Title:
Air-Void Stability, Part IV: Retempering
Author(s):
Michel Pigeon, Francois Saucier, and Patrick Plante
Publication:
Materials Journal
Volume:
87
Issue:
3
Appears on pages(s):
252-259
Keywords:
air-entrained concretes; field tests; freeze-thaw durability; retempering; stability; water; Materials Research
DOI:
10.14359/2199
Date:
5/1/1990
Abstract:
Eight laboratory mixes and eight field mixes were prepared to study the effects of retempering by adding water on the characteristics of the air-void system and to study air entrainment when an air-entraining admixture is added significantly after the initial mixing period. For each mix, four sets of samples were cast over a period of 90 min after initial water-cement contact: two before retempering (at 45 min), and two after. The modified point-count method (ASTM C 457) was used to determine the characteristics of the air-void system on each set of samples. The results show that retempering by adding enough water to increase the slump from approximately 50 mm to about 100 mm has no significant influence on the value of the air-void spacing factor, although it often causes a small increase in air content. The results also show that it is possible to entrain an adequate air-void system with a spacing factor of less than 200 æm if a normal dosage of the air-entraining agent (with a little water) is incorporated into the mix 45 min after the initial water-cement contact. An unsatisfactory air-void system can be corrected by adding more of the air-entraining agent after 45 min, but the quantity added must be important (i.e., more than 30 to 50 percent of the normal dosage) to lower significantly the value of the spacing factor. The results further show that small air-content variations (lower than 2 percent) should not be used to predict spacing factor variations.