Bsi bs en 01355 1997 (1999)

01148862 PDF BRITISH STANDARD BS EN 1355 1997 Determination of creep strains under compression of autoclaved aerated concrete or lightweight aggregate concrete with open structure The European Standar[.]

BRITISH STANDARD BS EN

1355:1997

Determination of creep

strains under

compression of

autoclaved aerated

concrete or lightweight

aggregate concrete

with open structure

The European Standard EN 1355:1996 has the status of a

British Standard

ICS 91.100.30

This British Standard, having

been prepared under the

direction of the Sector Board

for Building and Civil

Engineering, was published

under the authority

of the Standards

Board and comes

into effect on

15 October 1997

© BSI 10-1999

The following BSI references

relate to the work on this

standard:

Committee reference B/523

Draft for comment 93/110407 DC

ISBN 0 580 27477 2

Committees responsible for this British Standard

The preparation of this British Standard was entrusted to Technical Committee B/523, Prefabricated concrete and lightweight aggregate concrete with open structure, upon which the following bodies were represented: Aggregate Concrete Block Association

Autoclaved Aerated Concrete Association British Masonry Society

British Precast Concrete Federation Ltd

Department of the Environment (Building Research Establishment) Institution of Structural Engineers

Local Authority Organizations

Amendments issued since publication

Amd No Date Comments

BS EN 1355:1997

Contents

Page

ii © BSI 10-1999

National foreword

This British Standard has been prepared under the direction of Technical Committee B/523 and is the English language version of EN 1355:1996

Determination of creep strains under compression of autoclaved aerated concrete

or lightweight aggregate concrete with open structure, published by the European

Committee for Standardization (CEN)

A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Cross-references

Publication referred to Corresponding British Standard

EN 678:1993 BS EN 678:1994 Determination of the dry density of

autoclaved aerated concrete

EN 679:1993 BS EN 679:1994 Determination of compressive strength

of autoclaved aerated concrete

EN 992:1995 BS EN 992:1996 Determination of dry density of

lightweight aggregate concrete with open structure

EN 1354:1996 BS EN 1354:1997 Determination of compressive

strength of lightweight aggregate concrete with open structure

Summary of pages

This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages 2 to 8, an inside back cover and a back cover

This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on the inside front cover

EUROPEAN STANDARD

NORME EUROPÉENNE

EUROPÄISCHE NORM

EN 1355

December 1996

ICS 91.100.30

Descriptors: Concrete, cellular concrete, aggregates, mechanical tests, compression tests, creep tests, determination, creep strength

English version

Determination of creep strains under compression of autoclaved aerated concrete or lightweight aggregate

concrete with open structure

Détermination du fluage en compression du

béton cellulaire autoclavé et du béton de

granulats légers à structure ouverte

Bestimmung der Kriechverformungen unter Druckbeanspruchung von dampfgehärtetem Porenbeton und von haufwerksporigem Leichtbeton

This European Standard was approved by CEN on 1996-11-30 CEN members

are bound to comply with the CEN/CENELEC Internal Regulations which

stipulate the conditions for giving this European Standard the status of a

national standard without any alteration

Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the Central Secretariat or to any

CEN member

The European Standards exist in three official versions (English, French,

German) A version in any other language made by translation under the

responsibility of a CEN member into its own language and notified to the

Central Secretariat has the same status as the official versions

CEN members are the national standards bodies of Austria, Belgium,

Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,

Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and

United Kingdom

CEN

European Committee for Standardization Comité Européen de Normalisation Europäisches Komitee für Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels

© 1996 Copyright reserved to CEN members

Ref No EN 1355:1996 E

© BSI 10-1999 2

Foreword

This European Standard has been prepared by

Technical Committee CEN/TC 177, Prefabricated

reinforced components of autoclaved aerated

concrete or lightweight aggregate concrete with

open structure, the secretariat of which is held by

DIN

This European Standard shall be given the status of

a national standard, either by publication of an

identical text or by endorsement, at the latest by

June 1997, and conflicting national standards shall

be withdrawn at the latest by June 1997

In order to meet the performance requirements as

laid down in the product standards for prefabricated

components of autoclaved aerated concrete and of

lightweight aggregate concrete with open structure,

a number of standardized test methods are

necessary

According to the CEN/CENELEC Internal

Regulations, the national standards organizations

of the following countries are bound to implement

this European Standard: Austria, Belgium,

Denmark, Finland, France, Germany, Greece,

Iceland, Ireland, Italy, Luxembourg, Netherlands,

Norway, Portugal, Spain, Sweden, Switzerland and

the United Kingdom

Contents

Page

5.2 Shape and size of test specimens 4 5.3 Number of test specimens 4 5.4 Preparation of test specimens 4 5.5 Measurement of test specimens 5 5.6 Conditioning of test specimens 5

6.1 Age at loading and duration of sustained load 5

7 Investigations after the creep test 6

EN 1355:1996

1 Scope

This European Standard specifies a method of

determining the longitudinal long-term strains

(creep strains) of test specimens taken from

prefabricated components of autoclaved aerated

concrete (AAC)1) or lightweight aggregate concrete

with open structure (LAC) according to prEN 1520

due to a constant compression stress sustained over

a long period of time

2 Normative references

This European Standard incorporates by dated or

undated reference, provisions from other

publications These normative references are cited

at the appropriate places in the text, and the

publications are listed hereafter For dated

references, subsequent amendments to or revisions

of any of these publications apply to this European

Standard only when incorporated in it by

amendment or revision For undated references the

latest edition of the publication referred to applies

EN 678, Determination of dry density of autoclaved

aerated concrete

EN 679, Determination of compressive strength of

autoclaved aerated concrete

EN 992, Determination of dry density of lightweight

aggregate concrete with open structure

EN 1354, Determination of compressive strength of

lightweight aggregate concrete with open structure

prEN 1520, Prefabricated components of lightweight

aggregate concrete with open structure

3 Principle

Creep strains are determined on test specimens

taken from prefabricated components

The creep strain at a given age t (¼cc,t) is defined as

the total strain under compression at that age

(¼cc,tot,t), less the instantaneous strain under the

same stress occurring during the application of the

load (¼ci,t0), less the strains due to shrinkage from

the time of loading to the considered age (¼cs,t)

The strains due to shrinkage are determined on

unloaded control specimens identical to those used

in the creep test which are taken from the same

component and stored under the same conditions

4 Apparatus

a) Any saw, suitable for cutting reinforced AAC or

LAC components;

b) Callipers, capable of reading the dimensions of

the test specimens to an accuracy of 0,1 mm;

c) A straight-edge, feeler gauges (0,1 mm for

AAC, 0,5 mm for LAC, and 1,0 mm for both) and

a square;

d) A balance, capable of determining the mass of

the test specimens to an accuracy of 0,1 %;

e) Equalizing layers of soft fibreboard (only in the

case of LAC), with a thickness of (12 ± 2) mm and

a density of (250 to 400) kg/m3 to be inserted between the loadbearing surfaces of the test specimens and the platens of the compression testing machine (not required in the case of levelling the loadbearing surfaces by grinding or capping);

f) A loading frame, capable of applying and

maintaining the required compressive load on the test specimen(s) for the required period of time (in general at least one year), despite any length change of the test specimen(s) (see note 1) The header plates of the loading frame shall have sufficient stiffness, and their bearing surface shall not depart from a plane by more than 0,1 mm per 100 mm In any loading frame several test specimens may be stacked for simultaneous loading

Means shall be provided for measuring the load

to the nearest 3 % of the total applied load This may be a permanently installed pressure gauge

or a hydraulic jack or load cell inserted temporarily in the frame when the load is applied or adjusted

When a hydraulic load-maintaining element is used, several frames may be loaded

simultaneously through a central hydraulic pressure-regulating unit

When springs are used, care shall be taken to provide a spherical seated head, or a ball joint and end plates rigid enough to ensure uniform loading of the test specimens

g) A measuring device, for the determination of

the longitudinal length changes (strains) of the test specimens The apparatus may be portable or attached (see note 2)

If portable apparatus is used, gauge points shall

be attached to the test specimen in a positive manner which is normally done by glueing with rapid hardening glue

The gauge length shall be not less than 100 mm The gauge points shall be provided accurately on the longitudinal axes of the four longitudinal surfaces of the prismatic test specimens, and they shall be attached equidistant from the ends, the distance from the adjacent end being not less than 50 mm

1) A European Standard for prefabricated reinforced components of autoclaved aerated concrete is in preparation at CEN.

4 © BSI 10-1999

The device shall be capable of measuring strains

to the nearest 10 × 10–6(0,01 mm/m) for at least

one year without change in calibration

h) a room, capable of maintaining a temperature

of (20 ± 2) °C and a relative humidity

of (60 ± 5) %;

i) a ventilated drying oven, capable of

maintaining a temperature of (105 ± 5) °C

(see note 3)

NOTE 1 A usual frame consists of header plates bearing on the

ends of the loaded test specimens, a load maintaining element

that may be either a spring or a hydraulic capsule or ram,

connected with a cylinder of high pressure nitrogen and a

hydraulic pressure-regulating unit, and threaded rods to take the

reactions of the loaded system.

NOTE 2 Systems in which the varying length changes or

strains are compared with a constant-length standard bar are

considered most reliable.

NOTE 3 In addition, a ventilated drying oven capable of

maintaining a temperature of (40 to 60) °C can be helpful for

conditioning of test specimens.

5 Test specimens

5.1 Sample

The sample for the preparation of the test specimens

(usually at least one prefabricated component) shall

be taken in such a manner that it is representative

of the product to be investigated

5.2 Shape and size of test specimens

The reference test specimens shall be prisms with a

square cross-section of 100 mm × 100 mm and a

height of 300 mm

Test specimens of other sizes or shape may be used,

provided that the correlation to the results of tests

on the above reference test specimens is established

5.3 Number of test specimens

At least two test specimens for determination of creep (creep specimens) and two control specimens for determination of shrinkage shall be prepared from the central part of the component

(see Figure 1)

5.4 Preparation of test specimens

The specimens shall be cut not less than 2 d after autoclaving or casting, respectively The dust or the slurry of the process shall be removed

They shall be taken in such a way that their longitudinal axis is:

The specimens shall contain no reinforcing bars within the gauge length (If unavoidable, bars which are perpendicular to the longitudinal axis may be accepted in exceptional cases This shall be mentioned in the test report.)

The loadbearing surfaces of the creep specimens shall be plane, parallel to each other and

perpendicular to the longitudinal surfaces of the specimens

Planeness of loadbearing surfaces shall be checked across the two diagonals using a straight-edge and,

if necessary, a feeler gauge Deviations exceeding 0,2 mm shall be adjusted by cutting and/or grinding or by capping In the case of LAC, deviations up to 0,5 mm may be tolerated, provided that equalizing layers of soft fibreboard according

to 4 e) are used Deviations from planeness of the

other surfaces shall not exceed 1 mm

— in the case of AAC: perpendicular to the

rise of the mass during the manufacture;

— in the case of LAC: in the plane of the

compression force acting

in the component when used in the structure

Figure 1 — Sampling scheme

EN 1355:1996

The angle between the loadbearing surfaces and the

adjacent longitudinal surfaces of the creep

specimens shall not deviate from a right angle by

more than 1 mm per 100 mm This shall be checked

along both orthogonal middle axes of the

loadbearing surfaces by means of a square and

a 1 mm-feeler gauge or similar instrument Larger

deviations shall be corrected by cutting or grinding

5.5 Measurement of test specimens

The dimensions of the creep specimens and control

specimens shall be measured to an accuracy

of 0,1 mm, using callipers

Length and width of the cross-sectional area, Ac,

shall be measured at mid height at two opposite

longitudinal sides The cross-sectional area shall be

calculated using the mean values of the results of

the measurements

The height of the specimens shall be measured in

the middle of two opposite longitudinal sides

The volume V of the specimen shall be calculated by

multiplying Ac by the mean value of the results of

the height measurements

5.6 Conditioning of specimens

The test specimens shall be conditioned at a

temperature not exceeding 60 °C until their mass

related moisture content is (6 ± 2) % This may be

estimated by comparing their moist density with the

dry density determined in accordance with EN 678

for AAC or with EN 992 for LAC, respectively, on

companion specimens extracted from the same area

of the same component (see note)

After reaching the specified moisture content, the

test specimens shall be stored, protected against

moisture changes, for at least 72 h prior to the test

at (20 ± 2) °C for ensuring uniform moisture

distribution within the test specimen and thermal

equilibrium with the temperature in the laboratory

During the creep test the test specimens shall be

exposed to the surrounding air with a temperature

of (20 ± 2) °C and a relative humidity of (60 ± 5) %

Conditions other than the above reference

conditions may be chosen if required This shall be

indicated in the test report

The actual moisture content of the specimens at the beginning and at the end of the creep test and the dry density shall be determined For this purpose the specimens shall be weighed prior to the creep test, before applying any devices for measurement

of deformations and after completion of the creep test, after removal of gauge plugs etc Finally, they shall be dried to constant mass at (105 ± 5) °C

(see clause 7) If the removal of the adhesive fixed

gauge plugs is likely to remove concrete, the initial mass of the test specimen with and without gauge plugs shall be taken, and the appropriate correction shall be made in the calculations

NOTE The expected moisture content of a test specimen may be calculated according to equation (1):

6 Creep test

6.1 Age at loading and duration of sustained load

In the case of AAC the age at loading is optional

In the case of LAC the creep specimens shall be loaded at an age of 28 d, if not specified otherwise The applied load shall be sustained constant, in general for a period of at least 1 a It may be necessary to continue the test for a longer period, if the deformations are still increasing at a

considerable rate at that time

6.2 Loading details

Immediately before loading the creep specimens the compressive strength of the concrete shall be determined, according to EN 679 for AAC or

EN 1354 for LAC, respectively, on test specimens taken from the same sample

(1) where

È m,exp is the expected mass related moisture content, in

per cent;

Ô hum,t = mhum/V is the moist density of the test specimen,

calculated by dividing its moist mass mhum by its

volume V determined according to 5.5, in

kilograms per cubic metre;

Ô comp is the dry density of companion specimens

determined according to EN 678 (for AAC) or

EN 992 (for LAC), in kilograms per cubic metre.

6 © BSI 10-1999

At the time creep specimens are placed in the

loading frame, the end faces of the control

specimens for shrinkage measurement shall be

covered in order to provide the same drying

conditions as for the creep specimens

The creep specimens shall be placed in the loading

frame taking care in aligning the specimens to avoid

excentric loading

In the case of LAC, provided that the creep

specimens have not been ground or capped and the

deviations from planeness of the loadbearing

surfaces exceed 0,2 mm, equalizing layers of soft

fibreboard, as specified in 4 e), shall be inserted

between the loadbearing faces of the creep

specimens and the header plates of the loading

frame, and also between the individual creep

specimens, if several specimens are stacked in one

loading frame

After proper aligning the creep specimens (see note)

the load shall be applied at the specified intensity

which is usually chosen such that the resulting

stress is one third of the strength at the age of

loading, but not more than 40 % of that value

The duration of loading process should be as short

as practicable and shall in no case exceed 15 min

Strain readings shall be taken immediately before

and after loading, 2 h to 6 h later, after 1 d and then

at appropriate intervals, in general until at 1 a, so

that the curve representing the development of

strains with time can be reliably recorded Before

each strain measurement, the load shall be

controlled and adjusted, if deviating by more

than 2 % from the correct value

Strain readings on the control specimens shall be

taken on the same schedule as for the loaded

specimens

NOTE For control of centric loading it may be helpful to apply

a small preload not exceeding 25 % of the final sustained load

and to note the strain variation around each creep specimen,

after which if necessary, the load may be removed and the

specimens realigned for greater strain uniformity Strain

distribution may also be influenced by tightening or loosening the

nuts on the threaded reaction rods if this type of loading frame is

used (see note 1 in clause 4).

If possible, the strain variation around the

individual creep specimens should not

exceed ± 30 % of the mean strain

7 Investigations after the creep test

After finalizing the creep test the load shall be removed, and the creep specimens and the control specimens shall be weighed and subsequently dried

to constant mass at (105 ± 5) °C in order to determine the dry density on the basis of EN 678 or

EN 992, respectively, and the moisture content at the beginning and the end of the creep test according to equation (2):

8 Test results

The creep strain (cc, t at a given time t is calculated

by equation (3):

The creep strain ¼cc,t and the strains ¼cc,tot,t as well as

¼ci,t0, and ¼cs,t shall be indicated in the test report to the nearest 0, 010/00

(2) where

Èm is the mass related moisture content, in

per cent;

mhum is the mass of the test specimen

(without any gauge plugs) in the moist state, at the beginning or after

finalizing of the creep test, respectively,

in kilograms;

mdry is the mass of the test specimen

(without any gauge plugs), dried according to EN 678 (AAC) or

EN 992 (LAC), in kilograms

¼cc,t = ¼cc,tot,t– ¼ci,t0–¼cs,t (3) where

¼cc,t is the creep strain at a given time t, in per

mille;

¼cc,tot,t is the total strain of the loaded creep

specimen at the considered time t which

had occurred since the initial reading in the unloaded state immediately before application of the final sustained load, in per mille;

¼ci,t0 is the instantaneous strain due to the applied load (difference of readings immediately before and immediately after loading), in per mille;

¼cs,t is the mean value of the total strain of the unloaded control specimens (shrinkage specimens) from the time of loading of the creep specimens until the considered

time t, in per mille.