Autoclave Expansion of Portland Cement-Fly Ash Pastes

Abstract

The influence of the chemical composition of fly ash on the autoclave expansion of portland cement-fly ash pastes has been studied. The autoclave expansion tests were performed as described in ASTM C 151–81. Several of the cement-fly ash pastes tested exhibited severe expansive behavior. Free lime (CaO) was the only single variable that correlated well with the expansion observed in the autoclave tests. A multivariable model was generated in which lime, magnesium oxide, and tricalcium aluminate were the significant variables. The autoclave expansion of portland cement-fly ash pastes appears to be quite sensitive to the amount of free lime present in a given mixture.

Final Technical Progress Report

“…Free lime remaining in the concrete structure leads specimens to destructive volumetric expansion with the passing of time [24]. The water of hydration reaches the lime (CaO) entrapped in the hardened concrete, and produces calcium hydroxide as a reaction product:…”

“…The Reynolds-stress transport equations for an incompressible turbulent flow in Cartesian tensor form can be written as [24]: (24) ( )…”

“…This phenomenon has been observed during the curing procedure. The mechanism is described in detail under autoclaved cellular concrete (ACC) in section 5.3.3.3.1 [24].…”

“…Free MgO (periclase) in the system is undesirable due to slow hydration kinetics and causes resulting unsoundness in the hardened concrete [24,30,34]. Even though MgO exists as a minor constituent in cement (1.0%), the use of MgO as a reactant may result in adverse effects on the cementitious products.…”