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8/7/2019 Marine concrete Basics - Copy
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Marine Concrete Basics
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Construction in Marine Environment
References British Standard BSS 6349 Part- 1 Code of
practice for maritime structures
Eurocode EN 1990
International Navigation Association PIANC
(2001) Seismic Design Guidelines for Port
Structures, Report of Working Group 34
Technical Standards for Port and Harborfacilities in Japan , 1999 , Port and Harbor
Research Institute , Ministry of Transport , Tokyo
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Design Life
The estimated design life of a berth structure =
useful life of the structure with plant maintenance
This is a major concern influencing the design
For ordinary marine structures the design life
should be atleast 50 years: for berths serving
special industries, container traffic , oil traffic etc
30 years is more relevant Modern specialized cargo handling subject to
rapid development , may lead to early outdate of
berth facilities
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Design Life
For shore protection works and breakwaters a
design life of 100 years appropriate.
The total design and service life depends on
- the design engineers experiences in design
- the design standards, recommendations used
- correct materials used for the environment
- the construction and the contractors ability
- proper inspection , maintenance and repair of
any damage
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Design Life
Assessment of Factors Fatigue loading, corrosion, marine growth and
reduction in soil strength
Decide on acceptable degree on damage during
the structures lifetime during the design
Evaluate probabilities of particular limit states
Appraise economic feasibility , necessity to allow
for development and related matters Avoid slender members ; salt penetration and
corrosion in marine and environment factors
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Design Life
Assessment of Factors In case of a very exposed open berth structure
possibility of uplifting of the deck structure due to
waves passing under should be considered
The same live load for the whole terminal as the
live load used at the apron should be used ; to
achieve maximum flexibility in cargo handling
techniques Multipurpose berths should be designed for
container loads
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Design Life
Assessment of Factors If mobile cranes are used , provide for outrigger
reactions and bearing pressures imposed by the
maximum anticipated crane size
The outrigger reactions depend on crane lifting
capacity , radius of jib length
To reduce the effect of a concentrated point load
acting directly on a concrete deck slab , spread alayer of sand and asphalt on top of the concrete
slab
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Design Life
Assessment of Factors Berth structures which have direct road
connection to the public highway network , should
at least be designed for loads and accordance
with IRC Codes and Specifications
To prevent overloading of the berth structure the
allowable load should be marked in clear letters
and figures on a sign board at the airport Seismic performance requirements should be
established as per the current BIS Codes and
guidelines based on acceptable risk levels
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Concrete
Concrete is a material formed by mixing
cement
coarse & fine aggregate
water
chemical admixtures
mineral admixtures
Concrete must meet the requirements of- economy
- workability in fresh state
- strength and durability in hardened state
optional
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What is Good Concrete ?
Mix ingredients thoroughly as concrete leaves themixer
Concrete should not segregate while transporting
Should be capable of being easily placed in forms
Hardening should proceed undisturbed withoutdrying out of water necessary for hardening
Finished concrete should be compact & durable,surfaces free from honeycomb or air bubbles
It should be strong enough to meet the intendedpurpose
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Suitable Cement Content
No more cement should be used than is
necessary to produce the required workability,
density, surface finish and strength
Economy not the only factor for reducing cement
Shrinkage and consequent danger of cracks can
be reduced by keeping down the cement content
Workability maintained using admixtures Density, surface finish by proper placing methods
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Aggregates
General Crushed / uncrushed
gravel or crushed stone
Natural sand or
manufactured sand Acceptable quality should
be based on tests
specified in IS 383 and not
based on visualinspection and judgment
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Use of Rounded Aggregates
(Shingle / Gravel) IS:383 permits use of Shingle / GravelIS:383 permits use of Shingle / Gravel
Available in plenty in river beds / deposits inAvailable in plenty in river beds / deposits in
most parts of North India. Also availablemost parts of North India. Also availableselectively in other partsselectively in other parts
Cheaper than crushed aggregateCheaper than crushed aggregate
Environmental friendlyEnvironmental friendly
Many cities have banned use of crushersMany cities have banned use of crushers
Should be the first choice at any site, if availableShould be the first choice at any site, if available
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Batching, Mixing Concrete
Designed Mix Concrete Maintain water cement ratio
at specified value
Determine moisture content of
aggregates frequently,
according to weather conditions
Adjust the water to compensate for observed
moisture content; adjust the aggregates weight Batching plants are generally provided with
moisture probes connected to the control system
Moisture Meter
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Pan mixerTwin shaft mixer
Non-tilting Mixer,
Free Fall
10 x 7 Mixer
Tilting Drum, Free Fall
Batching Plant
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Transporting Concrete By head load (very rare)
Wheel barrows manual /mechanized
Tough riders, trucks, truck mixers
Concrete pumps
Concrete conveyors
Ropeways,Cable cars
Stationary Concrete
Pump
Motorised WheelBarrow (5-8 HP)
ToughRider
Manual
Truck Mixer
Concrete Conveyor
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Placement of Concrete
Hoists Tower Cranes
Concrete Pumps
Belt Conveyors
Concrete skipsCableways
Truck mounted
concrete pump
Belt Conveyor
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Site Concrete Testing Laboratory
Minimum Equipment Set of sieves, Precision weighing balance
Cement testing machine ( large projects )
Maximum / Minimum thermometer
Slump cone with tamping rod
Cube moulds with tamping rod
Curing tank, Temperature Control
Concrete setting time testing apparatus
Cube testing machine, 300 t capacity
Schmidt Rebound Hammer, Cover meter
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Concrete Workability- Definition
Concrete that can be readily compacted, easily
placed without segregation; during compaction,
the entrapped air is eliminated from the concrete
Sufficient workability to get compaction to
maximum density
Voids greatly reduces strength- entrapped air
bubbles /spaces left after excess water evaporates;excess water is avoided by proper mix design with
less water content & use of admixtures
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Factors Affecting Workability of
Concrete Water content
Aggregate type and grading
Aggregate cement ratio
Presence of admixtures
Fineness of cement
Temperature
Slump test is adequate for most of the situations
Special tests for self compacting concrete
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Workability of Concrete - IS:456-2000
Suggested Ranges of Slump (mm) Blinding concrete, shallow sections
pavements using pavers Very low
Mass concrete, lightly reinf. Section inslab, beam, wall, column, floor 25 - 75
Heavily reinforced sections inslab, beam, wall, column 50 - 100
Slipform / Pumped concrete 75 - 100
Trench fill / In-situ piling 100 - 150
Tremie concrete Very high
(175 200)
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Workability of Concrete
Pumped concrete Slump:100 mm at pour
point; excess slump leads
to segregation, blockage
Blockage results in oneshift loss, labor for clearing;
in extreme cases concrete
sets in the pipe line, difficult
or impossible to clear;
expensive pumping pipe
lines are abandoned
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