Thursday, September 19, 2013
Repair of Reinforced Concrete Structures
Commonly Encountered Problems
1. Spalling, cracking, water leakage, surface
erosion, staining.
2. Water and corrosion related deterioration
a improper design and detailing
b. cracks
c. carbonation
d. poor original quality concrete, porous
concrete
e. lack of maintenance or improper
maintenance
f. presence of chlorides
3.Volume changes - creep and shrinkage
4. Structural failure
5. Fire
Condition Assessment
1. Information Gathering
2. Field Survey
3. Field Tests
4. Laboratory Tests
Repair Methods & Material
1. Repair Materials
a.portland cement
b.polymer modified concrete
c. resin mixtures
d.substitute materials
Nomenclature
polymer concrete (PC): formed by polymerizing a mixture of a monomer and aggregate (no other bonding material) latex-modified concrete (LMC): also known as polymer portland cement concrete. Conventional concrete made by replacing part of mixing water with a latex.
polymer-impregnated concrete (PIC): produced by impregnating or infiltrating a hardened concrete with a monomer and subsequently polymerizing the monomer in situ.
Significance
Both PC and LMC have been in commercial use since the 1950s;
PIC was developed and has been in use since the 1970s.
Depending on the materials employed, PC can develop compressive strengths of the order of 140 MPa (20,000 psi) within hours or even
minutes and is therefore suitable for emergency concreting jobs in mines,
tunnels, and highways.
Significance -- LMC
LMC possess excellent bonding ability to old
concrete, and high durability to aggressive
solutions; it has therefore been used mainly
for overlays in industrial floors, and for
rehabilitation of deteriorated bridge decks.
Significance -- PIC
In the case of PIC, by effectively sealing the
microcracks and capillary pores, it is
possible to produce a virtually impermeable
product which gives an ultimate strength of
the same order as that of PC.
PIC has been used for the production of highstrength
precast products and for improving
the durability of bridge deck surfaces.
Polymer Concrete
Polymer concrete (PC) is a mixture of
aggregates with a polymer as the sole
binder. To minimize the amount of the
expensive binder, it is very important to
achieve the maximum possible dry-packed
density of the aggregate.
Polymer
Commercial products are available with a variety of
formulations, some capable of hardening to 105 MPa
(15,000 psi) within a few minutes without thermal
treatment.
Epoxy resins are higher in cost but offer advantages
such as adhesion to wet surfaces.
Styrene monomer, and methyl methacrylate (MMA) with
benzoyl peroxide catalyst and an amine promoter
are often used.
Products with increased strength have been obtained
by adding to the PC monomer system a silane
coupling agent, which increases the interfacial bond
between the polymer and aggregate.
Properties
Stress-Strain Diagram
Properties
Due to good chemical resistance and high initial
strength and modulus of elasticity, industrial use of
PC has been mainly in overlays and repair jobs.
Thermal and creep characteristics of the material are
usually not favorable for structural applications of
PC.
Polyester concretes are viscoelastic and will fail under
a sustained compressive loading at stress levels
greater than 50 percent of the ultimate strength.
Sustained loadings at a stress level of 25 percent did
not reduce ultimate strength capacity for a loading
period of 1000 hr.
Latex-Modified Concrete
The materials and the production technology
for concrete in LMC are the same as those
used in normal portland cement concrete
except that latex, which is a colloidal
suspension of polymer in water, is used as
an admixture.
Earlier latexes were based on polyvinyl acetate
or polyvinylidene chloride, but these are
seldom used now because of the risk of
corrosion of steel in concrete in the latter
case, and low wet strengths in the former.
Elastomeric or rubberlike polymers based on
styrenebutadiene and polyacrylate
copolymers are more commonly used now.
Latex
A latex generally contains about 50 % by
weight of spherical and very small (0.01 to 1
m in diameter) polymer particles held in
suspension in water by surface-active
agents.
The presence of surface-active agents in the
latex tends to incorporate large amounts of
entrained air in concrete; therefore, air
detraining agents are usually added to
commercial latexes.
10 to 25 percent polymer (solid basis) by weight of
cement is used in typical LMC formulations,
the addition of latex provides a large quantity of the
needed mixing water in concrete.
The application of LMC is limited to overlays where
durability to severe environmental conditions is of
primary concern.
LMC is made with as low an addition of extra mixing
water as possible; the spherical polymer molecules
and the entrained air associated with the latex
usually provide excellent workability.
Curing
The hardening of a latex takes place by drying
or loss of water.
Dry curing is mandatory for LMC; the material
cured in air is believed to form a continuous
and coherent polymer film which coats the
cement hydration products, aggregate
particles, and even the capillary pores.
Properties
The most impressive characteristics of LMC are its
ability to bond strongly with old concrete, and to
resist the entry of water and aggressive solutions.
It is believed that the polymer film lining the capillary
pores and microcracks does an excellent job in
impeding the fluid flow in LMC.
These characteristics have made the LMC a popular
material for rehabilitation of deteriorated floors,
pavements, and bridge decks.
Commonly Encountered Problems
1. Spalling, cracking, water leakage, surface
erosion, staining.
2. Water and corrosion related deterioration
a improper design and detailing
b. cracks
c. carbonation
d. poor original quality concrete, porous
concrete
e. lack of maintenance or improper
maintenance
f. presence of chlorides
3.Volume changes - creep and shrinkage
4. Structural failure
5. Fire
Condition Assessment
1. Information Gathering
2. Field Survey
3. Field Tests
4. Laboratory Tests
Repair Methods & Material
1. Repair Materials
a.portland cement
b.polymer modified concrete
c. resin mixtures
d.substitute materials
Nomenclature
polymer concrete (PC): formed by polymerizing a mixture of a monomer and aggregate (no other bonding material) latex-modified concrete (LMC): also known as polymer portland cement concrete. Conventional concrete made by replacing part of mixing water with a latex.
polymer-impregnated concrete (PIC): produced by impregnating or infiltrating a hardened concrete with a monomer and subsequently polymerizing the monomer in situ.
Significance
Both PC and LMC have been in commercial use since the 1950s;
PIC was developed and has been in use since the 1970s.
Depending on the materials employed, PC can develop compressive strengths of the order of 140 MPa (20,000 psi) within hours or even
minutes and is therefore suitable for emergency concreting jobs in mines,
tunnels, and highways.
Significance -- LMC
LMC possess excellent bonding ability to old
concrete, and high durability to aggressive
solutions; it has therefore been used mainly
for overlays in industrial floors, and for
rehabilitation of deteriorated bridge decks.
Significance -- PIC
In the case of PIC, by effectively sealing the
microcracks and capillary pores, it is
possible to produce a virtually impermeable
product which gives an ultimate strength of
the same order as that of PC.
PIC has been used for the production of highstrength
precast products and for improving
the durability of bridge deck surfaces.Polymer Concrete
Polymer concrete (PC) is a mixture of
aggregates with a polymer as the sole
binder. To minimize the amount of the
expensive binder, it is very important to
achieve the maximum possible dry-packed
density of the aggregate.
Polymer
Commercial products are available with a variety of
formulations, some capable of hardening to 105 MPa
(15,000 psi) within a few minutes without thermal
treatment.
Epoxy resins are higher in cost but offer advantages
such as adhesion to wet surfaces.
Styrene monomer, and methyl methacrylate (MMA) with
benzoyl peroxide catalyst and an amine promoter
are often used.
Products with increased strength have been obtained
by adding to the PC monomer system a silane
coupling agent, which increases the interfacial bond
between the polymer and aggregate.
Properties
The properties of PC are largely dependent on
the amount and properties of polymer in the
concrete.
PC made with MMA is a brittle material that
shows a nearly linear stress-strain
relationship with high ultimate strength, but
the addition of butyl acrylate produces a
more ductile material
Stress-Strain Diagram
Properties
Due to good chemical resistance and high initial
strength and modulus of elasticity, industrial use of
PC has been mainly in overlays and repair jobs.
Thermal and creep characteristics of the material are
usually not favorable for structural applications of
PC.
Polyester concretes are viscoelastic and will fail under
a sustained compressive loading at stress levels
greater than 50 percent of the ultimate strength.
Sustained loadings at a stress level of 25 percent did
not reduce ultimate strength capacity for a loading
period of 1000 hr.
Latex-Modified Concrete
The materials and the production technology
for concrete in LMC are the same as those
used in normal portland cement concrete
except that latex, which is a colloidal
suspension of polymer in water, is used as
an admixture.
Earlier latexes were based on polyvinyl acetate
or polyvinylidene chloride, but these are
seldom used now because of the risk of
corrosion of steel in concrete in the latter
case, and low wet strengths in the former.
Elastomeric or rubberlike polymers based on
styrenebutadiene and polyacrylate
copolymers are more commonly used now.
Latex
A latex generally contains about 50 % by
weight of spherical and very small (0.01 to 1m in diameter) polymer particles held in
suspension in water by surface-active
agents.
The presence of surface-active agents in the
latex tends to incorporate large amounts of
entrained air in concrete; therefore, air
detraining agents are usually added to
commercial latexes.
10 to 25 percent polymer (solid basis) by weight of
cement is used in typical LMC formulations,
the addition of latex provides a large quantity of the
needed mixing water in concrete.
The application of LMC is limited to overlays where
durability to severe environmental conditions is of
primary concern.
LMC is made with as low an addition of extra mixing
water as possible; the spherical polymer molecules
and the entrained air associated with the latex
usually provide excellent workability.
Curing
The hardening of a latex takes place by drying
or loss of water.
Dry curing is mandatory for LMC; the material
cured in air is believed to form a continuous
and coherent polymer film which coats the
cement hydration products, aggregate
particles, and even the capillary pores.
Properties
The most impressive characteristics of LMC are its
ability to bond strongly with old concrete, and to
resist the entry of water and aggressive solutions.
It is believed that the polymer film lining the capillary
pores and microcracks does an excellent job in
impeding the fluid flow in LMC.
These characteristics have made the LMC a popular
material for rehabilitation of deteriorated floors,
pavements, and bridge decks.
