CCANZ - Cements

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Cements

Types of Cement and Their Use

Portland & Blended Cements

Hydraulic cements produced in Australia and New Zealand fall broadly into two categories: Portland cements and blended cements.

The latter are mixtures of Portland cement with other materials which either possess cementitious properties of their own, e.g. ground granulated iron blastfurnace slags, New Zealand fly ashes, or which are pozzolanic in nature, i.e. they react with lime in the presence of water to form cementitious compounds, e.g. fly ash and silica fume.

Portland & Blended Cements

Hydraulic cements produced in Australia and New Zealand fall broadly into two categories: Portland cements and blended cements.

The latter are mixtures of Portland cement with other materials which either possess cementitious properties of their own, e.g. ground granulated iron blastfurnace slags, New Zealand fly ashes, or which are pozzolanic in nature, i.e. they react with lime in the presence of water to form cementitious compounds, e.g. fly ash and silica fume.

Portland and blended cements are manufactured in Australia to comply with the requirements of AS 3972 Portland and Blended Cements and in New Zealand to NZS 3122.

A number of different types of cements are covered by these Standards. A summary of their physical and chemical properties specified in both Standards is given in Table 1. AS 3972 and NZS 3122 are performance based specifications in which Portland and blended cements are defined in terms of their performance characteristics. As the raw materials used to produce Portland and blended cements can vary widely from locality to locality, the chemical composition of cements can also vary quite widely.

Nevertheless, with modern technology, from these diverse materials it is possible to produce cements which have similar physical characteristics. Hence, AS 3972 and NZS 3122 specify only those restrictions on chemical composition which are necessary to ensure satisfactory performance, e.g. upper limits on the MgO and SO contents to guard against excessive long-term volumetric expansion of the hydrated cement paste. Other special cements that are produced in New Zealand to NZS 3123 and NZS 3125 are based on Portland cement blends with pozzolan and limestone respectively.

AS 3972/NZS 3122 requirements*

Cement Types

GP GB HE LH SL SR

Chemical Limitations

Loss on ignition reported if required - no limit is specified

Sulphuric anhydride SO (max)% 3.5 3.5 3.5 3.5 3.5

MgO Portland cement clinker shall contain less than 4.5%

Physical Properties

Setting time

minimum (mins) 45 45 45 45 45

maximum (hrs) 6 10 6 10 10

Soundness maximum (mm) 5 5 5 5 5

Compressive strength minimum (MPa)

3 days - - 25 - -

7 days 35 20 40 10 -

28 days 45 35 - 30 -

3

3

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Peak temperature rise maximum °(C) - - - 23 -

Drying Shrinkage maximum (microstrain)

28-day - - - - 750

Sulfate expansion maximum (microstrain)

16-week - - - - -

* Determined in accordance with the methods set out in AS 2350.

Table 1: Summary of AS 3972/NZS 3122 requirements.

General Purpose Portland Cement - Type GP

Portland cements complying with AS 3972 or NZS 3122 may contain up to 10% mineral additions. Mineral additions are defined as being selected fly ash, granulated iron blast-furnace slag, limestone, amorphous silica, pozzolan, titanium dioxide, or combinations of these materials. Fly ash and slag are to comply with the requirements of AS 3582.1 and AS 3582.2 respectively. Portland cement is defined in AS 3972 and NZS 3122 as a hydraulic cement which is manufactured as a homogenous product by grinding together Portland cement clinker and calcium sulphate, and which at the discretion of the cement manufacturer may contain up to 10% of mineral additions, but limiting the amorphous silica to <5%. General purpose Portland cement is intended for use in most forms of concrete construction and should be specified where the special properties of the other types, such as low heat of hydration, are not required. As the raw materials used to produce Portland cements vary widely from location to location, Type GP cements may have a range of chemical compositions. The restrictions placed on the chemical and physical properties of Type GP cement by AS 3972 and NZS 3122 are those necessary to ensure satisfactory performance as a general purpose cement. NZS 3122 now specifies the 0.6% alkali level to restrict the total alkali content and assist in reducing the risk of damage from Alkali Silica Reaction when the cement is used in the limited areas of New Zealand where there are reactive aggregates.

General Purpose Blended Cement - Type GB

Blended cement is defined in AS 3972 and NZS 3122 as a hydraulic cement containing Portland cement and a quantity greater than 10% of fly ash or slag or both and/or up to 10% amorphous silica. Fly ash, slag and amorphous silica are to comply with the requirements of the relevant parts of AS 3582. General purpose blended cement is intended for use in most forms of concrete construction where the special properties of other cement types are not required. By varying the proportions of Portland cement and fly ash, slag, and amorphous silica in blended cement it is possible to produce cements with a fairly wide range of characteristics. In practice, the difference in properties between Types GP and GB may not be great, as both are formulated to be used in general building construction. Whilst the minimum strengths specified for Type GB cement in AS 3972 and NZS 3122 are lower than those for Type GP, it is not uncommon for their ultimate strengths to equal or exceed those of Type GP cement, provided moisture is available for a sufficient length of time.

High Early Strength Cement - Type HE

Type HE cement develops strength more rapidly than Type GP or Type GB cements. High early strength cement lends itself to applications where rapid strength development is required, e.g. when formwork is to be removed early for reuse. Rapid strength development is usually accompanied by a higher rate of heat evolution. Hence, Type HE cementshould not be used in thick concrete sections or in mass construction. On the other hand, its use for construction under cold weather conditions is beneficial. NZS 3122 now specifies the 0.6% alkali level to restrict the total alkali content and assist in reducing the risk of damage from Alkali Silica Reaction when the cement is used in the limited areas of New Zealand where there are reactive aggregates.

Low Heat Cement - Type LH

Type LH cement is intended for use where limitation of the heat of hydration (and hence the temperature rise in the concrete) is necessary to avoid unacceptable thermal stresses, such as in massive structures or in thick structural elements. Low heat cement may be a Portland or a blended cement provided it meets the requirements for temperature rise specified in AS 3972 and NZS 3122 Table 1. Low heat characteristics are achieved by reducing the content of the more rapidly hydrating compounds in cement or by blending with supplementary cementitious materials. This, generally, will result in a slower rate of strength development. Blended cements can have some inherent advantages in minimizing heat evolution because of their generally lower rates of strength gain. However, the ultimate strength of Type LH cement may be equivalent to, or higher than, that for other types of cement.

Shrinkage Limited Cement - Type SL

Within the scope of AS 3972 and NZS 3122, a cement characterized in terms of its shrinkage performance was required to reflect/cover the existing practice in some areas and applications. Type SL cement is intended for use where emphasis is placed on drying shrinkage and crack control in concrete structures (e.g. road pavements). Type SL cement may be a Portland or a blended cement provided it meets the drying shrinkage limit specified in AS 3972 and NZS 3122.

Sulphate Resisting Cement - Type SR

Sulfate resisting cement (Type SR) is no longer part of NZS 3122. Current New Zealand industry practice is for sulfate resisting concrete to be achieved by using Type GB cement or pozzolan and appropriate water and binder contents, compaction, and curing. If Type SR cement is required it must comply with AS 3972.

Portland Limestone Filler Cement

This cement is produced in New Zealand by intergrinding cement clinker with up to 15% by total weight of mineral limestone that has a minimum calcium carbonate content of 75%. Concretes produced from this cement generally show enhanced workability properties which is particularly useful on unformed surfaces. Some water addition savings are possible which allows for some strength adjustments. The cement is produced to comply with the provisions of NZS 3125 which also specifies limits on clay content and organic matter.

Portland Pozzolan Cement

Pozzolan has been in New Zealand in instances where a relatively low heat of hydration has been sought (e.g. as in mass concrete for hydraulic structures). The inclusion of a pozzolan has also served to inhibit harmful expansion that may result from alkali-aggregate interaction. Other characteristics of a Portland pozzolan concrete include relatively high long-



term strengths, reduced permeability, and in certain cases relatively low strengths at early ages. The properties of fresh concrete may also be modified, such as increased cohesiveness and resistance to segregation. The cement which could be regarded as a GB cement does have its own specification contained in NZS 3123.

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