Synthesis and Application of Superabsorbent Nanocomposites for Optimized Performance in Cement-based Materials

Fakourpour, Mahmoud | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44326 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Pourjavadi, Ali
  7. Abstract:
  8. Superabsorbent polymers are mainly used in baby diapers and in agriculture. A less known emerging and potentially important application is the internal curing of cement based materials. About a decade ago, pioneering works demonstrated that using SAP in concrete reduces autogenous shrinkage and cracking, and improves hydration of the cement matrix. However, problems like workability reduction, and deterioration of mechanical strength of the mixture are reported. In this thesis, nanocomposites using nanosilica and acrylic monomers were prepared and used to address the above problems. Nanocomposites exhibit enhanced mechanical strength and reduced sliding friction, compared with conventional polymers, which suggests their potential for better endurance in mixing process and, more importantly, a higher flowability of cementitious systems. Furthermore, mechanical properties of the cement matrix may enhance if the nanoparticles in the polymer matrix can take part in pozzolanic reaction. In this research, the effect of type and amount of monomers, and amounts of initiator and crosslinker were investigated with regard to swelling ratios in artificial and extracted pore solution and their effect on flowability of cement pastes. Results indicate that carboxylate groups in nanocomposite result in lower swelling ratios than sulfonate groups. Intermediate levels of carboxylate groups reduce the workability and higher amounts of crosslinker and intermediate levels of initiator increase it. A decreased flow is caused by sulfonate groups, especially at lower levels of crosslinker. The nanosilica content has little influence on the equilibrium swelling, but it affects flowability of pastes the same way the crosslinker does, and it is highly influenced by other factors such as type and content of ionic monomer. It appears that the interaction of nanocomposites with cementitious materials is mainly governed by electrostatic forces, and to some extent by their surface morphology. Compressive strength of mortars containing nanocomposites is increased in a few cases and might be due to the pozzolanic reaction of nanosilica. FTIR spectra and SEM images of nanocomposites’ microstructure provide evidence for successful pozzolanic reaction of nanosilica particles of the nanocomposites
  9. Keywords:
  10. Superabsorbent ; Nanocomposite ; Cements ; Concrete ; Internal Curing

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