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Concrete Specification and Maintenance Strategy for
Marine Structures
• Ir Peter Leung
Honorary Advisor to Standing
Committee on Concrete Technology
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Content
Part 1 – Specifications for Marine Structures in HK
Part 2 – Maintenance Strategy for Marine Structures
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Part 1: Specifications for Marine Structures in HK
• Durability and Design Life of Marine Concrete
Structures
• Factors affecting Durability of Marine Structures
• Conventional Specifications for Marine Concrete
• Durability Performance of Conventional Marine
Concrete Structures
• Development of Marine Concrete Specification
• Durability Performance of Marine Concrete
• Recommendations to enhance durability performance
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Durability
Prof. A.M. Neville, “Properties of Concrete”
It is essential that concrete should withstand the
conditions for which it has been designed, without
deterioration, over a period of years. Such concrete is
said to be durable.
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Design Life
Port Works Manual, 1996 edition
• The design life of a structure is taken to be its
intended useful life, and will depend on the purpose
for which it is required.
• Design life for all permanent marine structures should
be 50 years.
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Highway Structures Over Marine Environment
• 120 year design life
• For major structural elements, design life means
without replacement
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Factors Affecting Durability of Marine Structures
Internal Factors
• Properties of Concrete
• Quality of Raw Materials
• Strength of Aggregate
• Mix Composition
• Workmanship
• Curing
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Factors Affecting Durability of Marine Structures
Other Factors
• Alkali Aggregate Reaction
• Chemical Attack
• Abrasion and Weathering
• Creep and Shrinkage
• Corrosion of Reinforcement
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Environments Encountered
• Embedded below ground
• Submerged zone
• Tidal zone
• Splash zone
• Atmospheric zone
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Environments Encountered
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Marine Concrete Specification in Hong Kong
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Conventional Concrete Specification Specification Interim Specification
1994
Port Works Manual
1992
BS8110, BS6349
Design life 50 years 50 years Not stated
Minimum compressive
strength
45MPa 45MPa 40MPa
Maximum free
water/cementitious ratio
0.4 0.42 BS6349 states 0.45
Minimum concrete cover
for fully immersed, tidal,
and splash zones
60mm nominal cover 60mm nominal cover BS6349 states
50mm but
preferred 75mm
Minimum concrete cover
for aerated zone
60mm nominal cover 50mm nominal cover
Cement type OPC;
PFA (25-40%) replacement
mandatory
OPC SRPC not
permitted.
No codes specify
PFA, GGBS, CSF
Range of cementitious
content
360-430 kg/m3 375-550 kg/m3 350-400 kg/m3
Minimum slump 75mm 75mm -
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Durability of the Conventional Marine Concrete
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3 Years Old Pier Structures
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15 Years Old Pier Structures
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17 Years Old Pier Structures
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3 years existing 5 years
Chloride reaches threshold at cover of 60mm in 13 years
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Development of Marine Concrete Specification
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Development of Marine Concrete Specification to Improve Durability
• In 1995, the PWD of CEDD instigated a consultancy to
look into durability of its marine stock.
• CEDD’s Public Works Central Laboratory also carried
out another series of research on the influence of
microsilica on the strength and durability
characteristic of concrete
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12 Trial Mixes for Laboratory and In-situ Test
• Laboratory Tests
• Compressive Strength
Test
• Chloride Diffusion Test
• Sorptivity Test
• Site exposure test for 3
months and 6 months
• Chloride Diffusion Test
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Fig 3 - Mean Choride Profiles of PFA Concretes at 84 Days
0
0.5
1
1.5
2
2.5
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13 13-14
Distance from Core Surface (mm)
Chl
orid
e C
onte
nt (
% b
y m
ass
of d
ry c
oncr
ete)
Mix Without Micro-silica (Mix A)
Mix With Micro-silica (Mix A/S)
Results of Bulk Diffusion Test
Durability Performance Tests
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Details of Concrete Trial Mixes
Mix
Total Cementitious
Content (kg/m3)
Mineral Admixtures
(kg/m3)
Water/Cementitious
Ratio
Laboratory Test Results
Compressive Strength
(MPa)
Water Sorptivity
(mm/min0.5)
Chloride Diffusion
Coefficient
(10-12 m2/sec)
Field Test Results (Chloride diffusion coefficient at tidal zone after exposure for)
3 Months
(10-12 m2/sec)
6 Months
(10-12 m2/sec)
1
428
-
0.42
2
430
25% PFA
0.40
3
419
25% PFA
0.38
4
437
25% PFA
0.35
5
418
33% PFA
0.38
6
438
33% PFA
0.35
8
418
70% GGBS
0.35
9
419
10% CSF
0.38
10
417
25% PFA &
5% CSF
0.38
11
418
33% PFA &
5% CSF
0.38
73 61 64 69 55 63 65 71 83 60 54 67
0.175 0.150 0.125 0.105 0.110 0.115 0.085 0.095 0.110 0.120 0.130 0.105
3.25 5.10 5.15 3.60 3.35 6.20 2.10 1.75 2.75 4.50 4.50 1.40
4.2 6.1 4.4 3.9 5.8 4.7 2.7 2.8 2.7 4.6 4.3 2.0
3.2 3.1 3.1 1.9 2.4 2.5 1.6 1.4 2.5 3.0 2.6 1.8
7
420
70%
0.38
GGBS
0.38
12
419
70%
CSF
GGBS & 5%
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Marine Concrete Specification, 1998
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Comparison of Different of Concrete Specifications
Country Hong Kong UK
Specification Marine
Specification
1998
Interim
Specification
1994
Port Works
Manual
1992
BS8110, BS6349
Design life Not stated 50 years 50 years Not stated
Minimum compressive
strength
45MPa 45MPa 45MPa 40MPa
Maximum free
water/cementitious
ratio
0.38 0.4 0.42 BS6349 states 0.45
Minimum concrete
cover for fully
immersed, tidal, and
splash zones
75mm 60mm nominal
cover
60mm nominal
cover
Minimum concrete
cover for aerated zone
75mm 60mm nominal
cover
50mm nominal
cover
BS6349 states 50mm
but preferred 75mm
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Comparison of Different Concrete Specifications
Country Hong Kong UK
Specification Marine Specification
1998
Interim
Specification
1994
Port Works
Manual
1992
BS8110, BS6349
Cement type CSF (5-10%);
GGBS (60-75% for normal
application and up to 90%
for low heat application);
PFA (25-40%), not to be
used with GGBS
OPC;
PFA (25-40%)
replacement
mandatory
OPC SRPC not
permitted.
No codes specify
PFA, GGBS, CSF
Range of
cementitious content
380-450 kg/m3 360-430 kg/m3 375-550 kg/m3 350-400 kg/m3
Minimum slump 75mm 75mm 75mm -
Miscellaneous Equivalent sodium oxide
per m3 of concrete < 3kg
Flakiness Index < 30%
Elongation Index < 35%
Los Angeles Value≦ 30%
Sodium sulphate soundness
weighted average loss < 6%
- - -
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Durability Performance of Marine Concrete
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
10
20
30
40
50
60
70
80
90
10
0
Splash Zone
Conventional Concrete
(11 yrs)
Marine Concrete
(40 yrs)
Distance from surface [mm]
Ch
lori
de
con
ten
t [%
]
Ch
lori
de
con
ten
t [%
]
0.06
Projected chloride
profiles of micro-
silica concrete and
conventional
concrete at splash
zone
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Pictures of a 13 Years old Structures
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Pictures of a 15 Years old Structures
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Measures to Enhance Durability Performance
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
10
20
30
40
50
60
70
80
90
10
0
Splash Zone
Conventional Concrete
(11 yrs)
Marine Concrete
(40 yrs)
Distance from surface [mm]
Ch
lori
de
con
ten
t [%
]
Ch
lori
de
con
ten
t [%
]
0.06
Projected chloride
profiles of micro-
silica concrete and
conventional
concrete at splash
zone
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• Coating • Silane protection
• Epoxy coating
Silane protection
Measures to Enhance Durability Performance
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Measures to Improve Durability
• Concrete Coatings
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Measures to Enhance Durability Performance
• Coating
• Stainless Steel Rebars In Outer Layers
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Source: International Molybdenum Association
• Reinforcement: Stainless Steel Bars
Measures to Improve Durability
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Measures to Enhance Durability Performance
• Coating
• Stainless Steel Rebars In Outer Layers
• Rapid Chloride Penetration Test (CSI: Section 19)
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Durability Performance Tests
CS1:2010 - Section 19 Determination of concrete’s ability to resist chloride ion penetration
Chloride Ion Penetration Test
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Chloride Ion Penetration Test
Durability Performance Tests
Charge Passed
(Coulombs)
Chloride Ion Penetrability
>4000 High
2,000-4,000 Moderate
1,000-2,000 Low
100-1,000 Very Low
<100 Negligible
Mean value shall be less than 1,000 coulombs after curing for 28 days
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Part 2: Maintenance Strategies
• Maintenance Strategy for New Marine Structures
• Maintenance Strategy for Structures less than 10
years old
• Maintenance Strategy for Structures more than 10
years old
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Maintenance Strategy for New Marine Structures
Aim:
To minimize the need of concrete repair during the 50
years design life of the structure
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1. Strategy for New Marine Structures Preventive Maintenance Strategy 1.1 Marine Concrete Specification
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1. Strategy for New Marine Structures Preventive Maintenance Strategy 1.1 Marine Concrete Specification
1.2 Protective Coating
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Coal Tar Epoxy
Silane
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1. Strategy for New Marine Structures Preventive Maintenance Strategy 1.1 Marine Concrete Specification
1.2 Protective Coating
1.3 Corrosion Monitoring
To monitor the ingress of chloride and
effectiveness of coating
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CM Devices at Slab Soffit
Pak Sha Wan Public Pier
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CM Devices at Pile Cap
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Monitoring Box
Pak Sha Wan Public Pier
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co
ve
r
Steel bar
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2. Strategy for Structures < 10 Years Old 2.1 Assess the extent of chloride ingress
2.2 Protective Coating
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
10
20
30
40
50
Splash Zone
Dc = 10.32 x 10-13
m2/s
Distance from surface [mm]
Chlo
ride c
onte
nt
[%]
Chlo
ride c
onte
nt
[%]
0.06
Chloride Profile of
Marine Structure
After 3 Years of
Exposure
(OPC concrete)
Dc = 10.32x10-13m2/s
Cs = 1.45%
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3 years existing 5 years
Chloride reaches threshold at cover of 60mm in 13 years
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3. Strategy for Structures >10 Years Old 3.1 Install impressed current cathodic protection
30 years design life
Stops further corrosion
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3.2 Short term structural repairs
Prioritise repair by adopting a condition
audit system
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Example of a Condition Audit System
Visual Inspection
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Visual Inspection Carried out at low tide
Photographic and video records
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Example of a Condition Audit System
Visual Inspection
Database Assessment System
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Condition Audit System
Defect Codes
For ease of defect identification, recording
and future assessment
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S: Spalling
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S1: Spalling
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S2: Spalling to Expose Reinforcement
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C2: Cracks of Width < 1 mm
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DLM: Delamination
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Standard Proforma for Visual Inspection
Defects Spalling/Delamin. Crack Rust Other Defects
Element
Code
S1
(m2)
S2
(m2)
S3
(m2)
DLM
(m2)
C1
(N/F)
C2
(N/F)
C3
(m)
C4
(m)
C5
(m)
RS
(N/F)
CL
(m2)
EFF DP D HCB PD PR B
B/F4-G4 0.1 1.8,
1.2
0.5,
0.5,
0.6
1
B/G1-H1 0.3 N 0.5,
3,
N
B/G2-H2 0.2 F 0.6,
1,
1,
2,
1.4
3
C/G11 0.2 N N C/G12 0.1 F 0.6,
0.8
1 3,2
C/G13 F 2.5
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Database Assessment System
Categorization of defects
Calculation of frequency of defects for each
category
Deterioration index
Deterioration ranking
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Example of a Condition Audit System
Visual Inspection
Database Assessment System
Detailed Investigation
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Detailed Investigation Non-Destructive Tests
Inspection Windows
Cores for Compressive Strength Test
Cores for Chloride Profile Test
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3.3 Study the option of reconstruction
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Conclusion
Chloride ingress rate is substantially reduced
by the adoption of the marine concrete
specification
Results indicated that the durability of marine
structures are greatly enhanced by the
marine concrete specification
The service life will be further enhanced by
the application of suitable concrete coating
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Conclusion
Maintenance strategies for marine structures
could be based on concrete coating, cathodic
protection technique and an effective
structural condition audit system to prioritize
concrete repair work
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End of Presentation
Thank you!