Early Stage Microstructure Development of Cement Paste Modified by Crystalline Admixture

Abstract

The hydrophobicity enhancement of structural materials is a contemporary topic of discussion. This paper deals with the effect of crystalline admixture (CA) on the microstructure of the cementitious composite in first four weeks after the production. Previous investigation was performed on the referential specimens consisting only from pure cement. The samples of pure CA and cement modified by 1% of CA with same w/c ratio were examined and compared in this paper. By investigation of these materials on the micro-scale in the time, it is possible to identify the development of the microstructure of each and determine the impact of the modification. For this purpose, backscattered electrons microscopy (BSE) with energy-dispersive X-ray spectroscopy (EDX) was used for phase analysis as well as instrumental nano-indentation to obtain the micro-mechanical properties. The presented results show the evolution of mechanical properties and microstructure in time and the impact of the crystalline admixture on modified cement.

An overview of a twofold effect of crystalline admixtures in cement-based materials: from permeability-reducers to self-healing stimulators

“…Even though CAs have been increasingly used as permeability-reducers or healing stimulators, the information available on their chemical composition and characteristics is not progressing with the same proportion as their use. The vast majority of CAs are commercial products whose chemical composition is mostly kept confidential; there has been a general agreement based on the manufacturer's information that CAs are a mixture of different compounds, including silicates, pozzolans, slags and fillers [4][5][6][7][8][9][10][11][12]. However, some homemade formulations are based on carbonates, silicates, aluminates, tetrasodium EDTA, glycine and sodium acetate [34,37,45,47,48,66].…”

“…This mechanism is described by Eq. (1), and it also referenced in many works [6,7,11,16,20,24,29,30,62,[71][72][73][74]:…”

“…Esgandani et al [16] also suggested the intensified C-S-H production booted by the silica fume present in CAs composition. Finally, Hrbek et al [11] proposed the formation of C-S-H with low density caused by the incorporation of CaCO 3 and modified C 3 S in cement pastes with CA, based on the correlation between SEM and nanoindentation analysis. In general, these works used CAs predominantly composed of cement and sand.…”

“…At the same time, these products should ensure compatibility with the different binders and other concrete constituents. • The further hydration is the primary CA's mechanism, which provides healing products over time [6,7,11,16,20,24,29,30,62,[71][72][73][74]. Thus, the duration of the CA's effect should be investigated to satisfy the safety and maintenance requirements, as well as the durability and sustainability related aspects during the project's service life.…”