Properties of Repair Materials
In addition to conventional portland-cement concrete and
mortar, there are hundreds of proprietary repair materials
on the market, and new materials are continually being
introduced. This wide variety of both specialty and conventional
repair materials provides a greater opportunity
to match material properties with specific project requirements;
however, it can also increase the chances of selecting
an inappropriate material. No matter how carefully a
repair is made, use of the wrong material will likely lead
to early repair failure (Warner 1984). Some of the material
properties and their relative importance to durable
repairs are discussed in the following text. These properties
should be considered before any material is selected
for use on a repair or rehabilitation project.
a. Compressive strength. Although there is some
controversy over the required structural performance for
many repairs, it is generally accepted that the repair material
should have a compressive strength similar to that of
the existing concrete substrate. Assuming the need for
repair is not necessitated by inadequate strength, there is
usually little advantage to be gained from repair materials
with compressive strengths greater than that of the concrete
substrate. In fact, significantly higher strengths of
cementitious materials may indicate an excessive cement
content which can contribute to higher heat of hydration
and increased drying shrinkage. Repair of erosiondamaged
concrete is one area in which increased strength
(and corresponding higher erosion resistance) of the repair
material is desirable.
b. Modulus of elasticity. Modulus of elasticity is a
measure of stiffness with higher modulus materials
exhibiting less deformation under load compared to low
modulus materials. In simple engineering terms, the
modulus of elasticity of a repair material should be similar
to that of the concrete substrate to achieve uniform
load transfer across the repaired section. A repair material
with a lower modulus of elasticity will exhibit lower
internal stresses thus reducing the potential for cracking
and delamination of the repair.
Properties of Repair MaterialsIn addition to conventional portland-cement concrete andmortar, there are hundreds of proprietary repair materialson the market, and new materials are continually beingintroduced. This wide variety of both specialty and conventionalrepair materials provides a greater opportunityto match material properties with specific project requirements;however, it can also increase the chances of selectingan inappropriate material. No matter how carefully arepair is made, use of the wrong material will likely leadto early repair failure (Warner 1984). Some of the materialproperties and their relative importance to durablerepairs are discussed in the following text. These propertiesshould be considered before any material is selectedfor use on a repair or rehabilitation project.a. Compressive strength. Although there is somecontroversy over the required structural performance formany repairs, it is generally accepted that the repair materialshould have a compressive strength similar to that ofthe existing concrete substrate. Assuming the need forrepair is not necessitated by inadequate strength, there isusually little advantage to be gained from repair materialswith compressive strengths greater than that of the concretesubstrate. In fact, significantly higher strengths ofcementitious materials may indicate an excessive cementcontent which can contribute to higher heat of hydrationand increased drying shrinkage. Repair of erosiondamagedconcrete is one area in which increased strength(and corresponding higher erosion resistance) of the repairmaterial is desirable.b. Modulus of elasticity. Modulus of elasticity is ameasure of stiffness with higher modulus materialsexhibiting less deformation under load compared to lowmodulus materials. In simple engineering terms, themodulus of elasticity of a repair material should be similarto that of the concrete substrate to achieve uniformload transfer across the repaired section. A repair materialwith a lower modulus of elasticity will exhibit lowerinternal stresses thus reducing the potential for crackingand delamination of the repair.
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