Soundness test conducted in cement to verify that cement will not undergo a destructive expansion after setting. The expansion of restrained concrete members will result in severe tensile stresses that can result in cracking and spalling of casted concrete. The expansion could occur due to the reaction of free lime, magnesia, and calcium sulfate.
Free lime found in the clinker. Free lime inter-crystallized with other compounds, and it tends to expand during the hydration process. The expansion of free lime is more than calcium oxide. Magnesia reacting with water similarly as calcium oxide does.
But the crystalline formed due to the reaction of magnesia is deleteriously reactive, so it is unsound. Calcium sulfate can cause destructive expansion. The reaction of calcium sulfate will produce calcium sulfoaluminate (ettringite), which can result in the harmful expansion of cement.
A soundness test will be conducted using La Chatelier’s apparatus, shown in figure 1. For doing this test, a cement sample of a specific consistency is prepared and placed inside the split cylinder shown in figure 1. then, the cement is soaked in water for 24 hours. After 24 hours, the distance between indicator arms recorded (D1).
Then the sample submerged in boiling water for one hour. The distance between the indicator arms recorded again (D2). The expansion is D2-D1. The cement expansion should fall within the specified value in project specifications or the local codes.