SUNSTATE CEMENT - General Purpose type GP Cement

GENERAL PURPOSE PORTLAND CEMENT

Type GP Cement, previously known as Type A Portland Cement, is used primarily for general and major construction projects and in concrete product applications.

It is commonly used in concrete mortars and grouts where chemical attack is not a perceived risk.

Type GP complies with AS 3972.

CONCRETE PROPERTIES
Strength development. The strength development of Type GP cement is primarily dependent on the water - cement ratio. The following graph gives indicative data on the strength development of concrete produced using Type GP cement.

Age at test
Water/cement ratio = 0.66, Cement content = 320kg/m
Slump = 80mm, Total water = 210litres/m

Note data is based on concrete mixes containing no admixture, or other cement extenders etc., e.g. fly ash, blast furnace slag. Use of such products will alter the strength development characteristics of concrete containing Type GP Cement.

Effect of excess water. Use only the minimum amount of water to mix and place concrete. The graph following shows the reduction in compressive strength of concrete with the addition of water.

Water Added
Indicative representational only. Not to be used for calulation.

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 GP are:

Concrete mix design (including admixtures)
Temperature (ambient and materials)
Entrained air content
Compaction
Curing

CONCRETE MIX DESIGN
The cement content 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.

MIX PROPORTIONS BY VOLUME

Application
Type GP
Cement Stone or
Gravel Sand

High Strength & Watertight 1 3 1.5

General Use: Paths, Floors, etc. 1 4 2.5

Foundations & Large Masses 1 5 3

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.

Placing. AS 3600 gives requirements for handling, placing and finishing concrete. Minimum cover to reinforcement is 20 mm for the 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.

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 effective for lower grades of concrete. For concrete strengths of 40 MPa and above, curing is equally important. However, the type of curing mechanism is considered to be less critical.

Curing will also affect other concrete properties including:

Reduction in the potential for plastic cracking.
Improvements in surface quality, durability and impermeability.
An improvement in abrasion resistance.
Reduction in the carbonation rate. Variations in the duration of curing or uses of different curing methods may affect the initial colour of concrete.

COMPATIBILITY Type GP may be blended with other cements complying with AS 3972. It also is suitable to blend with fly ash and or blast furnace slag complying with AS 3582.

Type GP is compatible with admixtures complying with AS 1478.

MORTAR PROPERTIES
Mix design. The following table provides examples for use of Type GP for various exposure conditions.

Exposure Type GP Cement Hydrated Lime Sand

External - Exposed to sea air or spray (within 1km of the coast) 1 0.5 4

External - Other 1 1 6

Internal - Above damp course 1 1 6

Internal - Below damp course 1 0 3

Batching. AS 3700 requires batching to be carried out using buckets or other approved measuring devices. Accurate measurement of each material, including water, is essential to produce a consistent product.

Additives. Hydrated lime is recommended to improve workability. If plasticisers are used they must be added strictly in accordance with the manufacturer's recommendations. A serious loss of bond strength may occur if substitutions are used or products overdosed.

CEMENT PROPERTIES The following table provides an example of some typical cement properties of Type GP manufactured by Sunstate Cement Ltd.

Property Type GP As3972

Setting Time
Initial
1.30-2 hours 45mins (min)

Final
2.30-3 hours 10 hours (max)

Constancy of Volume (sounding test) 1.0 mm 5.0mm (max)

Fineness Index 400-440m²/kg

Compressive Strength
(Mortar) MPa
3 Day
34-36 MPa

7 Day
48-50 MPa 25 MPa (min)

28 Day
59-63 MPa 40 MPa (min)

WORKING INSTRUCTIONS
Storage. Contact with air and moisture will cause hydration of the cement and alter the cement properties. The 'shelf life' of Type GP is therefore dependent on the storage conditions. Bagged product should be stored off the ground and stacked to allow free circulation of air. Please note that bags are not waterproof.

It is recommended that Type GP be retested prior to use if the age of the cement exceeds three months.

Handling. A Material Safety Data Sheet can be obtained here.

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