Controlling Technology for Concrete Cracking Southeast university Jiangsu Research Institute of Building Science State Key Laboratory of High Performance

Controlling Technology for

Concrete Cracking

Southeast universityJiangsu Research Institute of Building Science

State Key Laboratory of High Performance Civil Engineering Materials

July, 2012

Changwen Miao

江苏省建筑科学研究院有限公司 Jiangsu Research Institute of Building Science 2

Outlines

Harmfulness of concrete cracking

Main reasons for concrete cracking

New technologies for concrete cracking

controlling

Harmfulness of concrete cracking


Concrete is the cornerstone for civil engineering, hydraulic and construction projects

Concrete cracking is a common problem in civil construction projects

Cracking is still a common problem of concrete

Affect the use of safety !Affect the use of safety !

Shorten the service life !Shorten the service life !

Huge economic loss !Huge economic loss !


Changing the force condition of the

concrete structure, leading to local and

even the overall failure of buildings

Weakening the stiffness of the concrete

buildings with the dynamic changes of

environment and loads

Reducing the structural seismic capacity,

threatening the overall stability and

safety of concrete structures

Concrete cracking declines structural capacity


Stage —Reducing the effective thickness of protective layerⅠ

Stage —Accelerating the transmission of environmental Ⅱ

aggressive media, air and moisture within the concrete structure

Stage —Shortening activation and corrosion time of Ⅲ

reinforcement, reducing the service life of concrete structures

Concrete cracking deteriorates structural durability

Concrete cracking

Stage Ⅰ

Aggressive media, air, moisture

intrusion

Stage Ⅱ

Reinforced steel bar initial corroding

Reinforced steel bar volume expansion

Stage Ⅲ


Main reasons for concrete cracking


The causes of cracks

Load-induced cracks ( structural cracks, about 5%-10%)

Cracks induced by direct stress of external loads (static , dynamic load) , and

Structural secondary stress

Deformation-induced cracks ( non-structural cracks, 80% or

more)

Coupling ( deformation and load ) effect-induced cracks (5 % to

10% ) Cracks induced by alkali-aggregate reaction, freezing and

thawing, uneven expansion, bad soundness and so on

Plastic shrinkageSelf-desiccation shrinkageDrying shrinkageTemperature shrinkageCarbonation shrinkage

Humidity changes

Temperature changes


Categories of concrete cracking

plastic cracks

Temperature cracks

Shear cracks

Settlement cracks

Corrosion cracks

Shrinkage (drying shrinkage, autogenous shrinkage) cracks


Shrinkage and cracking of concrete in plastic stage

The plastic phase can be divided into two stagesC

apill

ary

neg

ativ

e p

ress

ure

Time

No internal stress generated

No shrinkage stress inside the paste (saturated), mainly in the forms of

bleeding and plastic settlement

Shrinkage stress (pore negative pressure) generatedMainly in the forms of horizontal plastic deformation and settlement

Internal pore negative pressure rising

Stage 1 Stage 2


water

bleeding钢筋

Micro-crack formation caused by internal bleeding.

Cracks formation due to constraint of subsidence by reinforcement.

crack Settlement and bleeding


Aggregate


Bleeding rate≧ Evaporation rate Bleeding rate < Evaporation rate

cos

2

rP

Mechanics of plastic shrinkage and cracking

The shrinkage driving force is greater than the tensile strength between particles



Drying shrinkage cracking—Evaluation methods

Ring method—double ring

0 2 4 6 8 10

-40

-20

0

20

40

60

deformation /10-6

t i me/d

outer ri ng

i nner ri ng

Can test out the expansion and shrinkage stresses

Suitable for evaluation of expansive concrete(Patent Application No. : 201010100449.7 )



Autogenous shrinkage of concrete

Autogenous shrinkage-mechanics

Root reason: the total volume decreases during cement hydration process (chemical shrinkage) .

Autogenous shrinkage (Apparent volume decreases)

Chemical shrinkage

Hydration products

PoreCement

+

Water

Before hydration After hydration

Vol

um

e

Chemical shrinkage is about:

6.4×10-2 mL/g； Autogenous shrinkage is one of

the manifestations of chemical

shrinkage, chemical shrinkage

equals to the sum of autogenous

shrinkage and pore volume

formed


Autogenous shrinkage-mechanics

After structure formation, further hydration cause to the meniscus

generation inside the paste and the shrinkage stress

)ln(cos2

RHM

RT

rP

Initial state Before structure formation

After structure formation

Direct reason:



Autogenous shrinkage-testing methods

Concrete

Cement paste

Autogenous shrinkage(apparent volume decreases）

Corrugate pipe testing method

Solving the defect that test ends of pipe

debond with internal concrete in the

vertical length measurement;

Solving the interference of the probe to

the early test results by using non-

contact sensor technology;

Realizing the staged and whole process

testing since casting and molding,

improving data reliability and

continuity.



Autogenous shrinkage-testing methods

self-drying “time-zero”

Corresponding to the initial structure formation;

Corresponding to the starting point of autogenous shrinkage

Pore negative pressure testing method


time

Ph

ysic

al a

nd

mec

han

ical

ch

arac

teri

stic

par

amet

ers

Early shrinkage driving force test since self-drying zero

Application of semi permeable membrane characteristics of

the water-saturated porous ceramic probe Realizing the characterization of initial structure formation

and self- drying 0:00 Solving the leak problem of traditional testing method, with

test range upgrading 1 times Overcoming the international problem that traditional

method is difficult to test the shrinkage driving force in the

humidity stage


Temperature deformation and cracking of concrete

Temperature deformation—mechanics

2.Capillary pore stress relaxation

Additional expansion

Te

mp

eratu

re

risin

g

Delayed shrinkage

（ ignored usually）

Causing expansion

Thermal expansion deformation properties is significantly affected by humidity

1.Material inherent properties

3.Liquid phase migration


0 5 10 15 20 25 3025

30

35

40

45

50

55

60

65

70

75

80

85

90

cent

er t

empe

ratu

re o

f th

e th

ickn

ess

/o C

t i me/d

Center temperature rise increases with the cross-sectional dimensions of the structure

Adiabatic temperature risethickness

Cracking reason-Thermal stress caused by temperature difference between inside and outside

Temperature deformation and cracking

Tension zone

Compression zone

Temperature distribution

Stress distribution

Surface tension, internal compression



℃

Ta

T1 T2

temperature

Tl

% lel

1pl 2

pl

strain

time

3 4

t1 t2 t3 t

stress

destroy

Temperature decreases stage

Temperature rises stage

compression tension

t

t

t

creep

Strength curve

Tempreature deformation cracking

Crack criterion

Cracking when tensile stress caused by temperature deformation and creep is greater than the tensile strength of concrete



Crack resistance parameters

Temperature rising time,

Stress occurring time,

The first zero stress temperature TZ,1 ,

Temperature peak occurring time,

Maximum temperature Tmax ,

The second zero stress temperatureTZ,2 ,

Cracking temperature Tc ,

Maximum compressive stress σc,max

Maximum temperature Tmax

t

t

The first zero stress

temperature TZ,1

cracking temperature Tc

σc,max

Cracking stress c

Specimen stress (or center temperature) changes with age

Temperature rises stage

Constant temperature

stage

Rapid cooling stage

Temperature deformation cracking-Evaluation method

Temperature-stress testing machine



stre

ss（

MP

a）

age (d)

Elastic stress （ Hooker Theorem）

Relaxation stress

Measured stress(after relaxation)

0 7 14 21 280 7 14 21 280

4

8

12

0

4

8

12

strength

age (d)

Free-form deformation

Constraint + creep (cumulative effect)

000

stra

in（

）

creep

ThresholdDeformation recovery

Temperature deformation cracking-Evaluation method

Temperature-stress testing machine

Through controlling the total strain of the constrained specimen at 0, and combining with the reference specimen, functions describing parameters such as restraint stress, elastic modulus, creep coefficient and so on changing with time could be obtained.



Modern concrete cracking reasons are more complex

cement water

coarse aggregatefine aggregate

Conventional concrete

Modern concrete

Composition characteristicscomplex componentlow w/c ratiomore concent of cementitious materials

Performance characteristicslarge flowabilityexcellent mechanical propertiesgood durability

Optimizing

ratio

and

processesChemical admixturesMineral admixture



Impact of cement composition and admixture on the

cracking resistance

cement composition and admixture Cracking temperature

Fineness degree decreasing from 380m2/kg to

280m2/kg

Decreasing 9.5℃

Alkali content decreasing from 0.95% to 0.55% Decreasing 7℃

C3A content reduced by 4% Decreasing 6℃

Mixed with 17% fly ash Decreasing 2℃

Mixed with slag or silica fume Increasing the cracking

temperature

The greater the reduction value of cracking temperature, the better the cracking resistance



Impact of superplasticizer

• Lower w/c and cement consumption, improving mobility ;

• Increasing concrete shrinkage in the same w/c, dry shrinkage at 60d increased by 20%-40%

calcium lignosulfonateTraditional naphthalene

( condensation polymer )

shri

nkin

g pe

rcen

tage

(10

-6)

shri

nkin

g pe

rcen

tage

(10

-6)

Time / d Time / d

blank blank



Impact of W/C

Time / d

Au

toge

nou

s sh

rin

kag

e (1

0-6)

Compared to specimen with w/c 0.6:The autogenous shrinkage of specimens with w/c 0.5,0.45,0.4,0.35,0.3 and 0.25 at 1year increased by 175%, 250%, 275%, 335%,495% and 505%, respectively


The concrete strength grade is gradually increasing, while

tension and compression ratio is gradually decreasing

C30 concrete: Tension/compression, about 1/10-1/12

C50 concrete: Tension/compression, about 1/16


Brittleness increases, lead to a higher cracking risk


New technologies for concrete cracking controlling


General train of thought

Structure regulation and control

water evaporation

Dryin

g sh

rink

age Plastic

shrin

kage

Capillary negative pressure growth

Au

togenou

s shrin

kage

Hyd

ration

heat

Tem

peratu

re ch

anges

Temperature shrinkage

Inhibit water evaporation

Force resistance

Cracking

resistance

Driving force

Chemical shrinkage

Cementitious materials hydration

Environmental temperature

Strength, toughness, creep

Shrinkage compensation by expansion

crack resistance by fiber

Evaluation methodology

In-situ toughening

Hydration heat regulation


Curing technologies in early age

Hydration degree

Plastic stage Hardening stage

Initial setting, wiping the surface

Monolayers with high evaporation resistance ability

High performance curing materials with hydrophobic structure


Curing technologies in early age—water evaporation inhibition

Mechanism

Monolayers

bleeding

Concrete

air

water water evaporation

controllable structure with hydrophilic main chain and hydrophobic side chains

Inh

ibit

ion

ev

apor

atio

n b

y 75

%

Time / min

Wat

er e

vap

orat

ion

/ g

Inhibition evaporation by 75%


Curing technologies in early age—New conservation materials

concreteconcrete

concrete concrete

Mechanism

Water evaporation

Particle

aggregation

Membrane formation

Dense membrane with high evaporation resistance ability


Mortar mix proportion

1 2 43

Reference

Monolayers

Monolayers can effectively suppress the plastic cracking risk



Impact of monolayers on pore negative pressure

Monolayers can effectively delay the appearing time of pore negative pressure inflection point of the surface mortar



Impact of monolayers on plastic shrinkage

The monolayers can reduce about half of the plastic shrinkage in the horizontal direction




Engineering applications

Dingxin Airport in Gansu Province ( the largest in Asia) Xigaze Airport in Thibet

Suitable for terrible drying area, it could dissolve the problem of crack and crust on plastic concrete.



No curing

Curing materials

crack

Delaying the time when capillary negative

pressure begin to increase and reduce crack

risk.

0

20

40

60

80

0 1 2 3 4

(h)时间 (

kPa)

孔隙

负压

Non-curing

Effect

Curing materials

Time / hP

ore

neg

ativ

e p

ress

ure

(k

Pa)



The second double of the The second double of the Lanxin RailwayLanxin Railway

Taizhou bridge across yangzi river Taizhou bridge across yangzi river

Suitable for drying and high temperature condition, it could dissolve the problem of drying crack of hardening concrete at early stage.


General ideas

rP

2Water

Water

Schematic diagram of evaporation of capillary moisture

Effect of the reduction of surface tension on additional pressure on the curved surface

The surface area of the surface tension in the pore solution was significantly reduced, which can effectively reduce autogenous shrinkage and drying shrinkage of concrete.

Chemical techniques for shrinkage-reducing


Traditional low molecular shrinkage reducing agent

The effect of SRA with different dosages

content/%

slump/cm

gas content/%

compressive strength/MPa

3d 28d

0 12.0 2.7 28.5 45.1

0.5 13.0 1.8 26.3 44.5

1.0 15.0 2.0 24.3 42.3

2.0 18.5 1.9 22.4 39.8

The effect of SRA on Mechanical Properties of Concrete

(same amout of water)

Reduced shrinkage

Reduced strength

contradiction


The structure-activity relationship study found that the traditional low molecular shrinkage reducing agent can not fundamentally solve the problem of declining strength of concrete.


High dispersed comb copolymer shrinkage reducing agent The molecular tailoring technology was adopted to make the alkyl polyether with shrinkage reducing function and steric effect graft to the main chain of copolymer, then the structure-activity relationship between molecular structure and shrinkage performance of the grafted copolymer/cement/water composite system was studied, as a result, a new type amphiphilic and high dispersion comb copolymer class concrete shrinkage reducing agent has been invented, which realized the unity of shrinkage reducing and water reducing and dispersion.

Adsorption behavior regulation - dispersion

Side chainSide chain

Long side chainLong side chain

Short side chain (shrinkage reducing group)-shrinkage reducing,

dispersion

Long polyether side chain – steric effect

H2C C

R1

C

H2C

OMO

C

R1

X

L

OH2C

H2C O C

H

CH3

H2C O R2

x y z

n m



(a) condensed shrinkage (b) autogenous shrinkage before 1d

Impact on shrinkage at early ages

0 1 2 3 4 5 6 7 80

200

400

600

800

1000

1200

Settl

em

ent s

hrinka

ge (

×10

-6)

Time, t/h (30min after mixing)

FDN FDN＋2％SRA SRPCA

0 5 10 15 20 25

0

50

100

150

200

250

300

Sel

f-des

icca

tion

shrin

kage

(×

10-6)

Time, t/h (from initial setting)

FDNFDN＋SRA SRPCA

High dispersed comb copolymer shrinkage reducing agent


43% lower than the naphthalene series 53% lower than the naphthalene series


Impact on shrinkage in the mid- or late period

0 10 20 30 40 50 60 70 80 90 100

0

100

200

300

400

500

SRPCA

FDN+SRA

FDN

Dry

ing

shrin

kage

/(×

10-6)

Age/d0 10 20 30 40 50 60 70 80 90 100

-20

0

20

40

60

80

100

120

140

160

180

SRPCA

FDN+SRA

FDN

Aut

ogen

ous s

hrin

kage

/(

×10

-6)

Age/d

(a) drying shrinkage (b) autogenous shrinkage

42% lower than the naphthalene series at 28d



53% lower than the naphthalene series at 28d


The cracking area is 13% of that of naphthalene series, with crack width only 0.27mm.

Tablet plastic cracking experimental results

AdmixturesCrack

time/minMaximum crack width /mm Crack area/mm2

SRPCA 380 0.27 100.15

FDN 190 1.0 763.32

FDN+2%SRA 280 0.6 293.05

Impact on plastic cracking




AdmixtureAge of first racking Tc/d

Crack width Wd

0 d 1 d 3 d 7 d 14 d 28 d

SRPCA 6.5 0.397 0.535 0.744 0.936 1.093 1.134

FDN 4.5 0.989 1.261 1.75 1.824 2.022 2.033

FDN+2%SRA 7.0 0.693 0.767 0.846 0.933 1.106 1.155

The ring cracking test results

Crack width reduced more than 45% compared with the naphthalene series

Impact on shrinkage in the mid- or late period


Realizing a unified effect of water reducing and shrinkage reducing at a lower dosage, effectively reducing the plastic shrinkage, early and late autogenous shrinkage and drying shrinkage .



0 10 20 30 40 50 60 70 80 90 100-20

0

20

40

60

80

100

120

140

160

180

SRPCA

FDN+SRA

FDN

Aut

ogen

ous s

hrin

kage

/(

×10

-6)

Age/d


Shrinkage-reducing type polycarboxylate superplasticizer

_ _ _ _ _

Side chain (SRA)

Long side chain

Lower

content ， unified

function between

dispersion and red

uced shrinkage

shrinkage reducing

dispersion

0 5 10 15 20 25

0

50

100

150

200

250

300

Sel

f-des

icca

tion

shrin

kage

(×

10-6)

Time, t/h (from initial setting)

FDNFDN＋SRA SRPCA

(a) Autogenous shrinkage before 1st day (b) Autogenous shrinkage

53% lower than the naphthalene 53% lower than the naphthalene after 28 days


Engineering

applications

Applications of shrinkage-reducing type polycarboxylate superplasticizer

Shrinkage deformation and the maximum temperature rise are controlled within a reasonable rangeThe main structures were not cracked and leaking

Wuxi Lihu Tunnel

Suzhou Dushu Lake Tunnel

Model road tunnel

Gongboxia Hydropower Station

Applications of shrinkage reducing admixtures(SRA)CFRD concrete , the effects of reduced cracking is significant

Chemical reduction techniques


Shrinkage cracking characteristics: shrinkage caused by autogenous, dry and thermal factor

Characteristics of the environment: temperature and humidity history

Composition characteristics:low W/B ， low porosity

Com

pen

sating au

togenou

s and

therm

al sh

rink

age , and

redu

cing d

ry shrin

kage

Thought

Large expansive performance, low dehydration shrinkage

Small water requirement

Stable hydration products

Mutiple complex

between Ca and Mg

Imp

rove concrete an

ti-crackin

g capacity

Controlled and regulated expansive history

MgO with high activity

MgO with high activity

CaO by light burning

Early expansion

Medium-term expansion

Later expansion

Shrinkage-compensating technology by expansion

江苏省建筑科学研究院有限公司 Jiangsu Research Institute of Building Science

0 10 20 30 400

100

200

300

400 C30 Reference C30 SBTJM-MC C50 Reference C50 SBTJM-MC

defo

rmat

ion/

10-6

Time/d

0 30 60 90 120

-300

-200

-100

0

100

200

C30 Reference C30 SBTJM-MC C50 Referrence C50 SBTJM-MC

Time/d

Def

orm

atio

n/10

-60 30 60 90 120

-500

-400

-300

-200

-100

0

C30 Reference C30 SBTJM-MC C50 Reference C50 SBTJM-MC

Time/d

Def

orm

atio

n/10

-6

Expansion rate can be controlledAutogenous shrinkage can be inhibit

effectivelyDry shrinkage can be significantly

reduced so that stable period can be in advance. In the standard dry condition without curing, dry shrinkage rate for C50 with the content of 8% was only 45% of the reference concrete after 120 days.

Water curing

Waterproof curing

Dry curing

Deformation performance



C30 （ a ） reference （ b ） with expansive

agent C50 （ a ） reference （ b ） with expansive agent

Crack resistance performance---Ring method

Cracking time Initial crack width/mm

C30 reference 4d 21h 0.1

C30 with expansive

agent11d 3h

0.05

C50 reference 4d 18h 0.03

C50 with expansive

agent7d 16h

0.01

Cracking time and initial crack width



0 4 8 12 16

-0.8

-0.4

0.0

0.4

0.8

1.2

stress/MPa

t i me/d

reference

mi xed wi th expansi ve agent

0 2 4 6 8 10 12 14 16

-20

-15

-10

-5

0

5

10

deformation/10-6

t i me/d

i nner ri ng

outer ri ng

0 4 8 12 16

-8

-4

0

4

8

12

16

deformation/10

-6

ti me/d

i nner ri ng

outer ri ng

Crack resistance performance of concrete(drying shrinkage of double ring)

Reference Expansive agent

Crack resistance performance ---Improved ring method

Cracking time

development rate of the average

stress

(MPa/d)

Cracking risk

reference 14<TC 0.2>q>0.1 low

Expansive

agent14<TC 0.1>q Very low



Crack resistance performance—TSTM （ C30）


characteristic parameters of temperature-stress test

Parameter Unit Expansive agentNon expansive

agent

Maximum compressive stress MPa 0.78 0.29

Time corresponding to maximum compressive stress

h 49.3 37.9

Maximum expansion values( constraint) ×10-6 37.6 36.3

Maximum expansion values(free) ×10-6 220 148

Time corresponding to Maximum expansion values h 57.2 46.2

Maximum temperature ℃ 38.2 35.5

Maximum temperature rise ℃ 29.4 27.0

The second zero stress temperature ℃ 34.9 35.5

The second zero stress time h 109.0 70.9

Stress at room temperature(20℃ ） MPa 0.22 0.15

Cracking stress MPa >3.1 2.0

Stress reserves 92.9% 92.5%

Cracking time h >164.4 148.4

Comprehensive evaluation indexCracking temperature ℃ <-18.2 -7.9

Key testing parameters comparison


Falls Hydropower Station in Sichuan

Deformation in early age Deformation in later age

Engineering applications

Compensating concrete autogenous shrinkage on phased as well as whole process

Typical engineering

North Square of Nanjing South Station of Beijing-Shanghai high-speed railway

Olympic Sports Center in Xuzhou

Samsung sewage treatment plant in Suzhou Industrial Park

Phase II project of Nanjing Lukou International Airport

Zhenjiang Exit Underground Engineering

Media Center Building in Changzhou

0 4 8 12 16 20 24 280

20

40

60

80

100

120

140

160

180

龄期 (d)

自生

体积

变形

(×

10-6)

Au

toge

nou

s vo

lum

e d

efor

mat

ion

(10-6

)

Age/d



Thinking

Concrete temperature rising mainly due to: Rapid hydration and concentrated exothermic of C3A and C3S phases

Controlling technology of heat hydration

Time/h

hydr

ated

hea

t re

leas

e ra

te Stabilized reaction period

Rapid reaction period

Induction periodAcceleration and deceleration period

hydrate


0

1

2

3

4

0 2 4 6 8 10 12d时间（）

mw/g

放热

速率

（）

ThinkingMulti-hydroxy or polyhydroxy-containing structure

Adsorption and calcium chelation of hydroxyl in additive agent molecules

Inhibition of Ca(OH)2 crystallization

Reduce the hydration rate of C3A and C3S phase

Regulation of condensation process and hydrated heat release rate

Reference


Time/d

hydr

ated

hea

t re

leas

e ra

te(m

w/g

)



Controlling heat release of cement hydration

Improve capabilities of temperature control of Mass concrete

Controlling the process of cement hydration

Admixtures with special molecular structure

Peak value was reduced by 60%

168


No cracks in about 600m3 mass concrete in the third-phase project of Three Gorges.

High friction Zam Hydroelectric in Pakistan

Prather onzalez dam in SudanThree Gorges Project

Jinping Hydropower Station

Controlling technology of Heat hydration


In-situ toughening technology

Mechanism--chemical bonding

Silylated cement particles

Chemical bond formation

Structure of organic-inorganic hybrid

[

]

[

]

m m

Covalent bond

Cement-based materials

Cement-based materials



Concrete performance —Fracture energy 7d fracture energy

编号

（7d）

PH max

(KN)

KIC

(MPa·ξ𝐦)

W1

(N·m)

W2

(N·m)

GF

(N·m-1)

blank 3.26 0.81 0.578 0.242 96

1 3.96 0.98 1.137 0.398 179

2 3.82 0.94 1.212 0.615 213

28d fracture energy

编号

（28d）

PH max

(KN)

KIC

(MPa·ξ𝐦)

W1

(N·m)

W2

(N·m)

GF

(N·m-1)

blank 4.04 1.00 0.709 0.27 115

1 4.70 1.16 1.49 0.48 231

2 5.22 1.29 1.13 0.69 213

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.50.0

0.5

1.0

1.5

2.0

2.5

P/k

N

CMOD/mm

Reference Content 1% Content 0.5%

7d

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

P/k

N

CMOD/mm

Reference Content 1% Content 0.5%

28d

No.

No.



Project—Taizhou brigde （ Box girder—small thickness,

Low volume-surface area ratio ） Good dispersion ， w/b up to 0.33 ， Good fluidity retention

capacity

No cracks occurredreferencereference

toughening materialtoughening material


Conclusions

To control the concrete cracking is entirely possible as long as

appropriate measures are used.

Evaporation reducing and water-retention materials can reduce

water evaporation by up to 75%, which can improve the concrete

crack resistance significantly in early age.

Unlike traditional polycondensation type superplasticizer, the

new generation graft copolymer can realize molecular design and

graft appropriate functional groups to achieve the unity of water

reduction and shrinkage reduction.

Admixtures can control hydration exothermic process, improving

temperature control capabilities of mass concrete.


Conclusions

Multiple compound expanding agents of calcium oxide

and magnesium oxide, can play the expansion roles of active

calcium oxide and light burned magnesia in different periods,

to compensate for concrete shrinkage in the whole process, and

to enhance the crack resistance.

As the compressive strength is increased and tensile and

compressive strength ratio is decreased, in-situ toughening

technology can be used to enhance the fracture energy and

reduce the cracking risk of concrete.

Thank you!

Documents

Controlling Technology for Concrete Cracking Southeast university Jiangsu Research Institute of Building Science State Key Laboratory of High Performance