When referring to portland cement, “soundness” refers to the ability of a hardened cement paste to retain its volume after setting without delayed destructive expansion caused by excessive amounts of free lime (CaO) or magnesia (MgO), or both, when present in portland cement. Most portland cement specifications limit magnesia content and expansion. The typical autoclave expansion test places a small sample of cement paste into an autoclave (a highpressure steam vessel). So that autoclave test is used to determine the expansion in portland cement.