Rheological Characterization of Heterogeneous Materials with Evolving Properties

Abstract

The paper deals with the rheological characterization of different heterogeneous civil engineering materials that have time- dependent properties. Studies on cellular concrete, mortar, hydraulic concrete, and cold bituminous mixes are presented. The properties are monitored throughout setting and hardening. Such materials are heterogeneous mixtures containing solid particles, binder, fluids, and gas bubbles. For all of these materials, different formulations were investigated, such as water content, binder proportioning, and compaction level. A nondestructive device allows the setting to be monitored and to be clearly characterized. This device makes it possible to simultaneously study the propagation of compressional and shear waves in the same sample of material. To prevent diffraction of waves from heterogeneities, a condition of a long wavelength compared to the heterogeneity size is required, so low frequencies are used ~20-1,000 Hz!. Velocity and damping coefficients versus time are deduced, then related to rheological viscoelastic properties by an inverse analysis. The linear behavior of these materials under small strains is proved, and the measurements are very repetitive and sensitive to the nature and the component proportioning of the materials. The rheological evolutions of the different materials are presented and compared. It is shown that the normalized evolution of hydraulic concretes follows a single master curve for all of the different formulations investigated. Similar results are established for cellular concretes and mortars.