BS 812-109-1990 Testing aggregates - Methods for determination of moisture content《集料试验 第109部分 含水量的测定方法》.pdf

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1、BRITISH STANDARD BS 812-109: 1990 Testing aggregates Part 109: Methods for determination of moisture contentBS812-109:1990 This British Standard, having been prepared under the direction of the Cement, Gypsum, Aggregates and Quarry Products Standards Policy Committee, was published under the authori

2、ty of the Board of BSI and comes into effect on 29 June1990 BSI12-1998 The following BSI references relate to the work on this standard: Committee reference CAB/2 Draft for comment84/14033 DC ISBN0580188515 Committees responsible for this British Standard The preparation of this British Standard was

3、 entrusted by the Cement, Gypsum, Aggregates and Quarry Products Standards Policy Committee (CAB/-) to Technical Committee CAB/2, upon which the following bodies were represented: Aggregate Concrete Block Association Association of Consulting Engineers Association of Consulting Scientists Associatio

4、n of Lightweight Aggregate Manufacturers Brick Development Association British Aggregrate Construction Materials Industries British Cement Association British Ceramic Research Ltd. British Civil Engineering Test Equipment Manufacturers Association British Geological Sciences British Precast Concrete

5、 Federation Ltd. British Ready Mixed Concrete Association British Steel Industry Building Employers Confederation Calcium Silicate Brick Association Limited Chartered Institute of Building Concrete Society County Surveyors Society Department of the Environment (Building Research Establishment) Depar

6、tment of the Environment (Property Services Agency) Department of Transport Department of Transport (Transport and Road Research Laboratory) Electricity Supply Industry in England and Wales Federation of Civil Engineering Contractors Institute of Concrete Technology Institution of Civil Engineers In

7、stitution of Highways and Transportation Institution of Structural Engineers Institution of Water and Environmental Management Mortar Producers Association Limited Sand and Gravel Association Limited Society of Chemical Industry Amendments issued since publication Amd. No. Date CommentsBS812-109:199

8、0 BSI 12-1998 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Principles 1 4 Sampling 1 5 Preparation of test portions 1 6 Definitive, oven-drying method 1 7 Modified drying methods 2 8 Precision 3 9 Test report 3 Appendix A Recommendations for deter

9、mination of moisture content using the calcium carbide method 4 Appendix B Details of the evaluation of the precision data 5 Table 1 Minimum mass of test portion for moisture content determination 1 Table 2 Materials used in the evaluation of precision data 5 Table 3 Precision values for the determi

10、nation of moisture content 5 Publications referred to Inside back coverBS812-109:1990 ii BSI 12-1998 Foreword This Part of BS812 has been prepared under the direction of the Cement, Gypsum, Aggregates and Quarry Products Standards Policy Committee, and is a revision of clause 7 of BS812-2:1975, whic

11、h is withdrawn by amendment. It forms part of a general revision of the1975 edition of BS812. As each of the tests, or collection of related tests, is revised it is intended to issue it as a separate Part or Section of this standard. In the case of the definitive, oven-drying method for the determin

12、ation of the moisture content, only editorial changes have been made to the procedure described in the previous edition of clause 7 of BS812-2:1975. However, in the case of the subsidiary methods, although the modified drying method has been retained under the title of the high temperature method, t

13、he siphon-can and buoyancy methods have been omitted as they are rarely used. In their place methods based respectively on the use of a microwave oven and on the reaction of water in the aggregate with calcium carbide have been introduced. These tests are of more limited application than the oven-dr

14、ying method but are easier to carry out and provide rapid results. In the case of the calcium carbide method, the test procedure has been added as an appendix because of limited availability of information on the apparatus. It is intended that other British Standards should call up BS812 test method

15、s as the basis of compliance. Nevertheless, it is not intended that all aggregates should be subjected to all the listed tests. Specifications in other standards should call up only the relevant test methods. Reference should be made to BS812-101 for general guidance on testing aggregates, precision

16、 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 immunity from

17、legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to6, 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 t

18、able on theinside front cover.BS812-109:1990 BSI 12-1998 1 1 Scope This Part of BS812 describes the following three methods for the determination of the moisture content of aggregates: a) oven-drying method (definitive method); b) high temperature method; c) microwave-oven method for fine aggregate

19、only. It also describes the calcium carbide method in appendix A. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS812, the definitions given in BS812-100,BS812-101 andBS812-102 apply. 3 Principles 3

20、.1 The oven-drying method provides a measure of the total water present in a sample of aggregate and is the definitive procedure. The method comprises placing a test portion in a container and drying it at a temperature of105 5C until it reaches constant mass. Moisture content is determined by diffe

21、rence in mass and expressed as a percentage of the dry mass. 3.2 Three other methods are also included. NOTE1Two of these are based on the use of rapid drying methods and are basically variants of the oven-drying method but certain problems, which are described, may arise with their use which can le

22、ad to erroneous results being obtained. They cannot be regarded as definitive methods, but in favourable circumstances can give adequate results for quality control purposes in a fraction of the time taken by the oven-drying method (seenote2). NOTE2The results of the precision trials described in ap

23、pendix B showed that the precision of the subsidiary methods for moisture content is not much worse than that of the definitive, oven-drying method. For fine aggregates the subsidiary methods gave similar results to those given by the definitive method, i.e.they did not appear to be biassed. For the

24、 slag, the high temperature method showed a tendency to give lower results than the oven-drying method. It is thus important for the subsidiary methods to be calibrated against oven-drying for the full range of materials encountered in practice. 3.3 The third subsidiary method included as appendix A

25、 relies on the reaction of water in the aggregate with calcium carbide to evolve acetylene, the amount of which can be assessed by the pressure it generates. 4 Sampling The sample used for the test (the laboratory sample) shall be taken in accordance with the procedures described in clause 5 of BS81

26、2-102:1989. 5 Preparation of test portions Reduce the laboratory sample by the procedures described in clause 6 of BS812-102:1989 to produce a test portion of mass not less than the mass given inTable1 appropriate to the nominal size of the aggregate. Table1 Minimum mass of test portion for moisture

27、 content determination 6 Definitive, oven-drying method 6.1 Apparatus NOTEAll apparatus described should comply with the general requirements of BS812-100. 6.1.1 Balance(s), of suitable capacity, readable to0.1% of the mass of the test portion. NOTEIn general two balances, one of approximately5kg ca

28、pacity readable to1g and the other of approximately500g capacity readable to0.1g will suffice. If aggregate of larger than40mm nominal size is to be tested a balance of25kg capacity readable to10g will also be required. 6.1.2 Container(s), airtight, non-corrodible, of capacity suitable to the mass o

29、f the test portion. NOTEIf it is more convenient an open top container may be used to cool the test portion using an air-tight cabinet. 6.1.3 Ventilated oven, thermostatically controlled to maintain a temperature of105 5 C. 6.1.4 Scoop NOTEA convenient size is about200mm long and120mm wide; seeFigur

30、e1 of BS812-102:1989. Nominal size of aggregate Minimum mass of test portion mm kg 63 15 50 10 40 to20 5 20 to10 2 10 to5 1 less than5 0.5 NOTESome loss of water by evaporation is inevitable during sampling and sample reduction. Precautions should be taken to minimize evaporation losses by carrying

31、out all operations as expeditiously as possible and by storing the samples in airtight containers at all intermediate stages.BS812-109:1990 2 BSI 12-1998 6.1.5 Means of reducing the laboratory sample, either a sample divider of size appropriate to the maximum particle size to be handled, or, alterna

32、tively 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 shown inFigure2 of BS812-102:1989. 6.1.6 Thermometer, covering the range100C to 110C. 6.2 Procedure 6.2.1 Clean a container, with its lid if fitted, dry

33、it and then weigh it (M 1 ). Place the test portion prepared as described in clause5 in the container by means of the scoop, replace the lid and re-weigh the whole (M 2 ). 6.2.2 Remove the lid, place the container, lid, and test portion in the oven and dry at a temperature of105 5 C maintaining this

34、 temperature until the test portion has reached a constant mass. NOTENormally16h to24h is a sufficient period. 6.2.3 Remove the container and test portion from the oven then either replace the lid or place it in an air-tight cabinet and allow the whole to cool for0.5h to1h, after which weigh again (

35、M 3 ). 6.2.4 Carry out and record all weighings to an accuracy of0.1% of the mass of the test portion. 6.3 Calculation and expression of results Calculate the moisture content as a percentage of the dry mass from the following equation. where M 1is the mass of dry container and its lid in g; M 2is t

36、he mass of the container, lid, and wet test portion in g; M 3is the mass of the container, lid, and dry test portion in g. Express the value of moisture content to the nearest0.1% of the dry mass of the test portion. NOTEThe percentage by wet mass may also be calculated from this method if specifica

37、lly required. In this case the moisture constant (percentage by wet mass) is calculated from the following equation: 7 Modified drying methods 7.1 General When rapid results are required for quality control or other purposes any method of drying which drives off water without affecting the aggregate

38、 may be used. However it is essential that temperature in excess of500C be avoided. Flint and slag aggregates tend to spall and calcium carbonate aggregates decompose at high temperatures. NOTEWhen modified methods are used for quality control purposes, the tester should be experienced in the interp

39、retation of the test results. The test results may differ from those obtained by the definitive method. 7.2 High temperature method 7.2.1 Apparatus NOTEAll apparatus specified should comply with the general requirements of BS812-100. 7.2.1.1 Balance, of adequate capacity and accuracy and of such a t

40、ype as to permit weighing of the test portion and/or the tray. 7.2.1.2 Means of heating the test portion, e.g. a radiant heater or hotplate. 7.2.1.3 Shallow tray, suitable for the mass of aggregate being heated. 7.2.1.4 Spatula, or other implement for stirring the test portion during drying. 7.2.2 P

41、rocedure 7.2.2.1 Select the mass of the test portion of aggregate to be tested having regard to the purpose for which the result is required and the consequent need for the test portion to be representative of a bulk quantity. Prepare the test portion in accordance with clause5. NOTENormally a mass

42、of approximately1kg is suitable for coarse aggregates and0.5kg for fine aggregates. 7.2.2.2 Weigh the test portion (M 1 ), place it in the tray and heat it, taking care to ensure that the aggregate does not reach a temperature where spitting or decomposition could occur. NOTEA convenient method of d

43、etecting overheating of the aggregate is by the use of small pieces of white paper mixed with the aggregate. Overheating is indicated if the paper turns brown. 7.2.2.3 During heating stir the test portion frequently with the spatula to ensure even exposure of the aggregate to the air and the source

44、of heat. Keep the spatula in the tray until the test portion is dry to avoid loss of solid material. 7.2.2.4 When the test portion is considered to be dry, cool and weigh it and record the mass. Return it to the tray, heat it again for a further 5min and reweigh it. The test portion shall be regarde

45、d as dry when the difference between consecutive weighings does not exceed0.1% of the last recorded mass. Continue the cycles of heating and weighing until this condition is achieved and record the final mass as M 2 .moisture content M 2 M 3 () M 3 M 1 () - 100 % =moisture content M 2 M 3 () M 2 M 1

46、 () - 100 % =BS812-109:1990 BSI 12-1998 3 7.2.3 Calculation and expression of results Calculate the moisture content as a percentage of the dry mass from the following equation. Express the value of moisture content to the nearest0.1% of the dry mass of the aggregate. NOTEThe percentage by wet mass

47、may also be calculated from this method if specifically requested. 7.3 Microwave oven method; normally limited to fine aggregates NOTEThis method is not applicable to some materials (seenote2 to7.3.2.2). 7.3.1 Apparatus The apparatus shall be as described in6.1 except that the oven and airtight non-

48、corrodible containers shall be replaced by a well ventilated microwave oven and non-metal containers of sufficient capacity to hold the mass of the test portion. NOTE1Currently available microwave, ovens are unlikely to have a sufficient capacity to hold the mass of test portions given inTable1 for

49、coarse aggregates. NOTE2Metal containers cannot be used as they reflect microwaves. Materials such as porcelain and borosilicate glass which heat-up under the influence of microwaves and not just by conduction from the aggregate are preferable; this reduces the possibility of water vapour condensing on the cooler walls of the container before being carried away by air circulation. 7.3.2 Procedure 7.3.2.1 Carry out preliminary trials to ascertain the time required to dry the test portions and to