The production of cementitious compounds using calcareous diatomite raw materials and possible industrial uses

Abstract eng:
The present study deals with the use of calcareous diatomites, a naturally occurring amorphous silica- and calcite-rich raw material, for the production of C2S-rich clinker that will be used in mortars. The aim of the study is to lower the burning temperature from 1400-1500°C required for the production of the ordinary clinker, to 1000-1100°C, and hence to save energy. However, the resulted calcium silicate endproduct is expected to have lower compressive strength, because of the absence of other synthetic mineral phases such as C3S and C3A that contribute, besides early, to the development of late compressive strength. The selected diatomites were of different origin and came from the Greek islands of Zakynthos, Samos and Milos. Zakynthos diatomite is solely composed of biogenic silica [opal-A] and microcrystalline and biogenic calcite, whereas the other two deposits of Samos and Milos additionally contain minor amounts of smectite and volcanic glass respectively. Furthermore, two commercial calcareous diatomite samples from France were also examined for comparison purposes. XRD, SEM and XRF analysis were implemented for the characterization of the raw materials and end-products. In the range of 1000-1100°C, all ground bulk samples yielded larnite [C2S] followed by significant amounts of silica polymorphs such as quartz, tridymite, cristobalite, and wollastonite. To improve the efficiency of the raw materials to form C2S, different amounts of ground calcite were added to three diatomites, forming diatomite/added calcite mix in ranging ratios. It was found that in some mixtures lime and/or portlandite were also formed, besides the calcium silicates. The larnite-rich final product exhibits some compressive strength that under certain prerequisites could approach that of ordinary cement at later ages.

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