Freeze Thaw Resistance Of Concrete With Marginal Air Content

Freeze-thaw resistance is a key durability factor for concrete pavements. Recommendations for the air void system parameters are normally: 6 ± 1 percent total air, and spacing factor less than 0.20 millimeters. However, it was observed that some concretes that did not possess these commonly accepted thresholds presented good freeze-thaw resistance in laboratory studies. This study evaluated the freeze-thaw resistance of several "marginal" air void mixes, with two different types of air-entraining admixtures (AEA)-a Vinsol resin and a synthetic admixture. This study used rapid cycles of freezing and thawing in plain water, in the absence of deicing salts. For the specific materials and concrete mixture proportions used in this project, the marginal air mixes (concretes with fresh air contents of 3.5 percent or higher) presented an adequate freeze-thaw performance when Vinsol resin based air-entraining admixture was used. The synthetic admixture used in this study did not show the same good performance as the Vinsol resin admixture

Concrete durability in climates where freezing and thawing occurs is a continuing problem. It is particularly acute for highway and bridge structures, where de-icing salts are used to combat the effects of frost, snow and ice. These salts can cause damage to concrete and accelerate corrosion of reinforcements. This book presents the latest international research on this area, with contributions from North America and Europe which were presented at an international RILEM workshop.

This study, aimed at improving the freeze-thaw resistance of concrete, consists of three parts. Part I evaluates parameters affecting the freeze-thaw durability of concrete. A modification of the existing standard of method for determining the durability factor of concrete specimens is proposed, and a new procedure for fundamental transverse frequency (used in durability factor calculations) has been developed. Part II focuses on developing better methods for identifying nondurable aggregates, and has resulted in a rapid new test based on the hydraulic fracture of aggregates. Part III describes field experiments to evaluate the freeze-thaw resistance of a number of specified concrete mixes and the use of sealants to mitigate D-cracking. Preliminary field performance results are presented.

This book forms the proceedings of the international workshop to be held in Essen, Germany. This workshop summarises the conclusion of the technical committee's investigations into the resistance of concrete to freeze-thaw attack, specific in this to resistance with or without de-icing chemicals. It presents the RILEM recommendations on testing the freeze-thaw and de-icing salt resistance of concrete.

Discussion of the behaviour of various concrete structures exposed to freezing and thawing is followed by theories regarding mechanisms which cause this behaviour, and methods of preventing concrete deterioration.

The freeze-thaw resistance of concretes was studied. Nine concrete mixes, made with five cements and cement-Class C fly ash combinations, were exposed to freeze-thaw cycling following 110 to 222 days of moist curing. Prior to the freeze-thaw cycling, the specimens were examined by a low-vacuum scanning electron microscope (SEN) for their microstructure. The influcence of a wet/dry treatment was also studied. Infilling of ettringite in entrained air voids was observed in the concretes tested. The extent of the infilling depends on the period of moist curing as well as the wet/dry treatment. The concretes with 15% Class C fly ash replacement show more infilling in their air voids. It was found that the influence of the infilling on the freeze-thaw durability relates to the air spacing factor. The greater the spacing factor, the more expansion under the freeze-thaw cycling. The infilling seems to decrease effective air content and to increase effective spacing factor. The infilling also implies that the filled air voids are water-accessible. These might lead to concrete more vulnerable to the freeze-thaw attack. By combining the above results with field observations, one may conclude that the freeze-thaw damage is a factor related to premature deterioration of PCC pavements in Iowa.

Paper 1 presents laboratory freeze-thaw results as well as field observations on the major Michigan aggregate sources and is considered a first step in formulation of a policy regarding acceptance of future aggregates of unknown service behavior.