Civil Engineering Reference
In-Depth Information
modulus, compressive strength and compressive ductility are decreased. All
these effects increase with increasing the methylcellulose content (Fu and
Chung, 1996). The combined use of silica fume (15% wt of cement) and
methylcellulose (0.4% wt of cement) as admixtures was found to give concrete
exhibiting high bond strength to steel rebar (Fu and Chung, 1998).
ethylene-vinyl acetate (eVA) copolymer, as latex or re-dispersible powder,
is usually added to concrete to improve the fracture toughness, impermeability
and bond strength to various substrates. eVA copolymer reduces the calcium
hydroxide in the cement paste due to chemical interactions between Ca
2+
ions
and anions acetate released by eVA alkaline hydrolysis. These interactions
decrease the EVA flexibility, thus promoting the increase of elasticity modulus
of cement-based materials (Betioli et al., 2009).
Compared with polyvinyl alcohol (PVAl), polyvinyl acetate (PVAc)
yields concretes with better strength and chemical resistance properties due
to the formation of a strong chemical bond between the two phases, i.e.
cement and polymer. re-dispersible polymer powder of vinyl acetate-versatic
vinylester copolymer (VA-VeoVa) exhibits excellent water-reduction and
water-retention effects in cement concrete and improves concrete properties
effectively. Moreover, the addition of VA-VeoVA copolymer strongly reduces
the portlandite formation, being this result attributed principally to lower
Portland cement hydration (gomes and Ferreira, 2005).
The introduction of an epoxy resin, even at low ratios, increases the
corrosion resistance of the resulting PMC, due to the reduction of the concrete
permeability (el-Hawary and Abdul-Jaleel, 2010)
.
The epoxy emulsion has
a greater effect on improvement of properties of the mortar than the acrylic
one, at the same amount of polymer/cement ratio. Moreover, epoxy emulsion
is considered non-re-emulsifiable latex (Type II ASTM 1059) and, therefore,
it is not destabilized under humid and alkaline environment, but acrylic-based
mortar can be. Thus, epoxy emulsion-based mortar can be used for repair
works in humid and industrial environments (Aggarwal et al., 2007).
The results obtained by Morin et al. (2011) showed that the presence of
thin polymer layers at the paste aggregate interfaces in 'micro-concretes',
with a maximum aggregate diameter of 10 mm, can have a significant effect
on cracking behavior at much lower polymer dosages than those commonly
used in conventional polymer-modified mortars.
16.3.3 Durability
The durability of PMC to freeze-thaw is generally very high due to the
introduction of air in the latex concrete. on the other hand, the durability to
strong acids is not always appreciable, due to the alkalinity of concrete.
Concretes with the styrene-acrylic ester polymer or with vinyl-copolymer,
with a content of polymer of 7.5% wt. of cement, showed a higher resistance
