Use of GGBS Precast Plank with OPC Insitu Concrete Topping

in Construction of Semi-Precast Slab

Chi Sun POON

Department of Civil and Environmental Engineering

The Hong Kong Polytechnic University

1

Outline Background – GGBS in Concrete

Laboratory Scale Casting & Testing

Mechanical Properties

Drying shrinkage – standard prisms testing

Drying shrinkage – slab testing

Bonding strength – pull off testing

Scaled-up Casting & Testing

Load bearing shrinkage

Non-Destructive Testing (NDT)

Bonding strength – cored specimens

Highlights

2

Ground Granulated Blastfurnace Slag (GGBS)

by-product of steel manufacturing

Iron ore + Coke

Sinter

Limestone

Blast

Furnace

16000C

Slag

Molten Iron Alloying Elements

Electric

Arc

Furnace

Steel Ingots

Rolling and Casting

Chemical Composition

Compounds Content (%)

Silicon dioxide (SiO2) 30 - 40

Aluminum oxide (Al2O3) 8 - 18

Calcium oxide (CaO) 40 - 50

Magnesium oxide (MgO) 0 - 8

Ground Granulated Blastfurnace Slag (GGBS)

• Average particle size = 10 - 20 mm

• Surface area = 350-500 m2/kg

• Bulk density = 600 kg/m3

• Specific gravity = 2.9

Physical Characteristics

Particle size distribution

(mm) Dv10

Dv50

Dv90

Dvmean

0.81

9.07

32.36

13.66

Chemical composition (% by

mass)

MgO

Al2O3

SiO2

CaO

6.88

16.9

31.7

40.1

• Benefit of GGBS:

– increase long-term concrete strength

– lower heat of hydration and reduce cracking

– better water impermeability and improved resistance to corrosion and sulphate attack

extend Service Life and reduce Maintenance Cost

5

Reference:

GEO Report No. 258 – Final Report on Durability

and Strength Development of GGBS Concrete

Properties of GGBS Hardened Concrete

Development of compressive strength of ggbs concrete

Background

7

Housing Authority (HA) encourages the use of GGBS in precast

concrete components (e.g. facades, staircases)

Semi-precast floor slabs investigated

precast base (OPC/GGBS) + in-situ cast upper layer (OPC)

Major issue to be tackled – Compatibility (shrinkage & bonding)

8

PolyU Consultancy Study for HKHA • Two Series of test were conducted:

1. Laboratory Tests

2. Full-scale Mock-up

A) Three types of concrete were adopted

1. C35 OPC (for Insitu Topping)

2. C45 OPC (for Precast Plank as control)

3. C45 GGBS (for Precast Plank)

B) Five Combinations:

Single concrete type

1. C35 OPC Specimen

2. C45 OPC Specimen

3. C45 GGBS Specimen

Composite concrete:

4. C35 OPC + C45 OPC

5. C35 OPC + C45 GGBS

Mix Proportions Used

kg/m3 L/m3

Concrete type cement GGBS 20mm 10mm crush fine water admixture(D17D) admixture(QL-5)

C45/20 OPC 450 770 325 600

175

(w/c

=0.388)

5.34 litres

C45/20 GGBS 292 158 785 325 585 170

(w/b=0.377 6.86 litres

C35/20 420 690 285 710

205

(w/c=0.488

)

2.52 litres

9

10

Laboratory Tests Six tests were conducted:

1. 28-day Compressive Strength Test for 100mm x 100mm x 100mm Cube (Normal and Steam Curing)

2. Flexural Test for 150mm x 150mm x 750mm Composite Beams

3. Pull-off for 100mm x 100mm x 60mm Composite Sample

4. Pull-off for coring sample of 45.7mmf on 2m x 1m Composite Panels

5. 56-day Shrinkage for 75mm x 75mm x 285mm Concrete Specimens (Normal and Steam Curing)

6. 90-day Shrinkage for 2m x 1m Composite Panel

11

1) 28-day Compressive Strength Test • 100mm x 100mm x 100mm Cube

Laboratory Tests

Sample Normal Curing (MPa)

C35 OPC C45 OPC C45 GGBS

1 59.7 71.8 71.9

2 59.5 72.7 70.7

3 57.7 73 72.6

mean 59.0 72.5 71.7

Sample Steam Curing (MPa)

C35 OPC C45 OPC C45 GGBS

1 -

65.5 71.1 2 64.4 70.7 3 66.3 67.4

mean - 65.4 69.7

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2) 28-day Flexural Strength Test • 150mmx150mmx750mm Composite Beam

Laboratory Tests

Sample C35 OPC+C45 OPC C35 OPC+C45 GGBS (MPa)

1 6.01 5.91 2 6.32 5.93 3 5.57 6.21 4 5.61 6.98

mean 5.88 6.26

75mm

75mm

150mm

150mm

C35 OPC

C45 OPC / C45 GGBS

C35

OPC

C45

OPC /

C45

GGBS

A

A

Section A-A 150mm 150mm 150mm 150mm

Load

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3) Pull-off Strength • 100mm x 100mm x 60mm Composite Sample

Laboratory Tests

Sample C35 OPC+C45 OPC C35 OPC+C45 GGBS MPa MPa

1 2.43 C45 OPC 2.03 C45 GGBS 2 2.37 C45 OPC 2.19 C35 OPC 3 2.33 C45 OPC 1.78 C45 GGBS 4 2.13 C45 OPC 1.75 C45 GGBS 5 2.17 C45 OPC 2.11 C45 GGBS 6 2.28 C45 OPC 1.91 C45 GGBS 7 1.96 C45 OPC 1.7 C45 GGBS

Mean 2.24 1.92

30mm

30mm

100mm

C35 OPC C45 OPC /

C45 GGBS

Pull-out load

14

4) Pull-off Strength • 45.7mmf on 1m x 2m Composite Panel

Laboratory Tests

Sample C35 OPC+C45 OPC C35 OPC+C45 GGBS

MPa MPa 1 2.19 at C45 2.36 at C35 2 2.78 interface 2.27 at C35 3 2.33 at C45 1.52 at C35 4 2.51 at C45 1.86 interface 5 2.23 interface 1.83 interface 6 2.38 at C45 2.33 at C35 7 2.99 at C45 2.01 at C35

Mean 2.49 2.03

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5) 56-day Shrinkage • 75mm x 75mm x 285mm Concrete Specimens

Laboratory Tests

Sample Strain (10-6)

Normal Curing

Steam Curing

C35 OPC 411 -

C45 OPC 356 325

C45 GGBS 309 301

16

6) 90-day Shrinkage • 2m x 1m Composite Panel

Laboratory Tests

Sample Strain (10-6)

C35 OPC+C45 OPC C35 OPC+C45 GGBS

C35 OPC 492 298

C45 OPC 340 -

C45 GGBS - 155

Difference 152 143

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Laboratory Tests

Test Concrete Grade

C35 OPC

C45 OPC

C45 GGBS

C35 OPC + C45 OPC

C35 OPC + C45 GGBS

1 28-day Compressive strength (MPa)

normal curing

59 72.5 71.7 - -

steam curing - 65.4 69.7 - -

2) 28-day Flexural Strength (MPa)

- - - 5.88 6.26

3) Pull off strength for 100mm x 100mm x 60mm (MPa)

- - - 2.24

(No Interface Failure)

1.92 (No Interface

Failure)

4) Pull off strength 2m x 1m Composite Panels (MPa)

- - - 2.49

(Interface Failure = 2 of 7)

2.03 (Interface

Failure = 2 of 7)

5) 56-day Shrinkage (10-6)

normal curing

411 356 309 - -

steam curing - 325 301 - -

6) 90-day Shrinkage (10-6) - - - C35 OPC: 492 C45 OPC: 340

Diff: 152

C35 OPC: 298 C45 GGBS: 155

Diff: 143

Summary:

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Laboratory Tests 1. Compressive strength:

a. Normal Curing: C45 OPC > C45 GGBS (72.5MPa vs 71.7 MPa)

b. Steam Curing: C45 OPC < C45 GGBS (65.4MPa vs 69.7 MPa)

2. Flexural strength:

• OPC+OPC < OPC+GGBS (5.88MPa vs 6.26MPa)

3. Pull off tests (Specimens):

• OPC+OPC > OPC+GGBS (2.24MPa vs 1.92MPa)

• No Interface Failure

4. Pull off tests (Panel):

• OPC+OPC > OPC+GGBS (2.49MPa vs 2.03 MPa)

• Interface Failure = 2 of 7 for both OPC and GGBS Panels

5. Shrinkage:

a. Normal Curing: C45 OPC < C45 GGBS (356x10-6 vs 309 x10-6)

b. Steam Curing: C45 OPC < C45 GGBS (325x10-6 vs 301 x10-6)

6. Differential Shrinkage:

• OPC+OPC vs OPC+GGBS (Same order) (152x10-6 vs 143 x10-6)

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Full-scale Mock-up

• Based on the laboratory tests, the differential shrinkage

did not have significant effects on the interfacial bond of

OPC+GGBS

• Full scale mock-up was recommended to further verify

the technical viability under the actual loading and

workmanship on site

Plan View of Mock-

up

Full-scale mock up monitoring

20

21

Full-scale Mock-up

• Six tests were conducted:

1. 28-day Compressive Test for 100mm x 100mm x 100mm Cube

2. 56-day Drying Shrinkage of Concrete Prism

3. 180-day Drying Shrinkage of Mock-up Panels

4. Deflection of Panels

5. Pull-off Test for through core

6. Ultra Pulse Velocity (UPV) Test

• Similar to laboratory test, 3 types of

concrete and 5 different specimens were

adopted.

• Design Load on the semi-precast slab:

1. Partition Load = 2.14kPa

2. Finished Load = 0.84kPa

3. Live Load = 2.0kPa Section A-A

Full-scale mock up monitoring

22

Date Works Description

18/07/2016 Casting of bottom layer (C45OPC & C45GGBS)

25/07/2016 Casting of upper layer and upper wall (C35OPC)

26-27/07/2016 Installation of strain gauges at both sides of the top and bottom slabs

05/08/2016 Removal of supporting racks

12/08/2016 Installation of 2 strain gauges at mid-span and 1/4L on bottom of both slabs

26/08/2016 Setup of 2 dial gauges at mid-span on bottom of both slabs

17/06/2017 After one year casting, applied 4.98kPa (5.5 ton) loading

29/9/2017 Carrying out the first Ultrasonic test

15/12/2017 Carrying out the second Ultrasonic test & removal of load. The strain and deflection

were measured before unloading

22/12/2017 Conducting 12 pcs through cores for two panels

08/01/2018 Conducting Pull off test of cores (total 12 pcs at PolyU)

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1) 28-day Compressive Strength Test • 100mm x 100mm x 100mm Cube

Full-scale Mock-up

Sample Compressive Strength

(MPa)

C35 OPC 59.3

C45 OPC 72.5

C45 GGBS 79.4

24

Full-scale Mock-up

Sample Strain (1x10-6)

C35 OPC 417

C45 OPC 461

C45 GGBS 529

2) Drying Shrinkage of Concrete Prisms

25

Full-scale Mock-up

3) 180-day Shrinkage

Sample Strain (10-6)

C35 OPC + C45 OPC C35 OPC + C45 GGBS

C35 OPC -53 11

C45 OPC -2 -

C45 GGBS - 66

Difference 51 55

Note:

Negative means

shrinkage

Positive means expansion

26

Full-scale Mock-up 4) Deflection at mid-span

Sample Deflection (mm)

C35 OPC+C45 OPC 1.4410

C35 OPC+C45 GGBS 2.1055

• Design Load on the semi-precast

slab:

1. Partition Load = 2.14kPa

2. Finished Load = 0.84kPa

3. Live Load = 2.0kPa

Total = 4.98kPa

27

Full-scale Mock-up

5) Pull-off test for through core Sample

C35 OPC+ C45 OPC C35 OPC+ C45 GGBS

MPa MPa 1 0.553 C35 1.814 C35

2 0.999 C35 1.251 C35

3 1.337 C35 2.070 C45

4 1.731 C45 1.187 interface fail

5 1.567 C35 1.645 interface fail

6 1.416 C35 1.286 interface fail

Mean 1.267 1.542

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Full-scale Mock-up

6) Ultra Pulse Velocity (UPV) Test

• UPV test: based on BS EN 12504-4 and

ASTM C597-16 (BSI, 2004; ASTM, 2016)

• Results: No delamination was detected

Test Concrete Grade

C35 OPC

C45 OPC

C45 GGBS

C35 OPC + C45 OPC

C35 OPC + C45 GGBS

1) 28-day Compressive strength (MPa)

59.3 72.5 79.4 - -

2) 56-day Shrinkage of concrete prism (10-6)

417 461 529

3) 180-day Shrinkage of concrete prism (10-6)

- - - C35 OPC: -53 C45 OPC: -2

Diff: 51

C35 OPC: 11 C45 GGBS: 66

Diff: 55 4) Deflection (mm) - - - 1.4410 2.1055

5) Pull off strength (Panel) (MPa)

- - - 1.267

(No Interface Failure)

1.542 (Interface

Failure = 3 of 6)

6) Ultra Pulse Velocity (UPV) Test

- - - No

delamination No delamination

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Full-scale Mock-up Summary:

30

Full-scale Mock-up 1. Compressive strength:

• C45 OPC < C45 GGBS (72.5MPa vs 79.4 MPa)

2. Shrinkage:

• C45 OPC < C45 GGBS (Same order) (461x10-6 vs 529 x10-6)

3. Differential Shrinkage:

• OPC+OPC vs OPC+GGBS (Same order) (51x10-6 vs 55 x10-6)

4. Deflection:

• OPC+OPC < OPC+GGBS (1.441mm vs 2.1055mm)

5. Pull off tests:

• OPC+OPC < OPC+GGBS (1.267MPa vs 1.542MPa)

Interface Failure = 3 of 6 for OPC+OPC

No Interface Failure for OPC+GGBS

6. Ultra Pulse Velocity (UPV) Test:

• No lamination detected

• The structural performance of OPC+GGBS system was in general similar to that of OPC+OPC system.

• There is no delamination between the two layers of OPC + GGBS concrete and no significant differential shrinkage.

• Some interface failures in the core test in both laboratory and full scale mock-up, the average strength of OPC+GGBS was higher than OPC+OPC system in the pull-off test in full scale mock-up.

• Given to the above test results, GGBS precast plank can be safely adopted in the construction of semi-precast slab in HA’s building.

31

Conclusion

32

Thank You! Email: cecspoon@polyu.edu.hk