The volume expansion of hardened cement paste due to the presence of “dead-burnt” CaO

Abstract

Summary A detailed mechanism is put forward, based on new microscopic and electron-optical evidence, to explain the volume expansion of hardened cement paste due to the presence of dead-burnt CaO. It is shown that CaO first forms colloidal Ca(OH)2 and that subsequently these colloidal crystallites recrystallize to macro-crystals. During their growth from supersaturated solution, these secondary Ca(OH)2 crystals will develop a thrust against the constraining cement paste, thereby causing expansion. This process isfurther helped by the elongated habit of the secondary Ca(OH)2 crystals. The present results and those of other workers are discussed in the light of this and other hypotheses.