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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
12
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
13
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
15
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
17
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:
18
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)
19
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)
23
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
28
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
29
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: [email protected]