Causes of Concrete Deterioration

Technical & Installation Notes

General Notes

 General Principles: Assessment, Planning, Preparation, Execution

 General Principles: Causes of Concrete Deterioration
 Contact Us — General RPS Inquiries
 Contact Us About Concrete Strengthening Systems: FRP and FRCM

RPS Literature

 Fliers
 Application and Installation Guides
 Product Data Sheets
 Product Safety Data Sheets (SDS)

RPS Software And Apps

 Product Certifications

General Product Use Information

 Terms and Conditions of Sale

 Limited Warranty
 Warning

In order to effectively assess, plan, prepare and execute a successful repair, protection and strengthening
(RPS) strategy for concrete and/or masonry, it is important to understand the root cause of the
deterioration. Understanding the service conditions of the structure and matching the appropriate
product(s) to the performance requirements of the project will ensure a lasting repair tailored to the
specific needs of the owner.

The two main factors that influence concrete performance are:

 Placement Issues
 Service Condition Issues

Concrete failures can be the result of a combination of placement and/or service condition issues.
Cracking, spalling, leaking, premature or excessive wear, scaling, settlement, deflection and
disintegration are examples of conditions that lead to concrete failure. Understanding these failure modes
and their root cause is necessary to develop a successful repair strategy.

When planning an RPS strategy for deteriorated concrete, one must consider and address the following
in-service factors:

 Environmental conditions
 Chemical exposure
 Exposure to water and mobile debris
 Concrete properties (strength, type, aggregate, etc.)

Placement Issues
Proper concrete placement is essential not only to satisfy the design and service requirements of the
structure, but also to decrease the potential for premature deterioration and reduced lifespan. Identifying
defects in the assessment stage of an RPS project is important in developing the proper repair plan to
address the specific cause of the damaged concrete.

One of the most common defects in concrete is cracking. Cracking can be caused by inadequate
substrate or subbase preparation, high water-to-cement ratio, improper curing methods, poor concrete
consolidation, timing of control-joint installation and many other placement factors. Cracking can also be
caused by design-related issues such as inadequate reinforcement or insufficient control-joint spacing.

Excess water increases the water-to-cement ratio of concrete and increases workability; however, this
benefit is not without cost. The additional water eventually evaporates in the hydration (curing) process,
leaving a porous network of capillary voids and lower overall strength.

Excess water can also lead to segregation, or the settling of large aggregates to the bottom of the matrix,
resulting in reduced structural capacity and increased likelihood of cracking.

Proper curing involves maintaining an adequate moisture content and temperature in freshly-placed
concrete to allow for full hydration (curing) of the cement while the concrete develops its intended design
strength. The absence of moisture stops the hydration process which can lead to lower strengths. Rapid
moisture loss of freshly-placed concrete can also lead to plastic shrinkage cracking, which are random
shallow cracks on the surface of the concrete.

Poor consolidation can result from improper vibration and/or poor mix design. If the concrete does not
fully consolidate around the reinforcing steel, design capacity may not be reached, and cracking can
result.

Concrete expands and contracts with temperature changes. When these contraction forces exceed the
tensile strength of the concrete, cracking can occur. To influence where this cracking will occur, control
joints are installed, but the design and timing of control-joint installation are vital to their effectiveness.

Reinforcing steel (rebar) is used to increase the tensile strength of concrete. When tensile forces acting
upon a concrete element exceed its tensile strength, a crack may occur. Reinforcing steel controls the
width of the crack and can prevent complete failure of the element.

Common placement issues with concrete

Bug Holes

Cause: Entrapment of air bubbles on the formed concrete surface.

Effect: Uneven concrete surface, increased porosity due to increased surface area and poor appearance.
Rock Pockets

Cause: Improper consolidation between large aggregates and cement mortar during the placement
process creates large voids in concrete.

Effect: Reduction in strength and increased potential for water intrusion, corrosion of reinforcing steel and
reduced abrasion resistance.

Honeycombing

Cause: Improper consolidation of concrete due to lack of vibration or improper mix design.

Effect: Reduction in strength andincreased potential for water intrusion, corrosion of reinforcing steel and
reduced abrasion resistance.

Cold Joints

Cause: Delays in concrete placement where the initial lift of concrete hardens before subsequent lifts are
placed, resulting in a visible lineation and substandard bond between layers.

Effect: Water intrusion through the cold joint and corrosion of reinforcing steel.

Service Condition Issues

Common service condition issues with concrete

Corrosion of Metals

Causes: Chloride intrusion, oxygen-water exposure, corrosive chemical environment surrounding

reinforcing steel, drop in alkalinity, improper placement or concrete coverage of steel reinforcement
(rebar).

Effects: Corrosion and subsequent expansion of reinforcing steel leads to cracking and spalling, reducing
the structural capacity of the concrete.

Using concrete with a low water-to-cement ratio and proper rebar placement with adequate concrete
cover are common measures used to prevent metal corrosion.
Freeze-Thaw

Causes: Water-saturated concrete, combined with temperature cycling above and below 32°F (0°C).

Effects: Concrete absorbs water into its pores. When the water in the pores freezes, it expands, causing
scaling and delaminations.

High-strength concrete mix designs that incorporate air-entraining admixtures yield the best defense
against freeze-thaw damage. Specialty coatings and water repellents are also commonly used to
minimize water absorption and prevent freeze-thaw damage.

Chemical Attack

Causes: Exposure to acid rain, de-icing salts, in-service chemicals and naturally occurring sulfates in soils
and ground water dissolve the cement matrix which results in aggregate loss.

Effects: Loss of concrete cover and subsequent corrosion of reinforcing steel. Assessing potential
exposure before construction or repair can prevent premature deterioration.

Specific cement types, water-repellent sealers or chemically-resistant barrier coatings are all common
preventative measures to protect concrete against chemical attack.

Alkali-Aggregate Reaction

Cause: A chemical reaction between the alkali in cement and high-silica content aggregate forms a gel
around the aggregate, preventing proper bond between the aggregate and cement.

Effects: The gel expands in the presence of water, creating tension cracking around surface aggregate
and delaminations. Surface cracking promotes water intrusion which can lead to metal corrosion and
spalling.

Careful selection of aggregates and consideration of silica content can help prevent alkali-aggregate
reactions.

Erosion/Abrasion

Causes: Airborne or waterborne debris moving across the concrete surface.

Effects: Progressive section loss can lead to inadequate concrete cover and corrosion of the reinforcing
steel, reducing structural capacity.
High-strength, dense concrete and specialty abrasion-resistant coatings are the most effective means to
resist erosion and abrasion.