1、BRITISH STANDARD BS 1881-207: 1992 Testing concrete Part 207: Recommendations for the assessment of concrete strength by near-to-surface testsBS1881-207:1992 This British Standard, having been prepared under the direction of the Technical Sector Board for Building and Civil Engineering, was publishe
2、d under the authority of the Standards Board and comes into effect on 31 January 1992 BSI 12-1998 The following BSI references relate to the work on this standard: Committee reference CAB/4 Draft for comment 89/16059 DC ISBN 0 580 20365 4 Committees responsible for this British Standard The preparat
3、ion of this British Standard was entrusted by the Technical Sector Board for Building and Civil Engineering (B/-) to Technical Committee CAB/4, upon which the following bodies were represented: Association of Lightweight Aggregate Manufacturers Association of Metropolitan Authorities Association of
4、Quality Pulverised Fuel Ash Suppliers British Aggregate Construction Materials Industries British Cement Association British Civil Engineering Test Equipment Manufacturers Association British Precast Concrete Federation British Ready Mixed Concrete Association Building Employers Confederation Cement
5、 Admixtures Association Cementitious Slag Makers Association Concrete Society County Surveyors Society Department of the Environment (Building Research Establishment) Department of the Environment (Property Services Agency) Department of Transport Department of Transport (Transport and Road Research
6、 Laboratory) Electricity Industry in United Kingdom 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 National Ho
7、use-Building Council Sand and Gravel Association Society of Chemical Industry The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British Nuclear Fuels plc United Kingdom Atomic Energy Authority Amendments issued since publication Amd. No. Da
8、te CommentsBS 1881-207:1992 BSI 12-1998 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 General 1 4 Applications 1 5 Choice of test method 2 6 Internal fracture test 2 7 Pull-out test 5 8 Pull-off test 6 9 Penetration resistance test 8 10 Break-off t
9、est 9 11 Methods of establishing correlations between near-to-surface tests and strength 10 12 Assessment of structures 11 13 Report 11 Figure 1 Principal features of near-to-surface tests using commercially available apparatus 3 Table 1 Summary of near-to-surface test methods 2 Publication(s) refer
10、red to Inside back coverBS1881-207:1992 ii BSI 12-1998 Foreword This Part of BS 1881 has been prepared under the direction of the Technical Sector Board for Building and Civil Engineering. All aspects of testing concrete are being included as Parts of BS1881 from sampling fresh concrete to assessing
11、 concrete in structures. Part201 gives general guidance on the choice of non-destructive test methods, including a bibliography, and should be consulted for advice on methods which complement the use of near-to-surface strength tests or are useful as alternatives. In recent years, several tests and
12、devices have been developed which give a measure of the insitu strength of concrete near to the surface. Carrying out near-to-surface tests requires only one face of the concrete to be available and this face need not be as smooth as that required for some alternative tests. Although most of these t
13、ests measure a property of concrete related to its strength, correlation with compressive strength has to be established experimentally. The results obtained may be used to estimate the strength of the body of the concrete. However, placing, compacting and curing may make the concrete in the surface
14、 zone unrepresentative of the concrete at deeper levels. For some methods the same correlation can be used over a wide range of concrete types but this is not universally true. Care should be taken to ensure that the correlations adopted are relevant to the circumstances of use. Guidance on planning
15、 and interpreting tests to assess the strength of concrete in structures is given in BS6089, which refers to the use of near-to-surface methods. The tests described in this Part of BS1881 are those for which there is most experience at present. Other near-to-surface techniques may be proposed, usual
16、ly to meet some particular need, and their use is not precluded by this Part. The recommendations of clauses 3, 4, 5 and 11 to 13 may usefully be applied to such methods. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are respons
17、ible 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 12, aninside back cover and a back cover. This standard has been
18、 updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS 1881-207:1992 BSI 12-1998 1 1 Scope This Part of BS 1881 gives recommendations on tests that are designed to assess the strength of concrete by causing l
19、ocalized failure in a small zone, typically up to 75mm from the surface, according to the method. The recommendations cover the following test methods: a) internal fracture; b) pull-out; c) pull-off; d) penetration resistance; e) break-off. NOTEThe titles of publications referred to in this standard
20、 are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS1881 the definitions given in BS1881-201 and BS6100-6 apply. 3 General It should be recognized that an individual test result indicates the quality of the concrete only in the immediate vicinity of the test point.
21、 The mean result from a number of tests is needed to estimate the average quality of the surface zone. Near-to-surface tests should not be carried out where the surface concrete is known to be unrepresentative of the concrete in the structure, unless the purpose of the investigation is to assess the
22、 condition of this surface zone. In both cases, any correlation obtained as described in clause 11 will not be valid. The surface concrete can be damaged by aggressive agents such as fire, frost, corrosive liquids, etc. Tests should not be made on frozen concrete. The surface layer can also comprise
23、 a topping added subsequent to the compaction of the main body of concrete. All the test methods described in this Part of BS1881 produce a localized zone of surface damage. The need for localized repairs following testing, and the implications for the appearance and durability of exposed concrete s
24、urfaces, especially if the test is carried out adjacent to reinforcing steel, should therefore be considered. It is important that tests should be performed by trained and experienced staff if worthwhile results are to be achieved and it is recommended that two persons should normally be involved du
25、ring testing on site. 4 Applications 4.1 Comparative testing of concrete Near-to-surface test values may be laid down so that tests can indicate when handling and transport of precast units, application of prestress and the removal of formwork or temporary supports for structural members may commenc
26、e. More detailed guidance on the use of near-to-surface tests for assessing formwork striking times may be found in CIRIA Report No.73. These values should take due account of the limitations on accuracy of strength estimations for the particular test method used and the normal variations in propert
27、ies within cast concrete. The critical values for the near-to-surface test results should be established on the basis of laboratory calibration or past experience of performance. In acceptance testing or quality control procedures a small number of cores or destructive tests can be supplemented by a
28、 larger number of near-to-surface tests which are quicker to carry out and less damaging. 4.2 Estimation of in situ concrete strength Near-to-surface tests can be correlated with strength tests on standard concrete specimens or on drilled cores. The estimation of strength in a concrete structure by
29、near-to-surface testing should be made with considerable care and estimated values should be given only to the nearest 1N/mm 2 . In particular it should be remembered that the strength of the concrete near the surface may differ from that of the interior of a large mass and strength variations are l
30、ikely to exist over the depth of a member. It is essential that test locations selected should be representative of the concrete under investigation. General guidance on the assessment of concrete strength in structures is given in BS6089. Guidance on relating near-to-surface test results and streng
31、th is given in clause11 of this Part. Although the most common correlation is with compressive strength, results may also be related to tensile strength. 4.3 Checking the uniformity of concrete Near-to-surface tests can be used to define areas of different quality in a structural member and to locat
32、e areas appropriate for testing by other methods. The tests should be carried out at similar concrete maturity and ambient conditions. This approach can be applied to precast and in situ concrete. 4.4 Testing repairs to concrete Some near-to-surface tests are also an effective means of checking the
33、quality of repairs to concrete structures. When the bond between a substrate and a repair material is to be determined, either a pull-off test or break-off test should be used.BS1881-207:1992 2 BSI 12-1998 4.5 Long-term monitoring Near-to-surface tests should be considered for use in situations wher
34、e future deterioration of the surface concrete is expected and monitoring is required. 5 Choice of test method Selection of the most appropriate method should take account of the purpose of the testing and practical factors relating to the nature and position of the concrete under investigation. The
35、se will include the availability and reliability of strength correlations, the acceptability of surface damage, size of member to be tested, test complexity and preparation, access requirements and test positions. Experience with all the methods described is based primarily on testing concrete conta
36、ining aggregate of nominal size20mm or less. Caution should be exercised in interpreting results on concrete containing larger aggregates. More detailed guidance on planning an investigation is provided in BS1881-201. Some relevant details for each of the methods in this Part are given in Table 1. 6
37、 Internal fracture test 6.1 General The internal fracture test is based on the concept that a measurement of the tensile force required for a wedge anchor bolt to cause failure of the concrete can be related to the concrete compressive strength. Apparatus has been developed in which a bolt is insert
38、ed into a predrilled hole and loaded in tension through a reaction stand by means of a torquemeter acting on a greased nut. More consistent results are obtained using apparatus in which a direct axial load is applied to the bolt. See Figure1(a). A 6 mm diameter bolt set at 20mm depth as described in
39、 6.3 has been found to be suitable for use in concrete of compressive strength up to 40MPa. The recommendations in 6.2 and 6.3 are based on these sizes. If other sizes are used, different apparatus and criteria are required. Table 1 Summary of near-to-surface test methods Test method Number of valid
40、 tests required at a location 95 % confidence limits for strength estimate of in situ concrete Correlation requirements Preparation requirements Internal fracture (clause 6) 6 30 % Specific to loading method and concrete mix Hole drilling with masonry drill Pull-out (clause 7) 4 20 % General for nat
41、ural aggregates Either (a) cast-in insert or (b) drilling and under-reaming with specialist equipment Pull-off (clause 8) 6 ( 15 % in laboratory conditions) Specific to concrete mix Providing a dry flat concrete surface Partial coring if required Penetration resistance (clause 9) 3 20 % Specific to
42、aggregate No power supply or complex access required but safety precautions necessary Break-off (clause 10) 5 20 % Specific to concrete mix Test cylinder formed either (a) during casting or (b) by partial coring with specialist equipmentBS 1881-207:1992 BSI 12-1998 3 Figure 1 Principal features of n
43、ear-to-surface tests using commercially available apparatusBS1881-207:1992 4 BSI 12-1998 6.2 Apparatus 6.2.1 Roto-hammer drill, fitted with a nominal6mm hard-tipped bit. NOTEIt is important for the consistency of test results that the drilled holes have straight parallel sides and are uniform in dia
44、meter. Electropneumatic drills have been found to be suitable for this purpose. 6.2.2 Drill tip diameter gauge, to check that the drill bit has a diameter in the range 6.1mm to 6.4mm. 6.2.3 Air blower, capable of clearing drilled holes of debris. 6.2.4 Wedge anchor bolts, nominally identical, compat
45、ible with the loading system, with an ISO metric screw thread designation M6-6e complying with BS 3643-1. Nuts and washers to fit these bolts are required if the load is to be applied by a torquemeter. 6.2.5 Gauge, or other device, for checking the normality to the concrete surface of each inserted
46、wedge anchor bolt prior to testing, allowing a maximum deviation of 5 from the normal. 6.2.6 Reaction stand, consisting of a steel ring of internal diameter of at least 80mm with three supports to bear on the concrete surface that can be placed symmetrically around a bolt to transmit to the concrete
47、 the reactive load from the tension applied to the anchor bolt. 6.2.7 Loading system, capable of applying a tensile force to the bolt against the reaction onto the concrete surface through the reaction stand (see6.2.6). The loading system should be designed to allow the reaction stand to be placed s
48、ymmetrically about the bolt and should include a means for allowing for any slight deviation of the axis of the bolt from the normal to the concrete surface. The loading system should indicate either tensile force or torque to an accuracy of 3% in the anticipated working range. It should include a m
49、aximum value indicator that retains the reading when fracture and force release occur. The loading system should be calibrated by equipment, the accuracy of which is traceable to national standards, at yearly intervals or following adjustment or repair. 6.3 Test procedure 6.3.1 Test positions Test holes should be drilled (6.2.1) more than150mm apart and no closer than 75mm to an edge. They should be positioned so that all reinforcement is outside the expected conic fracture surface by at least one bar diameter or the maximum aggregate size, whichever is grea
