Contribution to the development of an additive for bulk waterproofing of cement-based materials

Scriptie/Masterproef: Doctoral Thesis

Samenvatting

For the last 10 years, silicone-based admixtures have been successfully used for bulk waterproofing treatment of cementitious materials. However, a reduction in mechanical properties of treated materials is rather observed and becomes a major problem for the in-situ application. A new concept of a knowledge-based integral water repellent has been designed in such a way that the negative effect on mechanical properties is significantly reduced. The technology comprises the delayed release of the hydrophobic agent (silicone resin) which is achieved by encapsulation of the resin in SiO2 shell. A multidisciplinary research was conducted in order to propose a model of the delayed release and the silica shell reaction mechanism in cement paste. Therefore, a study on the microcapsules reaction in calcium hydroxide solution was conducted by means of FTIR, DSC-TGA, surface tension measurements and chemical analysis by ICP- OES. It was shown that microcapsules flocculate in presence of Ca2+, what appears to be the main factor that contribute to the delayed release of the resin.
The influence of the microcapsules on Ordinary Portland (OPC) and Blast furnace slag (BFS) cement hydration process was compared with the emulsion of silane monomer and silicone resin. It was shown that the emulsion delays the setting and influences the early age hydration by prolonging the dormant period and decreasing the hydration heat. Cement microstructure and hydration products development was observed by SEM/ESEM. Quantitative analysis of hydration products was assessed by Rietveld analysis of XRD diffractograms. Emulsion induced a significant delay in the cement paste setting by changing the amount and morphology of ettringite and portlandite at very early age. Differently, microcapsules didn’t show any effect on these properties.
Experimental work on relevant mortars is done in order to prove the concept of a delayed release as a solution towards the decrease in mechanical properties. The influence of the new additive on setting, volume change, dynamic E-modulus and the compressive strength was analysed. New analytical techniques (AutoShrink, Ultrasonic Pulse Velocity and ConSensor) in combination with traditional ones (Penetration resistance test and compressive strength on cubes) were used. Microcapsules have successfully lowered the negative impact of silanes on the compressive strength and
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dynamic Young’s modulus. Moreover, it was showed that the microcapsules slightly influence autogenous deformation by increasing the shrinkage of mortars.
Microencapsulation of the silicone resin proved to be a promising solution for the bulk hydrophobic treatment of cementitious materials with no-influence on cement hydration.
Datum prijs2017
Originele taalEnglish
Prijsuitreikende instantie
  • Université libre de Bruxelles
BegeleiderM.p. Delplancke (Promotor)

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