concrete troubleshooting.pdf

7/23/2019 Concrete troubleshooting.PDF

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Concrete Troubleshooting

Presented by:

Michelle L. Wilson

Diagnosing What Went Wrong and Why

Presented at:

January 11, 2006

Portland Cement AssociationPortland Cement Association

Founded in 1916

Headquarters:Skokie, Illinois

USA

Mission: to improve and extend the

uses of portland cement and concrete

through market development,

engineering, research, education,

and public affairs work.


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Types of ConcreteTypes of Concrete

Bookcrete

Labcrete

Realcrete

Discussion:Discussion: Essentials of Quality Concrete

Avoiding Problems

Low Strength

Identifying Surface Defects

Causes

Prevention

Cure


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Quality ConcreteQuality Concrete A mixture of CEMENT, WATER, and

AGGREGATES that will meet the requirements

under which it is expected to serve.

Consistency

Workability

Uniformity

Bleeding

Setting &

Hardening

Fresh Concrete PropertiesFresh Concrete Properties


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Hydration

Drying Rate

Strength

Durability

Permeability &

Watertightness

Volume Stability &

Crack Control Aesthetics

Hardened Concrete PropertiesHardened Concrete Properties

Why do concrete problems occur?Why do concrete problems occur?


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Avoiding ProblemsAvoiding Problems

Design- Constructability

Mix Design

Materials Selection

Placement Procedures

Environment

Design

Workmanship Environment

Troubleshooting ConcreteTroubleshooting Concrete

Visual Distress

Meeting Strength


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Strength of ConcreteStrength of Concrete

Compressive

Strength-

Measured

Resistance of

Concrete to

Axial Loading.

Factors Impacting StrengthFactors Impacting Strength w/cm

Age

Air Content

Aggregate Bond

Handling

Curing

Temperature

Testing Errors


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Transporting Test CylindersTransporting Test Cylinders

After One Day

Packed in a Sturdy Box

Surrounded with Wet Sand or

Wet Saw Dust

Protected Against Freezing

Test Cylinders at the LabTest Cylinders at the Lab

ASTM C 39 Testing Cylinders

Capping

ASTM C 617 Capping

ASTM C 1231 Unbonded Caps

Measurements

Testing Maximum Load

Strength, within 10 psi

Conical Failure


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Typical Specification LimitsTypical Specification Limits

ASTM C 94 (ACI 318)

The average of any three

consecutive strength tests shall

be equal to, or greater than, the

specified strength, f c

.

No individual strength test shall

be more than 500 psi [3.5 MPa]

below the specified strength, f c.


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Low StrengthsLow Strengths

< 500 psi

Avg of 3

279524852510 +2460 = 24857

Avg of 3296530703040 + 3100 = 30706

Avg of 3298828302800 + 2860 = 28305

OK305829952980 + 3010 = 59904

OK309231403120 + 3160 = 62803

OK-30403060 + 3020 = 60802

OK-30953110 + 3080 = 61901

EvaluationAvg. of

3 Tests

Aver of 2

Strengths

Individual Strengths

fc = 3000

Test

What to Do?What to Do?

Increase Cementitious Materials

Change Mix Proportions

Reduce or Better Control Slump

Reduce Delivery Time

Closer Control of Air Content Improve Quality of Testing


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ApplyApply JudgementJudgement

1 in 100 Tests Fail Even ThoughConcrete Strength andUniformity May Be Satisfactory

Allowance for StatisticallyExpected Variations

Investigation of Low Strengths

Nondestructive Testing

Compressive Strengths of Cores

Identify Concrete Surface DefectsIdentify Concrete Surface DefectsACI 201.1 RACI 201.1 R

Blistering

Bugholes

Delaminations

Crazing

Cracking Honeycombing

Cold Joint

Discoloration

Staining

Efflorescence

Dusting

Freezing

Popouts Mortar Flaking

Scaling

Spalling


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When troubleshootingconcrete problems it is

important to relate the

symptom to causes of

distress and deterioration.

Surface DefectsSurface Defects--BlisteringBlistering

The irregular raising of a thin layer

at the surface of placed mortar or

concrete during or soon after

completion of the finishing

operation.


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Surface DefectsSurface Defects--BugholesBugholes

Small regular or irregular cavities,

usually not exceeding 15 mm in

diameter, resulting from

entrapment of air bubbles in the

surface of formed concrete during

placement and compaction.


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Surface DefectsSurface Defects--DelaminationDelamination

A separation along a plane

parallel to a surface. In the case

of a concrete slab, a horizontal

splitting, cracking, or separation of

a slab in a plane roughly parallel

to, and generally near, the upper

surface.


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Sealing The SurfaceSealing The Surface

Improper Tooling Traps Bleed Water

and Air Beneath Layer

of Mortar

Surface DefectsSurface Defects--CrazingCrazing

Fine, random cracks or fissures in

the surface of plaster, cement

paste, mortar, or concrete.


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Surface DefectsSurface Defects--CrackingCracking

A complete or incomplete

separation, of either concrete or

masonry, into two or more parts

produced by breaking or

fracturing.


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Surface DefectsSurface Defects--HoneycombingHoneycombing

Voids left in concrete due to

failure of the mortar to effectively

fill the spaces among course

aggregate particles.


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Surface DefectsSurface Defects--Cold JointCold Joint

Visible lines on the surfaces of

formed concrete indicating the

presence of joints where one

layer of concrete had hardened

before subsequent concrete was

placed.


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Surface DefectsSurface Defects--DiscolorationDiscoloration

A departure of color from that

which is normal or desired.


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Surface DefectsSurface Defects--StainingStaining

Spotted or mottled light or dark

blotches.


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Surface DefectsSurface Defects--EfflorescenceEfflorescence

Deposit, usually white, formed on

a surface, the substance having

emerged in solution from within

concrete or masonry and

subsequently having been

precipitated by evaporation.


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Surface DefectsSurface Defects--DustingDusting

Development of a fine, powdery

material at the surface of

hardened concrete.


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Use Ventilated HeatersUse Ventilated Heaters

Surface DefectsSurface Defects--FreezingFreezing

Up to 50% reduction of ultimate

strength can occur if frozen

Within a few hours

Before reaching a strength of

3.5 MPa (500psi)


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Surface DefectsSurface Defects--PopoutsPopouts

Conical fragment that breaks from

the concrete surface. A fractured

aggregate particle is often at the

bottom of the hole.


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Surface DefectsSurface Defects--Mortar FlakingMortar Flaking

A form of scaling over coarse

aggregate (popoffs)


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Surface DefectsSurface Defects--ScalingScaling

Local flaking or peeling away of

the near-surface portion of

concrete or mortar.


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Surface DefectsSurface Defects--SpallingSpalling

A fragment, usually in the shape

of a flake, detached from a larger

mass by a blow, by the action of

weather, by pressure, or by

expansion within the larger mass.


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Avoiding ProblemsAvoiding Problems

Design- Constructibility

Mix Design

Materials Selection

Placement Procedures

Environment

Good Design and

Prevention of Defects =Attractive, Quality Concrete

WhatWhats Wrong With This Picture?s Wrong With This Picture?


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