| Summary: | Concrete, due to its low cost, durability and fire resistance, is one of the world’s most
widely used construction materials. Concrete is typically reinforced with steel bars
and welded wire mesh. Since the cost of steel is increasing and steel corrosion is a
significant contributor to structural failure, it is advantageous to find an alternative
replacement reinforcement material which can not only replace the steel, but also
resist corrosion.
Over the past few decades, polymeric fibres have been used as concrete reinforcement.
The chemical bond between the polymeric fibre and the cementitious matrix
is an important factor in the fibre’s performance as a concrete reinforcement. Despite
the great importance of the chemical bonding at the polymeric fibre/concrete
interface, the chemical bonding at the interface is not well understood.
To investigate the chemical interactions between polymeric materials and concrete,
model systems of polymeric powder/white cement and polymeric fibre/white cement
were chosen, where white cement was chosen for its suitability for nuclear magnetic
resonance (NMR) experiments. The chemical interactions between poly(ethylenevinyl
acetate) (EVA), poly(ether imide) (PEI), and poly(vinylidene fluoride) (PVDF)
polymeric powders were studied via 13C NMR spectroscopy. It was found that EVA
admixture undergoes hydrolysis in a cementitious matrix and follows a pseudo-second
order kinetics model up to 32 days of cement hydration. PEI was also found to
undergo hydrolysis at the imide functional group in a cementitious matrix. PVDF
powder undergoes dehydrofluorination in the cementitious environment, producing a
brown coloured polymer which is a result of conjugation of the polymer backbone.
The interfacial transition zone between fluoropolymeric powder/white cement and
steel and polymeric fibres (high density polyethylene/polypropylene, poly(vinyl alcohol),
PEI, PVDF, and Nylon 6.6) was studied at short range using 19F, 27Al, and 43Ca
NMR spectroscopy and at long range using the scanning electron microscopy/energy
dispersive spectroscopy method. It was concluded that the chemistry of polymeric
fibres themselves can alter the surrounding interfacial transition zone such that the
calcium silicate hydrate favours a tobermorite or jennite-like structure, which could
contribute to a strong or weak interface.
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