Tânia N. Dias, Maria S. Ribeiro, Orlando A. Pereira, Elsa M. Pereira, João L. Feiteira
Polymer cement mortars
(PCMs) are traditional mortars with a new component, the polymer, which is added
to the mixing water to modify their properties. PCMs have been increasingly
used for the repair of reinforced concrete structures, mainly due to their
improved adhesion and reduced water absorption. Higher electric resistivity and
a higher resistance to carbonation are also expected, thus leading to a
potential increased resistance to corrosion of steel embedded in PCMs.
This paper reports both the
general concepts associated with polymer modification of cement mortar (CM) and
the results of an experimental investigation into the action of
styrene-butadiene and acrylic-styrene polymer additions on the corrosion rate
of steel embedded in carbonated CM. Air content, mechanical strength, water
absorption, resistance to carbonation,
and electrical resistivity of PCMs were determined as well as the
corrosion current of steel embedded in carbonated mortar in high humidity
environments. The microstructure of the corrosion products formed in steel
rebars embedded in PCMs was characterised by scanning electron microscopy
(SEM).
Results confirmed a
noticeable reduction in the corrosion rate of steel rebars embedded in
carbonated PCMs comparatively to unmodified CM. The physical barrier created by
the polymer film in the polymer-cement co-matrix, which reduces ionic mobility
and water absorption, is pointed out as the main explanation for the potential
of polymer additions in reducing corrosion rates.
Key words: Polymer mortar;
Polymer dispersion; Corrosion; Carbonation; Repair mortar.