Gypsum slag pozzolan cement (GSPC) binders have a significantly lower CO2 footprint than ordinary Portland cement (OPC) as they only contain a small amount of the latter. Nevertheless, these binders have some disadvantages like long-term durability issues and limited strength. This study investigates the potential of post-treatment and the impact of the pozzolan to improve these subjects.
We used a GSPC that contains alpha-hemihydrate calcium sulfate, ground granulated blast furnace slag, calcined clay, and OPC. In the reference sample, calcined clay was substituted by inert limestone powder. The samples were stored at 20 °C in two different environments: dry, i.e. at 65 % rel. humidity, and underwater. Thus, we want to examine if post-treatment of GSPC binders by keeping them wet for 28 days improves their properties. We also elucidate the effect of calcined clay in the composition.
The results show that storage under water increases the strength of GSPC binders compared to dry storage. This can be explained by a higher degree of hydration proven by thermogravimetric analysis, and significantly higher amounts of ettringite provided by X-ray diffraction analysis. At the same time, storage under water leads to a decrease in the calcium sulfate phases. For this, two possible explanations occurred in this work: leaching of sulphates or their incorporation in ettringite.
The GSPC and the reference sample without calcined clays showed only minor differences in the setting time and almost the same compressive strength after 28 days. This shows that the effect of calcined clays was limited in this study and could be explained by the fact that even in the reference sample portlandite was absent. Hence, any additional pozzolan added could not react.
This study illustrates that it is worthwhile to post-treat GSPC binders as it increases the strength of the binder. It also indicates that the amount of portlandite-consuming pozzolan in a GSPC binder has to be well-adjusted to the available portlandite in the system.
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Gypsum slag pozzolan cement (GSPC) binders have a significantly lower CO2 footprint than ordinary Portland cement (OPC) as they only contain a small amount of the latter. Nevertheless, these binders have some disadvantages like long-term durability issues and limited strength. This study investigates the potential of post-treatment and the impact of the pozzolan to improve these subjects.
We used a GSPC that contains alpha-hemihydrate calcium sulfate, ground granulated blast furnace slag, calc...
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