Mechanical Characteristics of Fresh and Hardened Gluminous Cement Pastes

Abstract

In this research the rheological properties of fresh aluminous
cement pastes were investigated mainly by means of a coaxial rotational viscometer. The effect of conversion on the pore structure of the hardened high alumina cement (HAC) pastes was monitored using a mercury intrusion porosimeter. A scanning electron microscope / KEVEX energy dispersive X-ray analysis combination, and in some instances a differential thermal analyser, were used to study the morphological changes in the interfacial zone between HAC pastes and various substrates.
A brief study was made of the feasibility of using by-product
phosphogypsum as a cheap additive to eliminate conversion effects in
HAC pastes.

The consistency of HAC fresh pastes was highly dependent on mixing
time and temperature. The development of a thixotropic structure on mixing involves a thermally activated process for which the activation energy was estimated to be 43+ 1 KJ/mole. The sensitivity of HAC pastes to mixing and storage conditions made it essential to develop stringent
procedures for specimen preparation, curing, and testing.

Mineralogical and pore size distribution studies on hardened HAC pastes have revealed a number of relationships between these two factors and the strength of the material. In addition, the shape of the pore size distribution curves was found to be directly related to the
mechanical and mineralogical conditions of the paste.

Analytical and morphological studies of the interfacial zone
developed between HAC pastes and various substrates indicated that
this zone is seriously affected by the conversion process. In general,
the paste side of the interface, which was initially largely made up of
small platelets of probbable composition C₂ (AF)H₈,  was converted to gibbsite
crystals of high variability of size and Shape.

Date of Award	Sept 1980
Original language	English
Awarding Institution	Aston University