Characterization of Strength and Durability of Ultra-High-Performance Concrete under Variable Curing Conditions

Abstract

One of the latest advancements in concrete technology is ultra-high-performance concrete (UHPC), a fiber-reinforced, densely packed material that exhibits increased mechanical performance and superior durability compared with normal- and high-strength concretes. UHPC has great potential to be used in the bridge market in the United States. However, to gain acceptance by designers, contractors, precasters, and owners, this material needs to be tested according to ASTM International and AASHTO standards, and new practices must be developed. The variability in performance that is based on new challenges of mixing and curing must also be considered. The effects of curing regimes and specimen age on the strength and durability properties of a fiber-reinforced UHPC was investigated. Regardless of when the thermal treatment was applied, UHPC consistently attained compressive stresses above 30 ksi (207 MPa), a modulus of elasticity of approximately 8,000 ksi (55 GPa), and a Poisson's ratio of 0.21. Flexural characteristics were enhanced with high-temperature curing. UHPC also demonstrated extremely high resistance to freeze–thaw cycling (with a durability factor of more than 100), coefficient of thermal expansion values only slightly higher than that of normal-strength concrete, and negligible chloride ion penetration. Furthermore, modified versions of ASTM and AASHTO standard testing methods were employed to aid in development of draft standards for testing some UHPC material properties in the United States that will eventually lead to a national design code.