This document discusses polymers used for concrete repair. It describes two main types of polymers: those used to modify cementitious systems and thermosetting resin systems like epoxy, polyester, and acrylic. Polymer latexes are used as admixtures in cementitious systems where they improve properties like strength, permeability, and bonding. Resin repair mortars are used for smaller repairs under 12mm and rely on impermeability for steel protection. Epoxy, polyester, and acrylic resins are discussed in more detail regarding their chemical curing processes and appropriate uses in concrete repair.

1. CHAPTER 2
POLYMERS FOR CONCRETE
REPAIR

2. INTRODUCTION
Concrete deterioration is mostly associated with
corrosion of steel reinforcement.
Therefore the natural choice for repair would be
impermeable highly alkaline cement based
materials analogous to the passivating nature of
highly alkaline cement matrix as in good quality
concrete.
However some situations demand repair
compositions containing polymers as admixtures
for cementitious systems or as high strength
binders.

3. TYPES OF POLYMERS USED
Polymers used in concrete repair consist of two
different types of materials:
1. Polymers used to modify cementitious
systems;
2. Reactive thermosetting resins: epoxy,
polyester and acrylic resin systems.

4. POLYMER MODIFIED CEMENTITIOUS
SYSTEMS
Polymers used as admixtures for cementitious
systems are milky white dispersions (latex) in
water.
Such mortar with latex provide alkaline
passivation protection of steel.
The polymer latex acts in several ways:
Water-reducing plasticizer
Improves bond between repair mortar and
concrete
Reduces permeability of repair mortar to water
Acts as integral curing aid
Increases tensile & flexural strength of mortar.

5. POLYMER MODIFIED CEMENTITIOUS
SYSTEMS
Unmodified cementitious mortar sets and
shrinkage occurs. Micro cracks are in the order
of 4-5 micrometers.
Addition of polymer latex controls micro crack
widths to 1-2 micrometers.
Polymers form ‘elastic bands’ across the micro
cracks, increasing tensile & flexural strengths,
and reducing permeability of mortar.
Different types of polymer latexes used as
admixtures for cementitious materials are:
Polyvinyl acetates (PVAc)
Styrene butadiene (SBR)
Polyvinylidene dichloride (PVDC)
Styrene acrylics.

6. POLYMER MODIFIED CEMENTITIOUS
SYSTEMS
PVDC latexes are not recommended for repair
mortars for RCC because of the possibility of
release of free chlorides in the long run.
On-site blending:
Polymer modified mortars are blended from
sand, cement, latex and water on site.
Lack of adequate quality control may result in
unsatisfactory mortars.
Pre-blended mortars:
Complete packs of latex and pre-blended sand
& cement available.
This mortar is used for repair of Reinforced
concrete where cover to be replaced is more than
12mm, but less than 25-30mm.

7. RESIN REPAIR MORTARS
For relatively smaller repair areas, cover less
than 12mm Resin Mortars are used.
In this case protection to steel reinforcement
depends on total impermeability.
Resin Mortar = Reactive Resin + Graded
aggregate.
Commonly used Resins: Epoxy, Polyester,
Acrylic.
These are Thermosetting Resins (they do not melt
or flow like thermoplastics when heated, but lose
strength gradually).
Resin mortars are supplied as 2/3 component
systems: Resin, Hardener & Filler.

8. EPOXY RESINS
Epoxy resins consist of reactive resin which can
be considered as ‘hooks’ and a hardener (also
called curing agent) considered as ‘eyes’.
Correct proportioning and thorough mixing are
imperative while using epoxy resins.
The curing (hooking up) of epoxy resins in an
exothermic reaction.
Rate of cure is temperature dependent.

9. UNSATURATED REACTIVE POLYESTER
RESINS
In polyester resin systems, the liquid resin
component contains both ‘blocked hooks’ and
‘eyes’ in the right proportion, intimately mixed.
The hardener (or catalyst) is required just to
initiate the ‘unblocking’ of the hooks.
This results in a chain reaction that continues
throughout the resin system.
The cure of the polyester resin system is also
exothermic.

10. UNSTAURATED ACRYLIC RESINS
Acrylic resin systems form high-strength
materials by similar chemical cure mechanisms
to the unsaturated reactive polymer resins
Acrylic resins are based on monomers of very low
viscosity, hence very high filler loadings are
possible and mortars tend to exhibit less
shrinkage.

11. SAFE HANDLING OF RESINS
Epoxy, Polyester and Acrylic resins require
handling with care.
Contact with resins, especially epoxy resins can
cause skin irritation.
Polyester and Acrylic resins contain volatile
constituents which are flammable.
Most acrylic resins are highly flammable with
flash points below 10 degree Celsius, and vapours
given off can cause toxic reactions.

12. SELECTION OF RESINS
Epoxy resins are most widely used in concrete
repair.
Polyester and Acrylic resins are used for small-
area repairs and where rapid strength
development is required.
In most repair situations, the polymer-based
repair material is bonded directly to concrete or
other cementitious material.

13. POLYMER BONDING AIDS
When applying conventional concrete, sprayed
concrete or sand/cement repair mortars, bond is
often a problem.
Water loss at the interface between repair mortar
and the prepared concrete prevents proper
hydration of cement matrix at the interface.
An epoxy resin or polymer latex bonding aid can
be used to bond green uncured concrete to
hardened concrete.
Many systems are available. Instructions have to
be followed carefully.

14. REPAIR OF CRACKS/RESIN INJECTION
Cracks in concrete greater than 0.3mm have to
be sealed to prevent ingress of moisture,
oxygen,etc..
It is imperative to establish the cause before
deciding on the appropriate methods/materials
for the repair.
Only then is it possible to restore the structure
to its original tensile/shear strength.
Low viscosity epoxy, acrylic or polymer resins
specifically developed for repairing cracks may
be used.