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1、BRITISH STANDARD BS 812-120: 1989 Incorporating Amendment No. 1 Testing aggregates Part 120: Method for testing and classifying drying shrinkage of aggregates in concrete UDC 625.07 + 691.22:620.168.2 + 620.172.23:697.93.001.33 BS 812-120:1989 This British Standard, having been prepared under the di
2、rection of the Cement, Gypsum, Aggregates and Quarry Products Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 31 July 1989 BSI 12-1998 The following BSI references relate to the work on this standard: Committee reference CAB/2 Draft for comm
3、ent 86/11434 DC ISBN 0 580 17303 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Cement, Gypsum, Aggregates and Quarry Products Standards Policy Committee (CAB/-) to Technical Committee CAB/2, upon which the following bodies were repre
4、sented: Aggregate Concrete Block Association Association of Consulting Engineers Association of Consulting Scientists Association of Lightweight Aggregate Manufacturers Brick Development Association British Aggregate Construction Materials Industries British Cement Association British Ceramic Resear
5、ch Ltd. British Civil Engineering Test Equipment Manufacturers Association British Geological Sciences British Precast Concrete Federation Ltd. British Ready Mixed Concrete Association British Steel Industry Building Employers Confederation Calcium Silicate Brick Association Limited Chartered Instit
6、ute of Building Concrete Society County Surveyors Society Department of the Environment (Property Services Agency) Department of the Environment (Building Research Establishment) Department of Transport (Highways) Department of Transport (Transport and Road Research Laboratory) Electricity Supply In
7、dustry in England and Wales Federation of Civil Engineering Contractors Institute of Concrete Technology Institution of Civil Engineers Institution of Highways and Transportation Institution of Structural Engineers Institution of Water and Environmental Management (IWEM) Mortar Producers Association
8、 Limited Sand and Gravel Association Limited Society of Chemical Industry Amendments issued since publication Amd. No.Date of issueComments 8773August 1995Indicated by a sideline in the margin BS 812-120:1989 BSI 12-1998i Contents Page Committees responsibleInside front cover Forewordii 1Scope1 2Def
9、initions1 3Principle1 4Sampling1 5Apparatus1 6Materials2 7Preparation of aggregate test portions2 8Preparation of test specimens2 9Test procedure2 10Calculation and expression of results3 11Precision3 12Test report4 Appendix A Classification of aggregate shrinkage5 Table 1 Precision estimates3 Table
10、 2 Categories of use5 Table 3 Recommended minimum testing frequency5 Publications referred toInside back cover BS 812-120:1989 ii BSI 12-1998 Foreword This Part of BS 812, prepared under the direction of the Cement, Gypsum, Aggregates and Quarry Products Standards Policy Committee, forms part of a g
11、eneral revision that is being made of the 1975 edition of BS 812. As each of the tests, or collection of related tests, is prepared, it is intended to issue it as a separate Part or Section of BS 812. This Part contains the test procedure for the determination of the drying shrinkage of aggregates.
12、The test was not included in previous editions of BS 812 but has now been included because there is a need to identify “shrinkable aggregates”. The increased shrinkage of concrete made with such aggregates may cause problems in structures whose design is based on the properties of “normal” concrete.
13、 Concrete made with such aggregates may also be less durable than equivalent “normal” concrete. The test has its origins in a method developed at the Building Research Establishment and which is described in BRE Digest 35 (1968 edition). The present test offers considerable advantages as it is a sim
14、pler procedure and the results are available in much less time. The precision of both the original BRE Digest 35 test and the procedure described here have been determined. They are not judged good enough to justify the four classifications suggested in BRE Digest 35 and a simpler classification int
15、o two categories is therefore included in appendix A. It is important to note that the results of the procedure described here differ from those produced by the Digest 35 method and the classifications in Digest 35 should not be applied to the results of the Part 120 procedure. It is intended that D
16、igest 35 will be withdrawn and a new BRE Digest on the drying shrinkage of aggregates issued taking account of the BS 812-120 method and classification and suggesting a method for testing aggregates which fall outside the scope of BS 812-120. It is intended that BS 812 test methods should be called
17、up by other British Standards as the basis for compliance. Nevertheless, it is not intended that all aggregates should be subjected regularly to all the listed tests. Requirements in other British Standard specifications will refer only to the relevant test methods. Some of the tests in other Parts
18、of BS 812 are of limited application, and advice on the use of simple tests is given, for example, when they can be used for a preliminary sorting of aggregates to see whether more expensive testing is justified. Reference should be made to BS 812-101:1984 for general guidance on testing aggregates,
19、 precision of test methods and variance arising from sampling errors. 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 immu
20、nity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii pages 1 to 6, 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
21、amendment table on the inside front cover. BS 812-120:1989 BSI 12-19981 1 Scope This Part of BS 812 describes the method for classifying the drying shrinkage of aggregates for use in concrete. It applies to aggregate combinations where the coarse aggregate nominal maximum size does not exceed 20 mm
22、and uses concrete prisms made with the coarse and/or fine aggregate to be tested. NOTE 1In those cases where the drying shrinkage of a source of coarse aggregate only or a source of fine aggregate only is required, the other component to be used should be, respectively, a fine or coarse aggregate of
23、 known low shrinkage. NOTE 2Aggregates are generally used in a moist condition. However, this procedure uses constant mass proportions and aggregates prepared in an oven dry condition to minimize practical difficulties in carrying out the test. This may have an influence on the shrinkage value obtai
24、ned and makes the method inappropriate for determining the shrinkage of particular concrete mixes. The use of constant mass proportions imposes some restriction on the applicability of the procedure. Experience is limited to aggregates having oven dry particle densities not less than 2 450 kg/m3 and
25、 to aggregate combinations in which the weighted combined water absorption is not greater than 3.5 % by mass when tested according to BS 812-107. Caution is necessary when interpreting results for aggregates with properties outside these values or where difficulty is experienced in compacting the sp
26、ecimens but advice on testing such aggregates will be given in a new BRE Digest on the shrinkage of natural aggregates in concrete (see foreword). NOTE 3The titles of the publications referred to in this standard are listed on inside back cover. 2 Definitions For the purposes of this Part of BS 812
27、the definitions given in BS 812-101 and BS 812-102 apply. 3 Principle Some aggregates change volume considerably from the wet to the dry state and this may affect the concrete in which they are incorporated. The drying shrinkage of a concrete containing such aggregate can be as much as four times gr
28、eater than that of concrete made with non-shrinkable aggregate. To determine the drying shrinkage of the aggregate under test it is mixed with cement and water and cast into prisms of specified dimensions. The prisms are subjected to wetting followed by drying at 105 C and the change in length from
29、the wet to dry state determined. The drying shrinkage of the aggregate is then calculated as the average change in length of the prisms as a percentage of their final dry lengths. 4 Sampling The samples used for the test (the laboratory samples) shall be taken in accordance with clause 5 of BS 812-1
30、02:1984. 5 Apparatus 5.1 A sample divider of size appropriate to the maximum particle size to be handled or, alternatively, a flat shovel and a clean, flat hard horizontal surface, e.g. a metal tray for use in quartering. NOTEA suitable divider is the riffle box illustrated in BS 812-102. 5.2 Test s
31、ieves of the sizes and apertures appropriate to the nominal size of aggregate to be tested. The test sieves shall comply with BS 410. 5.3 A balance of minimum capacity 5 kg having scale divisions of 1 g and having an error not greater than 2 g. 5.4 A gang mould suitable for casting three concrete pr
32、isms of dimensions 200 2 mm 50 2 mm 50 2 mm with a hemispherical button 8 mm diameter securely fixed to the centre of the inside faces of the 50 mm 50 mm ends of mould. NOTEIt is permissible for reference pieces (inserts) to be used as an alternative to cementing steel balls (see 6.3) in the prisms.
33、 Typical details of inserts are given in Figure 5, method 5 of BS 1881-5:1970. If inserts are used the seatings of the measuring apparatus are required to be hemispherical, 6 mm in diameter, and the ends of the invar rod (see 5.6) to be the same shape as that of the inserts. 5.5 A vibrating table co
34、mplying with BS 1881-108:1983. 5.6 Measuring apparatus which shall incorporate a dial gauge with scale divisions of 0.002 mm having a maximum error of 0.002 mm in any half revolution. This gauge shall be rigidly mounted in a measuring frame and shall have a recessed end which can be located upon 6 m
35、m diameter stainless steel balls cemented in the prisms (see 8.3). The other end of the frame shall have a similar recessed seating which can be located upon balls in the opposite end of the prisms. An invar steel rod, 205 1 mm long, with 6 mm hemispherical ends shall be used as a standard of length
36、 against which the readings of the gauge can be tested, thus enabling corrections to be made for any changes in the dimensions of the apparatus between successive measurements of the prisms. The invar steel rod shall be marked so that the same end can be kept uppermost during measurements. NOTEIt is
37、 permissible for alternative measuring devices to be used in place of the dial gauge, e.g. linear variable differential transducers, provided they are of at least equal performance and fitted with seatings compatible with the stainless steel balls or inserts. BS 812-120:1989 2 BSI 12-1998 5.7 A well
38、-ventilated oven, thermostatically controlled and capable of maintaining temperatures of 50 2 C and 105 2 C. A thermometer complying with the requirements of BS 593 shall be used to verify the temperature. NOTEIt is permissible to use different ovens for each temperature range. 5.8 A desiccator larg
39、e enough to contain three concrete prisms 200 mm 50 mm 50 mm containing anhydrous silica gel as the desiccant. 5.9 Trays, that can be heated in the ventilated oven without damage or change in mass. 6 Materials 6.1 Ordinary Portland cement complying with the requirements of BS 12. 6.2 Water of drinka
40、ble quality. 6.3 6 mm diameter stainless steel balls, or inserts (see note to 5.4). 7 Preparation of aggregate test portions 7.1 Reduce the laboratory samples of coarse and fine aggregate by the procedure described in clause 6 of BS 812-102:1984 to produce sub-samples that can be sieved after oven d
41、rying to give approximately 1 600 g of 20 mm to 10 mm size fraction, 800 g of 10 mm to 5 mm size fraction and 1 300 g of fine aggregate. 7.2 Spread the sub-samples on shallow trays and dry for at least 16 hours in the oven (see 5.7) set at a temperature of 50 C. 7.3 Reject all oversize and undersize
42、 from the coarse aggregate to give fractions all passing the 20 mm sieve and retained on the 10 mm sieve, and all passing the 10 mm sieve and retained on the 5 mm sieve. Reject from the fine aggregate all aggregate retained on the 5 mm sieve. 8 Preparation of test specimens 8.1 Proportioning Cast th
43、ree test prisms, using the amount of cement, aggregates and water required to make the three prisms as follows: 8.2 Mixing 8.2.1 Mix the concrete for the three prisms on a non-porous surface which has been wiped over with a damp cloth. Mix the cement and fine aggregate dry for 1 min with two trowels
44、. Add the coarse aggregate and mix dry until the mixture is uniform. Add the water and mix the whole for 3 min with two trowels. 8.2.2 Transfer the concrete to the gang mould and use as a vibrating table to compact the concrete in the mould in two approximately equal layers, for sufficient time to a
45、chieve full compaction. 8.2.3 On completion of the compaction of the concrete, smooth the surfaces of the prisms with a trowel. 8.3 Storage of specimens 8.3.1 Immediately after completion of compaction, cover the prisms with a flat impervious sheet (e.g. thin rubber, polyethylene or steel) making co
46、ntact with the upper edges of the moulds. Leave the prisms in this condition for 24 2 h at an ambient temperature of 20 5 C. 8.3.2 After 24 2 h, number the prisms for identification and designate one end of each as the top, this end always being uppermost during subsequent measurements. 8.3.3 Demoul
47、d the prisms. Where inserts are not used, cement stainless steel balls 6 mm in diameter into the indentations at the ends of the prisms. NOTEA cement/water grout has been found satisfactory for cementing balls in place. More than half of each ball should be embedded in the grout to aid retention. 8.
48、3.4 Then place damp hessian over the prisms and cover with a polyethylene sheet for a further 24 2 h at an ambient temperature of 20 5 C after which, wipe the surface of the balls clean, or where inserts have been used, wipe the ends of the inserts clean. 9 Test procedure 9.1 Carry out all measureme
49、nts at a temperature of 20 1 C. Measure each prism using the apparatus specified in 5.6 by placing the prism uppermost (previously marked) in the frame and obtaining a minimum reading to the nearest division while slowly rotating the prism. Before and after each measurement, check the length of the measuring apparatus against the invar rod and if the difference in these readings is greater than 0.002 mm remeasure the prisms. Record the measured difference in length between the prism and the invar rod to the nearest 0.002 mm.