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GENERAL PURPOSE BLENDED CEMENT (SLAG) |
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Type GB (Slag) Cement is a general purpose blended cement containing a nominal 30% ground blast furnace slag.
Sunstate Cement manufactures Type GB by grinding Portland cement clinker with granulated iron blast furnace slag selected for its particular mineral and chemical qualities. Type GB (Slag) is a versatile alternative to Type GP Portland cement and can replace it in most applications. The 28 day compressive strength performance is similar to Type GP, but it provides advantages in higher later age strength. Some adjustment to concrete mix design may be necessary. Less water will be required to achieve the same consistency as concrete using Type GP cement. Type GB (Slag) can also assist in controlling bleed rates where well graded fine sand is not available. Where early strengths are required concrete mixes should be modified to give the desired result. Strength development. The strength development of Type GB is primarily dependant on water -- cement ratio. The following graph gives indicative data on the strength development of concrete produced with Type GB.
Effect of excess water. Use only the minimum amount of water to mix and place concrete. The following graph shows the reduction in compressive strength of concrete with increased water addition.
The porosity of concrete made with excess water is also increased resulting in a structure with less resistance to chemical attack. Other factors which affect the strength and durability of concrete containing Type GB manufactured by Sunstate Cement Ltd are:
CONCRETE MIX DESIGN The cement content for each grade of concrete will be dependent on the nominated target strengths. AS 3600 "Concrete Structures" recommends minimum strengths to achieve adequate concrete durability for various exposure conditions. AS 1379 "The specification and manufacture of concrete" is the relevant standard for the production and ordering of concrete. For site mixed concrete the following mix proportions are suggested. Mix Proportions by Volume
Mixing. AS 1379 gives requirements for material quality and mixing pre-mix concrete. Recycled water may be used only where testing can demonstrate compliance with relevant section of AS 1379. Dissolved salts and organic matter may adversely affect the strength, durability and appearance of the concrete Sand contaminated by the above will have a similar effect.
Curing. A minimum curing period of seven days is recommended for all exposure classifications. Concrete should be maintained in a moist condition where practicable. Water sprays, wet sand or moisture-retaining techniques; such as polyethylene sheets or curing compounds have been used successfully. Curing should begin as soon as the selected technique allows. For normal class concrete, curing can produce a compressive strength 80 to 100% greater than concrete not subjected to curing. Water application or moisture retaining curing is more suitable for lower grades of concrete. For concrete strengths of 40 MPa and above, curing is equally important. However, the type of curing mechanism is believed to be less critical. Curing can also affect other concrete properties including:
Variations in the duration of curing or uses of different curing methods may effect the initial colour of concrete. The following table provides and example of some typical cement properties of Type GB (Slag) manufactured by Sunstate Cement Ltd.
Type GB (Slag) may be blended with other cements complying with AS 3972. It is also suitable to blend with flyash complying with AS 3582.1. Type GB (Slag) is compatible with admixtures complying with AS 1478. WORKING INSTRUCTIONS Storage. Contact with air and moisture will cause hydration of the cement and alter the cement properties. The ‘shelf life’ of Type GB is therefore dependent on the storage conditions. It is recommended that Type GB be retested prior to use if the age of the cement exceeds three months. Handling. A Material Safety Data Sheet can be obtained here.
Concrete Properties |
Concrete Mix | Mix Proportions |
Cement Properties |
Compatibility |
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It complies with AS 3972 Type GB.
Placing. AS 3600 gives requirements for
handling, placing and finishing concrete. Minimum cover to reinforcement is 20
mm for lowest exposure classification. The cover will need to be increased where
concrete is cast against the ground, for fire resistance and for exposure
classification other than A1.