A note on the occurrence of crystals of calcium hydroxide and ettringite in voids in hardened Portland cement paste

The occurrence of crystals of calcium hydroxide and ettringite (calcium sulphoaluminate) in hardened Portland cement, reported previously by others, is confirmed. Samples of hardened Portland cement paste prepared half a century ago at one of Canada's earliest cement plants were, on examination, found to contain voids in which well developed crystals had formed. The crystals occurred as thin plates and needles that were identified by optical microscopy and X-ray diffraction as calcium hydroxide and ettringite, respectively. It is of interest that the calcium hydroxide had not been altered to carbonate even though the cement samples had been stored for a long time under conditions that would be expected to promote this change.Ce document confirme l'apparition de cristaux d'hydroxyde de calcium et d'\ue9ttringite (sulpho-aluminate de calcium) dans le ciment Portland durci, qui a d\ue9j\ue0 \ue9t\ue9 rapport\ue9e par d' autres chercheurs. Des \ue9chantillons de p\ue2te de ciment Portland durcis ont \ue9t\ue9 pr\ue9par\ue9s il y a cinquante ans dans une des premi\ue8res cimenteries du Canada o\uf9, au cours d'un examen, on avait d\ue9couvert la formation de cristaux dans les vides. Les cristaux avaient des formes de plaques et d' aiguilles minces qui ont pu \ueatre observ\ue9es au microscope optique et avec un appareil de diffraction aux rayons X. Ils \ue9taient compos\ue9s d'hydroxyde de calcium et d'ettringinte respectivement. Il est int\ue9ressant de remarquer que l' hydroxyde de calcium ne s'est pas transform\ue9 en carbonate m\uea me si les \ue9chantillons de ciment ont \ue9t\ue9 stock\ue9s pendant une tr\ue8s longue p\ue9riode dans des conditions qui auraient d\ufb favoriser ce type de transformation.Peer reviewed: NoNRC publication: Ye