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 (PCA, 1988). This destructive expansion is caused by excessive amounts of free lime (CaO) or magnesia (MgO). Most portland cement specifications limit magnesia content and expansion. The typical expansion test places a small sample of cement paste into an autoclave (a high pressure steam vessel). The autoclave is slowly brought to 2.03 MPa (295 psi) then kept at that pressure for 3 hours. The change in specimen length due to its time in the autoclave is measured and reported as a percentage. ASTM C 150, Standard Specification for Portland Cement specifies a maximum autoclave expansion of 0.80 percent for all portland cement types.
Standard Test Methods
- AASHTO T 107 and ASTM C 151: Autoclave Expansion of Portland Cement