Identifying performance criteria for UK concretes under freeze–thaw exposure test conditions

Performance criteria for concrete subjected to freezing and thawing conditions (−22°C to 24°C, with 3.0% sodium chloride freezing medium) using a scaling test method from a European technical specification were investigated. A total of 57 concretes were considered, covering various binder types (Portland cement (CEM I) and combinations with fly ash, ground granulated blast-furnace slag (GGBS) and limestone), binder proportions, strength classes and non-air-entrained (NAE) and air-entrained (AE) concretes. Reduced scaling was generally noted for the NAE concretes with increasing strength, and between comparable-strength concretes when air entrainment was used. While the GGBS concretes generally showed improved performance compared with the other concretes, it was difficult to identify consistent trends in the data between them. Increasing the air content also mainly led to improvements, while the reverse occurred (in AE concretes) with increasing addition level. Cast faces generally performed less well than cut surfaces (according to the method in the European technical specification), although the effect noticeably reduced with air entrainment. The data for 28 freeze–thaw cycles suggests that, for NAE concrete meeting current prescribed requirements, a scaling limit of around 1.0 kg/m2 would apply. For AE concrete, the corresponding limit is less than 0.5 kg/m2. Other practical issues associated with applying performance criteria for specifying concrete are discussed.