Technical Questions

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Unsoundness in portland cement

Q. What is unsoundness in portland cement, and how is it detected and avoided?


A. Concrete that shows excessive expansion after setting is said to contain unsound cement. In former times, this was a serious problem for concrete. In more recent times, better manufacturing, testing, and controls have almost completely eliminated unsound cement. Unsoundness is caused by free lime and magnesia in the clinker in sufficient quantity so that, upon hydration, excessive expansion and damage to concrete can occur. The presence of such is detected by the autoclave expansion test ASTM C 151. Unsoundness can be avoided by minimizing these expansive constituents.


References:  SP-1(02); ACI 225R-19; E3-13; ASTM C150; ASTM C151; ASTM C595; ASTM C1157

Topics in Concrete: Cementitious Material; Concrete Fundamentals

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