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Cementitious Materials for Concrete: Standards, selection and properties
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Cementitious Materials for Concrete:
Standards, selection and properties
Portland cement extenders SANS 1491: Part 1 - Ground granulated blast-furnace slag
Cementitious materials for concrete are fine mineral powders. When these materials are mixed with water, they react chemically to form a strong rigid mass that binds aggregate particles together to make concrete. The cementitious materials dealt with in this leaflet are all based on portland cement and many contain a cement extender. This publication gives information on the standards that apply in South Africa to cementitious materials for concrete; provides guidance on the selection of cementitious materials for various applications; includes graphs of strength performance; and discusses, briefly, the manufacture and properties of cementitious materials and fillers. The effect of cementitious materials on dimensional stability of hardened concrete is outside the scope of this publication. Note: Masonry cements that comply with SANS 50413 are not included in this leaflet because they are not intended for use in concrete. The national foreword of this standard reads: This part of SANS 50413 gives the definition and composition of masonry cements as commonly used in Europe for bricklaying, blocklaying, for rendering and plastering only, and not for concrete. Users are therefore cautioned to use the cements only for their intended purpose.
SANS 1491: Part 2 - Fly ash SANS 1491: Part 3 - Silica fume
These standards are discussed below.
2.1 SANS 50197-1
The standard specifies a number of properties and performance criteria. Composition and strength are required to be displayed by the manufacturer on the packaging of each cement produced.
The standard specifies composition of cements according to the proportion of constituents, ie portland cement, extenders and fillers, as shown in Table 2 (overleaf). As can be seen from Table 2, the standard permits many different combinations of composition. In practice, however, the manufacturers are constrained by what is technically and economically feasible. The number of combinations that are currently being produced in South Africa is fewer than the number permitted by the standard. For the performance of a particular cement users should consult the the revelant producer for these details. Helpline numbers are given in section 4.
2.1.2 Compressive strength requirements
The standard specifies strengths which are determined in accordance with SANS 50196-1 Methods of testing cement. Part 1: Determination of strength; using a water:cement ratio of 0,5. (The method is not the same as the cube test used for concrete.) Strengths are shown in Table 1. Note that strengths must clear an early-age (2 or 7 days) hurdle; classes 32,5 and 42,5 must fall within a window at 28 days.
2. Standards applicable to concrete
Cementitious materials for concrete, available in South Africa, include common cements and portland cement extenders. Applicable standards are: Common cements SANS 50197-1 - Cement - Part 1: Composition, specifications and conformity criteria for common cements Note that it is illegal to sell cement in South Africa if it does not have the SABS mark indicating its compliance with the requirements of the standard.
SANS 50197-1 lists other physical and chemical requirements with which cements must comply. These are monitored by the manufacturer and compliance is confirmed by external audit control sample testing. Details can be found in SANS 50197-2.
Table 1: Compressive strength requirements of SANS 50197-1
Strength	class Compressive strength, MPa Early strength	2 days	7 days	Standard strength 28 days 32,5	42,5	52,5 62,5
Table 3: Physical requirements of SANS 1491 for ground granulated blast-furnace slag (GGBS), fly ash (FA) and silica fume (SF)
Requirement	Specific surface/fineness Minimum compressive strength Minimum glass content	Soundness	GGBS	FA	SF
32,5N	-	16,0 32,5R	10,0	42,5N	10,0	42,5R	20,0	52,5N	20,0	52,5R	30,0	-
Maximum water requirement Minimum reactivity
Composition, percentage by mass(a)
Table 2: Common cements: SANS 50197-1
Notation of products (types of common cement)
Clinker Blast- Silica Burnt Pozzolana Fly ash furnace fume shale natural natural sili calca slag cal- ceous reous cined P Q V W T K S D(b) 95 - 100	-	-	-	-	6 - 10	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20	21 - 35	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20	21 - 35	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20	21 - 35	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20	21 - 35	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20	21 - 35	-	-	-	-	80 - 94	6 - 20	65 - 79	21 - 35	90 - 94	80 - 94	65 - 79	80 - 94	65 - 79	80 - 94	65 - 79	65 - 79	80 - 94	65 - 79	80 - 94	65 - 79	80 - 94	65 - 79	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-
L -	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20	21 - 35	-	-
LL -	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	6 - 20
Minor addition al constit uents 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0-5 0 - 5	0-5
Portland cement	CEM I	CEM II A-S	CEM II B-S	CEM II A-D	CEM II A-P	CEM II B-P	CEM II A-Q	CEM II B-Q	CEM II A-V	CEM II B-V	CEM II B-W	CEM II A-T	CEM II B-T	CEM II A-L	CEM II B-L	CEM II A-LL	CEM II B-LL	CEM II A-M	CEM II B-M	CEM III A	CEM III B	CEM III C	CEM IV A	CEM IV B	CEM V A	CEM V B
Portland-slag cement Portland-silica fume cement	Portland	pozzolana cement Portland-fly ash CEM II cement Portland-burnt shale cement Portland	limestone cement Portland	composite cement(c) Blastfurnace CEM III cement Pozzolanic CEM IV cement(c) Composite CEM V cement(c)
CEM II A-W	80 - 94
21 - 35	0 - 5
80 - 94	65 - 79	35 - 64	36 - 65	20 - 34	66 - 80	5 - 19	81 - 95	65 - 89	45 - 64	-	-	-	-	-	-	-	-	-
6 - 20	21 - 35	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-
11 - 35	36 - 55	18 - 30	31 - 50	-	-
40 - 64	18 - 30	20 - 39	31 - 50
(a) The values in the table refer to the sum of the main and minor additional constituents. (b) The proportion of silica fume is limited to 10%. (c) In portland-composite cements CEM II A-M and CEM II B-M, in pozzolanic cements CEM IV A and CEM IV B, and in composite cements CEM V A and CEM V B, the main constituents other than clinker shall be declared by designation of the cement.
2.2 SANS 1491: Parts 1, 2 and 3
This standard defines the specific material, states the chemical and physical requirements, and specifies packing and marking, inspection and methods of test. Physical requirements that apply are summarised in Table 3.
content of a cement increases, the rate of compressive strength development at early ages is reduced. The extent of this reduction can be assessed by comparing the different performance curves. Table 4 gives guidelines for selecting cement type for various applications. Unless stated otherwise, the strength class of the common cement may be 32,5N or higher.
Cementitious materials used for concrete may be: A common cement (see Table 2) on its own.
4. Strength performance
For accurate and current details of the performance of a particular branded product, consult the technical representatives of the manufacturer. Holcim South Africa........0860-141-141 Lafarge South Africa ......(011) 257-3100 NPC................................(031) 450-4413/11 PPC. ................................0800-023-470 Holcim Silica Fume.........0860-141-141 Ash Resources. ...............(011) 886-6200 Slagment.........................(011) 864-9900
A site blend of a common cement and a cement extender, combined in the concrete mixer while the concrete is being mixed. Extenders must comply with SANS 1491 and must not be used without portland cement.
Note: As discussed in section 2.1.1, not all the cements shown in Table 2 are necessarily available in South Africa. It should also be noted that generally as the extender
Table 4: Guidelines for selecting cements for concrete
The cement is normally selected for economy. Any of the SANS 50197-1 common cements should be suitable. Site blends of CEM I cement with 50% GGBS or 30% FA have been extensively and successfully used in South Africa. A site blend of CEM I cement and about 8% SF is technically feasible but there is relatively little local experience of its use.
Conventional structural	concrete in a non-aggressive	environment
Large placements where temperature rise, due to heat Best results are likely to be achieved with cements with extender contents in excess of 50% GGBS or 30% FA. of reaction, is to be kept as low as possible. Choice of cement will depend mainly on strength requirements at early ages. High early strengths, without steam curing, will be achieved most economically with cements of strength grade 42,5R and higher and with low extender content. Cements with higher extender content are better suited to steam curing. Where there is no requirement for rapid strength gain, the choice of cement should be based on economy. Provided the elements have sufficient strength to allow handling at an early age, typically the day after casting, the choice of cement should be based on economy. Strength class should be 42,5N or higher. The inclusion of about 8% SF is common practice in this application. Other cement extenders may also be used for technical or economic benefits. Superplasticizer is an essential ingredient in high-performance concrete: the compatibility of the specific cementitious material and the superplasticizer is important.
Structural precast	Precast bricks, blocks and pavers	High-performance concrete	(High-strength concrete)
Floors, roads and pavements Concrete for these applications must develop strength rapidly enough to permit joint sawing before the concrete with sawn joints	cracks due to restrained drying shrinkage. The mature concrete must have good abrasion resistance. These properties are likely to be achieved most economically with cements with extender content not greater than 30%, and of strength grade 42,5N or higher.	Reinforced concrete in marine Research done with South African materials has shown that best results are achieved with extender contents environment	of either 50% GGBS, 10% SF, 40% GGBS + 10% SF, or 30% FA.	Concrete made with alkali-reactive aggregate	Concrete exposed to sulphate attack	The cement should contain not less than 40% GGBS, or 20% FA, or 15% SF. However, the use of SF at this high replacement level usually results in sticky concrete requiring the use of a superplasticizer.	Fortunately, this type of attack is rare in South Africa. A CEM I cements resistance to sulphate attack depends largely on its C3A content. CEM I cements with C3A contents below about 9 to 10% give markedly higher sulphate resistance than those with C3A contents above 9 to 10%. South African CEM I cements have C3A contents below 10% and therefore give relatively high sulphate resistance. International experience suggests that using high levels of GGBS in concrete will improve sulphate resistance. There are no South African data on which to base guidance to local users. The sulphate-resisting properties of concrete, made with specific materials, should therefore be investigated before a GGBS blend is specified. The inclusion of a minimum of 30% FA should improve the sulphate resistance of concrete. There are no South African data on which to base guidance on the use of SF for sulphate resistance.
5. Manufacture and properties
In this section, only materials available in South Africa are discussed.
5.1 Portland cement
Portland cement is the basis of all common cements covered by SANS 50197-1 (see Table 2) and of site blends that include a cement extender. The main raw materials used in the manufacture of portland cement are limestone and shale which are blended in specific proportions and fired at high temperatures to form cement clinker. A small quantity of gypsum is added to the cooled clinker which is then ground to a fine powder portland cement. When portland cement is mixed with water to form a paste, a reaction called hydration takes place. As a result, the paste gradually changes from a plastic state into a strong rigid solid. The hardened cement paste acts as a binder in concrete and mortar. Hydration is an exothermic reaction, ie it provides heat. The hydration of portland cement (PC) produces two main compounds:	calcium silicate hydrate (CSH) and	calcium hydroxide (lime). CSH provides most of the strength and impermeability of the hardened cement paste. Lime does not contribute to strength but its presence helps to maintain, in the pore water, a pH of about 12,5, which helps to protect the reinforcing steel against corrosion.
Because extenders do not dissolve rapidly, extremely fine extender particles act as nuclei for the formation of calcium silicate hydrate which would otherwise form only on the cement grains. This fine-filler effect brings about a denser and more homogeneous microstructure of the hardened cement paste and the aggregate-paste interfacial zones, resulting in improved strength and impermeability. The extent of the fine-filler effect depends on the content of extremely fine particles in the extender. Fine particles of filler materials, eg limestone, can also exhibit the fine-filler effect. Concrete in which part of the portland cement is replaced by an extender produces heat at a rate slower than that of a similar concrete made with portland cement only. The slower the rate of heat development, the lower the temperature rise and therefore the smaller the likelihood of thermal cracking. The manufacture and mechanism of action of portland cement extenders and limestone filler in concrete are discussed in sections 5.2.1 to 5.2.4. The effects of these materials on the properties of concrete are summarised in Table 5. Effects tend to increase with increased level of substitution. Improvements to the properties of hardened concrete, brought about by the use of extenders, can be realised only if the concrete is properly cured.
5.2.1 Ground granulated blast-furnace slag
Ground granulated blast-furnace slag (GGBS) is a byproduct of the iron-making process. The hot slag is rapidly chilled or quenched (causing it to become glassy) and ground to a fine powder. When mixed with water, GGBS hydrates to form cementing compounds consisting of calcium silicate hydrate. The rate of this hydration process is however too slow for practical construction work unless activated by an alkaline (high pH) environment. When portland cement and water are mixed, the pH of the water rapidly increases to about 12,5 which is sufficient to activate the hydration of GGBS. Even when activated by PC, GGBS hydrates more slowly than PC. The effect of GGBS on the properties of concrete depends on the properties of the portland cement, the GGBS content of the cementitious material and the fineness of the GGBS.
5.2	Portland cement extenders and fillers
Portland cement extenders and fillers are materials used with portland cement, and must never be used on their own. The main reasons for the widespread use of portland cement extenders are: Cost saving extenders are generally cheaper than portland cement. Technical benefits extenders improve impermea bility and durability of the hardened concrete; some extenders improve the properties of concrete in the fresh state. The portland cement extenders discussed below differ from each other but are all less reactive than portland cement. This property affects the rate of early-age strength gain, causes the fine-filler effect, and affects the rate of heat development due to cementing reactions. Substituting a portland cement extender for part of the portland cement in a concrete reduces the rate of strength gain at early ages. The extent of the reduction increases with increasing substitution level.
5.2.2 Fly ash
Fly ash (FA) is collected from the exhaust flow of furnaces burning finely ground coal. The finer fractions are used as a portland cement extender. Ultra-fine FA is sold as a separate product.
FA reacts with calcium hydroxide, in the presence of water, to form cementing compounds consisting of calcium silicate hydrate. This reaction is called pozzolanic and FA may be described as a synthetic pozzolan. The hydration of portland cement produces significant amounts of calcium hydroxide, which does not contribute to the strength of the hardened cement paste (see section 5.1). The combination of FA and PC is a practical means of using FA and converting calcium hydroxide to a cementing compound.
5.2.4 Limestone filler
This is limestone, finely ground but not chemically processed. When mixed with portland cement and water, finely ground limestone is chemically virtually inert (although there may be some minor reactions). Depending on its fineness, limestone may however act as a fine filler in fresh paste. Limestone may be used as a filler in common cement or as a workability improver in masonry cement. The effect of limestone on the properties of concrete or mortar depends on the specific limestone, whether a grinding aid is used in production, and the fineness of the limestone. Note: The limestone (CaCO3) used in cements complying with SANS 50197-1 is not to be confused with: building lime (hydrated or slaked lime Ca(OH)2) which is used in mortars and plasters. road lime (also hydrated or slaked lime Ca(OH)2) which is used in road material stabilisation or modification. quick lime (CaO) which is highly aggressive and is used in the metallurgical industry. agricultural lime which, although chemically similar to the limestone used for cement, has less stringent com	positional requirements. There is no Ca(OH)2 or CaO used in cements complying with SANS 50197-1.
Silica fume (SF) is the condensed vapour by-product of the ferro-silicon smelting process. SF reacts with calcium hydroxide, in the presence of water, to form cementing compounds consisting of calcium silicate hydrate. This reaction is called pozzolanic and SF may be described as a synthetic pozzolan. Because the hydration of PC produces calcium hydroxide (see section 5.1), the combination of SF and PC is a practical means of using SF and improving the cementing efficiency of PC. In addition to the chemical role of SF, it is also an effective fine filler. The extremely small SF particles in the mixing water act as nuclei for the formation of calcium silicate hydrate which would otherwise form only on the cement grains. SF will also change the microstructure of the interfacial zone. The result is a more homogeneous microstructure that has greater strength and lower permeability. (To ensure thorough dispersion and effective use of the SF, the use of plasticising admixtures is recommended.).
For Table 5: Effects of extenders and limestone filler on the properties of concrete, see overleaf.
Table 5: Effects of extenders and limestone filler on the properties of concrete
Prolongs duration, reduces total amount
Slight retardation
Ultra-fine FA increases cohesiveness
Slight improvement with some aggregates
Improves: lower water requirement for given slump Slight reduction, especially at lower temperatures
Reduces: higher water requirement for a given slump Marginal reduction of 1-day strength
Rate of early-age strength gain
Reduces, especially at lower temperatures
Response to steam curing
Pore structure of paste Density of aggregatepaste interfacial zones Impermeability of concrete
Improvement, especially with ultra-fine FA
Rate of chloride diffusion Alkaliaggregate reaction
Reduces: improves protection of embedded steel against corrosion
Prevent or retards if content is sufficient (See Table 4)
PO Box 168, Halfway House, 1685 Tel (011) 315-0300 Fax (011) 315-0584 e-mail info@cnci.org.za website http://www.cnci.org.za
Published by the Cement & Concrete Institute, Midrand, 2000, reprinted 2002, 2003, 2005, 2006. Cement & Concrete Institute
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