Introduction
Under this theme, ACBM will apply the knowledge gained in earlier and current rheological studies to much broader issues of processing and microstructure. A major goal is to explore links between processing and microstructure, how microstructure controls processing, and how processing modifies the microstructure. Ultimately, the goal is to treat concrete as a complex fluid whose rheological properties can be related to its processing operations — pumping, consolidation, etc.

Basic Rheology
ACBM has made considerable progress in understanding the flow behavior and microstructure of both dispersed and flocculated suspensions near their gel points. These studies will be extended to better understand the process of yielding in both shear and compression, using both model materials and cement suspensions. A new approach taken in the program will be to investigate compressive behavior of flocculated suspensions, which plays a key role in processing (e.g., solid / liquid separations, ceramics processing, and casting and consolidation of concrete) and is dominated by two poorly understood rheological properties — compressive yield stress and permeability. Analogous to the behavior in shear, the compressive yield stress is that stress below which the network of flocculated particles deforms elastically, and above which it deforms irreversibly. Permeability of the solid particulate network also affects the rate by which the network collapses. Both compressive yield stress and permeability are controlled by microstructure, specifically by the number and strength of interparticle forces. These give rise to frictional forces, which resist particle rotation and sliding, such that particles do not simply collapse to random close packing when an external load is applied, but rather compress to some new density and microstructure in equilibrium with the applied load. ^Top

Rheology of Advanced Cement-Based Materials
ACBM has developed unique methodologies for studying the processing of polymer-cement composites which couple torque measurement during shear mixing with rheological analysis of the paste prior to hardening. This has led to the first quantitative measures of the mixing-induced mechano-chemistry of these systems. This data provides a base for quantifying paste rheology and allows the prediction of scale-up behavior. Although applied to initially, high shear roll-mill processing, it can also be applied to extrusion. ACBM has developed extruded composites containing short fibers to provide mechanical properties (high tensile strength and considerable strain hardening) heretofore achieved only with continuous fibers. Extruded sheets produced with relatively modest amounts of short fibers (2-4% by volume) have tensile strengths of about 8 MPa and show strain hardening at strains of 1% or more. ^Top

Coordinator: Leslie Struble (University of Illinois)

Compressive Rheology of Cementitious Systems
PI: Charles Zukoskii (University of Illinois)

Concrete Rheology
PI: Leslie Struble (University of Illinois)

Microwave Enhanced Curing of Concrete
PI: D. Lynn Johnson (Northwestern University)

Synthesis and Characterization of Novel OrganocementComposites
PI: Jennifer Lewis and Anthony McHugh (University of Illinois)

Extrusion Processing of High Performance & Fiber-Reinforced Cement Composites
PI: Surendra Shah (Northwestern University) and Anthony McHugh (University of Illinois)

Multi-Scale Modeling and Experimental Investigation of the Rheology of Fresh Mortar
PI: Hamlin Jennings (Northwestern University)