Mechano-chemical aspects of the processing/property/structure interactions in a macro-defect-free cement

Abstract

Abstract Relationships between mixing conditions, relaxation properties of the formed paste, and the morphology and flexural strength of hardened composites have been studied for a macro-defect-free cement (MDF). Torque and temperature were monitored in a Banbury-type mixer as a function of temperature and mixing rate. The behavior of the torque-time curves as well as activation energies derived from the temperature dependence of the mixing time suggest that a mechano-chemical crosslinking takes place between the polymer and cement phases during mixing. The viscoelastic relaxation characteristics of MDF pastes processed to varying degrees were determined using a biaxial squeeze flow device. Relaxation times and their trends with mixing are consistent with the formation of an increasingly dense network structure in the paste. Flexural strengths of the hardened material display a behavior with mixing conditions which suggests that an optimal structure forms during that portion of the mixing process preceding breakdown of the paste. This conclusion is supported by the evidence of scanning electron micrographs which show the structure formation for a given set of mixing conditions.