BS EN 14629-2007 混凝土结构保护和修理用产品和系统.实验方法.硬化混凝土中氯化物含量测定.pdf

BRITISH STANDARD BS EN 14629:2007 Products and systems for the protection and repair of concrete structures Test methods Determination of chloride content in hardened concrete The European Standard EN 14629:2007 has the status of a British Standard ICS 91.100.30 BS EN 14629:2007 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 April 2007 © BSI 2007 ISBN 978 0 580 50528 7 National foreword This British Standard was published by BSI. It is the UK implementation of EN 14629:2007. The UK participation in its preparation was entrusted by Technical Committee B/517, Concrete, to Subcommittee B/517/8, Protection and repair of concrete structures. A list of organizations represented on B/517/8 can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Amendments issued since publication Amd. 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This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by September 2007, and conflicting national standards shall be withdrawn at the latest by September 2007. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. It has been prepared by sub-committee 8 “Products and systems for the protection and repair of concrete structures“ (Secretariat AFNOR). This European Standard is one of a series dealing with products and systems for the protection and repair of concrete structures. It describes a method for determining the chloride content of hardened concrete. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. EN 14629:2007 (E) 4 Introduction Steel reinforcement in concrete may be at risk of corrosion if the concrete is contaminated by chlorides. ENV 1504-9 defines the principles for protection and repair of concrete structures which have suffered or may suffer damage or deterioration and gives guidance on the selection of products and systems which are appropriate for this intended use. EN 1504-10 requires that the concentration of chlorides be considered when decisions about the removal of concrete are made. To establish whether there is a risk of corrosion of the steel reinforcement due to a higher chloride content within the concrete than the critical threshold value, the chloride content within the concrete cover and especially at the surface of the steel reinforcement should be determined. Assessment may be made in the field using a variety of rapid test methods, which are not included in this standard. For accurate determination of chloride content, concrete samples need to be taken from the structure, prepared for chemical analysis and analysed. For chemical analysis of the concrete with respect to the chloride content either Volhards method or potentiometric titration are used as the reference methods. The chloride content may be expressed as a percentage of chloride by mass of cement or of concrete. The chloride content by mass of cement may be derived using either an assumed value for the cement content of the concrete or a value which has been determined by chemical analysis or from construction records. EN 14629:2007 (E) 5 1 Scope This standard describes two methods for the determination of the total (free and bound) acid soluble chloride content of hardened concrete or mortar. This information is intended for use in estimating the risk of chloride induced corrosion of the steel reinforcement. It may be used on samples of powder obtained either by drilling or from cores or fragments removed from concrete structures or on other appropriate laboratory specimens. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 384, Laboratory glassware - Principles of design and construction of volumetric glassware 3 Materials and apparatus 3.1 Chemicals Deionised water with an electrical conductivity less than 2 S/cm; Nitric acid (5 mol/l); Silver nitrate solution (0,02 mol/l); Ammonium thiocyanate (NH4SCN) solution (0,1 mol/l); Ammonium ferric sulfate indicator solution (100 ml of a cold saturated solution of NH4Fe(SO4)2 and 10 ml diluted nitric acid); 3,5,5-trimethylhexanol. NOTE For the potentiometric method, additional reagents may be required as specified by the electrode manufacturer to ensure the proper functioning of the electrode. These will be specified in the manufacturers instructions for the electrode. 3.2 Apparatus Crushing and grinding equipment (as required to prepare samples); 1,18 mm sieve or smaller; ventilated oven, controlled to maintain a temperature of (105 5) °C; balance capable of weighing up to 5 g to an accuracy of 1 mg; desiccator; burette, accurate to 0,05 ml; 250 ml glass beaker; magnetic stirrer; EN 14629:2007 (E) 6 heat source; vacuum filtering facility (Buchner funnel, filtration flask, medium-textured filter paper); 250 ml volumetric flask; pipettes accurate to 0,1 ml; if required, potentiometric titration facility (eg. Ag/AgCl electrode or similar, high resistance mV-meter, burette accurate to 0,05 ml or automatic titration equipment). All volumetric glassware shall be of class A accuracy as defined in ISO 384. 4 Test procedure 4.1 Sampling 4.1.1 Sampling plan Sampling shall be in accordance with a plan prepared for the assessment or repair works by a suitably qualified person. When specifying the locations from which concrete is to be removed, specific care shall be taken of the load bearing capacity and reinforcement of the elements to be sampled. The plan shall take into account: the size, form, location, orientation, age and structural design of the structure; the results of visual surveys and any other available information about possible deterioration; the aggregate size and the heterogeneous nature of the concrete; exposure conditions, eg. salt water splash zones. On site checks shall be carried out to ensure that the concrete to be sampled is representative of the elements to be investigated and to confirm the location of reinforcement, which should not be damaged during sampling. The plan shall specify the approximate number, location and depth of samples, including the depth increments. Typically increments do not exceed 25 mm, and it is usual to discard the surface layer. NOTE All holes or damage to the structure from sampling should be repaired or protected immediately to prevent further deterioration. 4.1.2 Collecting powder samples When drilling for powder samples the diameter of the drilling tool and therefore the number of drill holes required to obtain a sufficient sample size is determined by the maximum aggregate size. The powder is collected in separate depth increments, as specified in the sampling plan. A minimum sample size of approximately 1 g is required. NOTE A drill diameter of 20 mm and two holes is normally sufficient to provide 1 g of powder per mm depth of increment. For concrete containing aggregates of maximum size of 20 mm a 20 mm drill should be used. A sample of at least 20 g is normally collected to ensure that it is representative of all of the concrete constituents and not just the aggregate. For larger aggregate sizes a larger drill diameter and sample size should be used. EN 14629:2007 (E) 7 4.1.3 Taking core samples A core diameter of 30 mm to 50 mm, depending on the maximum aggregate size, is usually recommended. Larger sizes may be required for large aggregate sizes. Cores shall be marked to indicate their location and orientation with respect to the original concrete surface. For determination of chloride profiles related to the distance from the concrete surface, the cores may be cut into slices as specified in the sampling plan, without using cooling fluid, or may be ground in increments to obtain powder samples. 4.2 Grinding Where the sample requires grinding, it shall be dried in an oven to constant weight at (105 5) °C and then allowed to cool to room temperature, for example in a desiccator. When cool it shall be ground to a fine powder to pass a 1,18 mm sieve or smaller, and then homogenised. 4.3 Chemical analysis 4.3.1 General requirements The mass of samples shall be given in grams to the nearest 0,001 g and volumes given in millilitres to the nearest 0,05 ml. Approximately one sample out of every 20 samples (or one sample from every batch if less than 20 samples in the batch) shall be an interlaboratory standard concrete dust specimen of known chloride content. Occasional duplicate analyses, in which the same sample is analysed twice and the results compared, shall also be carried out to confirm the accuracy of the analysis. NOTE In selecting samples for duplicate analyses note should be taken of the results obtained, in particular of any results which fall outside general trends such as a reduction of chloride concentration with sample depth. 4.3.2 Dissolving chlorides Between 1 g and 5 g of concrete powder shall be weighed and placed in a 250 ml beaker, wetted with 50 ml water, and 10 ml of 5 mol/l nitric acid added, followed by 50 ml hot water. NOTE 1 Adding concentrated acid allows the lab to use a dispenser. This saves time and avoids cross contamination. The addition of hot water quickens boiling and avoids spitting. The mixture shall be heated until boiling and boiled for at least 3 min, stirring continuously. If necessary the mixture shall be filtered immediately using medium-textured paper, washing the beaker, the stirrer and the residue on the filter. NOTE 2 It is not necessary to filter the solution for potentiometric titration. 4.3.3 Blank solution Carry out the same procedure with no concrete test portion. 4.3.4 Determination of chloride content 4.3.4.1 Volhards Method (Method A) Add 5 ml of silver nitrate solution by pipette into the test solution and stir vigorously to precipitate the chloride. EN 14629:2007 (E) 8 If the chloride content is high, and a large amount of precipitate is formed, a floculating agent such as 3,5,5-trimethylhexanol may be added. It can be added after the silver nitrate, so the chloride level can be judged from the amount of precipitate formed. NOTE The smell of 3,5,5-trimethylhexanol is overpowering and it is recommended to use it as little as possible. Add 5 drops of indicator solution and titrate with the ammonium thiocyanate solution one drop at a time, while continually agitating the solution until the faint reddish-brown coloration no longer disappears. Record the volume V1 of solution used in the titration. An early end-point, at less than 1 ml of ammonium thiocyanate addition, indicates that the test solution demands more silver nitrate solution than the 5,0 ml already added. In this case a further 5 ml of AgNO3 shall be added and the titration continued until the end point is reached a second time. Record the volume V1 of solution used to reach the second end point. This procedure may be repeated up to three times. If the sample contains too much chloride then repeat from the beginning (4.3.2) with a smaller sample mass. Calculate the chloride content as percent of chloride ion by mass of sample using the following formula: CC = 3.545 * f * (V2-V1) / m V1 volume of the ammonium thiocyanate solution used in the titration ml; V2 volume of the ammonium thiocyanate solution used in the blank titration ml; m mass of the concrete sample g; f molarity of silver nitrate solution. 4.3.4.2 Potentiometric titration (Method B) The chloride content is determined with 0,1 M silver nitrate solution in a potentiometric titration. Consumption of silver nitrate solution (V3) in the titration is noted. The first derivative method is to be used. First derivative is a technique of adding small aliquots of titrant to the sample, recording the potential changes, and applyin