THESIS
2018
xxi, 128 pages : illustrations (some color) ; 30 cm
Abstract
Cement-based materials has high compressive strength but is relatively weak in tension,
and its porosity can lead to physical and chemical deterioration. Polymers, on the other
hand, are weak in compression but have relatively high tensile capacities and provide
good resistance to physical and chemical attack. Integration of these two materials can
yield composites with excellent strength and durability properties. In this thesis, the
preparation and characterization of cement-organic composites were conducted. Also, the
mechanism for performance enhancement of such composites was further studied.
Firstly, by controlling the temperature in the hydration process of Ca
3SiO
3, non-aggregated
Ca(OH)
2 nanoparticles were synthesized, with diameters 5 nm. These
nanoparticles were appl...[
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Cement-based materials has high compressive strength but is relatively weak in tension,
and its porosity can lead to physical and chemical deterioration. Polymers, on the other
hand, are weak in compression but have relatively high tensile capacities and provide
good resistance to physical and chemical attack. Integration of these two materials can
yield composites with excellent strength and durability properties. In this thesis, the
preparation and characterization of cement-organic composites were conducted. Also, the
mechanism for performance enhancement of such composites was further studied.
Firstly, by controlling the temperature in the hydration process of Ca
3SiO
3, non-aggregated
Ca(OH)
2 nanoparticles were synthesized, with diameters < 5 nm. These
nanoparticles were applied to improve the mechanical properties of polyacrylamide
hydrogels. The tensile stress and stretch ratio at rupture of the enhanced NC gel could
achieve 430 KPa and 121 with only 40-p.p.m. nanoparticle content. The NC gel
containing 200-p.p.m. nanoparticles could revert to 90% of its original size after enduring
100-MPa compressive stress. Moreover, the possibility of using cement particles to
replace Ca
3SiO
3 for generating nano particles and enhancing PAM hydrogels was
investigated. It turned out that the nano Ca(OH)
2 particles could be obtained from cement
suspension, with Polycarboxylate ether (PCE) as the dispersant. And the enhancement
effect to the polymer network was similar. It implied that nanoparticles for significant
hydrogel enhancement could be mass-produced as Portland cement were cheap and
available at every corner of the world, which made it possible to produce the cost-effective
engineering hydrogels with excellent mechanical properties.
Secondly, in addition to employing cement generated nano particles to enhance the
organic materials, the effect of organic material on property enhancement of cement-based
materials was investigated. Based on the strong chemical bonding between Ca
2+
and PAM, the PAM/cement composite with the continuous interpenetrating network was
produced by a simple in-situ polymerization process. The continuous polymer-cement
network in the composite, as evidenced by SEM, EDS and Tof-sims results, could greatly
improve the flexural strength of the composite. With only 1% polymer content, the
flexural strength increased almost three times and at the same time the compressive
strength could still be maintained almost the same value with OPC reference specimens.
Inspired by the high viscosity of cement slurry after adding the PAM gels, a double
framework lightweight cement composite was developed by applying high water/cement
ratio in the fabrication process. This unique double network provided the possibility of
achieving lightweight cement composite by simple adjusting the proportion of gel
solution. Also, the density, mechanical and thermal properties of LW cement composite
were controllable.
Finally, besides Ca
3SiO
3 and cement, the feasibility of using other inorganic salts like
magnesium oxide to produce tiny nanocrystals to enhance the hydrogels was investigated.
It had been demonstrated by the experiments that MgO could also be used to generate
nano particles to strengthen hydrogel. It could be summarized to a general method to
produce nano particles, i.e. controlled ion release and nano crystal particle formation from
an inorganic filler. Such method would have a great potential to be used in future.
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