Civil Engineering Reference
In-Depth Information
phenols reacted with ethylene) (Mehta and Monteiro, 2006). The presence of
such agents leads to the incorporation of air in concrete. Since an excess of
air inclusion is detrimental for the mechanical properties of PMC as well as
for its durability, air detraining agents are, then, usually added to commercial
latexes (Wang et al., 2005).
PMCs are mixed with water and directly added to the cement/aggregate
mixes, using the same equipment and tools used for mortar or concrete.
They display a better workability over standard concrete. The slump tends
to increase with polymer/cement ratio. This was attributed to the anti-friction
action of polymeric particles and to the presence of air bubbles. The resistance
to bleeding and segregation of latex-modified mortar or concrete is excellent
in spite of their larger flowability characteristics (Paiva et al., 2006).
At the same level of polymer/cement ratio, better performance, especially
resistance to freeze-thaw cycles, is obtained by pre-mixing polymer with sand
(Wu et al., 2002). Curing under wet conditions, such as water immersion or
moist curing, is detrimental to PMC. The PMCs require, in fact, a different
curing method: the best properties are achieved by a combined wet and dry
curing (Knapen and Van gemert, 2009a). The setting and hardening of PMC
are delayed to some extent in comparison with ordinary cement concrete,
depending on the polymer type and polymer/cement ratio (ohama, 1998;
Puterman and Malorny, 1998).
According to gajbhive et al. (2010), the polymers are adsorbed on the surface
of cement hydration products and a weak interaction takes place between
these products and the polymer. PMC hardening evolution is influenced by
both cement hydration and polymer film formation processes in their binder
phase. The cement hydration generally precedes the polymeric film formation,
formed by coalescence of polymeric particles in latexes (Beeldens et al.,
2001). Chemical reactions may also take place between the polymeric film
and cement hydrates and aggregates, improving the properties of hardened
latex-modified mortar and concrete (Ohama, 1998).
The tendency of certain water-soluble polymers to retard the flocculation
of the cement particles minimizes the formation of a water-rich layer around
the aggregate surfaces. They also provide a more uniform distribution of
un-hydrated cement particles in the matrix. Both effects enable a reduction
in the interfacial transition zone
(Knapen and Van gemert, 2011).
The presence of polymers influences the morphology of the Ca(OH)
2
crystals
developed by the Portland cement hydration. Polymer bridges are formed
between the layered Ca(oH)
2
crystals, increasing the interphase bonding and
producing a better structure. Water-soluble polymers are found to improve
further the internal cohesion of the cement paste. The strengthening of the
hardened paste results in a significantly lower crack formation (Knapen
and Van gemert, 2009b). PMC has an excellent adhesion strength and
durability and it is, therefore, widely used as a repairing material, enabling
