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Sub- Concrete Technology

Topic-Repair technology for concrete structure

Sem-6^th

Branch- Civil Engineering

ER.S.DAS/Er. Sasmita Gochhayat

HOD,CIVIL ENGINEERING

AY:2021-2022

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Repair technology for concrete structures

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CONTENT

INTRODUCTION
SYMPTOMS, CAUSES AND PREVENTION AND REMEDY OF DEFECTS DURING CONSTRUCTION
CRACKING OF CONCRETE DUE TO DIFFERENT REASONS
REPAIRS OF CRACKS FOR DIFFERENT PURPOSES
SELECTION OF TECHNIQUES
POLYMER BASED REPAIRS
COMMON TYPES OF REPAIRS

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INTRODUCTION

Though concrete is a relatively durable building materials, it may suffer damage bor distress during its service life due to a number of reasons.

The structural causes of distress of concrete may include externally applied and environmental loads exceeding the design stipulation , accidents and subsidences. The other causes may be drying shrinkage , thermal stress , weathering, chemical reactions and corrosion of reinforcement.

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SYMPTOMS, CAUSES, PREVENTION & REMEDY

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Symptoms :

Cracks in horizontal surface, as concrete stiffens or very soon thereafter.
Cracks in thick sections, occuring as concrete cools.
Blowholes in form faces of concrete.
Voids in concrete.
Erosion of vertical surface, in vertical streaky pattern.
Color variations.
Powdery formed surface.
Rust strains.
Lack of cover to reinforcement.

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Causes:

Structural deficiency resulting from errors in design, loading criteria, unexpected overloading, etc.
Structural deficiency due to construction defects.
Damage due to fire, floods, earthquakes, cyclones etc.
Damage due to chemical attack.
Damage due to marine environments.
Damage due to abrasion of granular materials.
Movement of concrete due to physical characteristics.
Surface retardation, caused by sugars in certain timbers.
Scouring: Water moving upwards against form faces.

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Prevention:

Change in mix design
Use air entrainment
Shelter during placing. Cover as early as possible.
Improve vibration. Use appropriate release agent.
Improve compaction. Reduce maximum size of aggregate
Prevent leakage of grout. Use absorbent formwork.
Ensure unformity of all relevant factors.
More care in applications of release agents and removal of formwork.
Provide better support for reinforcement. More accurate steel fixing. Greater tolerances in detailing.

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Remedy:

Seal by brushing in cement or low viscosity polymer.
Seal cracks.
Fill with polymer- modified fine mortar .
Inject resins.
Rub in polmer- modified fine mortar.
Apply surface coating.
Clean with dilute acid or sodium citrate/ sodium dithionite. Apply surface coating.

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CRACKING OF CONCRETE

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Definition: A complete or incomplete separation of either concrete or masonry into two or more parts produced by breaking or fracturing.�Cracks are categorized as occurring either in plastic concrete or hardened concrete.
Reason :

#1 - Excess water in the mix

#2 - Rapid drying of the concrete

#3 - Improper strength concrete poured on the job

#4- Never pour concrete on frozen ground.

#5 – Lack of control joints

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Types of Cracks in Concrete

1. Plastic shrinkage concrete cracks : While plastic shrinkage cracks can happen anywhere in a slab or wall, they almost always happen at reentrant corners or with circular objects in the middle of a slab .Plastic shrinkage cracks are typically very narrow in width and barely visible. While nearly invisible, it is important to remember that plastic shrinkage cracks don’t just exist on the surface, they extend throughout the entire thickness of the slab.

2. Expansion concrete cracks : When concrete expands, it pushes against anything in its way (a brick wall or adjacent slab for example). When neither has the ability to flex, the expanding force can be enough to cause concrete to cracks.

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3. Heaving concrete cracks: When the ground freezes, it can sometimes lift many inches before thawing and settling back down. This ground movement brought on by the freezing and thawing cycle is a huge factor contributing to concrete cracking.

4. Settling concrete cracks : Settling cracks typically occur in situations where a void is created in the ground below the concrete surface.

5. Concrete cracks caused by overloading the slab: After a heavy rain or snowmelt when the ground below is soft and wet, excessive weight on the slab can press the concrete down and result in cracks. Residential homeowners who place large recreational vehicles or dumpsters on their driveways are more likely to see this type of cracking.

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6. Concrete cracks caused by premature drying: There are two common types of cracks brought on by premature drying.

Crazing cracks are very fine, surface cracks that resemble spider webs or shattered glass. When the top of a concrete slab loses moisture too quickly, crazing cracks will likely appear. While unsightly, crazing cracks are not a structural concern.
Crusting cracks typically happen during the concrete stamping process, which is a way of adding texture or pattern to concrete surfaces. On sunny or windy days where the top of the slab dries out quicker than the bottom, the top of the concrete surface can become crusty. When the stamp is embedded, it pulls the surface apart near the stamped joints and causes small cracks around the outside edges of the “stones”

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REPAIRS OF CRACKS

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For different purposes:

The repair of concrete structures may vary between just giving a cosmetic treatment and a total replacement. By a proper investigation and by using well – designed equipment, tools and materials, a number of structure which may appear to have been damaged beyond repair can be reinstated economically.

Repair method can be selected depending upon the cause and extent of damage, importance of the structural element, and its location. The different purposes for repair of concrete :-

To increase strength or restore load carrying capacity
To restore or increase stiffness
To improve functional performance
To provide water tightness
To improve appearance of concrete surface
To improve durability
To prevent access of corrosive material to reinforcement

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REPAIR TECHNIQUES ~

There are several concrete crack repair methods and techniques used. The repair of cracked or damaged structures is discussed under two distinct categories, namely, ordinary or conventional procedure; and special procedures using the latest techniques and newer material.

Ordinary Procedure

Superficial or fine cracks are generally removed by treating the surface with whitewash, soft distemper, silicate cement paint,etc.The methods and materials used for the repair of patches of deteriorated concrete in the structures are described below. The repair is carried out in four steps.

Preparation of surface
Selection of material
Application of material:- The methods generally used for filling the material are:

a) Drypacking

b) Concrete replacement

c) Mortar replacement

d) Grouting

e) Large volume prepacking of concrete

f) Shotcreting or guniting

4. Curing of repair work

Special Procedure

The polymers have been recently introduced in concrete technology for multi- purpose applications in the repair and maintenance of concrete building and other structures . The polymers used in concrete repair principally consist of two different types of material:

1. Polymers used as modifiers for cementing systems

2. Reactive- thermosetting resins

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Epoxy Injection

Routing and sealing

cement grout.

Dry packing method

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Polymer based repair:

The polymer concrete includes composite prepared by one of the following methods.

Polymer Impregnated Concrete (PIC)

Polymer Cement Concrete (PCC)

Polymer Concrete ( PC)

The polymer systems commonly used are the following :

Methyl-methacrylate(MMA)
MMA+ 10 per cent trimetholpropane trimethacrylate(TMPTA)
Styrene and polyesterstyrene
Methanol
Vinyl monomer

The polymer based crack repair can be affected in the following sections:

1. Polymer impregnated

2. Drilling and plugging

Drilling and Plugging