ology and Codes Troubleshooting Troubleshooting Fre

Concrete Problems

Concrete Techno
Freshly Freshly-Mixed 

Concrete Concrete Problems Problems 

z Construction errorsz Design errorsz Slump lossz Workabilityz Cement-admixture compaz Settingz Mix temperaturez Air content control
Construction Error

z

H

2O Concrete

z Improper Alignment 

of Forms

z Consolidation

z Movement of Fo

 While concre

setting, can icracking or s

z Consolidationz Location of Steel

 Not Secured

cracking or s

 Water enter

– F-T

z Settling of Concz Sub grade settl
Design Errors

z Inadequate Structural Design

 Spalling – high compressive or high torsion or sh

stresses

 Cracking – tensile Poor Design Details

WLocalized stress concentrationsWWater Ponding

WAbrupt changes in sectionWInsufficient steel or reentrant corners or opWInadequate provisions for deflectionWIncompatibility of materials

– Mod. E, thermal

WPoorly Designed Expansion jointsWNeglecting Creep
SLUMP
Slump Loss


Workability

z Slump Loss

 Cement False Set Cement-admixture Incompa Sequence of Admixture Add

Sequence of Admixture Add

z Pumping

 Cement Content Fly Ash Aggregate Content/ Gradati
Cement - Admixtu

Admixtu

C tibilit Compatibility
Mini – Slump Con

Slump Con

T t es



Proposed Version of Mi

Proposed Version of Mi

Slump Cone Test

z Cement: 500gz W/C: 0.50z Mixing water temperature: 22 1 Cz Mixing Schedule: 0.5 min. mix 

– 2 min

– 1.5 min. mix

z Mixing rpm: 13,000z Testing Schedule:

 2,5; Remix – 15, 30, 45 min.

z Remixing: 2 min. prior to test 1,200 rp

1 min.
Mini – Slump Cone Tes

Slump Cone Tes
TEA

z Accelerates C3Az Retards C3S
Setting Time Setting Time
Spot Setting

z Coke or Coffeez Cigarsz Reshipped Concretez Admixture Overdosez Wrong Concretez Shipped From Two Plants
If the Concrete Isn’t S

z Eventually it Willz Don’t Overwork Slabsz Prevent Moisture Eva

pora

z Prevent Freezing

Setting Time

z Pozzolansz Temperaturez Contamination

 Sugar Water

FORMS
Effect of Hot Weather on Ra

Hardening
Effect of Cold Weather on R

of Hardening
Setting Time 

z Cement

 Type

• Fineness• Chemistry
Setting Time 

z Admixtures

 Type Dosage
Mix Temperature

z Slumpz Slump Lossz Water

 Retempering

z W/Cz Finishing
Temperature Vs. Water Requirement


Low Temperature Effects
Mix Temperature 

(Continued)

z Baptizingz Air Contentz Stren

g p th Develo

pment

z Long-term Strength


Baptizing

z Higher W/Cz Reduces Air Contentz Promotes Scalin

g
Delaminations of Troweled Su

z More like to form if:

 Underlying concrete sets slowly – Cool  Retardation

WRetardersWFly Ash

 High A/E Premature finishing Bleeding or air rising Jitterbug Dry shake in A/E Sticky concrete Thicker slabs Placed in vapor barrier
Finishing

z Float as soon as concrete 

been struck off

 Only one or two passes

z DO NOT SEAL THE SURFAC

DO NOT SEAL THE SURFAC

 Do not tip bull floats

z Floating must end before 

bleed water rises to surfa

z Wait for concrete to stop 

bleeding
Finishing (continued)

z Finishing During Bleeding

 Scaling Dusting Blisters Crazing

z Troweling

 Not for outside work Not for outside work Will be slippery when wet Trowel burns Tilting – chatter

z NO SPRINKLING OR CEMENT ON SURFACz Cure ASAP and water sheen has disappe
Did You Seal the 

Surface?

z A Simple test

 Leave a small test area 

without finishing (no bfloating)

 Compare to bull floated  If bleed water appears 

test area (unfinished arbut not on the bull floaarea, then bull floating sealed surface

Control of A

Content in 

Concrete
Total Target Air Conten

for Concrete

Nominal max. Aggregate Size,in.

Severe Exposure 

Moderate Exposure 

Mild Expo

3/8

7 1/2

6

4 1/2

Project specifications usually allow within -target value

3/8

7

-1/2

6

4

-1/2

1⁄2 7 5-1/2 4 3⁄4 6 5 3-1/2 1 6 4-1/2 3 1-1/2 5-1/2 4-1/2 2-1/2 
High Air Content
Air-Void Clusters at Void Clusters at 

Interface
Air Content

z AEAz Verify by L-Tz Chan

ges in Materials

z Sequence of AEA Additionz PCA Manual on Control of 

Content


Freshly Freshly-Mixed 

Concrete Problem

z Bleedingz Erratic batchingz Stickinessz Harshnessz Segregationz Yield
BLEEDING AND FINISHING 

RELATED PROBLEMS
Bleeding

z Subsidencez Capacity vs rate Capacity vs. rate






Bleeding

z W/Cz Scalingz Air velocit

y over surface

z Cement finenessz Cement contentz Fly Ash
Bleeding (continued

z Air contentz Admixtures

 WRA Plasticizers Chlorides

z Aggregates










Bleeding Bleeding - Durabilit

Durabilit

z Scalingz Mortar flakingz Surface delaminationsz Blistersz Sand streaking
Erratic Batching
Weighing



Moisture 

C ti ompensation


Slump

z Wetz Dry
Slump - Wet

z W/Cz Strengthz Air content

 Air-void system

z Durability
Shrinkage and Water Cont
Slump – Wet (continu

Wet (continu

z Shrinkagez Cracksz Permeabilityz Pumping
Slump - Dry

z Finishingz Pumpingz Consolidationz Erratic strengthsz Air content
Sticky Mixes

z Worst condition combinat

 Wet Over sanded mixes A/E On hot, dry day

z Use less sand (150 – 200 I

with A/E
Stickiness

z Finesz Aggregate cleanliness and 

gradation

z Cementz Air-entrainmentz Pumping
Stickiness (continue

z Bleedingz Finishingz Overworkin

g( 

 surface 

(loss 

z Mineral admixture

 Fly ash Silica fume
Harsh Mixes

z Lack paste –low cementitious contenz Use air (3-4%)z Use some more

 Fine sand

or

 Fly ash

or

 Cement

z AGAIN-DO NOT BAPTIZE CONCRETE

to aid finishing use fog spray w/o 

water being worked into slab is safe
Segregation

z Cause

 Excessive slump Over vibration

z Use

 A/E S.P. Drop chutes (3-4 ft)
Yield

z Causes

 Miscalculation of form vo Deflection – distortion of  Irregular subgrade

WPlacement over poorly 

prepared granular fill

WSettlement of subgrade
Yield - Miscalculatio

Miscalculatio

z 1/8 in. in 4 in. slab = 3% 

shortage or 1 yd in 32 yd
Yield - Subgrade Subgrade

z Irregular subgradez Placement over granular fz Settlementz To determine in-place thic

 Radar Cores
Yield (continued)

z Remedies

 Run ASTM C138 Measure formwork accu

WNear end of large pour

accurately measure remvolume to adjust remaitrucks
Yield (continued)

z Remedies

 Add ~ 2% Stiffer forms Check proper elevation o
Mixing Water

z Delivery tickets

 Provide allowable H

2

O

 DO NOT exceed W/CM
Summary

z Many sources of fresh con

problems

z Construction errorsz Design errorsz Material issuesz Do not exceed w/cm!
Questions?