1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationUse of control charts in the production of concretePD CEN/TR 16369:2012National forewordThis Published Document is the UK implementation of CEN/TR 16369:2012. The UK participatio
2、n in its preparation was entrusted by Technical CommitteeB/517, Concrete, to Subcommittee B/517/1, Concrete production and testing.A list of organizations represented on this committee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisio
3、ns of a contract. Users are responsible for its correct application. The British Standards Institution 2012.Published by BSI Standards Limited 2012 ISBN 978 0 580 76828 6 ICS 03.120.30; 91.100.30Compliance with a British Standard cannot confer immunity from legal obligations.This Published Document
4、was published under the authority of the Standards Policy and Strategy Committee on 30 November2012.Amendments issued since publicationDate Text affectedPUBLISHED DOCUMENTPD CEN/TR 16369:2012TECHNICAL REPORT RAPPORT TECHNIQUE TECHNISCHER BERICHT CEN/TR 16369 October 2012 ICS 91.100.30; 03.120.30 Eng
5、lish Version Use of control charts in the production of concrete Utilisation des cartes de contrle pour la production du bton Anwendung von Qualittsregelkarten bei der Herstellung von Beton This Technical Report was approved by CEN on 20 May 2012. It has been drawn up by the Technical Committee CEN/
6、TC 104. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway
7、, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2012 CEN All rights of exploitation in any
8、 form and by any means reserved worldwide for CEN national Members. Ref. No. CEN/TR 16369:2012: EPD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 2 Contents Page Foreword 4Introduction .51 Scope 72 Symbols and abbreviations 73 Statistics for Concrete 83.1 Normal distribution of strength 83.2 Characteristic
9、 strength and target strength .83.3 Standard deviation 103.4 Setting the target strength . 134 Simple Data Charts . 145 Shewhart Charts . 155.1 Introduction . 155.2 Shewhart action criteria . 165.2.1 Points beyond UCL or LCL 165.2.2 Points beyond UWL or LWL 165.2.3 Patterns within control limits 165
10、.3 Control of standard deviation 165.4 Example Shewhart chart 165.5 Modified application of Shewhart control chart 176 CUSUM . 196.1 Introduction . 196.2 Controlling mean strength . 226.3 Controlling standard deviation 226.4 Controlling correlation . 236.5 Design of V-mask 246.6 Action following cha
11、nge 247 Multivariable and Multigrade Analysis . 267.1 General . 267.2 Multivariable 267.3 Multigrade 278 Speeding the Response of the System 288.1 Early age testing . 288.2 Family of mixes concept 289 Guidance on Control Systems 309.1 Abnormal Results . 309.2 Handling mixes outside the concrete fami
12、ly . 309.3 Handling mixes not controlled by compressive strength requirements 319.4 Test rates . 329.5 Action following change 3310 EN 206-1 Conformity Rules for Compressive Strength 3310.1 Basic requirements for conformity of compressive strength 3310.2 Assessment period . 3410.3 Conformity rules f
13、or compressive strength . 3410.4 Achieving an AOQL of 5 % with CUSUM 3610.5 Non-conformity . 3711 Implementing Control Systems . 3812 CUSUM Example . 38PD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 3 12.1 Reference mix and concrete family . 3812.2 Main relationship . 3912.3 Applying adjustments . 4012.4
14、 CUSUM calculation 4112.5 CUSUM action following change . 4512.6 Further data and a change in standard deviation 47Bibliography 51PD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 4 Foreword This document (CEN/TR 16369:2012) has been prepared by Technical Committee CEN/TC 104 “Concrete and related products”
15、, the secretariat of which is held by DIN. 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. PD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 5
16、 Introduction It is safe to assume that ever since manufacturing commenced, attempts have been made to control the process in order to improve quality and drive down costs. The application of statistical techniques to manufacturing was first developed by physicist Walter A. Shewhart of the Bell Tele
17、phone Laboratories in 1924. Shewhart continued to develop the idea and in 1931 he published a book on statistical quality control 1. Shewhart recognised that within a manufacturing process there were not only natural variations inherent in the process, which affected quality but there were also vari
18、ations that could not be explained. Shewhart recognised that it is possible to set limits on the natural variation of any process so that fluctuations within these limits could be explained by chance causes, but any variation outside of these limits, special variations, would represent a change in t
19、he underlying process. Shewharts concept of natural and special variations is clearly relevant to the production of concrete at a ready-mixed plant or precast factory and the requirement to achieve a specified compressive strength. Natural variations exist in the process due to variation in the raw
20、materials (aggregate grading, chemical composition, etc), batching accuracy, plant performance, sampling and testing, etc. Special causes of variation outside of the natural variations could be due to changed constituent materials being used, weigh-scales losing accuracy, a new batcher, problems wit
21、h testing equipment, etc. Control charts have found widespread use in the concrete industry in both ready-mixed concrete and precast concrete sectors as a tool for quality control. Control charts can be applied to monitor a range of product characteristics (e.g. cube/cylinder strength, consistence,
22、w/c ratio), constituent materials (aggregate grading, cement strengths, etc.) or production (batching accuracy). Their most common application of control charts is as a means of continuously assessing compressive strength results in order to: check whether target strengths are being achieved; measur
23、e the variations from target (all products vary); identify magnitude of any variation; objectively define action required (e.g. change w/c ratio) to get the process back on target; identify periods and concretes where the strength was less than specified so that investigations can be carried out and
24、 corrective action taken. The use of control charts should not be treated in isolation from the rest of production control. For example routine checking and maintenance of weigh equipment will minimise the risk of a weigh-scale failure. Control charts provide information about the process, but the i
25、nterpretation of the information is not a mechanical process. All the information available to the concrete producer should be used to interpret the information and make informed decisions. Did a change in quality occur when a new batch of constituent was first used? Is all the family showing the sa
26、me trend? Are other plants using similar materials showing a similar trend? Such information leads to the cause of the change in quality being identified and appropriate action being taken. For example a loss of accuracy in the weigh-scales should lead to repair, maintenance and re-calibration and n
27、ot a change in mix proportions. Where a change in mix proportions is required, the use of control charts can lead to objectively defined changes in proportions. Effective control of concrete production is more easily achieved when there are good relationships with the constituent material suppliers,
28、 particularly the suppliers of cementitious materials. Early warning of a change in performance from the constituent material supplier should be part of the supply agreement, e.g. that stock PD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 6 clinker is being used during the maintenance period, and on the b
29、asis of this warning, the producer will decide the appropriate action. Some producers use changes in cement chemistry to predict changes in concrete strength. Effective production control is about using all this information to produce concrete conforming to its specification. Effective production co
30、ntrol, which includes the use of control charts, significantly reduces the risk of non-conformity benefiting both users and producers of concrete. There are drawbacks to the existing method of assessment of conformity of mean strength adopted in EN 206-1 3 including not following the CEN Guidance on
31、 the evaluation of conformity 2. It is believed that control charts (already widely used as a quality assurance tool in factory production control) would provide an alternative and better means of ensuring the characteristic strength is achieved and it is a method that follows the CEN Guidance. PD C
32、EN/TR 16369:2012CEN/TR 16369:2012 (E) 7 1 Scope This Technical Report reviews various control systems that are currently used in the concrete industry and, by the use of examples, show how the principles are applied to control the production of concrete. This CEN/TR provides information and examples
33、 of the use of method C in Clause 8 of prEN 206:2012. 2 Symbols and abbreviations AOQ Average outgoing quality AOQL Average outgoing quality limit CmraConstant giving the cement content increase required to produce a 1N/mm2increase in strength dc Change in cement content Dl Decision interval G Gradi
34、ent fciIndividual test result for compressive strength of concrete fckSpecified characteristic compressive strength fcmMean compressive strength of concrete k Statistical constant LlLower limit LCL Lower control limit LWL Lower warning limit n Number of samples qnStatistical constant that depends up
35、on n and the selected AOQL s Sample standard deviation UCL Upper control limit UWL Upper warning limit xiTest result NOTE According to EN 206-1 3, a test result may be the mean value of two or more specimens taken from one sample and tested at one age. x Mean value of n test results Estimate for the
36、 standard deviation of a population PD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 8 3 Statistics for Concrete 3.1 Normal distribution of strength Compressive strength test results tend to follow a normal distribution as illustrated in Figure 1. A normal distribution is defined by two parameters, the mea
37、n value of the distribution and the standard deviation ( ), which is the measure of the spread of results around the mean value. A low standard deviation means that most strength results will be close to the mean value; a high standard deviation means that the strength of significant proportions of
38、the results will be well below (and above) the mean value. The area under the normal distribution between two values of x represents the probability that a result will fall within this range of values. The term tail is used to mean the area under the normal distribution between a value, e.g. a compr
39、essive strength, and where the frequency is effectively zero. For strength it is the lower tail, i.e. low strength results, that is important but for other properties, e.g. consistence, both the lower and upper tails are important. Key X cube strength, N/mm Y frequency 1 target mean strength 2 speci
40、fied Characteristic strength, fck3 minimum strength (fck 4) 4 tail Figure 1 Illustration of concrete strength distribution At the extremes of the strength range for a given set of constituent materials, the assumption of a normally distributed set of data may not be valid. It is not possible to have
41、 strengths less than zero and most concretes have a ceiling strength beyond which they cannot go. In these situations the data set is skewed. However as low strengths are of concern to specifiers, an assumption of normally distributed data does not lead to problems in practice. 3.2 Characteristic st
42、rength and target strength EN 206-1 3 specifies the characteristic compressive strength of concrete in terms of a standard cylinder test or a standard cube test carried out at 28 days. The characteristic strength is defined in EN 206-1 3 as the “value of strength below which 5 % of the population of
43、 all possible strength determinations of the volume of concrete under consideration, are expected to fall”. Put simply this means that if every single batch was tested, 5 % of the results would fall within the lower tail of the normal distribution that starts 1,64 below the actual mean strength. How
44、ever the actual mean strength will not be known until the concrete has been PD CEN/TR 16369:2012CEN/TR 16369:2012 (E) 9 produced and tested and therefore the target mean strength (TMS) is usually set at some higher value to ensure the concrete achieves at least the specified characteristic strength.
45、 The target mean strength is given in Equation (1): TMS = fck+ k (1) where TMS = target mean strength fck= characteristic compressive strength = estimate for standard deviation of population k = statistical constant k = the margin The fixed point in the distribution is the specified characteristic s
46、trength and as the margin increases and/or the standard deviation increases, the target mean strength increases, see the following Example. EXAMPLE The target mean strength for a specified characteristic strength of C25/30 is given in Table 1. A standard deviation ( ) of 3 N/mm2is typical of a concr
47、ete with low variability and a value of 6 N/mm2represents high variability. Table 1 Target mean strength for specified characteristic strength of 30 N/mm2(cube) Margin Area in lower tail (i.e. percentage below characteristic strength) Target mean strength (cube), N/mm2 = 3 N/mm2 = 6 N/mm21,64 5 % 35
48、 40 1,96 2,5 % 36 42 2,00 2,28 % 36 42 2,33 1,0 % 37 44 3,0 0,13 % 39 48 The numbers in this table have been rounded. A concrete strength below the characteristic strength is not a failure as statistically 5 % of the results are expected and accepted as to fall below this value. However for structur
49、al safety reasons, a batch with a concrete strength significantly below the characteristic strength is excluded, even though it forms part of the expected population. Consequently EN 206-1 3 specifies a minimum strength requirement for individual results (fci) of (fck 4). Any batch below this strength is a non-conforming batch. The risk of non-conformity decreases as the margin increases. Statistics are
