Q.: Does the use of I or 2 percent calcium chloride in concrete weaken the concrete measurably? Why does concrete containing calcium chloride seem to work better?

A.: The addition of calcium chloride tends to increase the early strength of concrete though it may slightly decrease the ultimate strength. We are not sure why calcium chloride should seem to make the concrete more workable, if it does, unless it is the combined effect of shortening the setting time and decreasing the rate of bleeding.