Inventive Microstructural and Durability Investigation of Cementitious Composites Involving Crystalline Waterproofing Admixtures and Portland Limestone Cement

Abstract

The durability of a cement-based material is mainly dependent on its permeability. Modifications of porosity, pore-structure and pore-connectivity could have significant impacts on permeability improvement, which eventually leads to more durable materials. One of the most efficient solutions in this regard is to use permeability reducing admixtures (PRA). Among these admixtures for those structures exposed to hydro-static pressure, crystalline waterproofing admixtures (CWA) have been serving in the construction industries for decades and according to ACI 212—chemical admixtures’ report, it has proven its capability in permeability reduction and durability-enhancement. However, there is substantial research being done on its durability properties at the macro level but very limited information available regarding its microstructural features and chemical characteristics at the micro level. Hence, this paper presents one of the first reported attempts to characterize microstructural and chemical elements of hydration products for cementitious composites with CWA called K, P and X using Scanning Electron Microscopy (SEM). Backscattered SEM images taken from a polished-section of one CWA type—K—admixture were analyzed in ImageJ to obtain paste matrix porosity, indicating a lower value for the CWA-K mixture. X-ray analysis and SEM micrographs of polished sections were examined to identify chemical compositions based on atomic ratio plots and brightness differences in backscatter-SEM images. To detect chemical elements and the nature of formed crystals, the fractured surfaces of three different CWA mixtures were examined. Cementitious composites with K admixture indicated needle-like crystal formation—though different from ettringite; X and P admixtures showed sulfur peaks in Energy Dispersive Spectrum (EDS) spectra, like ettringite. SEM images and X-ray analyses of mixtures incorporating Portland Limestone Cement (PLC) indicated lower-than-average porosity but showed different Si/Ca and Al/Ca atomic ratios.

The Effect of Crystalline Waterproofing Admixtures on the Self-Healing and Permeability of Concrete

“…As a result, the water penetration depth in concrete with incorporated CWA should be lower compared to the water penetration depth in reference concrete, which is confirmed by the authors in [ 10 , 14 ] but also disputed in [ 15 ]. As previously described, CWA also promotes self-healing of cracks [ 16 , 17 , 18 , 19 , 20 ]. The research presented in [ 18 ] implies that each CWA produces different products/crystals responsible for reducing water penetration and self-healing of concrete.…”

“…As previously described, CWA also promotes self-healing of cracks [ 16 , 17 , 18 , 19 , 20 ]. The research presented in [ 18 ] implies that each CWA produces different products/crystals responsible for reducing water penetration and self-healing of concrete. Regarding self-healing, the width of cracks that can heal completely varies in the studies; the completely healed cracks in [ 16 , 17 ] are up to 0.1 mm wide, in [ 18 ] up to 0.3 mm wide, while in the studies [ 19 , 20 ] even cracks with a width up to 0.4 mm were healed.…”

Textile Reinforced Concrete in Combination with Improved Self-Healing Ability Caused by Crystalline Admixture

“…This modified concrete can stop the penetration of pressurized water, which has been proven several times in the past [ 5 , 6 , 7 , 8 , 9 ]. The waterproofing of concrete with crystalline admixture has also been proven by numerous laboratory studies [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], as well as the durability of this concrete [ 18 , 19 , 20 , 21 ]. Furthermore, the durability in aggressive environments was successfully tested as well [ 22 , 23 , 24 , 25 ].…”

Hydrophobicity Improvement of Cement-Based Materials Incorporated with Ionic Paraffin Emulsions (IPEs)

“…Cement-based materials are non-uniform porous materials that are easily permeated by harmful substances in water, thereby deteriorating their structural durability. Hydrophobicity is a key index to evaluate impermeability, corrosion resistance and durability of cement-based materials [ 1 , 2 , 3 , 4 , 5 , 6 ]. Hydrophobicity improvement of cement-based materials is effective to improve their corrosion resistance and durability via the decrease of their permeability, which deserves extensive attention [ 7 , 8 , 9 , 10 , 11 ].…”