Freeze-Thaw Resistance of Nonproprietary Ultrahigh-Performance Concrete

In cold regions, early deterioration of concretes due to freezing and thawing is a major concern. This study determined the freezing and thawing resistance of ultrahigh-performance concretes (UHPCs) made with different pozzolanic-material types (Class F fly ash, natural pozzolan, and silica fume) and combinations, as well as varying steel fiber contents (0%, 2%, and 3%) and shapes (straight and hooked) using conventional fine aggregate. A total of thirty 28-day cured UHPCs were used to assess their mass loss after 70 freeze and thaw (F-T) cycles (48 h per cycle). The pre- and post-F-T compressive and splitting tensile strengths of the studied UHPCs were also obtained and examined. The outcome of this study revealed that the studied UHPCs displayed excellent resistance against freezing and thawing deterioration. The post-F-T-exposed UHPCs gained strength due to the availability of unhydrated pozzolanic materials, coupled with favorable curing environment. Among the utilized pozzolanic-material combinations, UHPCs made with silica fume and Class F fly ash, as a partial replacement for the cement, performed the best against freezing and thawing, whereas the companion mixtures containing only Class F fly ash to replace a portion of the cement showed the highest mass loss. The addition of straight steel fibers had a more positive influence on the freezing and thawing resistance than hooked fibers.