Masonry Magazine January 1966 Page. 43
All-Weather Conference Report
William E. Dickinson
ADMIXTURES
FOR ALL-WEATHER
CONSTRUCTION
This paper was presented at MCAA's All-Weather Conference held recently in Chicago. Mr. Dickinson has served the Calcium Chloride Institute in various capacities since 1946 when he was appointed field engineer. In 1960 he was elected President of the Institute. Mr. Dickinson has gain national recognition as an authority on proper use of calcium chloride.
In recent years the acceptance and use of admixtures concrete has grown tremendously. There was a time when many engineers and concrete technicians were very insistent that nothing but water, aggregate and cement be used in the manufacture of concrete. A reflection of the change in this attitude is found in the statement in 1940 by P. H. Bates, that "The use of admixtures should not be frowned upon or scorned. On the contrary their development and study should be highly commended and mastered."
In my opinion two things have contributed greatly to the change in attitude. First was the discovery of the improvement in the durability of concrete made possible by air entrainment. Secondly, the increase in year-round construction brought about by World War II and the continuation of all-weather concreting since. This led to greatly expanded use of accelerators for cold weather concreting.
An admixture is defined in ASTM Designation C-125 as "A material other than water, aggregate and portland cement (including air-entraining portland cement and portland blast furnace slag cement) that is used as an ingredient of concrete and is added to the batch immediately before or during its mixing."
An admixture is used to modify the properties of concrete in such a way as to make it more suitable for the work at hand. Under certain conditions, use of a suitable admixture may impart desirable characteristics which cannot be secured as economically by other methods.
Some of the more important modifications of properties of concrete which have been the objectives of use of admixtures are:
a) Improvement of workability.
b) Acceleration of the rate of strength development at early ages.
c) Retardation or acceleration of initial setting.
d) Modification in rate of, and capacity for, bleeding.
e) Increase in durability or in the resistance to special conditions of exposure, including application of ice-removal salts.
f) Control of alkali aggregate expansion.
g) Decrease in the permeability to liquids.
The American Concrete Institute's Committee 212 on "Admixtures for Concrete", has classified the admixture field into 15 groups as follows:
1) Accelerating mixtures.
2) Water-reducing admixtures and set-controlling admixtures.
3) Grouting admixtures.
4) Air-entraining admixtures.
5) Air-detraining admixtures.
6) Gas-forming admixtures.
7) Expansion-producing admixtures.
8) Finely divided mineral admixtures.
(continued on page 46)