A. Kamen

Thermal Effects on Physico-Mechanical Properties of Ultra-High-Performance Fiber-Reinforced Concrete

Material characterization tests of an Ultra High Performance Fiber Reinforced Concrete (UHPFRC) were performed at various ages. A linear relationship was obtained between the mechanical properties and the degree of hydration. In parallel, the influence of curing conditions on the physico-mechanical properties and the time dependent behavior of this UHPFRC was investigated. A temperature increase accelerated the hydration process at early age and therefore improved the material’s compressive strength and the carrying capacity in four point bending tests, but at a long term, a higher temperature had inverse effects on the mechanical properties. Moreover, at a 20 °C temperature cure, the UHPFRC exhibited autogenous shrinkage at long term comparable to normal concrete. An increase of curing temperature increased the autogenous shrinkage. This effect may be due to the hydration and the self-desiccation processes which are accelerated at high temperatures.

Viscoelastic behavior of a strain hardening Ultra High Performance Fiber Reinforced Concrete

UHPFRC viscoelastic behavior under compressive stresses has been investigated both in sealed and drying conditions. The tests results showed a high potential of creep of our UHPFRC when compared with another reactive powder concrete and a high performance concrete. This effect may be due to the high volume paste in the UHPFRC (88%) which increases the creep rate as it is the paste which deforms. According to our results, non-linear creep is reached beyond 43% of compressive stress. In the non-linear domain, creep under sealed conditions is close to that obtained under drying conditions. Existing models were applied to predict the UHPFRC creep and to validate their application for such materials. In parallel, shrinkage has been studied both in sealed and drying conditions. The test results showed that the investigated UHPFRC, despite its high paste volume, exhibits moderate autogenous shrinkage when compared to cement paste with similar water cement ratio. Autogenous shrinkage tends to stabilize beyond 6 months.