1、BRITISH STANDARD BS7542:1992 Method of test for Curing compounds for concreteBS7542:1992 This British Standard, having beenprepared under the directionof the Technical SectorBoard for Building and Civil Engineering was publishedunder the authority ofthe Standards Board and comesinto effect on 31Janu
2、ary1992 BSI 07-1999 The following BSI references relate to the work on this standard: Committee references CAB/3 Draft for comment DDI/17 ISBN 0 580 20360 3 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Technical Sector Board for Build
3、ing and Civil Engineering (B/-) to Technical Committee CAB/3, upon which the following bodies were represented: Brick Development Association British Aggregate Construction Materials Industries British Cement Association British Ceramic Research Ltd. British Precast Concrete Federation British Ready
4、 Mixed Concrete Association Building Employers Confederation Cement Admixtures Association Concrete Society County Surveyors Society Department of the Environment (Building Research Establishment) Department of the Environment (Property Services Agency) Department of Transport Electricity Industry i
5、n United Kingdom Federation of Civil Engineering Contractors Institute of Concrete Technology Institution of Civil Engineers Institution of Structural Engineers Mortar Producers Association Plasterers Craft Guild Society of Chemical Industry The following bodies were also represented in the drafting
6、 of the standard, through subcommittees and panels: Association of Consulting Engineers Association of Consulting Scientists Department of Transport (Transport and Road Research Laboratory) Institution of Highways and Transportation Amendments issued since publication Amd. No. Date CommentsBS7542:19
7、92 BSI 07-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Principle 1 4 Materials 1 5 Apparatus 1 6 Preparation of mortar 2 7 Procedure 4 8 Calculation of results 5 9 Report 6 Figure 1 Mortar mould for specimens 2 Figure 2 Metal screed 3 Figure
8、3 Metal tray 4 Table 1 Grading of sand 1 Publication(s) referred to Inside back coverBS7542:1992 ii BSI 07-1999 Foreword This British Standard has been prepared under the direction of the Technical Sector Board for Building and Civil Engineering and supersedes DD147:1987 which is withdrawn. Concrete
9、 has to be prevented from drying out after placing so that the cement can hydrate and form a dense structure that will be strong and impermeable. Moisture loss from concrete cast into moulds or formwork can be controlled by delaying demoulding or stripping, but this practice cannot be applied to lar
10、ge horizontal surfaces such as those of roads. These surfaces have to be covered as soon as possible and one method is to apply a curing membrane. Curing compounds are materials sprayed in solution onto the surface of freshly placed concrete from which the solvent evaporates to leave a membrane whic
11、h prevents loss of water. This membrane has to form on a wet and rough surface and yet be continuous and impermeable. A test to assess the effectiveness of curing compounds by simulating their performance in use was introduced a few years ago. The reproducibility of test results was found to be poor
12、 resulting in contractual problems for both the supplier and the user. The original test has now been refined following considerable development work by the Cement Admixtures Association, which included investigating other test methods. The method applies specifically to curing compounds dissolved i
13、n organic solvents. It enables comparative tests to be made under standardized conditions to obtain good repeatability and reproducibility. The curing compound is therefore applied to a particular mortar having a finely brushed and level surface. The performance of curing compounds applied to a conc
14、rete may, in practice, be expected to be significantly affected by the concretes constituents, composition, properties in the fresh state, texture and slope. The time of application of the curing compound and the prevailing ambient conditions will also be significant. In addition to laboratory tests
15、, trials under site conditions are therefore essential to determine the application rate and subsequent performance of curing compounds for each intended use. For water-based emulsions, a modification of this method has been suggested, involving a short period of pre-drying before application of the
16、 curing compound. Insufficient test data currently exist for its inclusion in this standard. 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 no
17、t of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, 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
18、be indicated in the amendment table on the inside front cover.BS7542:1992 BSI 07-1999 1 1 Scope This British Standard describes a method for the laboratory determination of the water retention efficiency of organic solvent based, membrane-forming curing compounds for concrete. NOTEThe titles of the
19、publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard the following definitions apply. 2.1 curing maintenance of a sufficient moisture content in freshly placed concrete to ensure hydration of the binder and hence devel
20、opment of strength 2.2 curing compound liquid applied as a coating which dries to form a curing membrane 2.3 curing membrane film formed on the surface of freshly placed concrete to assist curing 3 Principle The curing compound to be tested is applied as a uniform coating, usually by spraying, to th
21、e levelled surface of freshly mixed mortar in a metal mould. The coated specimen and an uncoated control specimen are then transferred to a warm curing cabinet in which dry air is circulated. The specimens are kept in the cabinet for3days and then weighed. The efficiency of the curing compound in fo
22、rming a membrane which reduces moisture loss is calculated from the measured loss in mass of the specimens, after correction for the loss of solvent from the coated specimen. 4 Materials 4.1 Portland cement, complying with BS12 that has been specially selected for the purpose of testing admixtures.
23、It shall be identified as “CAA Reference Cement” and shall be stored in an airtight container. NOTEBCA Specification Cement, meeting the requirements of the Cement Admixtures Association Reference Cement (CAAReference Cement), and its specification can be obtained from Wexham Developments Limited, W
24、exham Springs, Slough SL36PL. 4.2 Natural silica sand, oven dry with a rounded particle shape complying with BS882, except that the grading shall be as given in Table 1 1) . Table 1 Grading of sand 4.3 Mould release agent, comprising petroleum jelly, mineral oil or a similar commercial mould release
25、 agent. 5 Apparatus 5.1 Moulds, that are of corrosion resistant metal, do not distort, are watertight and of the following size (see Figure 1). a) Top, internal: b) Depth:(50 2)mm. c) Top flange: width at least12mm. 5.2 Balance, capable of weighing the filled moulds (each weighing about6.5kg) and re
26、adable to the nearest0.1g. 5.3 Cabinet, complying with BS2648, for storing specimens at a temperature of(38 1) C and at a relative humidity of(35 5)%. It shall have three perforated or mesh shelves each capable of supporting two specimens during testing so as to ensure a clear space of at least40mm
27、on all sides of the individual specimen and between specimens and the side walls of the cabinet 2) . The cabinet shall be equipped to circulate air over the specimens at an approximate rate of0.5m/s. NOTEA relative humidity of(35 5)% can be produced by placing a large open vessel containing a satura
28、ted aqueous solution of magnesium chloride in the bottom of the cabinet during the test. 5.4 Spray equipment, designed to permit the curing compound to be aspirated and applied evenly to the surface of the test specimen 2) . 1) For information on the availability of suitable sands, write to Customer
29、 Information, BSI, Linford Wood, Milton Keynes MK146LE. Sieve size Proportion retained 1.18 mm 6004m 3004m 1504m % None 0 to10 60 to88 94 to100 2) For information on the suppliers of suitable cabinets and spray equipment, write to Customer Information, BSI, Linford Wood, Milton Keynes MK146LE.150+50
30、 mm 300+50 mm.BS7542:1992 2 BSI 07-1999 5.5 Mixer, as described in 8.3 of BS4551:1980, electrically driven and of nominal capacity12kg. 5.6 Compacting equipment, either a vibrating table or a vibrating hammer with a foot40mm square, or a compacting bar made from a non-absorbent material, approximate
31、ly200mm long and with a foot40mm square. 5.7 Metal screed,(148 1)mm long, of L-shaped cross section approximately50mm 25mm, the shorter side having a sharpened leading edge. The screed shall be supported across the top of the mould by a200mm long rigid member that can slide on the flanges while hold
32、ing the screed horizontal. The height of the screed shall be adjustable to give a uniformly flat surface finish to the mortar(7 1)mm from the top of the mould (seeFigure 2). 5.8 Metal tray, with sides at least3mmhigh and having an area approximately equal to that of the surface of the test specimen
33、(see Figure 3). 5.9 Hydrometer, complying withBS718. 5.10 Pain brush, 50 mm wide, medium soft. 6 Preparation of mortar 6.1 Number of specimens Prepare at least three pairs, each comprising a test specimen and a control specimen, for each curing compound to be tested. 6.2 Batching and mixing The mort
34、ar shall contain one part by mass of cement(4.1), three parts by mass of sand (4.2) and0.44parts by mass of water. The mortar batch size shall be just sufficient to prepare two specimens, i.e.one test specimen and its corresponding control specimen. Bring all the materials to a temperature of(20 5)
35、C before starting the mixing and carry out the mixing in a room at this temperature. Place the sand and cement in the mixing bowl and mix dry for1min. Add the water and continue mixing for a further2min. Stop the mixer and scrape any unmixed material from the bottom and sides of the bowl. Restart th
36、e mixer and mix for a further2min. 6.3 Moulding specimens Prepare each pair of specimens within20min after the completion of mixing. Dimensions are in millimetres. For tolerances see 5.1. Figure 1 Mortar mould for specimensBS 7542:1992 BSI 07-1999 3 Dimensions are in millimetres. For tolerances see
37、5.7. Figure 2 Metal screedBS7542:1992 4 BSI 07-1999 Thoroughly clean two moulds (5.1), lightly coat them with mould release agent (4.3), weigh them to the nearest0.1g and record the masses as m 1andm 2 . Then place a layer of mortar approximately25mm deep in each of the moulds. Compact this layer an
38、d a second layer as described in a) or b). a) Tamp the mortar50times with the compacting bar (5.6). Place a second layer of mortar, sufficient to overfill the moulds slightly and compact it in a similar manner. Fill indentations formed by tamping and approximately level the surface using a vigorous
39、compactive effort (slapping action) with the palms of the hands. NOTERubber gloves should be worn to prevent contact of the hands with the wet mortar, which is alkaline and can cause skin irritation. b) Compact the layer using the vibrating table or the vibrating hammer (5.6), place a second layer t
40、o overfill the moulds slightly and compact it by the same means. Level the mortar(7 1)mm from the top of the mould by a shaving action using the metal screed(5.7). Make the minimum number of passes of the screed, working along the length of the mould in both directions, to produce a uniform surface,
41、 free from undulations and surface defects. NOTEThe screed should not be pulled backwards across the mortar surface in such a way as to produce a floated finish. Finally, brush the surface lightly with the paint brush (5.10) to remove small defects and produce a uniform matt finish. Weigh each fille
42、d mould and record the masses, m 3and m 4 , to the nearest0.1g immediately prior to the application of the curing compound (see 7.1.3). 7 Procedure 7.1 Application of the curing compound 7.1.1 Sampling and preparation Take a representative sample of the curing compound by the appropriate method desc
43、ribed in Appendix A of BS5075-1:1982. Stir it thoroughly and determine its relative density at room temperature by means of the hydrometer (5.9). Calculate from the relative density the mass required to give the coverage rate in 7.1.2. The mass of the material applied shall be within 0.5g of that re
44、quired to give the specified coverage rate. 7.1.2 Coverage rate Apply the curing compound at the coverage rate recommended by the manufacturer. Where no rate has been recommended, apply at a rate of(0.20 0.01)L/m 2 . Figure 3 Metal trayBS7542:1992 BSI 07-1999 5 7.1.3 Method of application Immediatel
45、y after weighing, apply the curing compound to the test specimen with the spray equipment (5.4), or in the manner recommended by the manufacturer. If spraying is not used, record the method used. Agitate pigmented materials well during application to ensure that a representative sample is applied to
46、 the test specimen. Hold the spray gun so that its nozzle is pointing downwards as near to the vertical as possible and at the height required to produce a fine mist spray that will give uniform application and minimum over-spray. Coat the test specimen uniformly by applying several layers over the
47、whole surface until the coverage rate given in 7.1.2 is reached. Check the coverage rate by repeated weighing and complete the whole application procedure in not more than2min. NOTEAdequate ventilation should be maintained during spraying, to limit exposure to the solvent vapour. 7.1.4 Storing in th
48、e cabinet After applying the curing compound, wipe the flange of the mould, weigh the test specimen, m 5 , and then immediately place it and its control specimen on the lowest shelf of the cabinet (5.3). When the second pair of specimens has been prepared and weighed, move the first pair up one shel
49、f and place the second pair on the lowest shelf. Repeat the same procedure for the third pair of specimens. The total time for making the specimens, coating the test specimen and placing the pair in the cabinet shall not exceed2h. NOTEPrecautions should be taken to avoid any concentration of flammable solvent vapour, as it evaporates from the coated specimens, in and around the cabinet. 7.2 Determination of loss in mass Keep the specimens in the cabinet for72h 15min after applying the curing compound. Weigh the specimens to the nearest0.1g and
