Page 338 - Construction Waterproofing Handbook

7.6 CHAPTER SEVEN
Additives also promote initial set and cure time, allowing substrates to withstand traf-
fic in as little as 4 hours after placement. This can be very desirable in remedial or restora-
tion work on parking decks.
Whereas capillary admixtures produce chemical reactions that fill the microscopic
pores left by hydration, polymer admixtures produce reactions that eliminate or reduce
these microscopic pores. Polymer mixes also reduce the shrinkage that leads to cracking
and fissures in a substrate, allowing water penetration. These features provide the charac-
teristics of low absorption that makes polymer concrete highly resistant to chloride attack.
Polymer concrete products do not completely waterproof a structure. They are subject to
cracking should structural, thermal, or differential movement occur.
Due to the high costs of polymer concrete, these materials are often used as overlays,
not as complete substitutes for conventional concrete. These materials are used in renova-
tions of existing concrete walks, bridges, and parking garage decks. They are also used for
warehouse and manufacturing plant floors, where high-impact strength and chemical resis-
tance are necessary.
Polymer mixes are also chosen for installations not over occupied spaces, such as
bridges, tunnels, and decks, where additional structural properties such as high compres-
sive strength are necessary. In remedial installations such as parking decks, where rein-
forcing steel too close to the surface has caused concrete spalling, polymers provide an
overlay to restore structural integrity. (See Table 7.5.)

POLYMER ADMIXTURE APPLICATION

Polymer admixtures that are added to cement paste do not require any specific surface
preparation. Polymer concrete applied as an overlay requires that existing substrates be
thoroughly cleaned to remove all dirt, oil, grease, and other contaminants. Exposed rein-
forcing steel is sandblasted and coated with a primer or epoxy coating before overlay
application. Existing decks should be thoroughly checked for delaminated areas by the
chain-drag method and repaired before overlay application.
Polymer products added to concrete mixes require that proper mixing and preparations
be used. Applications including overlays require proper proportioning and mixing accord-
ing to the manufacturer’s recommendations. Materials are placed and finished as conven-
tional concrete. Working times with polymer concrete are substantially less than with
conventional concrete.
In preparation for overlays to existing substrates, concrete should be sufficiently damp
to prevent moisture from being absorbed from the polymer overlay mix. Polymers require

TABLE 7.5 Properties of Polymer Concrete

Advantages Disadvantages
Thin applications Cost
High strength Not completely waterproof
Chemical resistance No movement capability