Effect of monocarboaluminate carbonation on mechanical properties and microstructure of lime-metakaolin mortars

Effect of monocarboaluminate carbonation on mechanical properties and microstructure of lime-metakaolin mortars

Článek WoS

In order to improve the properties of fresh and hardened lime mortars, hydraulic or pozzolanic materials have been added to air lime since ancient times. It has been observed through laboratory research and in practice that some lime-pozzolan mortars, especially lime-metakaolin mortars, deteriorate in their properties over time. Although the instability of calcium aluminate hydrates in an alkaline environment has been the main explanation for this deterioration, it can be assumed that the carbonation of the monocarboaluminate also has a significant influence, as confirmed in this paper. The consequences of carbonation of lime-metakaolin mortars with five different types of metakaolin in three doses, with the aim of confirming the carbonation products of monocarboaluminate and determining the influence of the metakaolin composition and its dose on the formation of monocarboaluminate were investigated in the framework of an experimental analysis. The carbonation of monocarboaluminate was confirmed with the formation of metastable forms of calcium carbonate (aragonite and vaterite) and cryptocrystalline aluminum hydroxide, identified mainly by X-ray diffraction analysis, thermogravimetry, 27Al MAS NMR spectroscopy and scanning electron microscopy. As a result of the carbonation of monocarboaluminate, the porosity of the mortars increased because the reaction products have a smaller molar volume than the reactants, resulting in a decrease in flexural and compressive strength. Metakaolin with a higher amorphous Al2O3 content than 29 % may present a risk of deterioration in the properties of lime-metakaolin mortars.

In order to improve the properties of fresh and hardened lime mortars, hydraulic or pozzolanic materials have been added to air lime since ancient times. It has been observed through laboratory research and in practice that some lime-pozzolan mortars, especially lime-metakaolin mortars, deteriorate in their properties over time. Although the instability of calcium aluminate hydrates in an alkaline environment has been the main explanation for this deterioration, it can be assumed that the carbonation of the monocarboaluminate also has a significant influence, as confirmed in this paper. The consequences of carbonation of lime-metakaolin mortars with five different types of metakaolin in three doses, with the aim of confirming the carbonation products of monocarboaluminate and determining the influence of the metakaolin composition and its dose on the formation of monocarboaluminate were investigated in the framework of an experimental analysis. The carbonation of monocarboaluminate was confirmed with the formation of metastable forms of calcium carbonate (aragonite and vaterite) and cryptocrystalline aluminum hydroxide, identified mainly by X-ray diffraction analysis, thermogravimetry, 27Al MAS NMR spectroscopy and scanning electron microscopy. As a result of the carbonation of monocarboaluminate, the porosity of the mortars increased because the reaction products have a smaller molar volume than the reactants, resulting in a decrease in flexural and compressive strength. Metakaolin with a higher amorphous Al2O3 content than 29 % may present a risk of deterioration in the properties of lime-metakaolin mortars.

Monocarboaluminate; Carbonation; Metakaolin; Vaterite; Aragonite; Aluminum hydroxide

Monocarboaluminate; Carbonation; Metakaolin; Vaterite; Aragonite; Aluminum hydroxide

VYŠVAŘIL, M.; KŘIŠTOF, M.; ŽIŽLAVSKÝ, T.; BAYER, P.; DVOŘÁK, K.; MORAVEC, Z.; SPYCHAL, E.

19.09.2025

Elsevier Ltd

1879-0526

Construction and Building Materials

492

Spojené království Velké Británie a Severního Irska

143034

13

https://www.sciencedirect.com/science/article/pii/S095006182503185X