BRITISH STANDARD BS 6073-2:1981Incorporating Amendment No. 1

Precast concrete masonry units —

Part 2: Method for specifying precast concrete masonry units

UDC 691.327:006

BS 6073-2:1981

This British Standard, having been prepared under thedirection of the Cement,Gypsum, Aggregates and Quarry Products Standards Committee, was published under theauthority of the ExecutiveBoard and comes into effect on31 July 1981

© BSI 12-1998

The following BSI references relate to the work on this standard:Committee reference CAB/11 Draft for comment 79/10450 DC

ISBN 0 580 12190 9

Cooperating organizations

The Cement, Gypsum, Aggregates and Quarry Products Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following:

Association of Consulting EngineersAssociation of County CouncilsAssociation of District CouncilsAssociation of Metropolitan AuthoritiesAutoclaved Aerated Concrete Products Association*British Precast Concrete Federation Ltd*.British Quarrying and Slag Federation *British Railways BoardBritish Ready Mixed Concrete AssociationBritish Steel IndustryCement Admixtures Association*Cement and Concrete Association*Cement Makers’ Federation*Chemical Industries AssociationConcrete Society Limited*County Surveyor’s SocietyDepartment of the Environment (PSA)Department of the Environment (Building Research Establishment)*Department of the Environment Transport and Road Research LaboratoryDepartment of TransportFederation of Civil Engineering Contractors*Gypsum Products Development AssociationInstitute of QuarryingInstitution of Civil EngineersInstitution of Highway EngineersInstitution of Municipal EngineersInstitution of Public Health EngineersInstitution of Structural Engineers*Institution of Water Engineers & ScientistsNational Federation of Building Trades Employers*Natural Environment Research Council (Institute of Geological Science)Royal Institute of British Architects*Royal Institution of Chartered SurveyorsSand and Ballast Hauliers and Allied Trades AllianceSand and Gravel Association Limited*Society of Chemical Industry*Stone Federation

The organizations marked with an asterisk in the above list, together with the following, were directly represented on the Technical Committee entrusted with the preparation of this British Standard:

Aggregate Concrete Block AssociationAssociation of Lightweight Aggregate ManufacturersBritish Ceramic Research AssociationBritish Concrete Masonry AssociationChartered Institution of Building ServicesConcrete Brick Manufacturers AssociationConsumer Standards Advisory Committee of BSIElectricity Supply Industry in England and WalesModular Society Limited

Amendments issued since publication

Amd. No. Date of issue Comments

4508 30 March 1984 Indicated by a sideline in the margin

BS 6073-2:1981

© BSI 12-1998 i

Contents

PageCooperating organizations Inside front coverForeword ii

1 Scope 12 References 13 Definitions 14 General 15 Basic requirements 16 Purchaser’s additional and optional requirements 27 Notification to manufacturer and supplier 3

Appendix A Information to be given by the purchaser withhis enquiry and order 5Appendix B Routine rapid control test of compressive strengthof blocks by manufacturer (fibre board test) 5Appendix C Determination of block density, concrete density andnet area of hollow blocks 6

Figure 1 — Typical profiled ends of blocks 3Figure 2 — Compliance procedure for special categoryof manufacturing control 4

Table 1 — Work sizes of blocks 1Table 2 — Work sizes of bricks 2

Standards publications referred to Inside back cover

BS 6073-2:1981

ii © BSI 12-1998

Foreword

This British Standard has been prepared under the direction of the Cement, Gypsum, Aggregates and Quarry Products Standards Committee.This Part of BS 6073 is a method for specifying precast concrete masonry units, intended to be read in conjunction with BS 6073-1, which is a specification for precast concrete masonry units.When revising BS 2028, BS 1364:1968, the committee carried out a survey of block sizes in common use. It was found that no particular thicknesses predominated and hence there was no possibility of specifying a standard range. Furthermore, forthcoming changes in legislation relating to energy conservation made it probable that new sizes of blocks would be developed in the near future. Similarly, no one strength was in general use. It also became clear that similar minimum performance criteria were also applicable to concrete bricks so the opportunity was taken to extend this revision to replace BS 1180:1972.The committee therefore decided to produce the revised standard in two Parts. Part 1 is a conventional specification giving the minimum levels of performance applicable to all concrete masonry units whilst this Part gives a method of specifying masonry units of different sizes and strengths and also masonry units having properties not covered by Part 1.Appendix A lists the essential information which should be given to the manufacturer for an enquiry or order to be fully understood.Appendix B describes a rapid method of checking compressive strengths of blocks which may be used by manufacturers for routine quality control.Appendix C gives a method of measuring block density and concrete density, which may be used when checking conformity with recommendations of other British Standards, such as BS 5628-1.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.

Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 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.

BS 6073-2:1981

© BSI 12-1998 1

1 ScopeThis Part gives a method for specifying precast concrete masonry units complying with the requirements of BS 6073-1 and describes the compliance procedure for the special category of manufacturing control.

2 ReferencesThe titles of the standards publications referred to in this standard are listed on the inside back cover.

3 DefinitionsFor the purposes of this Part, the definitions given in BS 6073-1 apply.

4 GeneralThe purchaser shall specify masonry units in accordance with clause 5, which gives basic requirements, and clause 6, which gives additional and optional requirements.

5 Basic requirements5.1 General. The purchaser shall specify that the masonry unit is to comply with all the requirements of BS 6073-1 and shall further specify:

a) the size required (see 5.2);b) compressive strength, where this is greater than the minimum compressive strength given in BS 6073-1, i.e. 2.8 N/mm2 for blocksand 7.0 N/mm2 for bricks (see 5.3).

5.2 Sizes. The purchaser shall specify the work size, that is the face dimensions and thickness of the masonry unit. Table 1 gives work sizes of blocks. Table 2 gives work sizes of bricks.NOTE 1 To obtain the co-ordinating size of a masonry unit, add the nominal joint width, which is normally 10 mm, to the length and height of the unit given in Table 1 or Table 2. (The thickness remains unchanged.)NOTE 2 Other work sizes are available and in use. No single manufacturer necessarily produces the complete range of work sizes shown.

Table 1 — Work sizes of blocksThickness mm 60 75 90 100 115 125 140 150 175 190 200 215 220 225 250

Length Height

mm mm

390 190 x x x x x x x x x

440 140 x x x x x x x x x

440 190 x x x x x x x x x

440 215 x x x x x x x x x x x x x x x

440 290 x x x x x x x x x

590 140 x x x x x x x x

590 190 x x x x x x x x

590 215 x x x x x x x x x x x

BS 6073-2:1981

2 © BSI 12-1998

Table 2 — Work sizes of bricks

5.3 Compressive strength. For blocks of thickness 75 mm or greater, and for bricks, the purchaser shall specify the minimum compressive strength that shall apply in place of the minimum permissible average crushing strength G given in clause 10 of BS 6073-1:1981.

For example, where a purchaser specifies that a block shall be of a minimum compressive strength of 7.0 N/mm2, this signifies that a sample of 10 blocks tested in accordance with B.1 ofBS 6073-1:1981 shall have an average crushing strength not less than 7.0 N/mm2 and not less than (0.9 × 7.0) + 0.62S N/mm2 where S is the standard deviation for the sample.The following compressive strengths for concrete masonry units are commonly used for design purposes. The graphs in Figures 1(a) to 1(d) of BS 5628-1:1978 allow interpolation between these compressive strengths.

Other compressive strengths are available and in use. No single manufacturer necessarily produces the complete range given above.NOTE A rapid method of checking compressive strengths of blocks which may be used by manufacturers for routine quality control is given in appendix B.

6 Purchaser’s additional and optional requirements6.1 Type of masonry unit. Where the purchaser requires a certain type of masonry unit, he shall indicate which of the types described in clause 3 of BS 6073-1:1981 is required.

Where the purchaser requires a brick of minimum compressive strength 40 N/mm2 and minimum cement content 350 kg/m3, he shall specify a special purpose brick.

6.2 Materials. Where the purchaser requires a certain type of material, he shall indicate which of the materials described in clauses 4, 5 and 6 of BS 6073-1:1981 is required. If the purchaser wishes to impose a restriction on the use of materials permitted in BS 6073-1, he shall indicate the required restriction.

6.3 Shape and tolerances. Where the purchaser requires special shapes of masonry unit, e.g. quoin or closure units, or units for which special tolerances are necessary, such as exposed aggregate blocks or blocks for fair faced masonry, he shall agree the shape or tolerances and appropriate methods of measurement with the manufacturer.NOTE Typical profiled ends of blocks are shown in Figure 1.

6.4 Additional properties. Where the purchaser wishes to specify masonry units having performance requirements not covered by BS 6073-1, he shall specify the requirements and the appropriate British Standard test method(s).

The purchaser shall also specify any other required properties, such as net area, density, colour and texture.NOTE A method for determining net area and density of blocks is given in appendix C.

Thickness mm 90 103

Length Height

mm mm

290 90 x

215 65 x

190 90 x

190 65 x

Blocks Bricks

N/mm2 N/mm2

2.8 7.0

3.5 10.0

5.0 15.0

7.0 20.0

10.0 30.0

15.0 40.0

20.0

35.0

BS 6073-2:1981

© BSI 12-1998 3

6.5 Quality control and compliance procedure for special category of manufacturing control. Where the purchaser requires masonry units to be subject to the special category of manufacturing control described in 27.2.1 of BS 5628-1:1978, the following requirements shall apply.

a) The manufacturer shall operate a quality control scheme in which sampling is carried out at a rate of not less than 0.02 % of production or two blocks per day or 15 bricks per day, whichever is the greater.b) Such a quality control scheme shall be available for inspection by prospective purchasers and/or their representatives, provided a prior appointment is made.c) Where an independent sample is taken, the pass/fail criteria for compressive strength as determined by the following procedure shall be used in place of those given in clause 10 of BS 6073-1:1981.

1) Calculate the compressive strength , and the standard deviation, S1, for a sample of ten masonry units tested in accordance with appendix B of BS 6073-1:1981.2) If

and

where G is the specified strength, the consignment shall be accepted.

3) If , the consignment shall be

rejected.

4) if or if

, a second sample of ten units shall be tested.

5) Calculate the compressive strength, , and the standard deviation, S2, for the second sample.

6) If , the

consignment shall be rejected.7) If , the consignment shall be accepted.

This procedure is illustrated in Figure 2.

6.6 Identification of masonry units. Where the purchaser requires additional means of identifying the masonry units, he shall agree the method with the manufacturer.

7 Notification to manufacturer and supplierIf the purchaser requires independent tests, he shall give the manufacturer and supplier adequate notice in writing prior to taking samples so that all parties may be represented when the samples are taken, and so that the testing laboratory shall be selected to the mutual satisfaction of manufacturer, supplier and purchaser.

Figure 1 — Typical profiled ends of blocks

x1

x1>G

x1> 0.9G 0.62S1,+( )

x1 0.9G<

0.9G < x1 G <

0.9G x1< 0.9G 0.62S1+<

x2

x2 G< or x2 0.9G 0.62S2+<

x2 > G and x2 > 0.9G 0.62S2+

BS 6073-2:1981

4 © BSI 12-1998

Figure 2 — Compliance procedure for special category of manufacturing control

BS 6073-2:1981

© BSI 12-1998 5

Appendix A Information to be given by the purchaser with his enquiry and order

The following particulars cover the essential details to be given by the purchaser to the manufacturer for an enquiry and order to be fully understood.

a) Quantity1).b) Work size dimensions and thickness in the order of length × height × thickness1) (see 5.2).c) Compressive strength of blocks 75 mm or greater in thickness or of bricks (see 5.3).d) Type of masonry unit (see 6.1).e) Specific requirements for constituent materials (see 6.2).f) Special shapes and/or tolerances (see 6.3).g) Requirements for additional properties (see 6.4).h) Whether special category of manufacturing control is required (see 6.5).i) Whether additional means of identification is required (see 6.6).j) Handling requirements, such as palletization, strapping or mechanical off-loading1).

Appendix B Routine rapid control test of compressive strength of blocks by manufacturer (fibre board test)

B.1 General. The following method may be used by a manufacturer as a rapid method of checking the compressive strength requirements for blocks, for his own routine control purposes. Details of the mortar cap test used to establish compliance with the standard are given in appendix B ofBS 6073-1:1981. A correlation between results obtained using the two test methods may be derived as described in B.6.

B.2 Apparatus. Use the testing machine described in B.1.1.3 of BS 6073-1:1981.

B.3 Preparation of specimens. Rub the bed faces of specimens to be capped with fibre board with a carborundum stone to remove any fins or high spots.

Immerse the specimens in water at a temperature of between 10 °C and 25 °C for at least 16 h before being used for tests. Other conditioning processes, including dry storing, may be adopted, provided that:

a) the conditioning used shall be the same as that used when determining any relationship between results derived from compressive strength tests on fibre board and mortar capped specimens;

b) the conditioning shall be used consistently in any quality control scheme.

B.4 Test procedure. Remove each specimen from its conditioning environment about 30 min before it is to be tested and allow to drain under damp sacking or similar material. Test the specimen whilst it is still in a wet condition.

Wipe the bearing surfaces of all the platens clean and remove any loose grit or other material from the surfaces of the specimen which are to be in contact with the platens.Place the specimen in the machine between two new pieces of 12 mm insulating board complying with the requirements of BS 1142-3. Ensure that the board overhangs the specimen by a minimum of 5 mm along each edge and the centre of mass of the specimen coincides with the axis of the machine.Apply the load without shock and increase it continuously up to a rate of 5 N/mm2 per minute, for blocks of specified compressive strength up to and including 7 N/mm2, or 10 N/mm2 per minute, for blocks of specified compressive strength greater than 7 N/mm2. Ensure that the maximum loading rate is reached as soon as possible but in any case before the load causes a stress on the block exceeding 70 % of the specified compressive strength or reaches 300 kN, whichever is the sooner.Adjust the rate of loading while the fibre is still compressing to give the stated values as soon as the indicator shows that the load is being taken up.Maintain the appropriate rate of loading as far as possible up to failure.

B.5 Calculation of compressive strength. Calculate the crushing strength of each specimen and the average crushing strength of the sample in accordance with B.4 of BS 6073-1:1981.

B.6 Correlation of fibre board test and mortar cap test results. The fibre board test is likely to give values for compressive strength of blocks lower than those obtained from tests on mortar capped blocks. However, the results of fibre board tests may be taken to indicate the compressive strength of the blocks unless an acceptable relationship between mortar cap tests and fibre board tests has been established for the particular type and strength of block being tested.

1) Allowances for breakage or other wastage on site are the responsibility of the purchaser.

BS 6073-2:1981

6 © BSI 12-1998

Such a relationship may be taken as being established when the results from at least 40 mortar capped specimens and 40 fibre board capped specimens from each particular compression testing machine have been compared. The results should be taken for pairs of specimens (one mortar capped and one fibre board capped) from similar positions within the manufacturer’s mould.When a relationship has been established, the results from fibre board capped specimens may be modified in accordance with the following equations.

where

Appendix C Determination of block density, concrete density and net area of hollow blocks

C.1 Determination of density

C.1.1 Measurement of volume of cavities. Select three blocks per consignment of 1 000 or part thereof.

Place the blocks on a thin sheet of foam rubber or other resilient material with the open ends of the cavities uppermost.Close any cavities at the ends of the block by clamping flat sheets of 13 mm insulating board to the ends of the block without distortion. Ignore the effects of tongues or grooves.Fill a one litre glass measuring cylinder accurately with dry sand which has been graded between a 300 µm BS test sieve and a 600 µm BS test sieve, both sieves complying with the requirements of BS 410.Fill the cavities with the sand by pouring from the cylinder, refilling if required, keeping the cylinder lip within 25 mm of the top of the cavity and pouring steadily and striking off level.Return to the cylinder any sand struck off and note, in ml, the total volume of sand used to the nearest 50 ml. Convert this volume to the equivalent volume in mm3 of the cavities to the nearest 250 mm3.

Calculate the gross volume of the block to the nearest 250 mm3 by multiplying the average thickness (see appendix A of BS 6073-1:1981) by the specified length and height of the block. (Ignore formed protrusions and indentations).Express the volume of cavities in each block as a percentage of the gross volume of the block. Record to the nearest 5 % the greatest volume of cavity detected.

C.1.2 Determination of concrete volume. Remove all random flashings with carborundum stone.

Measure to the nearest 1 mm, using calipers and rule as described in appendix A of BS 6073-1:1981, the dimensions of formed indentations and protrusions on the external faces and ends of the block.Calculate the algebraic sum of the volume of all indentations and protrusions to the nearest 250 mm3 (Treat volume of indentation as negative and volume of protrusion as positive.) Calculate the concrete volume, to the nearest 250 mm3, using the following equation.

Vc = V1 – V2 + V3

where

C.1.3 Determination of block density and concrete density. Dry three blocks for at least 16 h in a ventilated oven having the temperature controlled at 105 ± 5 °C.

Cool the blocks to ambient temperature and weigh.Repeat these steps until the mass lost in one cycle does not exceed 0.05 kg.Calculate the block density and the concrete density by using the following equations.

where

x is the quotable value of compressive strength

a is the result obtained from the test of fibre board capped specimens

b is the arithmetic mean of mortar cap test results

c is the arithmetic mean of fibre board cap test results

x a bc---×=

Vc is the concrete volume

V1 is the gross volume of the block

V2 is the volume of cavities and voids

V3 is the algebraic sum of volume of indentations and protrusions

rb is the block density (in kg/m3)

m is the oven dry mass (in kg)

V1 is the gross volume (in m3)

rbmV1-------=

rcmVc------=

BS 6073-2:1981

© BSI 12-1998 7

where

Record the mean densities of the three blocks to the nearest 10 kg/m3.

C.2 Determination of net area of hollow blocks. Obtain the mean height from six height measurements using the method for measuring thickness described in A.1.4 of BS 6073-1:1981.

Calculate the net area using the following equation.

where

NOTE The net area of hollow blocks is required for assessing the characteristic compressive strength of walls of hollow concrete blocks filled with in-situ concrete(see 23.1.7 of BS 5628-1:1978).

rc is the concrete density (in kg/m3)

m is the oven dry mass (in kg)

Vc is the concrete volume (in m3)

A is the net area (in m2)

Vc is the concrete volume (in m3)

h is the mean height (in m)

AVc

h------=

8 blank

BS 6073-2:1981

© BSI 12-1998

Standards publications referred to

BS 410, Specification for test sieves.BS 1142, Fibre building boards.BS 1142-3, Insulating board (softboard).BS 5628, Code of practice for the structural use of masonry.BS 5628-1, Unreinforced masonry.BS 6073, Precast concrete masonry units.BS 6073-1, Specification for precast concrete masonry units.

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