1、BRITISH STANDARD BS 1881-208: 1996 Testing concrete Part 208: Recommendations for the determination of the initial surface absorption of concrete ICS 91.100.30BS1881-208:1996 This British Standard, having been prepared under the directionof the Sector Board for Building and Civil Engineering, was pu
2、blished under the authorityof the Standards Board and comes into effect on 15 September 1996 BSI 12-1998 The following BSI references relate to the work on this standard: Committee reference B/517/1 Draft for comment 95/106828 DC ISBN 0 580 26201 4 Committees responsible for this British Standard Th
3、e preparation of this British Standard was entrusted by Technical Committee B/517, Concrete, to Subcommittee B/517/1, Concrete production and testing, upon which the following bodies were represented: Association of Lightweight Aggregate Manufacturers Association of Metropolitan Authorities British
4、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 Admixtures Association Cementitious Slag Make
5、rs Association Concrete Society County Surveyors Society Department of the Environment (Building Research Establishment) Department of the Environment Department of Transport (Highways Agency) Electricity Association Federation of Civil Engineering Contractors Federation of Piling Specialists Instit
6、ute of Concrete Technology Institution of Civil Engineers Institution of Structural Engineers Institution of Water and Environmental Management National House-Building Council Quality Ash Association Sand and Grovel Association Society of Chemical Industry Amendments issued since publication Amd. No
7、. Date CommentsBS1881-208:1996 BSI 12-1998 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Applications 1 5 Factors influencing the initial surface absorption of concrete 2 6 Apparatus 2 7 Calibration of apparatus 5 8 Procedure 5 9 Fac
8、tors affecting test results 7 10 Precision 7 11 Test report 7 Figure 1 Assembly of typical absorption apparatus 3 Figure 2 Typical cap suitable for clamping onto a smooth horizontal surface 4 Figure 3 Typical cap suitable for use on a vertical surface 4 Table 1 Determination of period of movement 6
9、Table 2 Correction factors to convert readings to an equivalent value at 20 C 7 List of references Inside back coverBS1881-208:1996 ii BSI 12-1998 Foreword This Part of BS1881 has been prepared by Subcommittee B/517/1. It supersedes clause6 of BS1881-5:1970 which has been deleted. All aspects of tes
10、ting concrete are included as Parts of BS1881 from sampling fresh concrete to assessing concrete in structures. BS1881-201:1986 Guide to the use of non-destructive methods of test for hardened concrete gives general guidance on the choice of non-destructive test methods and should be consulted for a
11、dvice on methods which complement the measurement of initial surface absorption or are useful as alternatives. In this Part of BS1881, recommendations for surface absorption differ from those in clause6 of BS1881-5:1970 in the omission of the requirement for a measurement at 2h after commencing the
12、test since this is no longer regarded as providing useful additional information in practice. Recommendations on applications, factors influencing results and interpretation is also provided. The method given in this standard provides a low pressure assessment of the water absorption of the concrete
13、 surface. Other tests currently under development involve higher pressures or surface drilling and the results from such tests will be governed by properties of the concrete not necessarily related to surface absorption. A British Standard does not purport to include all the necessary provisions of
14、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, pages1 to 8, an inside ba
15、ck 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.BS1881-208:1996 BSI 12-1998 1 1 Scope This Part of BS1881 gives recommendations for a method of determining
16、 the initial surface absorption of oven dried concrete, of concrete in the laboratory which cannot be oven dried and of site concrete. Recommendations are given on areas of application of this method and the interpretation of results. 2 References 2.1 Normative references This Part of BS1881 incorpo
17、rates, by dated or undated reference, provisions from other publications. These normative references are made at the appropriate places in the text and the cited publications are listed on the inside back cover. For dated references, only the edition cited applies; any subsequent amendments to or re
18、visions of the cited publication apply to this Part of BS1881 only when incorporated in the reference by amendment or revision. For undated references, the latest edition of the cited publication applies, together with any amendments. 2.2 Informative references This Part of BS 1881 refers to other p
19、ublications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions. 3 Definitions For the purposes of this Part of BS1881 the definitions in BS6100-6.2
20、 apply together with the following: 3.1 location region of concrete that is being assessed and that, for practical purposes, is assumed to be of uniform quality 3.2 initial surface absorption rate of flow of water into concrete per unit area at a stated interval from the start of the test and at a c
21、onstant applied head 3.3 surface zone zone of concrete immediately behind the surface NOTEThe thickness of the zone that influences the result of this test may range between a few millimetres and several centimetres depending on the nature and condition of the concrete. 4 Applications 4.1 General Th
22、is test method provides data for assessing the uniaxial water penetration characteristics of a concrete surface. The applied pressure of 200mm head of water is worse than the severest weather exposure in the UK due to driving rain. The results may be considered to be related to the quality of finish
23、 and to the durability of the surface under the effects of natural weathering. The results are of little relevance to behaviour under higher water pressures, and cannot be used to assess the permeability of a body of concrete. This test method can be applied to exposed aggregate or profiled surfaces
24、 provided that a watertight seal can be obtained with the apparatus. The test is not applicable to specimens or areas showing obvious porosity, honeycombing or cracking. Misleading results can be obtained when tests are performed on thin concrete sections through which water could penetrate during t
25、he test. Tests should not be repeated at positions within an area affected by previous tests. 4.2 Quality control 4.2.1 Precast concrete The test is most reliably applied to precast concrete units which can be tested under standardized dry conditions. Results obtained may be compared with predetermi
26、ned acceptance limits. 4.2.2 Cast stone Details of recommended acceptance requirements for cast stone are given in BS1217 on the basis of results obtained by this method. 4.2.3 In situ concrete It is difficult to achieve standardized drying conditions for in situ concrete although generalized classi
27、fication limits relating to surface weathering characteristics have been proposed which can be applied to in situ test results. The method has been successfully used on this basis to assess compliance with specifications for weathering performance 1) . Combinations of initial surface absorption and
28、cover to reinforcement have been proposed 2) . 4.3 Comparability surveys Since it is sensitive to surface finish as well as to the quality of the concrete in the surface zone, the test provides a means of comparative assessment of these characteristics. With careful interpretation, the test may usef
29、ully be applied to in situ concrete construction. 1) Permeability testing of site concrete A review of methods and experience. Concrete Society Technical Report 31 2) Levitt.M. The ISAT for limit state design for durability. Concrete. Vol 19, No.7, p 29. July 1985.BS1881-208:1996 2 BSI 12-1998 5 Fac
30、tors influencing the initial surface absorption of concrete Guidance concerning their influence upon the interpretation of results in practical circumstances is given in clause9. All the following factors affect the surface absorption of concrete: a) moisture conditions; b) concrete mix; c) aggregat
31、e; d) surface finish and type; e) curing; f) age of concrete; g) cracking (visible cracks should be avoided); h) water type; i) temperature. Although impurities in the water can influence the rate of absorption, this effect may be disregarded provided that the water is of potable quality. However, d
32、istilled or de-ionized water shall be used for calibrating the capillary tube (see7.2). 6 Apparatus 6.1 Test assembly, comprises a watertight cap which is sealed to the concrete surface and connected by means of flexible tubes to a reservoir and a capillary tube with a scale. A control tap is fitted
33、 to the connection between the reservoir and cap. A typical test assembly is illustrated inFigure 1. 6.2 Cap, of any suitable rigid non-corrodible impermeable material providing a minimum area of water contact with the surface to be tested of5000mm 2 . NOTEIt is useful for the cap to be made of a tr
34、ansparent material such as a clear acrylic, polyester or epoxy resin (reinforced if necessary) as this allows the operator to observe the filling of the cap with water and the displacement of the air. An inlet and an outlet tube are fixed into the cap, the former connecting to the reservoir and the
35、latter to the capillary tube. The outlet is so positioned that it is at the highest part of the cap to allow all trapped air to escape. A suitable cap for clamping onto horizontal concrete specimens with a relatively smooth surface as illustrated inFigure 2. This has a soft elastomeric gasket to pro
36、vide a watertight seal. It is possible for the gasket to be glued to the surface of smooth dry laboratory specimens. In cases where either the surface of the concrete is not smooth, or the cap cannot be clamped onto the surface to be tested, the cap should have a knife edge for contact with the conc
37、rete. Recommendations for fixing the cap to the test surface is given in8.2. A suitable cap for testing vertical or sloping surfaces or soffits is illustrated inFigure 3. 6.3 Connections 6.3.1 Inlet. The inlet tube to the cap is connected to the reservoir by a flexible tube of sufficient length to e
38、nable a head of water between 180mm and220mm above the surface of the concrete under test to be maintained, and is fitted with a tap. 6.3.2 Outlet. The outlet tube from the cap is connected to the capillary tube by a flexible tube of sufficient length to enable the capillary tube to be set horizonta
39、lly at a head of water between 180mm and 220mm above the surface of the concrete under test. 6.4 Reservoir, of glass or plastics material of about100mm diameter. 6.5 Capillary tube and scale. A length of precision bore glass capillary tubing at least 200mm long and with a bore of 0.4mm to 1.0mm radi
40、us, determined as described in7.2, is fixed to a scale calibrated by the procedure described in7.3. NOTEThe length of capillary tubing necessary to accommodate the full range of possible initial surface absorption values indicated inTable 1 will depend upon the radius of the capillary bore and the c
41、ap size. The scale is marked in divisions as described in7.3. For a cap of the minimum dimensions given in6.2, a capillary bore of 0.4mm radius and concrete of high initial absorption, the length required would exceed 1m. To limit the length of tube to a convenient value, a combination of cap size a
42、nd capillary bore should be chosen to accommodate the range of initial surface absorptions anticipated. The more permeable the concrete, the larger the bore or the length needs to be. The capillary tube protrudes beyond one end of the scale for connection to the outlet of the cap. 6.6 Stands and cla
43、mps, to support the reservoir and capillary tube and scale, allowing for adjustments within the ranges given in6.3. 6.7 Stop watch or clock, accurate to 0.5 s. 6.8 Measuring cylinder, of 10ml capacity conforming to BS604. 6.9 Thermometers, accurate to the nearest 0.2C, suitable for measuring the tem
44、perature of the water and of the concrete surface. 6.10 Drying oven, ventilated, in which the temperature is controlled at (105 5)C. 6.11 Cooling cabinet, dry airtight vessel of sufficient capacity to contain the specimens to be tested. 6.12 Balance, of appropriate capacity to weigh the specimens to
45、 the accuracy required by8.1.2.BS 1881-208:1996 BSI 12-1998 3 Figure 1 Assembly of typical absorption apparatusBS1881-208:1996 4 BSI 12-1998 Figure 2 Typical cap suitable for clamping onto a smooth horizontal surface Figure 3 Typical cap suitable for use on a vertical surfaceBS1881-208:1996 BSI 12-1
46、998 5 7 Calibration of apparatus 7.1 General The calibration of the capillary tube is arranged so that the movement of water along it during 1min, as read directly from the scale, equals the initial surface absorption inml/(m 2 .s) at a constant head and temperature during the test. 7.2 Radius of bo
47、re of capillary tube Measure the length of the capillary tube(6.5) and record it to the nearest millimetre. Flush the tube through with soap solution, followed by at least25ml of distilled or de-ionized water. Clamp the tube horizontally and connect it to the reservoir(6.4) by means of the flexible
48、tube(6.3.1) fitted with a tap. Fix the reservoir such that a head of water of(200 5) mm is maintained during the course of the calibration. Close the tap and fill the reservoir with distilled or de-ionized water to the specified level. Determine the temperature of the water using the thermometer(6.9
49、) and ensure that this is within1C of ambient. Open the tap and, when a steady discharge occurs, place the measuring cylinder(6.8) under the open end and begin to collect the water. Record in seconds the time required to collect 10ml of water. Repeat this procedure twice more and calculate the mean of the three times. Calculate the bore radius of the capillary tube, r, in millimetres, from the following equation: where 7.3 Capillary scale From the dimensions of the cap, taking account of the seal geometry, calculate the area of contact of the wat
