Influence of air-void system on freeze-thaw durability of concrete.

The objective of this study was to determine the influence of air-void characteristics (i.e. air content, air-void size distribution) of the entrained air and the capillary pore structure of the hydrated cement in concretes on the freeze-thaw durability of concrete. Freeze-thaw durability was determined according to ASTM C666 method B; the air-void characteristics were calculated from ASTM C457 using the linear traverse method, and from image analysis results. The capillary pore structure of concrete was measured using mercury intrusion porosimetry. Two different water-cement ratio (0.3 and 0.4) concretes were studied at three different air contents (4.5%, 6.0% and 7.5%). The air-void system was varied using two different air entraining agents, and the importance of aggregate quality and silica fume on frost resistance was studied using two different quality coarse aggregates and two different silica fume contents (0% and 10% by weight of cement). To limit the number of specimens a partial factorial design methodology was used. It was shown that spacing factor based on the concept of protected paste volume, as used in Power's, Fagerlund's, and an equation proposed in this study, is not adequate for the prediction of freeze-thaw durability of different concretes. The capillary pores, which are the source of freezing, need to be considered as well. In addition to air-void characteristics the capillary pore volume seems to be an important parameter to be considered. Two-way analysis of variance showed that type of air entraining agent, quality of aggregate, and content of condensed silica fume have a major effect on freeze-thaw durability of concrete.Ph.D.Applied SciencesCivil engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128825/2/9208611.pd