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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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