BS 1881-part 209-90

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    BS 1881 :

    Part

    209 : 1990

    UDC 666 972 691 32

    620 1

    British

    Standard

    Testing

    concrete

    Part209

    ecommendations o r

    t h

    measurement

    of dynamic modulus

    of elasticity

    Essais des betons

    Partie

    206

    ecommandations relativesau rnesurage du module dynamique d blasticitb

    Priifung von Beton

    Teil 206.

    Empfehtungen

    fur die Messung

    des

    dynamischen

    E

    lastizitatsmoduls

    ljl

    I I ^_.+. ^-.. ,

    YO

    COPYING

    WITHOUT

    B SI PERMISSION EXCEPT

    S

    PERMITTED Y COPYRIGW

    L W

    . . ~ . . ., .;...

    y :

    '

    .

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    ..-

    S

    188

    : Part

    2 9 : 199

    Foreword

    Committee responsible

    Page

    Inside

    front cover

    Back cover

    Rsecrmmsndationr

    Scope

    2

    2

    Definitions 2

    3

    Applications

    4 Principle

    5

    Summary of the test method

    2

    6

    Apparatus

    2

    7 Methods

    of testing laboratory made specimens

    3

    8

    Calculations 4

    9

    Report

    4

    Test

    configuration

    for determination

    of

    dynamic

    modulus

    of

    el sticity

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    BS 1881 Part 209

    :

    1990

    Recommendations

    1

    Scope

    5 Summary ofthe

    est

    method

    This Part of BS

    1881

    gives recommendations for the

    determination of dynamic modulus of elasticity of plain

    concrete in t h e laboratory using resonance of vibration

    in the longitudinal mode.

    NOTE. The titles of the publications

    referred

    to in this standard

    sra lis td on the inside

    back

    comr.

    2 Definitions

    For the purposes of this Part of

    BS

    1881 the definitions

    given in BS 3683

    :

    art 4

    and BS 6100

    :

    Part 6 apply,

    together with the following.

    2.1 resonance. Condition in which the frequency of a

    vibration applied to a body

    s

    equal to one of the natural

    frequencies of vibration of that body

    NOTE. This concurrence of frequencies maximizes the amplitude

    of vibration

    in

    the body.

    2.2 longitudinal

    made

    of vibration. Mode in which

    compression waves travel through

    a

    prismatic specimen

    in the direction parallel to its length.

    NOTE 1 The W a M S are

    partially reflected by the

    end

    faces of

    the spe imen

    and

    thus travel to and fro within

    it.

    NOTE

    2.

    Other

    modes

    exist such

    as

    transverse nd torsional.

    2.3

    fundamsntal frequency. Lowest resonant frequency

    a t

    which a body wil l vibrate in

    a

    particular mode.

    2.4 dynamic modulus of elasticity of concrete ED

    .

    Ratio of the stress to that part of the strain corresponding

    to elastic deformation only.

    NOTE. The modulus obtained

    refers to

    tho initial tangent

    to

    the

    non-linear stresdstrain relationship far concrete which does not

    obey Hooke s Law. It is normally appreciably larger than the

    statically rneasurod value obtained by the method described

    in BS

    1881 P a n 121.

    Applications

    Measurement of dynamic modulus is most commonly used

    for comparative testing of concretes in the laboratory and

    for assessing degradation in durability

    tests,

    e.g. in freezing

    and thawing

    tests.

    4

    Principle

    An elastic or partially elastic body will vibrate i f struck a

    blow. Each body possesses many modes

    of

    vibration and

    in geometrical bodies well defined modes may be identified.

    This method

    i s

    concerned only with identifying the funda-

    mental longitudinal mode of vibration

    in

    concrete prisms.

    The frequency a t which this vibration occurs depends

    largely on the dynamic modulus of elasticity, density,

    and length of the specimen.

    A-variable frequency oscillator

    imparts

    an alternating force

    to the specimen

    and

    the response i s sensed by an accelero-

    meter or vibration pick-up. The amplitude of vibrations is

    monitored by an indicator and when

    a

    resonant frequency

    i s reached, the indicator shows he amplitude to

    be

    at

    a

    well defined maximum.

    If his resonant frequency s the fundamental frequency

    it is

    related to the modulus of elasticity

    of

    the concrete

    through the equation in clause 8.

    6

    Apparatus

    6 1

    Variable frequency oscillator providing

    a

    variable

    narrow- band sinusoidal output from

    500

    Hz o 20

    kHz

    with power adjustable from zero to

    a t

    feast 2 W.

    The frequency of the oscillator output should be indicated

    within

    n

    accuracy of

    f 0.5 96

    The output of a good quality oscillator tuned to

    a

    given

    frequency should not contain more than 2 of i t s ampli-

    tude in the second and third harmonics of the frequency

    and should have a stability within

    +

    5 of the operating

    voltage.

    6.2 Exciter,

    of which the part in contact with the specimen

    should have

    a

    mass

    of

    not more than

    0.2

    of the mass of

    the specimen.

    6.3

    Pick-up, of which any part in contact wi th the

    specimen should have amass of not more than

    0.2

    of

    the mass of the specimen. The vibration pick-up should

    have no resonances at frequencies

    below 20

    kHz.

    6.4 Amplitude indicator,

    consisting of

    a

    voltmeter or

    cathode ray oscilloscope incorporating appropriate

    amplification facilities.

    6.5

    Support

    consisting of

    a

    pair of horizontal steel bars

    between which the specimen can be

    clamped.

    The width

    of

    the contact area of the clamping bars should not exceed

    one twentieth o f the length of the specimen. The ban

    can be positioned by threaded vertical rods attached to

    a

    rigid baseboard

    which

    also carries the exciter and pick-up

    mounting posts as shown in figure 1. The baseboard stands

    an soft elastomeric pads on

    a

    rigid workbench to reduce

    the effects of extranzous vibrations transmitted through

    the laboratory floor.

    Alternatively, the specimen may

    l i e

    on a block of foam

    rubber provided that the exciter and pick-up centrelines

    re

    normal

    to

    the specimen s end faces.

    6.6

    Balance

    of appropriate capacity to

    weigh

    the specimen

    to the accuracy required by 7.2.

    6.7 Vernier calliper complying with BS

    887,

    capable

    o

    measuring the lateral dimensions of the specimen to the

    accuracy required

    by

    7.2.

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    7

    Methodrs f testing

    laboratary

    made

    specimens

    The laboratory made specimens should be prisms of circular

    or square section with a length not less than three nor

    more than five times the maximum transverse dimension.

    Specimens should preferably

    be

    beams made in accordance

    with BS I881 Part 109 and then cured in accordance

    with BS l t Part 1.

    7.2

    Preliminary

    mmrremm*

    Immediately before testing, the length and density of each

    specimen should

    e

    obtained rom

    t h e

    fol lowing procedures.

    (a)

    Lengrh.

    Calculate the mean length,

    L

    (in mm) from

    at least four symmetrically placed measurements read

    to an accuracy of 1 mm.

    b) Density. Weigh the specimen in air and record i t s

    mass. MA. (in kg) to an accuracy of * 0.25 .

    Determine the volume, V, (in m3 of the specimen

    either from i t s dimensions or by water displacement

    as follows.

    1 Dimension For a beam, calculate the mean

    width,

    a,

    and depth. 6 in mrn) from

    at

    least six

    measurements of each dimension spaced equally

    along i t s length read to an accuracy of 0.25 mm.

    Then

    V L b a x

    lW9

    For a cylindrical specimen, calculate the mean

    diameter,

    d,

    (in

    mm

    from

    a t

    least

    six

    measurements

    spaced equally along i t s length read to an accuracy

    of 0.25 mm. Then

    (2)

    Water

    displacement.

    Weigh the specimen in water

    and record its apparent loss in mass, ML, in kg) to

    an accuracy of 0.25

    96

    Then

    V =

    ML/

    pw

    where

    p is

    the density of water which may

    be

    taken as

    1

    kg/m3

    at ambient temperature.

    Method 2 should not be used for unsaturated

    specimens.

    Calculate the density, p, {in kg/m3)of the specimen

    from the equation

    p =

    MAIV.

    BS

    1881

    Part 2 9 1990

    Specimens should ss ld in a condition appropriate to

    the

    purpose of the investigation.

    Where specimens have

    been

    stored in water they should

    be

    tested immediately on removal from the water, whilst they

    are s t i l l satwand.

    Surface

    water and grit should be wiped

    off the specimen.

    The specimen should e clamped or balanced at

    i t s

    centre

    on

    the

    fixed support.

    Contact should be made between the vibrating part of the

    exciter and the centre of one end face of the specimen by

    means of a weak adhesive or y Qentle spring loading.

    Contact should

    be

    made between a piezo-electric vibration

    pick-up and the opposite end of the specimen in

    a

    similar

    way,

    s

    indicated in figure

    1.

    Alternativety, an electro-

    magnetic non-contactingpick-up can be used in accordance

    with the manufacturer s recommendations. Ensure that the

    axes of

    the

    transducers are in the centre of and normal to

    the end faces of the specimen.

    The exciter should be driven by the variable frequency

    oscillator and the oscillations received from the pick-up

    should be fed to the amplitude indicator to show the

    changes in amplitude received.

    The frequency of excitation shouid

    be

    varied until

    a

    resonance

    i s

    obtained and the frequency noted. Resonance

    will be recognized when the amplitude indicator shows a

    peak response.

    As

    the frequency i s further varied,

    the indicator may show the existence of several resonant

    frequencies, some of these relating to modes of vibration

    other than longitudinal.

    The identification of the fundamental frequency in the

    longitudinal mode requires care. Generally the required

    frequency produces the greatest response on the indicator

    for given settings of the output and gain controls. As a

    check, with the specimen

    set

    up as shown in figure 1,

    resonance should also be obtainable at a frequency three

    times that of the fundamental frequency.

    Ifdifficulties are s t i l t encountered, an approximate value

    for the dynamic modulus of elasticity of the concrete

    may

    be

    obtained from a pulse transit time measurement

    (see BS 1861 Part

    203).

    This value may then be

    substituted into the equation in clause

    8

    to yield

    n

    approximate value for the desired resonant frequency.

    The search for the exact frequency may then be confined

    to a narrow range about the value so calculated.

    Instrument manufacturer s li terature sometimes provides

    very useful instructions for identifying the fundamental

    frequency. Once identified, this value should be recorded,

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    BS 1881 Part 2 9 1990

    The

    dynamic modulus of elasticity

    of

    concrete.

    E D

    in G N / ~ ' ) or each specimen should becalculated to the

    nearest0.5 G N / ~rom the formula

    ED =

    4 n Z ~ 2 p 1 0 1 5

    where

    L

    i s the length of the specimen

    {inrnrn);

    n

    is

    the fundamental frequency in the longitudinal

    mode of vibration

    of

    the specimen in

    Hz);

    p

    s

    the density

    of

    the specimen in kg/rn3 .

    NOTE. This formula appli

    to

    all uniform specimens

    of

    constant

    crossmion

    9

    Report

    9.1 General

    The report should affirm t h a t

    t h e

    dynamic modulus of

    elasticity of concrete

    was

    determined

    in

    accordance with

    th recommendations given in S

    1881

    Part 209

    :

    1990.

    9 1 Information to be included

    in

    the

    tmt

    mport

    9.2.1 Obl ory

    informarion.

    The following information

    should

    be

    included

    in

    the test report:

    a)

    date of

    test;

    (b)

    description and nominal size

    of

    the specimenwith

    any

    identifying mark;

    c)

    age

    of the specimen when tested;

    d) conditions in which t he specimen had been stored

    between manufacture and testing;

    el the calculated dynamic rnodulus,of elasticity

    of

    the concrete.

    9.2.2

    dditional

    information.

    When requested,

    t h e following information should also be included in

    t he

    test

    report:

    a)

    the fundamental frequency;

    bj the measured dimensions of the specimen;

    c) the density

    of the

    specimen

    a t

    the time of testing.

    From oscillator

    I I

    Figure

    1

    Tart configuration for determination

    of dynamic

    modulus

    of

    elasticity

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    Publications rehrrd

    to

    BS

    887

    Specifmion

    or

    procision vernier callipers

    BS

    1881

    Testing concrete

    Part 10B Method for rnakiw tret

    bkuns

    from fresh conerste

    art

    11

    1 Method of normal curingof trct rpseimsnr mC method

    art 121 Method for determination of M i c

    modulw of

    elasticity in compression

    PM 2 t

    Guide m the

    u

    of non dsrtructivs

    methodsof

    test for

    hardened

    concrete

    Part 2 3 Raommendrtionr

    for

    mssruromant of wlocity

    of

    ultrasonic pulses in

    conente

    BS

    68

    Glosmry

    of terms

    used in

    non destructive testing

    Part 4 Uttnronic flmdetaction

    BS

    6100

    Giorsary

    of buildingand civil snginssrinp terms

    Part6

    Cbncrete

    and alartsr

    Referred

    to in the

    foreword

    onlv.

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    BS 1881 :

    art 209

    : 1990

    This Brit* Ston&rd. having baenprepad

    under

    ?he d i m i o n of

    the Canmt Gypsum, Agpngrnr and Quarry ProductrStandirds

    Policy Committss, war publish& under ths authority of the B o d

    o fM and come inta

    ffw

    on 3 Apri l

    1800

    British Sttindads Institution,

    1990

    ISBN 680 17926

    The following BSI rsfsrances relate t o he work on this standard:

    Committee &rsncs CAB14

    Oreft

    for

    comment

    88110608

    BritishStmdvds Institution . Incoroorated by Royal Charter, BSI is

    the i nd mn de nt national body for the prepamtion of British

    Standards.

    It s

    the UK member of the International Organization

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    UK

    sponsor of the British National

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    implementing

    the

    standard, of mecss~arydetsils such as

    symbols

    and

    size type or grade designations. Enquiries should

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    British Standards are revised, when

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    Committees responsiblefor this BritishStandard

    The

    prepention of this British Standardwar entrusted by the

    Cement Gypsum, Aggrsgates and Quarry Products Standards

    Policy Committee (CAB/-)

    to Technicel

    Committee CA /4,

    upon which the following bodies were repnrentsd:

    Association o f Lightwsi& t ggregate Manufscturers

    Aslociation of Metropolitan Authorities

    Association of Quality P u l m r i d

    Fuel

    Ash

    Supplism

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    A m i a t i o n

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    P m t

    oncrete F&ration

    British Ready Mixad Concrete Association

    Building Ernploysrr' Confaderation

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    EstaMishmmtl

    Amendments

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    since publication

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    Services

    Agency)

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    of

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