Tasks and Activities:

Fundamental, experimental, and numerical investigations are being conducted in this project to advance current understating of the behavior of enhanced clay-pelletized mixtures subjected to high temperatures (up to 190°C) and hydration. The project outcomes will be achieved via a combined experimental and analytical/computational approach.

The figure below shows schematically the main Tasks envisaged in this project together with the main interactions between them. The subsections below describe the logical path that will be followed to ensure the achievement of the proposed project objectives.

Task 1: A comprehensive review of the existing literatures on former research according to this topic is conducted.

Task 2: Macroscopic experimental investigation (Lead TAMU): The macro-scale experimental investigation contemplates both element-scale tests, heating and hydration (scaled barrier-prototype) column tests that mimic the THM conditions expected in the EBS. The aim is to characterize the THM behavior of pellet mixtures and to identify key mechanisms and processes associated with mass and heat transport in these types of materials.

Task 3: Fabric/microfabric experimental investigation (Lead SNL): The investigation associated with the imaging of inter- and intra- pellet behavior help understand the underlying microscopic phenomena behind the observed macroscopic material behavior. It also complements the information gathered from the macroscopic tests. To quantify behavior at scales ranging from single micropores to interactions between pellets, we carry out an experimental regime aimed at imaging at stress, temperature, and humidity conditions during pellet wetting and drying, and as well examine thermal conductivity of augmented pellet assemblies at a range of consolidation and suction conditions. These are accomplished by a TAMU graduate student intern at SNL supervised by the SNL team of Xiong, Matteo, and Dewers.

Task 4: Constitutive modeling (Lead TAMU): The information gathered through the macro and micro experimental investigations planned in this project will be integrated to develop/upgrade hydraulic, thermal, and mechanical constitutive models for clay-pellets mixtures. We also use published data associated with this type of material. The starting point is double structure model for expansive soils that explicitly distinguishes two basic structural levels: the macrostructure, that corresponds to the granular skeleton formed by clay-pellets (with the macro- inter-pellets voids between them); and the microstructure, corresponds to the high-density clay-pellets (with the micro- intra-pellets voids inside them).

Task 5: Numerical modeling and applications (Lead TAMU): The activities associated with the numerical modeling are centered on the extension of the fully coupled THMC finite element (FE) 3D program CODE_BRIGHT to deal with enhanced clay-pellets mixtures characterized by a heterogeneous micro-fabric. This code is based on a multiphase/multispecies mathematical formulation that consists of three main sets of equations: 1) balance equations (i.e. momentum balance, internal energy balance, and species mass balance: water, air, solid and chemical species); 2) constitutive equations (e.g. Darcy’s and Fourier’s laws, retention curve, stress-strain relationship), and 3) equilibrium restrictions (e.g. psychrometric law and Henry’s law, to account for dissolve gas in liquid). CODE_BRIGHT was upgraded to deal with double porosity clayed materials.