Title: Why Does Ultrahigh-Performance Concrete (UHPC) Exhibit Such Low Shrinkage and Such Low Creep?
Author(s): P. Acker
Publication: Symposium Paper
Appears on pages(s): 141-154
Keywords: constitutive equations; creep; micromechanics; physical analysis; shrinkage; viscoplasticity; viscoplasticity
Recent experimental results (creep tests and indentation tests at a nanometer scale) on Ductal®, a non-brittle (fiber-reinforced) ultrahigh-performance concrete (UHPC), show that only one constituent of this composite, the C-S-H phase, exhibits creep. Former creep tests on hydrated cement paste have shown a very high creep rate of the cement gel which decelerates very slowly (much more slowly than concrete creep). Furthermore, these results provide a clear explanation for the observations of a strong correlation between shrinkage and creep values. The reason is, when hydration rate becomes negligible (typically after a few weeks), the dominant part of shrinkage is nothing but the viscoplastic response of the cement gel to the internal stress which is applied by the liquid phase on the pore surface. This statement makes wrong the last argument against the explanation of shrinkage by capillary tension, the so-called argument of reversibility. Creep aging, as well as the very low creep of high-strength concretes can be explained by the consumption of creep potential by the hygral stress. Several coupling effects between creep and shrinkage can be explained, as for example the so-called PICKETT effect.