BS EN 1926:2006 Natural stone test methods. Determination of uniaxial compressive strength

EUROPEAN STANDARD

EN 1926

NORME EUROPÉENNE EUROPÄISCHE NORM

December 2006

ICS 73.020; 91.100.15

Supersedes EN 1926:1999

English Version

Natural stone test methods - Determination of uniaxial compressive strength Méthodes d'essai des pierres naturelles - Détermination de la résistance à la compression uniaxiale

Prüfverfahren für Naturstein - Bestimmung der einachsigen Druckfestigkeit

This European Standard was approved by CEN on 9 November 2006. 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. This European Standard exists 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, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

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© 2006 CEN

All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

B-1050 Brussels

Ref. No. EN 1926:2006: E

EN 1926:2006 (E)

Contents

page

Foreword......................................................................................................................................................................3 1

Scope ..............................................................................................................................................................4

2

Normative references ....................................................................................................................................4

3

Principle..........................................................................................................................................................4

4

Terms and Definitions ...................................................................................................................................4

5

Symbols ..........................................................................................................................................................4

6

Apparatus .......................................................................................................................................................5

7 7.1 7.2 7.3 7.3.1 7.3.2 7.4

Preparation of specimens.............................................................................................................................5 Sampling .........................................................................................................................................................5 Test specimens ..............................................................................................................................................5 Surface preparation .......................................................................................................................................5 General............................................................................................................................................................5 Capping with mortar ......................................................................................................................................6 Conditioning of specimen before testing....................................................................................................6

8 8.1 8.2 8.3

Procedure .......................................................................................................................................................6 Measuring the specimen ...............................................................................................................................6 Placing the specimen in the testing machine.............................................................................................6 Loading ...........................................................................................................................................................6

9

Expression of results ....................................................................................................................................6

10

Test report ......................................................................................................................................................7

Annex A.1 A.2 A.3 A.4 A.5 A.6 A.6.1 A.6.2 A.6.3 A.6.4 A.7 A.8 A.9

A (normative) Determination of the compressive strength of armourstone ...........................................9 Scope ..............................................................................................................................................................9 Normative references ....................................................................................................................................9 Principle..........................................................................................................................................................9 Definitions and symbols ...............................................................................................................................9 Apparatus .......................................................................................................................................................9 Preparation of specimens.............................................................................................................................9 Sampling .........................................................................................................................................................9 Test specimens ..............................................................................................................................................9 Surface preparation .....................................................................................................................................10 Conditioning of specimen before testing..................................................................................................10 Procedure .....................................................................................................................................................10 Expression of results ..................................................................................................................................10 Test report ....................................................................................................................................................10

Annex B (informative) Determination of the point load strength index of natural stone.................................12 B.1 General..........................................................................................................................................................12 B.2 Background ..................................................................................................................................................12 B.3 Correlation data ...........................................................................................................................................12 Annex C (normative) Statistical evaluation of the results ...................................................................................13 C.1 Scope ............................................................................................................................................................13 C.2 Symbols and definitions .............................................................................................................................13 C.3 Statistical evaluation of test results ..........................................................................................................14 Annex D (informative) Bibliografy related to Annex B.........................................................................................16 Bibliography ..............................................................................................................................................................17

2

EN 1926:2006 (E)

Foreword This document (EN 1926:2006) has been prepared by Technical Committee CEN/TC 246 “Natural stones”, the secretariat of which is held by UNI. 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 2007, and conflicting national standards shall be withdrawn at the latest by June 2007. This document supersedes EN 1926:1999. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

3

EN 1926:2006 (E)

1

Scope

This European standard specifies a method for determining the uniaxial compressive strength of natural stones.

2

Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 197-1, Cement – Part 1: Composition, specifications and conformity criteria for common cements EN 12390 (all parts), Testing hardened concrete EN 12670:2001 Natural stone - Terminology EN 13383-1:2002, Armourstone - Part 1: Specification

3

Principle

The specimens, after mechanical preparation of surfaces or, if needed, after capping, are laid and centred on the plate of a testing machine. A uniformly distributed load is applied and increased continuously until failure occurs.

4

Terms and Definitions

For the purposes of this document, the terms and definitions given in EN 12670:2001 apply.

5

Symbols

h

height of the specimen, in millimetres;

l mean value of the lateral dimension, i.e. the distance between opposite vertical faces of the specimen (if cubic), in millimetres; d

mean value of the diameter of the specimen (if cylindrical), in millimetres;

A cross-sectional area of the specimen before testing, in square millimetres; F

failure load, in Newtons;

R

uniaxial compressive strength of the specimen, in Megapascals;

R mean value of the uniaxial compressive strength, in Megapascals;

s

standard deviation;

v

coefficient of variation.

4

EN 1926:2006 (E)

6

Apparatus

6.1

A surface grinder.

6.2

A lapping machine if final preparation of the specimens is needed.

6.3 A test machine of appropriated force, in accordance with EN 12390 and calibrated according to this standard. 6.4

A time counter accurate to 1 s.

6.5

A ventilated oven which can maintain a temperature of (70 ± 5) °C.

6.6

A weighing instrument which has an accuracy of 0,1 g.

6.7

A linear measuring device with an accuracy of 0,05 mm.

6.8

Air conditioned room with a temperature of (20 ± 10) °C.

7

Preparation of specimens

7.1

Sampling

The sampling is not the responsibility of the testing laboratory, unless specially requested. At least 10 specimens are to be tested and the direction of any existing plane of anisotropy recorded.

7.2

Test specimens

Test specimens shall be cubes with (70 ± 5) mm or (50 ± 5) mm edges or right circular cylinders whose diameter and height are equal to (70 ± 5) mm or (50 ± 5) mm. The lateral dimension or the diameter of the specimen shall be related to the size of the largest grain in the rock by the ratio of at least 10:1. If the maximum observed dimension of the grains exceeds 7 mm, it is recommended to have a larger number of specimens in order to obtain representative results. The axis of the specimen shall be normal to the planes of anisotropy, e.g. bedding planes, foliation, etc. (figure 1a and 2a). If a test with orientation of loading parallel to the planes of anisotropy is required, another set of specimens with the same dimensional characteristics shall be prepared (Figure 1b and 2b).

7.3 7.3.1

Surface preparation General

The faces to which the load is to be applied shall be flat to a tolerance of 0,1 mm in any 100 mm and such that the top surface lies between two parallel planes which are parallel to the bottom surface, and not greater than 1mm apart for every 100 mm The sides of the specimen shall be smooth and free of abrupt irregularities and straight to within 0,3 mm over the full length of the specimen. To meet the above requirements the specimens shall be finished on either a lathe or surface grinder, with final preparation on a lapping machine if needed. Capping with mortar according to the procedures indicated in 7.3.2 is to be used only if the indicated tolerances are not obtainable with the prescribed mechanical preparation. This condition shall be clearly indicated in the test report.

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EN 1926:2006 (E)

7.3.2

Capping with mortar

It is possible to cap the specimen using a mortar made with cement CEM I 52,5 R according to EN 197-1 and then waiting until the cement has hardened.

7.4

Conditioning of specimen before testing

Specimens, whether capped or uncapped, shall be dried at (70 ± 5) °C to constant mass. This is assumed to have been attained when the difference between two weighings at an interval of (24 ± 2) h is not greater than 0,1% of the mass of the specimen. After drying and prior to testing the specimens shall be stored at (20 ± 5) °C until the thermal equilibrium is reached. After that, the tests shall be performed within 24 h.

8 8.1

Procedure Measuring the specimen

The cross-sectional dimensions of the test specimen (lateral dimension for cubic diameter for cylindrical test specimens) shall be measured to the nearest 0,1 mm by averaging two measures taken at right angles to each other at about the upper-height and two about the lower-height h of the specimen. The average lateral dimension l or the average diameter d shall be used for calculating the cross-sectional area. The height of the specimen shall be determined to the nearest 1,0 mm.

8.2

Placing the specimen in the testing machine

Wipe the bearing surfaces of the testing machine clean and remove any loose grit from the bed faces of the specimen. Align the specimen carefully with the centre of the ball-seated platen, so that a uniform seating is obtained. Do not use any packing material.

8.3

Loading

Load on the specimen shall be applied continuously at a constant stress rate of (1 ± 0,5) MPa/s. The maximum load on the specimen shall be recorded to the nearest 10kN.

9

Expression of results

The uniaxial compressive strength R of each specimen is expressed by the ratio of the failure load of the specimen and its cross-sectional area before testing, by the equation:

R=

F A

The result shall be expressed in Megapascals with at least two significant figures. The mean value R shall be calculated to the nearest 1 MPa.

6

(1)

EN 1926:2006 (E)

10 Test report The test report shall contain the following information: a) unique identification number for the report; b) number, title and date of issue of this European standard; c) name and address of the testing laboratory and the address where the test was carried out if different from the testing laboratory; d) name and address of the client; e) it is the responsibility of the client to supply the following information: 

petrographic name of the stone;



commercial name of the stone;



country and region of extraction;



name of the supplier;



direction of any existing plane of anisotropy (if relevant to the test), clearly indicated on the sample or on each specimen by means of two parallel lines;



name of the person or organization which carried out the sampling;



surface finish of the specimens (if relevant to the test);

f)

date of delivery of the sample or of the specimens;

g) date when the specimens were prepared (if relevant) and the date of testing; h) number of specimens in the sample; i)

dimensions l (or d ) and h in millimetres and the failure load F measured without any decimal place;

j)

surface preparation of the specimens and their conditioning before testing;

of each specimen, in kiloNewtons

k) orientation of the axis of loading with respect to the existing planes of anisotropy; l)

compressive strength R of each specimen, in Megapascals with at least two significant figures;

m) mean value

R of compressive strength, in Megapascals to the nearest 1 MPa;

n) standard deviation s , in Megapascals to the nearest 1 MPa, and the variation coefficient v ; o) all deviations from the standard and their justification; p) remarks. The test report shall contain the signature(s) and role(s) of the responsible(s) party(s) for testing and the issue date of the report. It shall also state that the report shall not be partially reproduced without written consent from the testing laboratory.

7

EN 1926:2006 (E)

Key a)

load normal to the planes of anisotropy

b)

load parallel to the planes of anisotropy

Figure 1 — Cubic test specimens

Key a)

load normal to the planes of anisotropy

b)

load parallel to the planes of anisotropy

Figure 2 — Cylindrical test specimens

8

EN 1926:2006 (E)

Annex A (normative) Determination of the compressive strength of armourstone

A.1 Scope This annex specifies the method for the determination of compressive strength of stones of different size and irregular shape, which are used in hydraulic protection and regulation structures. The term armourstone is used for such materials.

A.2 Normative references See clause 2.

A.3 Principle See clause 3. For materials to be used as armourstone, specimens shall be tested in a condition indicating their strength in water and in their weakest orientation with respect to any existing plane of anisotropy.

A.4 Definitions and symbols See clauses 4 and 5.

A.5 Apparatus See clause 6.

A.6 Preparation of specimens A.6.1 Sampling The sample shall be taken in accordance with annex A of EN 13383-1:2002.

A.6.2 Test specimens Each specimen shall be prepared from a separate piece of armourstone. Test specimens shall be cubes with (50 ± 5) mm edges or right circular cylinders whose diameter and height are equal to (50 ± 5) mm. For the pieces of armourstone whose compressive strength is lower than or equal to 40 MPa, the use of cubes with (70 ± 7) mm edges or right circular cylinders whose diameter and heigth are equal to (70 ± 7) mm are allowed. The lateral dimension or the diameter of the specimen should be related to the size of the largest grain in a representative piece of the material by a ratio of at least 10:1. For coarse-grained material, cubes or cylinders having an edge or diameter no greater than 150 mm are admitted. In this case, the maximum dimensions of the grains shall be indicated in the test report.

9

EN 1926:2006 (E)

The axis of the specimen shall be parallel to the planes of anisotropy, e.g. bedding planes, foliations, etc. If a test with orientation of loading normal to the anisotropy is required, another set of specimens with the same dimensional characteristics shall be prepared.

A.6.3 Surface preparation As in main text, 7.3.

A.6.4 Conditioning of specimen before testing Test specimens shall be fully immersed in tap water at a room temperature of (20 ± 10)°C for (48 ± 4) h and tested for strength within 1 h of removal from the water, taking care to minimise any changes in moisture content of the specimen prior to testing.

A.7 Procedure As in main text, clause 8.

A.8 Expression of results As in main text, clause 9.

A.9 Test report The test report shall contain the following information: a) unique identification number of the report; b) number, title and date of issue of this European standard; c) name and address of the testing laboratory and the address where the test was carried out if different from the testing laboratory; d) name and address of the client; e) it is the responsibility of the client to supply the following information: 

petrographic name of the stone;



commercial name of the stone;



country and region of extraction;



name of the supplier;



direction of any existing plane of anisotropy (if relevant to the test) to be clearly indicated on the sample or on each specimen by means of two parallel lines;



name of the person or organization which carried out the sampling;



surface finish of the specimens (if relevant to the test);

f)

date of delivery of the sample or of the specimens;

10

EN 1926:2006 (E)

g) date when the specimens were prepared (if relevant) and the date of testing; h) number of specimens in the sample; i)

dimensions l (or d ) and h in millimetres and the failure load F measured without any decimal place;

j)

surface preparation of the specimens and their conditioning before testing;

of each specimen, in kiloNewtons

k) orientation of the axis of loading with respect to the rock anisotropy; l)

compressive strength R of each specimen, in Megapascals with at least two significant figures;

m) mean value

R of compressive strength, in Megapascals to the nearest 1 MPa;

n) standard deviation s , in Megapascals to the nearest 1 MPa, and the variation coefficient v; o) description of any specimen breakages that occurred during specimen preparation, detailing the number of such breakages; p) all deviations from this standard and their justification; q) remarks. The test report shall contain the signature(s) and role(s) of the responsible party(ies) for the testing and the issue date of the report. It shall also state that the report shall not be partially reproduced without the written consent from the laboratory.

11

EN 1926:2006 (E)

Annex B (informative) Determination of the point load strength index of natural stone

B.1 General This informative annex is given to provide a simple method for the factory production control of the uniaxial compressive strength of natural stone and stone used in hydraulic structures.

B.2 Background The point load strength index is widely used in rock mechanic applications for obtaining a rapid and cheap assessment of the variability in rock source strength and is therefore ideal for use in factory production control.

B.3 Correlation data To use point load strength index data to obtain estimates of uniaxial compressive strength, the ideal correlation equation to use is one based on a preliminary study of the particular rock source in question. The point load strength test method to be used is the suggested method of the International Society for Rock Mechanics (ISRM), 1985, see reference in Annex D. If a correlation for the specific rock type is not available, the general correlation equation given in the reference in Annex D is as follows: 

Uniaxial Compressive Strength = 22 times Point Load Strength Index

It is based on an extensive investigation of a wide range of strong and weak rocks. It will not give a very accurate prediction of compressive strength for all rock types, however, it is recommended as the best researched single correlation factor to predict the compressive strength of all rock types. An aspect ratio of 2:1 for length to diameter of cylinders is assumed for the compressive strength data in the above correlation equation.

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EN 1926:2006 (E)

Annex C (normative) Statistical evaluation of the results

C.1 Scope This annex establishes a method for the statistical treatment of test results obtained following the natural stone test method described in this standard.

C.2 Symbols and definitions Measured values

x1, x2, .. xi .., xn

Number of measured values

n

x= Mean value

1 n

Standard deviation

s=±

Coefficient of variation

v=

∑x

i

i

∑ ( xi − x )² n −1

s (for individual values) x

x ln = Logarithmic Mean

1 n

∑ ln x

i

i

∑ (ln x − xln )

Logarithmic Standard deviation

sln = ±

Maximum value

Max

Minimum value

Min

Lower expected value

E=e

Quantile factor

ks see table 1

i

2

n −1

( x ln −( k ⋅s )) s ln

where ks (quantile factor) is given in Table 1

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EN 1926:2006 (E)

C.3 Statistical evaluation of test results For the calculation of the mean value normal distribution is assumed.

(x ) , the standard deviation (s) and the coefficient of variation (v), a

When calculating the lower expected value (E), a logarithmic normal distribution is assumed. The lower expected value (E) corresponds to the 5 % quantile of a logarithmic normal distribution for a confidence level of 75%. Table C.1 Quantile factor (ks) in dependence on the number of measured values (n) in correspondence to the 5% quantile for a confidence level of 75%

14

n

ks

3

3,15

4

2,68

5

2,46

6

2,34

7

2,25

8

2,19

9

2,14

10

2,10

15

1,99

20

1,93

30

1,87

40

1,83

50

1,81

8

1,64

EN 1926:2006 (E)

The following examples should help to clarify the method: EXAMPLE 1 values:

Calculation of mean value, standard deviation, maximum value and minimum value of 6 measured

Measurement no

Measured value x

1

2000

2

2150

3

2200

4

2300

5

2350

6

2400 --------

Mean value

2333

Standard deviation

147

Maximum value

2400

Minimum value

2000

EXAMPLE 2 Calculation of mean value, standard deviation, coefficient of variation and lower expected value of 10 measured values:

From table 1 for: n=10

Measurement no

Measured value x

(ln x)

1

2000

(7,60)

2

2150

(7,67)

3

2200

(7,70)

4

2300

(7,74)

5

2350

(7,76)

6

2400

(7,78)

7

2600

(7,86)

8

2750

(7,92)

9

2900

(7,97)

10

3150

(8,06)

---------

---------

Mean value

2480

(7,807

Standard deviation

363

(0,143)

Variation coefficient

0,15

ks=2,1

lower expected value 1819

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EN 1926:2006 (E)

Annex D (informative) Bibliography related to Annex B

The International Society for Rock Mechanics convened a Working Party to produce a ‘Recommended Suggested Method’ for the determination of the point load strength index. The reference is as follows: Franklin, J.A. [co-ordinator] (1985), Suggested method for determining Point Load Strength, International Society for Rock Mechanics Commission on Testing Methods, (revised version). International Journal of Rock Mechanics, Mining Sciences and Geomechanical Abstracts., Vol 22, pp 51-60.

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EN 1926:2006 (E)

Bibliography

[1]

EN 1925, Natural stone test methods – Determination of water absorption coefficient by capillarity.

[2]

EN 1936, Natural stone test methods – Determination of real density and apparent density, and of total and open porosity.

[3]

EN 12370, Natural stone test methods – Determination of resistance to salt crystallisation.

[4]

EN 12371, Natural stone test methods – Determination of frost resistance.

[5]

EN 12372, Natural stone test methods – Determination of flexural strength under concentrated load.

[6]

EN 12407, Natural stone test methods – Petrographic examination.

[7]

EN 12440, Natural stone – Denomination criteria.

[8]

EN 13161, Natural stone test methods – Determination of flexural strength under constant moment.

[9]

EN 13364, Natural stone test methods – Determination of the breaking load at dowel hole.

[10]

EN 13373, Natural stone test methods – Determination of geometric characteristics on units.

[11]

EN 13755, Natural stone test methods – Determination of water absorption at atmospheric pressure.

[12]

EN 13919, Natural stone test methods - Determination of resistance to ageing by S02 action in the presence of humidity.

[13]

EN 14066, Natural stone test methods – Determination of resistance to ageing by thermal shock.

[14]

EN 14146, Natural stone test methods – Determination of the dynamic modulus of elasticity (by measuring the fundamental resonance frequency).

[15]

EN 14147, Natural stone test methods – Determination of resistance to ageing by salt mist.

[16]

EN 14158, Natural stone test methods – Determination of rupture energy.

[17]

EN 14205, Natural stone test methods – Determination of Knoop hardness.

[18]

EN 14231, Natural stone test methods – Determination of the slip resistance by means of the pendulum tester.

[19]

EN 14579, Natural stone test methods – Determination of sound speed propagation.

[20]

EN 14580, Natural stone test methods – Determination of static elastic modulus.

[21]

EN 14581, Natural stone test methods – Determination of linear thermal expansion coefficient.

[22]

EN 14157, Natural stone test methods – Determination of the abrasion resistance.

17