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

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.