SIST EN 14647:2005
(Main)Calcium aluminate cement - Composition, specifications and conformity criteria
Calcium aluminate cement - Composition, specifications and conformity criteria
This European Standardt gives a general definition of calcium aluminate cement and its composition. It includes requirements for the mechanical, physical and chemical properties and also states the conformity criteria and the related rules.
Calcium aluminate cement used as a constituent material of formulated mixes for specific applications (e.g. dry mixes) is outside the scope of this European Standard.
NOTE Guidance for the correct use of calcium aluminate cement in concrete and mortars is given in Annex A.
Tonerdezement - Zusammensetzung, Anforderungen und Konformitätskriterien
Diese Europäische Norm enthält eine allgemeine Definition des Tonerdezements und seiner Zusammensetzung.
Sie enthält Anforderungen an die mechanischen, physikalischen und chemischen Eigenschaften sowie
Festlegungen bezüglich der Konformitätskriterien und die zugehörigen Regeln.
Tonerdezement, der als Bestandteil von Rezepturen für besondere Anwendungen (z. B. Trockenmischungen)
verwendet wird, ist nicht Gegenstand dieser Europäischen Norm.
ANMERKUNG Hinweise für eine fachgerechte Verwendung von Tonerdezement in Beton und Mörtel sind in Anhang A
(informativ) enthalten.
Ciment d'aluminates de calcium - Composition, spécifications et criteres de conformité
La présente Norme européenne donne une définition générale du ciment d'aluminates de calcium et de sa composition. Il fixe les exigences relatives aux propriétés mécaniques, physiques et chimiques, et établit également les criteres de conformité ainsi que les regles correspondantes.
La présente Norme européenne ne couvre pas le ciment d'aluminates de calcium lorsqu'il est utilisé comme constituant de préparations formulées pour des applications spécifiques (comme par exemple les mélanges secs).
NOTE L'Annexe A fournit des lignes directrices pour l'utilisation correcte du ciment d'aluminates de calcium dans le béton et les mortiers.
Kalcijev aluminatni cement – Sestava, zahteve in merila skladnosti
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Calcium aluminate cement - Composition, specifications and conformity criteriaKalcijev aluminatni cement – Sestava, zahteve in merila skladnostiCiment d'aluminates de calcium - Composition, spécifications et criteres de conformitéTonerdezement - Zusammensetzung, Anforderungen und KonformitätskriterienTa slovenski standard je istoveten z:EN 14647:2005SIST EN 14647:2005en91.100.10ICS:SLOVENSKI
STANDARDSIST EN 14647:200501-december-2005
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 14647October 2005ICS 91.100.10 English VersionCalcium aluminate cement - Composition, specifications andconformity criteriaCiment d'aluminates de calcium - Composition,spécifications et critères de conformitéTonerdezement - Zusammensetzung, Anforderungen undKonformitätskriterienThis European Standard was approved by CEN on 22 July 2005.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 Central Secretariat 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 Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2005 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 14647:2005: E
EN 14647:2005 (E) 2 Contents Page Foreword.3 Introduction.4 1 Scope.5 2 Normative references.5 3 Terms and definitions.5 4 Calcium aluminate cement (CAC).6 5 Constituents.6 5.1 Calcium aluminate cement clinker.6 5.2 Grinding aids.7 6 Cement type and composition.7 7 Mechanical, physical and chemical requirements.7 7.1 Compressive strength.7 7.2 Initial setting time.7 7.3 Chemical requirements.8 8 Standard designation.8 9 Conformity criteria.8 9.1 General requirements.8 9.2 Conformity criteria and evaluation procedure.9 Annex A (informative)
Guidance for the use of calcium aluminate cement in concrete and mortar.14 A.1 Introduction.14 A.2 Specific characteristics of calcium aluminate cement.15 A.3 Hydraulic properties.16 A.4 Production of calcium aluminate cement concrete.20 A.5 Admixtures.21 A.6 Use of calcium aluminate cement in particular conditions.22 A.7 Rapid test to estimate the minimum long term strength of calcium aluminate cement concretes.23 A.8 Bibliography.24 Annex B (informative)
Water-soluble hexavalent chromium.25 Annex ZA (informative)
Clauses of this European Standard addressing the provisions of EU Construction Products Directive.26 ZA.1 Scope and relevant characteristics.26 ZA.2 Procedure for the attestation of conformity of products.28 ZA.3 CE marking and labelling.30 Bibliography.33
EN 14647:2005 (E) 3 Foreword This European Standard (EN 14647:2005) has been prepared by Technical Committee CEN/TC 51 “Cement and building limes”, the secretariat of which is held by IBN/BIN. 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 April 2006, and conflicting national standards shall be withdrawn at the latest by July 2007. This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free 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 European Standard. The requirements in this European Standard are based on the results of tests on cement in accordance with EN 196-1, -2, -3, -5, -6, and –7. The scheme for the evaluation of conformity of calcium aluminate cement is specified in EN 197-2. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EN 14647:2005 (E) 4 Introduction Calcium aluminate cement was developed during the latter stages of the nineteenth century as an alternative to calcium silicate cement (Portland cement) to prevent structural elements from serious sulfate attack. Whilst it is suitable for sulfate resistance it was also found to be exceptionally rapid hardening and resistant to high temperatures. It was this rapid hardening property that led to more general use particularly in precast applications. The hydration of calcium aluminate cement is substantially different from that of Portland cement in that the calcium aluminate hydrates formed depend upon the temperature at which hydration takes place. At low and normal temperatures (less than 40 °C) the hydration process leads to a temporarily high strength. This situation can last for several days or many years, depending mainly upon temperature and humidity, before stable long term hydrates develop. This process, known as conversion, is inevitable. It is the result of a phase transition in the hardened paste of cement and is accompanied by a decrease in strength to a minimum stable level. Misunderstanding of this conversion process and unsuccessful attempts to maintain the temporary high strength led to failures in several countries during the 1960's and 1970's. In one of the reported failures, the strength of concrete, made with calcium aluminate cement, was reduced even further as a result of chemical attack. Chemical resistance is reduced when porosity of concrete is increased by a high water/cement ratio and conversion. As a result, calcium aluminate cement has been, and remains, excluded from the list of cements permitted in structural concretes in some countries. Guidance for the correct use of this cement is given in Annex A. It includes a method which allows the long term strength, i.e. after conversion, to be predicted. NOTE 1 Calcium aluminate cement can be produced in a blastfurnace, using a process of reductive fusion (a method used in Germany until the 1980's) but the cement will have a high level of sulfides which would exclude it from this European Standard. NOTE 2 Calcium aluminate cement has previously been known by several alternative names in different countries, e.g. — high alumina cement; — aluminous cement; — high alumina melted cement.
EN 14647:2005 (E) 5 1 Scope This European Standard gives a general definition of calcium aluminate cement and its composition. It includes requirements for the mechanical, physical and chemical properties and also states the conformity criteria and the related rules. Calcium aluminate cement used as a constituent material of formulated mixes for specific applications (e.g. dry mixes) is outside the scope of this European Standard. NOTE Guidance for the correct use of calcium aluminate cement in concrete and mortars is given in Annex A. 2 Normative references The following referenced documents are indispensable for the application of this European Standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 197-2:2000, Cement — Part 2: Conformity evaluation EN 196-1, Methods of testing cement — Part 1: Determination of strength EN 196-2, Methods of testing cement — Part 2: Chemical analysis of cement EN 196-3, Methods of testing cement — Part 3: Determination of setting time and soundness EN 196-7, Methods of testing cement — Part 7: Methods of taking and preparing samples of cement 3 Terms and definitions For the purposes of this European Standard, the following terms and definitions apply. 3.1 autocontrol testing continual testing by the manufacturer of cement spot samples taken at the point(s) of release from the factory/depot 3.2 control period period of production and dispatch identified for the evaluation of the autocontrol test results 3.3 characteristic value value of a required property outside of which lies a specified percentage, the percentile Pk of all the values of the population 3.4 specified characteristic value characteristic value of a mechanical, physical or chemical property which in the case of an upper limit is not to be exceeded or in the case of a lower limit is, as a minimum, to be reached 3.5 single result limit values value of a mechanical, physical or chemical property which - for any single test result - in the case of an upper limit is not to be exceeded or in the case of a lower limit is, as a minimum, to be reached
EN 14647:2005 (E) 6 3.6 allowable probability of acceptance CR for a given sampling plan, the allowed probability of acceptance of cement with a characteristic value outside the specified characteristic value 3.7 sampling plan specific plan which states the (statistical) sample size(s) to be used, the percentile Pk and the allowable probability of acceptance CR 3.8 spot sample sample taken at the same time and from one and the same place, relating to the intended tests. It can be obtained by combining one or more immediately consecutive increments (see EN 196-7) 4 Calcium aluminate cement (CAC) Calcium aluminate cement is a hydraulic binder i.e. it is a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions and processes and which, after the hydration process has produced stable hydrated phases after conversion, retains its strength and stability. Cement conforming to this European Standard shall, when appropriately batched and mixed with aggregate and water, be capable of producing concrete or mortar which retains its workability for a sufficient time and shall after defined periods attain specified strength levels and also possess long term volume stability. The main component is monocalcium aluminate (CaO·Al2O3). Other mineralogical compounds include calcium alumino-ferrites, dicalcium silicate, and calcium silico-aluminate or gehlenite. Hydraulic hardening of calcium aluminate cement is primarily due to the hydration of monocalcium aluminate, but other chemical compounds may also participate in the hardening process. Calcium aluminate cement consists of individual small grains of calcium aluminate clinker statistically homogeneous in composition resulting from quality assured production and material handling processes. The link between these production and material handling processes and the conformity of calcium aluminate cement to this European Standard is elaborated in EN 197-2. 5 Constituents 5.1 Calcium aluminate cement clinker Calcium aluminate cement clinker is produced by fusing or sintering a precisely specified mixture of aluminous and calcareous material.
EN 14647:2005 (E) 7 5.2 Grinding aids Grinding aids are chemical substances or proprietary products added to the calcium aluminate cement clinker during the grinding process to enhance the efficiency of the process. The total quantity of grinding aid on a dry basis shall not exceed 0,2 % by mass of the cement. Grinding aids shall not promote corrosion of reinforcement or impair the properties of the cement or of concrete and mortar made with the cement. 6 Cement type and composition Except for grinding aids that may be used in manufacture, as stated in 5.2, calcium aluminate cement shall be composed of only calcium aluminate cement clinker. 7 Mechanical, physical and chemical requirements 7.1 Compressive strength The compressive strength of calcium aluminate cement shall not be less than 18,0 MPa at 6 h and 40,0 MPa at 24 h, when tested in accordance with EN 196-1 at 6 h and 24 h (see also Table 1) under the following conditions: - composition of the mortar shall be 1 350 g of CEN Standard sand, 500 g of calcium aluminate cement, and 200 g of water, i.e. a water/cement ratio of 0,40; - all specimens shall be demoulded after 6 h ± 15 min; - specimens to be tested at 6 h shall be tested immediately after demoulding; - specimens to be tested at 24 h shall be stored in water after demoulding, and tested at
24 h ± 15 min. 7.2 Initial setting time The initial setting time, determined in accordance with EN 196-3, shall not be less than 90 min (see also Table 1). Other methods than EN 196-3 may be used provided that they give results correlated and equivalent to those obtained with EN 196-3. Table 1 — Mechanical and physical requirements given as characteristic values Compressive strength (MPa) Initial setting time at 6 h at 24 h (min) ≥ 18,0 ≥ 40,0 ≥ 90 NOTE 1 Calcium aluminate cements are very rapid hardening so 28 day strengths at 20 °C are not relevant. It is traditional to test conformity for strength at these early ages. NOTE 2 Values obtained from these tests should not be used for design purposes for concrete. An explanation of the strength development of calcium aluminate cement concretes and a method for predicting their minimum long term strength is given in Annex A.
EN 14647:2005 (E) 8 7.3 Chemical requirements The properties of calcium aluminate cement shall conform to the requirements listed in Table 2 when tested in accordance with the European Standard referred to. NOTE Some European countries have regulations for the content of water-soluble hexavalent chromium (see Annex B). Table 2 — Chemical requirements given as characteristic values Property Test reference Requirements a Alumina content (as Al2O3) EN 196-2 35 % ≤ Al2O3 ≤ 58 % Sulfide content (as S-2) EN 196-2 ≤ 0,10 % Chloride content EN 196-2 ≤ 0,10 % Alkali content b EN 196-2 ≤ 0,4 % Sulfate content (as SO3) EN 196-2 ≤ 0,5 % a Requirements are given as percentage by mass of the final cement. b Expressed as Na2O equivalent (Na2O + 0,658 K2O).
8 Standard designation Calcium aluminate cement conforming to this European Standard shall be identified by: Calcium aluminate cement EN 14647 CAC The notation CAC covers definition (Clause 4), composition (Clauses 5 and 6) and requirements (Clauses 7 and 9). NOTE 1 European cements are normally identified by type and a figure indicating the strength class. With calcium aluminate cement, care must be taken when assessing strength, due to the difference that is seen in cement hydration and hence strength development. Consequently it is normal that the designation of calcium aluminate cement does not refer to a strength class. NOTE 2 A more extensive description of the strength development of calcium aluminate cement in concrete and mortar is given in Annex A. 9 Conformity criteria 9.1 General requirements Conformity of calcium aluminate cement to this European Standard shall be continually evaluated on the basis of testing of spot samples. The properties, test methods and the minimum testing frequencies for the autocontrol testing by the manufacturer are specified in Table 3. Concerning testing frequencies for cement not being dispatched continuously and other details, see EN 197-2. For certification of conformity by an approved certification body, conformity of cement with this European Standard shall be evaluated in accordance with EN 197-2. NOTE This European Standard does not deal with acceptance inspection at delivery.
EN 14647:2005 (E) 9 Table 3 — Properties and test methods and minimum testing frequencies for the autocontrol testing by the manufacturer and the statistical assessment procedure
Minimum testing Statistical assessment procedure Property Test frequency Inspection by
method a b Routine Initial variables d attributs e
situation period
Strength
EN 196-1 2/week 4/week x
Initial setting time EN 196-3 2/week 4/week x
Alumina content EN 196-2 2/month 1/week
x Chloride content EN 196-2 2/month c 1/week
x Alkali content EN 196-2 1/month 1/week
x Sulfate content EN 196-2 1/month 1/week
x Sulfide content EN 196-2 1/month 1/week
x a Where allowed in the relevant part of EN 196, other methods than those indicated may be used provided they give results correlated and equivalent to those obtained with the reference method. b Methods used to take and prepare samples shall be in accordance with EN 196-7. c When none of the test results within a period of 12 months exceeds 50 % of the characteristic value, the frequency may be reduced to one per month. d If the data are not normally distributed, then the method of assessment may be decided on a case by case basis. e If the number of samples is at least one per week during the control period, the assessment may be made by variables.
9.2 Conformity criteria and evaluation procedure 9.2.1 General Conformity of calcium aluminate cement with this European Standard is assumed if the conformity criteria specified in 9.2.2 and 9.2.3 are met. Conformity shall be evaluated on the basis of continual sampling using spot samples taken at the point of release and on the basis of the test results obtained on all autocontrol samples taken during the control period. 9.2.2 Statistical conformity criteria 9.2.2.1 General Conformity shall be formulated in terms of a statistical criterion based on: specified characteristic values for mechanical, physical and chemical properties as given in 7.1, 7.2 and 7.3; percentile Pk, on which the specified characteristic value is based, as given in Table 4; allowable probability of acceptance CR, as given in Table 4.
EN 14647:2005 (E) 10
Table 4 — Required values for Pk and CR
Mechanical requirements Physical and
6 h strength 24 h strength chemical
(Lower limit) (Lower limit) requirements The percentile Pk on which the
characteristic 10 % 5 % 10 % value is based
Allowable probability
of acceptance CR 5 %
NOTE Conformity evaluation by a procedure based on a finite number of test results can only produce an approximate value for the proportion of results outside the specified characteristic value in a population. The larger the sample size (number of test results), the better the approximation. The selected probability of acceptance CR controls the degree of approximation by the sampling plan. Conformity with the requirements of this European Standard shall be verified either by variables or by attributes as described in 9.2.2.2 and 9.2.2.3 as specified in Table 3. The control period shall be 12 months. 9.2.2.2 Inspection by variables For this inspection the test results are assumed to be normally distributed. Conformity is verified when the following Equation(s) (1) and (2), as relevant, are satisfied: x
-
kA
x
s ≥
L (1) and x +
kA
x
s ≤
U (2) where x is the arithmetic mean of the totality of the autocontrol test results in the control period;
s is the standard deviation of the totality of the autocontrol test results in the control period;
kA is the acceptability constant;
L is the specified lower limit given in Tables 1 and 2 referred to in 7.1 and 7.3;
U is the specified upper limit given in Table 2 referred to in 7.3. The acceptability constant kA depends on the percentile PK on which the characteristic value is based, on the allowable probability of acceptance CR and the number n of the test results. Values of kA are listed in Table 5.
EN 14647:2005 (E) 11 Table 5 — Acceptability constant kA
kA a Number of test for PK = 5 % for PK = 10 % results n (24 h strength, lower limit) (other properties) 20 to 21 2,40 1,93 22 to 23 2,35 1,89 24 to 25 2,31 1,85 26 to 27 2,27 1,82 28 to 29 2,24 1,80 30 to 34 2,22 1,78 35 to 39 2,17 1,73 40 to 44 2,13 1,70 45 to 49 2,09 1,67 50 to 59 2,07 1,65 60 to 69 2,02 1,61 70 to 79 1,99 1,58 80 to 89 1,97 1,56 90 to 99 1,94 1,54 100 to 149 1,93 1,53 150 to 199 1,87 1,48 200 to 299 1,84 1,45 300 to 399 1,80 1,42 > 400 1,78 1,40 NOTE Values given in this table are valid for CR = 5 %. a Values of
kA
valid for intermediate values of n may also be used.
9.2.2.3 Inspection by attributes The number cD of test results outside the characteristic value shall be counted and compared with an acceptable number cA, calculated from the number n of autocontrol test results and the percentile PK as specified in Table 6. Conformity is verified when the Equation (3) is satisfied: cD
≤
cA (3)
EN 14647:2005 (E) 12 The value of cA depends on the percentile PK on which the characteristic value is based, on the allowable probability of acceptance CR and on a number n of the test results. Values of cA are listed in Table 6. Table 6 — Values of cA Number of test results n a cA for PK = 10 % 20 to 39 0 40 to 54 1 55 to 69 2 70 to 84 3 85 to 99 4 100 to 109 5 110 to 123 6 124 to 136 7 NOTE
Values given in this table are valid for CR = 5 %. a If the number of test results is n < 20 (for PK = 10 %) a statistically based conformity criterion is not possible. Despite this, a criterion of cA = 0 shall be used in cases where n < 20.
9.2.3 Single result conformity criteria In addition to the statistical conformity criteria, conformity of test results to the requirements of this document requires that it shall be verified that each test result remains within the single result limit values specified in Table 7.
EN 14647:2005 (E) 13 Table 7 — Limit values for single results Property Limit values for single results
Strength (MPa) 6 h 15,0
lower limit value 24 h 38,0
Initial setting time (min)
lower limit value
75
Alumina content (%) a
lower limit value 33
upper limit value 60
Sulfide content (%) a
upper limit value 0,15
Chloride content (%) a
upper limit value 0,10
Alkali content (%) a b
upper limit value 0,5
Sulfate content (%) a
upper limit value 0,6 a By mass of the final cement. b Expressed as Na2O equivalent (Na2O + 0,658 K2O).
EN 14647:2005 (E) 14 Annex A
(informative)
Guidance for the use of calcium aluminate cement in concrete and mortar A.1 Introduction Calcium aluminate cement that is produced in conformity to this European Standard can be used, provided it is permitted by national regulations, in construction applications that require the special properties of concretes and mortars made with this cement. The purpose of this annex is to provide guidance for the use of calcium aluminate cement in concrete and mortar. NOTE Applying this annex A does not imply compliance with provisions valid in the place of use of the CAC concrete. To ensure that requirements of stability and durability are met, it is essential to take into account the conversion phenomenon. For design purpose, only strength after conversion shall be considered.
As for any conventional concrete, final performance depends on water/cement ratio, aggregate type and grading, mix proportions, production and placement. Special care has to be taken on the impact of water/cement ratio on strength level after conversion.
For historical reasons, for structural use of calcium aluminate cement based concrete, a total water/cement ratio not greater than 0,40 (corresponding to an effective water/cement ratio of about 0,33 to 0,36) is recommended to achieve satisfactory converted strength. At this level of water/cement ratio, when admixture is not used, the minimum cement content to ensure a paste volume compatible with a good workability is 400 kg/m3. However, any mix design should be chosen in order to meet strength and durability requirements for the intended application. For non-structural applications, it is possible to obtain appropriate converted strength and durability with a total water/cement ratio greater than 0,40. For any use of calcium aluminate cement based concrete, converted strength shall always be estimated with appropriate procedure to ensure conformity with design specifications (see A.7). Furthermore proper attention should also be given to durability of concrete. Calcium aluminate cement is not intended to be used as a general replacement for the common cements in EN 197-1. Its use will be in specialised areas which stem from its special properties: - normal setting time but rapid hardening; - resistance to temperature, abrasion and chemical attack; - normal hardening rate in cold weather (see A.6.1).
If concrete is made in accordance with the principles given in this annex, it does not imply any conformity to national or international codes for design.
EN 14647:2005 (E) 15 A.2 Specific characteristics of calcium aluminate cement A.2.1 Hydration of calcium aluminate cement As the main component of calcium aluminate cement is monocalcium aluminate, its hydration produces calcium aluminate hydrates and insoluble alumina trihydrate without liberating calcium hydroxide (portlandite). This means that CAC concrete has good resistance to many aggressive agents (see A.3.5 and A.6.3). A.2.2 Nature of the hydrates and conversion process The following customary abbreviations are used: A = Al2O3; C=CaO; H=H2O. CAC hydration always starts with the formation of the metastable hexagonal hydrates CAH10 and C2AH8. CAH10 and C2AH8 change with time to form the stable cubic hydrate, C3AH6 and gibbsite AH3, following the reactions shown below: 3 CAH10 Æ C3AH6 + 2 AH3 + 18 H; 3 C2AH8Æ 2 C3AH6 + AH3 + 9 H. This evolution, which is known as conversion is inevitable and irreversible, but the minimum strength level after conversion can be estimated. Complete conversion may take several years at 20 °C, but accelerates rapidly as temperature increases, as shown in Figure A.1, which gives two examples of the effect of temperature on the time taken to reach minimum strength after conversion. For example when concrete temperature is maintained above 80 °C, stable hydrates can be formed within only a f
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