SIST EN 13813:2003
(Main)Screed material and floor screeds - Screed material - Properties and requirements
Screed material and floor screeds - Screed material - Properties and requirements
It defines for fresh screed material the performance related to working time, consistency, pH value and for hardened screed material, compressive strength, flexural strength, wear resistance, surface hardness, resistance to uindentation, resistance to rolling wheel, shrinkage and swelling, modulus of elasticity and bond strength. It provides for the evaluation of conformity of the product to this draft European standard. The marking requirements for products covered by this draft European standard are included. This standard covers screed materials as defined in prEN 13318.
Estrichmörtel, Estrichmassen und Estriche - Estrichmörtel und Estrichmassen - Eigenschaften und Anforderungen
Der vorliegende Europäische Norm-Entwurf legt Anforderungen an Estrichmörtel fest, die für Fußbodenkonstruk-tionen in Innenräumen eingesetzt werden.
Um eine anwendungsbezogene Norm zu erhalten , wird nach Möglichkeit nur auf die Eigenschaften eines Produkts Bezug genommen und das Herstellungsverfahren nur dann einbezogen, wenn dies zur Beschreibung der Produkteigenschaften unbedingt erforderlich ist.
Es werden folgende Kennwerte festgelegt: für Estrichfrischmörtel die Verarbeitungszeit, die Konsistenz und der pH-Wert und für erhärtete Estrichmörtel die Druckfestigkeit, die Biegezugfestigkeit, der Verschleißwiderstand, die Oberflächenhärte, die Eindringtiefe, der Widerstand gegen Rollbeanspruchung, das Schwinden und Quellen, der Biegeelastizitätsmodul, die Haftzugfestigkeit, die Schlagfestigkeit, das Brandverhalten, die akustischen Eigen-schaften, die Wärmedämmung und die chemische Beständigkeit.
Diese Kennwerte stellen die Grundlage für die Bewertung der Konformität des Produkts mit dieserEuropäischen Norm dar.
Anforderungen an die Kennzeichnung der Produkte, die von dieser Europäischen Norm abgedeckt werden, sind ebenfalls enthalten.
Dieser Norm gilt für Estrichmörtel, wie in EN 13318 definiert.
Wenn Fußbodenbelagssysteme eingesetzt werden, um das Lastaufnahmevermögen einer Betonkonstruktion zu schützen oder wieder herzustellen, müssen zusätzlich zu den Anforderungen dieser Norm auch die Anforderungen nach prEN 1504-2:2000 erfüllt werden.
Konstruktive Estriche, d. h. Estriche, die einen Beitrag zur Tragfähigkeit eines Bauwerks leisten, werden von dieser Norm nicht abgedeckt.
ANMERKUNG Diese Norm kann zusammen mit Anwendungsrichtlinien und nationalen Festlegungen auf Estrichmörtel angewendet werden, die auf der Baustelle vom gleichen Unternehmer hergestellt und verlegt werden.
Matériaux de chapes et chapes - Matériaux de chapes - Propriétés et exigences
Cette Norme européenne spécifie les exigences applicables au matériau pour chape destiné a la construction de planchers en intérieur.
Pour faciliter la rédaction d'une norme liée aux performances, la présente norme ne concerne, dans toute la mesure du possible, que les propriétés du produit et non ses méthodes de fabrication sauf si cela est inévitable dans la description des caractéristiques du produit.
Pour le matériau pour chape frais, elle définit les performances liées au temps de mise en ?uvre, a la consistance, a la valeur du pH et, pour le matériau pour chape durci, a la résistance a la compression, a la résistance a la flexion, a la résistance a l'usure, a la dureté de surface, a la résistance a l'indexation, a la résistance au roulement, au retrait et au gonflement, au module d'élasticité, a la force d'adhérence, a la résistance a l'impact, a la réaction au feu, a la performance acoustique, a la résistance thermique et a la résistance chimique.
Elle permet l'évaluation de la conformité du produit par rapport a la présente Norme européenne.
Cette norme couvre les matériaux pour chape comme défini dans l'EN 13318.
Les exigences de marquage des produits couverts par la présente Norme européenne sont incluses.
Les chapes structurales, c'est a dire qui contribuent a la capacité de résistance a la charge de la structure, sont exclues de cette norme.
NOTE Cette norme peut etre utilisée en conjonction avec des cahiers de prescription et des spécifications nationales pour du matériau pour chapes fabriqué sur le chantier et coulé par le meme entrepreneur.
Estrihi - Materiali za estrihe - Lastnosti in zahteve
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Screed material and floor screeds - Screed material - Properties and requirementsEstrihi - Materiali za estrihe - Lastnosti in zahteveMatériaux de chapes et chapes - Matériaux de chapes - Propriétés et exigencesEstrichmörtel, Estrichmassen und Estriche - Estrichmörtel und Estrichmassen - Eigenschaften und Anforderungen91.100.10Cement. Mavec. Apno. MaltaCement. Gypsum. Lime. MortarICS:SIST EN 13813:2003enTa slovenski standard je istoveten z:EN 13813:200201-marec-2003SIST EN 13813:2003SLOVENSKI
STANDARD
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13813October 2002ICS 91.100.10English versionScreed material and floor screeds - Screed material - Propertiesand requirementsMatériaux de chapes et chapes - Matériaux de chapes -Propriétés et exigencesEstrichmörtel, Estrichmassen und Estriche - Estrichmörtelund Estrichmassen - Eigenschaften und AnforderungenThis European Standard was approved by CEN on 14 September 2002.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Management Centre or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2002 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13813:2002 E
EN 13813:2002 (E)2ContentspageForeword.4Introduction.51Scope.52Normative references.53Terms and definitions, symbols and abbreviations.73.1Terms and definitions.73.2Symbols and abbreviations.74Materials.75Classification and requirements.75.1General.75.2Properties and classification.85.2.1Compressive strength.85.2.2Flexural strength.95.2.3Wear resistance.95.2.4Surface hardness.105.2.5Resistance to indentation.105.2.6Resistance to rolling wheel for screed material intended to be covered with floor covering.115.2.7Setting time.115.2.8Shrinkage and swelling.115.2.9Consistency.125.2.10pH-value.125.2.11Modulus of elasticity in flexure.125.2.12Bond strength.125.2.13Impact resistance.125.3Special characteristics.135.3.1General.135.3.2Electrical resistance.135.3.3Chemical resistance.135.3.4Reaction to fire.135.3.5Release of corrosive substances or corrosiveness of screed materials.135.3.6Water vapour permeability.135.3.7Thermal resistance.135.3.8Water permeability.135.3.9Impact sound insulation.135.3.10Sound absorption.145.3.11Other characteristics.146Evaluation of conformity.146.1General requirements.146.2Initial type tests.146.3Factory Production Control (FPC).146.3.1General.146.3.2Process Control.156.3.3Screed material.156.3.4Traceability.156.3.5Labelling.156.3.6Records.167Designation.16
EN 13813:2002 (E)38Marking, labelling and packaging.179Conformity criteria and assessment procedure.179.1General requirements.179.2Conformity criteria for physical, mechanical and chemical properties and evaluationprocedure.179.2.1General.179.2.2Statistical conformity criteria.179.2.3Assessment based on individual results.20Annex ZA (informative)
Clauses of this European Standard addressing essential requirements orother provisions of EU Directives.21ZA.1Scope and relevant characteristics.21ZA.2Procedures for the attestation of conformity of floor screed material.26ZA.2.1System(s) of attestation of conformity.26ZA.2.2EC Certificate and Declaration of conformity.29ZA.3CE conformity marking.30Bibliography.34
EN 13813:2002 (E)4ForewordThis document EN 13813:2002 has been prepared by Technical Committee CEN/TC 303 "Floor screeds and in-situfloorings in buildings", the secretariat of which is held by DIN.This European Standard shall be given the status of a national standard, either by publication of an identical text orby endorsement, at the latest by April 2003, and conflicting national standards shall be withdrawn at the latest byJuly 2004.This document has been prepared under a mandate given to CEN by the European Commission and the EuropeanFree Trade Association, and supports essential requirements of EU Directive(s).For relationship with EU Directive(s), see informative annex ZA, which is an integral part of this document.According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain,Sweden, Switzerland and the United Kingdom.
EN 13813:2002 (E)5IntroductionThe properties required of a screed are related to its use.They are considered in two groups: those relating to the fresh, unhardened screed material and those relating tothe hardened screed material.The properties achieved depend essentially on the type or types of binder used and their respective proportions.The type of aggregates, admixtures and/or additions used can achieve special properties.1 ScopeThis European Standard specifies requirements for screed material for use in floor construction internally.To support the aim of achieving a performance related standard, as far as practicable this standard refers only tothe properties of the product and not to its method of manufacture, except when this is unavoidable in the de-scription of the characteristics of the product.It defines for fresh screed material the performance related to setting time, consistency, pH value and for thehardened screed material, compressive strength, flexural strength, wear resistance, surface hardness, resistanceto indentation, resistance to rolling wheel, shrinkage and swelling, modulus of elasticity, bond strength, impactresistance, reaction to fire, acoustic performance, thermal resistance and chemical resistance.It provides for the evaluation of conformity of the product to this European Standard.The marking requirements for products covered by this European Standard are included.This standard covers screed materials as defined in EN 13318.Structural screeds, i.e. those that contribute to the load bearing capacity of the structure, are excluded from thisstandard.NOTE
This standard can be used in conjunction with codes of application and national specifications for site made screedmaterial produced and laid by the same contractor.2 Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text, and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).EN 1062-3, Paints and varnishes - Coating materials and coating systems for exterior masonry and concrete - Part3: Determination and classification of liquid-water transmission rate (permeability).EN 1081, Resilient floor coverings – Determination of the electrical resistance.prEN 1504-2, Products and systems for the protection and repair of concrete structures – Definitions, requirements,quality control and evaluation of conformity – Part 2: Surface protection systems.
EN 13813:2002 (E)6EN 12086, Thermal insulating products for building applications - Determination of water vapour transmissionproperties.prEN 12354-6, Building acoustics - Estimation of acoustic performance of buildings from the performance ofelements - Part 6: Sound absorption in enclosed spaces.EN 12524, Building materials and products - Hygrothermal properties - Tabulated design values.EN 12664, Thermal performance of building materials and products - Determination of thermal resistance bymeans of guarded hot plate and heat flow meter methods - Dry and moist products of medium and low thermalresistance.prEN 12697-20, Bituminous mixtures - Test methods for hot mix asphalt - Part 20: Indentation using cube ormarshall specimens.prEN 12697-21, Bituminous mixtures - Test methods for hot mix asphalt - Part 21: Indentation using platespecimens.EN 12706, Adhesives - Test methods for hydraulic setting floor smoothing and/or levelling compounds -Determination of flow characteristics.EN 13318, Screed materials and floor screeds – Definitions.prEN 13454-2, Binders, composite binders and factory made mixtures for floor screeds based on calcium sulfate -Part 2: Test methods.EN 13501-1, Fire classification of construction products and building elements – Part 1: Classification using testdata from reaction to fire tests.prEN 13529, Products and systems for the protection and
repair of concrete structures - Test method -
Resistanceto high chemical attack.prEN 13872, Methods of test for hydraulic setting floor smoothing and/or levelling compounds - Determination ofdimensional change.prEN 13892-1, Methods of test for screed materials - Part 1: Sampling, making and curing specimens for test.prEN 13892-2, Methods of test for screed materials - Part 2: Determination of flexural and compressive strength.prEN 13892-3, Methods of test for screed materials - Part 3: Determination of wear resistance-Böhme.prEN 13892-4, Method of test for screed materials – Part 4: Determination of wear resistance-BCA.prEN 13892-5, Methods of test for screed materials - Part 5: Determination of wear resistance to rolling wheel -Methods for screed material for wearing layer.prEN 13892-6, Methods of test for screed materials - Part 6: Determination of surface hardness.prEN 13892-7, Methods of test for screed materials - Part 7: Determination of resistance to rolling wheel - Methodsfor screed material with floor coverings.prEN 13892-8, Methods of test for screed materials - Part 8: Determination of bond strength.EN ISO 140-6, Acoustics - Measurement of sound insulation in buildings and of building elements - Part6: Laboratory measurements of impact sound insulation of floors (ISO 140-6:1998).EN ISO 178, Plastics - Determination of flexural properties (ISO 178:1993).EN ISO 354, Acoustics - Measurement of sound absorption in a reverberation room (ISO 354:1985).
EN 13813:2002 (E)7EN ISO 354/A1, Acoustics - Measurement of sound absorption in a reverberation room - Amendment 1: Testspecimen mountings for sound absorption tests (ISO 354:1985/AMD1:1997).EN ISO 6272, Paints and varnishes - Falling-weight test (ISO 6272:1993).3 Terms and definitions, symbols and abbreviations3.1Terms and definitionsFor the purpose of this European Standard, the terms and definitions described in EN 13318 apply.3.2Symbols and abbreviationsThe following abbreviations are used in this European Standard for screeds in relation to the binder used:CTcementitious screedsCAcalcium sulfate screedsMAmagnesite screedsASmastic asphalt screedsSRsynthetic resin screedsThe following abbreviations are used in this standard for designation of the properties:Cfor compressive strengthFfor flexural strengthAfor wear resistance "Böhme"RWAfor wear resistance to rolling wheelARfor wear resistance "BCA"SHfor surface hardnessICfor resistance to indentation on cubesIPfor resistance to indentation on platesRWFCfor resistance to rolling wheel with floor coveringEfor modulus of elasticityBfor bond strengthIRfor impact resistance4 MaterialsBinders, aggregates, admixtures, additives and water with established suitability for screed material shall be used.5 Classification and requirements5.1 GeneralThe requirements and properties specified in this standard shall be defined in terms of the test methods and pro-cedures referred to in this standard. For these tests the screed material shall be sampled and the test specimensmade and cured in accordance with prEN 13892-1.Where flooring systems are used to protect or reinstate the integrity of a concrete structure, the requirementsaccording to prEN 1504-2 shall also be fulfilled in addition to the requirements of this standard.The conformity criteria given in the following subclauses relate to initial type tests and production control. Theproduction control system shall be detailed in the Quality Manual.
EN 13813:2002 (E)8NOTE
The screed properties under site conditions cannot always be directly comparable with the screed material propertiesobtained under laboratory conditions, due for instance to variations of mixing, compaction or curing.5.2 Properties and classificationThe properties to be tested are listed in Table 1.Table 1 — Screed materials and tests which apply to each typeScreedmaterialsbased oncompressive strengthflexural strengthwear resistance "Böhme"wear resistance "BCA"wear resistance to rollingwheelsurface hardnessresistance to indentationresistance to rolling wheelwith floor coveringsetting timeshrinkage and swellingconsistencypH valuemodulus of elasticityImpact resistancebond strengthCementNNNa
(one ofthree)O-OOOOOOOaOCalciumsulfateNNOOOO-OOOONO-OMagnesiteNNOOONa-O-OOOO-OMasticasphalt--OOO-NO-------SyntheticresinOO-Na (one oftwo)O-O-OO-ONaNKeyN
NormativeO
Optional, where relevant-
not relevanta
only for screed material intended for wearing surfacesFor each type of binder, the age where the performances shall be achieved is defined in prEN 13892-1. Where themanufacturer can demonstrate that the required classes of properties can be achieved at an earlier age, this agemay be included in the designation provided all declared class values are achieved at this age.5.2.1 Compressive strengthThe compressive strength, for cementitious screed, calcium sulfate screed and magnesite screed materials, shallbe declared by the manufacturer, and may be declared for synthetic resin screed materials. The compressivestrength shall be determined in accordance with prEN 13892-2.The compressive strength shall be designated by a "C" (for Compression) followed by the compressive strengthclass in N/mm2, in accordance with Table 2.
EN 13813:2002 (E)9Table 2 — Compressive strength classes for screed materialsClassC5C7C12C16C20C25C30C35C40C50C60C70C80Compressivestrength inN/mm25712162025303540506070805.2.2 Flexural strengthThe flexural strength, for cementitious screed, calcium sulfate screed and magnesite screed materials, shall bedeclared by the manufacturer. The flexural strength shall be determined in accordance with prEN 13892-2.The manufacturer may declare the flexural strength for synthetic resin screed materials. The flexural strength ofsynthetic resin screed shall be determined in accordance with EN ISO 178 for screed materials intended to beapplied at a thickness of 5 mm or less, or with prEN 13892-2 for other screed materials.The flexural strength is designated with "F" (for Flexural) followed by the flexural strength in N/mm2, in accordancewith Table 3.Table 3 — Flexural strength classes for screed materialsClassF1F2F3F4F5F6F7F10F15F20F30F40F50Flexuralstrengthin N/mm212345671015203040505.2.3 Wear resistanceThe wear resistance for cementitious screed materials and for synthetic resin screed materials, to be used aswearing surfaces, shall be determined in accordance with prEN 13892-3 (wear resistance Böhme) or with prEN13892-4 (wear resistance BCA) or with prEN 13892-5 (wear resistance to rolling wheel) and shall be declared bythe manufacturer. To declare the wear resistance for cementitious screed materials, the manufacturer may choosebetween the three test methods and for synthetic resin screed materials between the wear resistance BCA and thewear resistance to rolling wheel.A manufacturer of a screed material other than cementitious or synthetic resin screed material to be used as awearing surface may choose to determine and declare the appropriate wear class utilising these methods.Another test method may be used, if a correlation with prEN 13892-3, with prEN 13892-4 or with prEN 13892-5 isproved with the screed material.The wear resistance Böhme is designated by "A" (for Abrasion) followed by the abrasion quantity in cm3/50 cm2, inaccordance with Table 4.Table 4 — Wear resistance Böhme classes for cementitious and other scread meterialsClassA22A15A12A9A6A3A1,5Abrasion quantity incm3/50 cm22215129631,5The wear resistance BCA is designated by an "AR" (for Abrasion Resistance) followed by the maximum wear depthin 100 mm, in accordance with Table 5.
EN 13813:2002 (E)10Table 5 — Wear resistance BCA classes for cementitious and other screed materialsClassAR6AR4AR2AR1AR0,5Maximum wear depth in mm60040020010050The wear resistance to rolling wheel is designated by "RWA" (for Rolling Wheel Abrasion) followed by the abrasionquantity in cm3, in accordance with Table 6.Table 6 — Wear resistance to rolling wheel classes for cementitious and other screed materialsClassRWA300RWA100RWA20RWA 10RWA1Abrasion quantity incm3300100201015.2.4 Surface hardnessThe surface hardness for magnesite screed materials, to be used as wearing surfaces, shall be declared by themanufacturer and as an option may be declared for other screed materials with fine aggregates (< 4 mm). Thesurface hardness shall be determined in accordance with prEN 13892-6.The surface hardness is designated with "SH" (for Surface Hardness) followed by the surface hardness in N/mm2,in accordance with Table 7.Table 7 — Surface hardness for magnesite and other screed materialsClassSH30SH40SH50SH70SH100SH150SH200Surface hardness inN/mm2304050701001502005.2.5 Resistance to indentationThe manufacturer shall declare the resistance to indentation of mastic asphalt screed materials. The resistance toindentation shall be determined on cubes in accordance with prEN 12697-20 or on plates in accordance withprEN 12697-21.The resistance to indentation of mastic asphalt screed materials shall be designated by "I" (for Indentation), "C" or"P" (for Cube or Plate) to indicate the test method applied, followed by the maximum indentation value in 0,1 mm,in accordance with Tables 8a and 8b.For tests of mastic asphalt screed materials on plates with a cross sectional area of the indentation pin of 31,7mm2, with indentation also measured in 0,1 mm, classes are designated by IP and Roman numerals I to IV, inaccordance with Table 8c.The designation "H" signifies material for use in heated screeds.
EN 13813:2002 (E)11Table 8a — Hardness classes on cubes - Load applied 525 N - Indentation in units of 0,1 mmHardness classes - Test conditionsICH10IC10IC15IC40IC100(22 ± 1) °C; 100 mm2; 5 h£ 10£ 10£ 15——(40 ± 1) °C; 100 mm2; 2 h£ 20£ 40£ 60——(40 ± 1) °C; 500 mm2; 0,5 h———15-4040-100Table 8b — Hardness classes on plates - Load applied 525 N - Indentation in units of 0,1 mmHardness classes - Test conditionsIP10IP12IP30IP70(40 ± 1) °C; 100 mm2; 31min£ 10£ 1210 - 30£ 70Table 8c — Hardness classes on plates - Load applied 317 N - Indentation in units of 0,1 mmHardness classes - Test conditionsIP IIP IIIP IIIIP IV45 °C; 31,7 mm2; 1 min£ 11———35 °C; 31,7 mm2; 1 min—£ 9£ 8£ 305.2.6 Resistance to rolling wheel for screed material intended to be covered with floor coveringThe resistance to rolling wheel, for all screed materials for screeds intended to be covered with floor covering, maybe declared by the manufacturer. The resistance to rolling wheel shall be determined in accordance withprEN 13892-7.The resistance to rolling wheel is designated by
"RWFC" (for Rolling Wheel Floor Covering) followed by the rollingwheel load in N, in accordance with Table 9.Table 9 — Resistance to rolling wheel classes for all screed materialsClassRWFC150RWFC250RWFC350RWFC450RWFC550Load in N1502503504505505.2.7 Setting timeA manufacturer of cementitious or calcium sulfate screed material may declare the setting time of the screedmaterial determined in accordance with prEN 13454-2.5.2.8 Shrinkage and swellingA manufacturer of a screed material, other than mastic asphalt, may declare the shrinkage value and swelling valueof the screed material, in mm/m, determined in accordance with prEN 13454-2 or in accordance with prEN 13872where the product is intended to be applied at a thickness less than 10 mm.
EN 13813:2002 (E)125.2.9 ConsistencyA manufacturer of a screed material, other than mastic asphalt, may declare the consistency, in mm, determined inaccordance with prEN 13454-2; where the consistency value is greater than 300 mm, it may be determined inaccordance with EN 12706.5.2.10 pH-valueFor calcium sulfate screed material the pH value shall be greater than or equal to 7 when determined inaccordance with prEN 13454-2, for cementitious and magnesite screed material a manufacturer may declare thepH value in accordance with prEN 13454-2.5.2.11 Modulus of elasticity in flexureThe modulus of elasticity in flexure of a screed material other than mastic asphalt may be declared by themanufacturer and designated by "E" (for Elasticity) followed by the modulus of elasticity in kN/mm2, in accordancewith Table 10. The modulus of elasticity shall be determined in accordance with EN ISO 178.Table 10 — Modulus of elasticity in flexure classes for cementitious, calcium sulfate, magnesite andsynthetic resin screed materialClassE1E2E5E10E15E20higher in multiples of 5Modulus ofelasticity in flexurein kN/mm212510152025 – 30 – etc5.2.12 Bond strengthThe bond strength for synthetic resin screed materials shall be declared by the manufacturer, and as an option maybe declared for cementitious, calcium sulfate and magnesite screed materials. The bond strength shall bedetermined in accordance with prEN 13892-8.The bond strength shall be designated by "B" (for B
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