Title:
Bubble Characteristics as They Pertain to Compressive Strength and Freeze-Thaw Durability
Author(s):
Paul F. Gutmann
Publication:
Materials Journal
Volume:
85
Issue:
5
Appears on pages(s):
361-366
Keywords:
air-entrained concretes; air-entraining agents; air entrainment; chemical analysis; coalescing; freeze-thaw durability; compressive strength; Materials Research
DOI:
10.14359/2278
Date:
9/1/1988
Abstract:
Known air-entraining additives are not entirely satisfactory with respect to the stability of the air bubbles in concrete and have a tendency to either lose air or increase air as mixing time is extended. Another disadvantage is the reduction of compressive strengths of a 10 percent strength loss per 1 percent increase in entrained air. It is believed that this loss is due in part to irregular bubble sizing and the coalescence of bubbles in the mix causing large voids that reduce the compressive strength. The object of this research program was to improve the air-entrained portland cement concrete, which included an additive that would entrain an air-void system having desirable characteristics when used over a wide dosage range and, also, have a superior dosage response relative to similar known additives. Another objective of this research program was to provide improved strength results that include an additive that entrains an air-void system and increases compressive strengths over known air-entraining agents. Microscopic examination of a methyl ester-derived Cocamide diethanolamine produced bubbles that were spherical, having thick walls with no coalescence, while wood-resin bubbles were relatively thin-walled and tended to be less than spherical with some shapes oblong and coalescence observed. It was believed that this difference would produce a more stable air content and more uniform bubble structure in portland cement concrete. Test results on concrete with the use of a Cocamide diethanolamine produced by a methyl ester process produced a stable volume of air having the desirable size and distribution, and, compared to known air-entraining agents, increased the resistance to freeze-thaw durability by 400 percent and increased compressive strengths 25 percent in early ages and 10 percent in later ages.