Jointing and Crack Control

7/25/2019 Jointing and Crack Control

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www.getcracking.com.au

CONCRETE SLAB

TECHNOLOGY

JOINTING AND CRACK CONTROLFOR CONCRETE SLABS ON GROUND

IN WAREHOUSES AND INDUSTRIAL BUILDINGS


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CRACKS

1.Concrete shrinkage restraint2.Use of steel reinforcement for crack width

control how eective is it?

JOINTS3.New prolems for !oints caused " use of#$

%aser screeds &ard$wheeled forklifts

ALTERNATIVE SOLUTION - CRACK CONTROL

- JOINT OPENING CONTROL

'.(echanical cracking of sawcut !oints

C)NC*+,+ -%/- )N 0*)UN


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ll concrete shrinks as it cures even with admitures4

,o avoid cracking5 must avoid restraining concreteshrinkage

*estrained -hrinkage (inimising*estraint

C)NC*+,+ -&*6N70+ *+-,*6N,


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-)U*C+- )8 *+-,*6N,

-ugrade8riction

-la 9enetrations

-et$downs

-la ,ied to:alls


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+,6%6N0 8)* -,*+-- *+%6+8


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-U/0*+ *+-,*6N,

-tress due to sugrade restraint

depends on -ugrade material

%ength of pour


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-tress is maimum in the centre of the sla

Crack usuall" occurs in centre of sla ;rst

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-U/0*+ 8*6C,6)N N C*C7 +



CRACKS



JOINTS3.New prolems for !oints caused " #$


ALETERNATIVE SOLUTION FOR CRACKCONTROL


C)NC*+,+ -%/- )N 0*)UN



-teel mesh in concrete slas onground#$

oes not prevent cracks

oes not increase load carr"ingcapacit"

-teel is used to control crack width

U-+ )8 -,++% (+-&



Continuousl" *einforced Concrete

9avements

>.@ $ >.A@ steel

,ight cracks at close centres

:orks fairl" well

+pensive

U-+ )8 -,++% (+-&



6ndustrial /uilding slas on ground

(uch less steel $ >.1@ $ >.1B@ steel

9oor crack width control for large pours

-awcut !oints open wide at mesh

discontinuities 9oor control of sawcut !oint widths

U-+ )8 -,++% (+-&



-teel uantit" reuired dependson#$ %ength of pavement with

continuous reinforcement -ugrade friction

(agnitude of thermal shrinkage (agnitude of dr"ing shrinkage *euired crack width *euired crack spacing Use of stress concentrators e.g.

sawcuts4 9avement thickness ConcreteDs tensile strength iameter of steel reinforcement Eield stress of steel reinforcement

+-60N C)N-6+*,6)N

-,++% (+-& +-60N 6-C)(9%6C,+F

U-+ )8 -,++% (+-&



*estricts cracks opening

%imits crackDs ailit" toaccommodate shrinkageCreates more cracks

Concrete pump reuired for

accurate mesh positioning 6ncreased ;nes in concrete mi

design%eads to increased concrete

shrinkage%eads to increased !oint widths

6ncreased cost of construction

9*)/%+(- CU-+ /E -,++% (+-&



Creates residual tensile stress in the sla dds to other stresses from

pplied loads -hrinkage stressesto increase risk of cracking

9*)/%+(- CU-+ /E -,++% (+-&



Can create plastic settlement cracks

0rid of cracks mirroring ars in meshelow

9*)/%+(- CU-+ /E -,++% (+-&



iGcult to place and compactconcrete

9oor compaction reduces concrete

strength

9*)/%+(- CU-+ /E -,++% (+-&



-teel manufacture creates greenhouse gas

emissions (ass of C)2emissions from steel manufacture

and distriution is appro. twice the weight ofsteel

e.g. 1B>>m2of -%H2 mesh I 12 tonnes of C)2

9*)/%+(- CU-+ /E -,++% (+-&



CRACKS

1. Concrete shrinkage restraint2. Use of steel reinforcement for crack width control

how eective is it?Use of steel mesh in slabs on ground to

control cracking is far from ideal

JOINTS

3. New prolems for !oints caused " #$ &ard$wheeled forklifts %aser screeds

ALETERNATIVE SOLUTION FOR CRACK CONTROL

'. (echanical cracking of sawcut !oints

C)NC*+,+ -%/- )N 0*)UN



&ard$wheeled forklifts re here to sta" improved forklift stailit"4

Cause damage to unprotected !oint edges Joint armouring of construction !oints

iGcult to accuratel" install +pensive

9*)/%+(- CU-+ /E &*$:&++%+ 8)*7%68,-



6ncreasing use of laser screeds +conomies with large pours up to 3>>>m2per da".

%arge pours lead to :ide openings at construction !oints ominant sawcut !oints at centre of pour

9*)/%+(- CU-+ /E %-+* -C*++-

11mm wide sawcut5 3 months after concreteplacement

+asil"damaged "

hard wheeledforklifts



CRACKS



JOINTS3.New prolems for !oints caused " #$


ALETERNATIVE SOLUTION FOR CRACKCONTROL


C)NC*+,+ -%/- )N 0*)UN


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C)N


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(+C&N6C%%E 6NUC6N0 C*C7


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J)6N, C*C76N0 (C&6N+


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Use of steel mesh in slas on ground to control cracking is far fromideal

/" mechanicall" cracking sawcut !oints5 soon after concreteplacement *andom shrinkage cracks eliminated Joints open more evenl"

:ith shrinkage cracks controlled to sawcut !oints the following can e

eliminated -teel reinforcing mesh and its associated prolems Concrete 9umps

:ith !oints opening relativel" evenl" -emi$rigid sealants can e used to protect !oints No need for !oint$edge armouring

:ithout steel reinforcing mesh 0reenhouse gas emissions are greatl" reduced

(+C&N6C% C*C76N0 )8 -:CU, J)6N,-


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Jointing and Crack Control