Modelled phase assemblage of a hybrid cement as a function of the curing temperature
Source: BAM, Division Technology of Construction Materials
Hybrid cements are composites of ordinary Portland cement or Portland clinker and supplementary cementitious materials (SCMs), e.g., ground granulated blast furnace slag and/or fly ash, activated by an alkali salt or an alkaline solution. Based on their composition, hybrid cements can be considered intermediates between ordinary Portland cement and alkali-activated materials. The advantage of these cements is the combination of advantageous properties, i.e., a low heat of reaction typical for alkali-activated materials, while maintaining sufficient early and late compressive strength, usually encountered in ordinary Portland cement.
Additionally, chemical similarities between hybrid cements and ancient Roman concrete indicate a similar chemical durability against saline solutions, e.g., sea water. These properties make hybrid cements promising materials for the construction of sealing structures in nuclear waste repositories in Germany. In this context, microstructural analyses were performed on hybrid cements and accompanied by thermodynamic modelling. The results show that curing at 10 °C , representative of certain underground structures (sealing structures), lead to an increased compressive strength. Microstructural analysis and thermodynamic modelling showed an increased formation of strätlingite, a calcium-aluminum layered double hydroxide with an interlayered alumosilicate ion, at 10 °C curing temperature. This leads to a densified microstructure and thereby to an increased compressive strength.
The influence of curing temperature on the strength and phase assemblage of hybrid cements based on GGBFS/FA blends
Ricky Henning, Patrick Sturm, Daniel A. Geddes, Sylvia Keßler, Brant Walkley, Gregor J. G. Gluth
Frontiers in Materials, vol. 9, Article No. 982568, 2022
BAM Safety of Structures department
BAM Technology of Construction Materials division