reaction called hydration slows down as temperatures drop, and when the temperature of our mortar mix is below 40° F., the hydration process virtually comes to a standstill. In order to obtain hydration and, consequently, hardening and full strength development of our mortar, we must have temperatures above 40° F. in our mortar mix. Because of this the temperature at which we will begin our special procedures for cold-weather construction are temperatures below 40° F.
When the temperature is below 40° but still above freezing, we recommend that all materials should be covered. Stockpiles of sand and stockpiles of masonry units should be protected to prohibit the entry of excess moisture and, consequently, the freezing of this moisture should the temperature drop below 32° F.
Another recommendation which is very important is mixing water should be heated. This will help obtain favorable temperatures in our mortar so the hydration process can be fully accomplished. The reason we recommend heating the mixing water is that it is perhaps the easiest of material to heat plus the fact that pound for pound it is a better carrier of heat than any of the materials that go into a mortar mix; for that matter, any of the materials that go into our masonry wall.
The mixing water should not be heated over 160° F. If it is, there is a possibility that flash set may occur when the hot water and our masonry cement or portland cement are brought into contact with each other.
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