Study on autoclave expansion deformation of MgO-admixed cement-based materials

In order to increase appropriately the magnesium oxide (MgO) balanced content in hydraulic concrete, a new approach is scientifically explored to add the magnesium oxide content on the basis of the autoclave test principle and changing the cement-based materials and specimen sizes in the autoclave test. The result shows that the autoclave expansion rates (y) of the specimens vary with the magnesium oxide-admixed content (x) in an exponential manner, which can be illustrated as y = y₀ + Ae^R₀x. This trend is irrespective of the cement-based material or the specimen size and the mixing amount of fly ash. There is an inflection point on the curve indicating the variation in the autoclave expansion rate with magnesium oxide content when the magnesium oxide content increases to a certain level. The magnesium oxide content corresponding to the inflection points on the curve is different according to different cement-based materials and specimen size. It is suggested to adapt the magnesium oxide content corresponding to the inflection point on the curve as the balanced content of magnesium oxide-admixed concrete, and the simulated mortar specimen could act as the autoclave specimen, whose size is 30 mm × 30 mm × 300 mm. This content, determined by the present study, is about 2–3 percentage points more than that of all the current methods.