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Plast- PR 462 (Retarding Admixture)
Uses The unique dual function of PLAST- PR 462 improves both mixing water efficiency and delays initial set of concrete mixes. This improvement can be utilised to provide increased strength, density and workability without increase in cement, whilst retardation of setting times enables avoidance of 'cold joints' where delays in transporting and placing concrete occur. Towers, chimneys, high buildings, slipform structures, tunnel / shaft lining, offshore construction and in-situ piles. Advantages
- Easy Dumping - improves workability, cohesion and extends setting time. Provides protection against delays and stoppages.
- In-situ Piling - Avoidance of 'cold joints', helps easy, casing removal.
- Ready mixed concrete - Increased workability and extended setting times minimizes risks associated with long distance deliveries in hot weather.
- Slip forming - Facilitates keeping a workable concrete 'face' under difficult conditions.
- Larger pours - Possible with extended placing and compaction times and avoidance of 'cold joint'
- Increased ultimate strength - Higher strengths without increase in cement content or reduction in workability.
- Cement savings - Can be obtained by maintaining original strength and workability.
- Improved cohesion - Reduces bleeding and segregation where poor sand gradings are unavoidable
Description PLAST- PR 462 is a dark brown liquid based on selected lignosulphonates. When added to concrete mixes the admixture is absorbed onto the cement particles. It then acts as a dispersing agent which breaks down agglomerates of cement particles and enables the water in the mix to perform more efficiently. PLAST- PR 462 delays the initial hydration of the cement which results in retardation of the setting time. However, once the concrete has undergone initial set, the hardening process continues normally. Technical Support Sigmacheme advice can be sought on mix design aspects especially to produce high workability concrete without segregation. Sigmacheme provides advisory service for 'on-site' assistance and guidance on evaluation of trials and usage.
Properties
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Chloride content
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Nil to 15456
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Specific gravity
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1.170 -1.190 at 27 cC
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Compatibility
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Compatible with all types of cements.
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Setting times: Initial and final set times will be related to cement type and ambient temperature. Graph below illustrates the approximate degree of retardation over any PLAST- PR 462 retardation Vs. Dosage at constant water content Cohesion / Segregation: Improved dispersion of cement particles increases cohesion properties and reduces the probability of segregation and sand runs. Permeability: Improved workability facilitates placing and compaction. Reduced water cement ratio increases density and makes the concrete more waterproof. Compressive strength: Table 1 shows typical results where increased workability is obtained at original W/C and increase in strength where workability is maintained and W/C reduced. Application instructions Dosage PLAST- PR 462 will normally be added at a rate between 0.1 and 0.30 litres / 50 kg cement depending on the slump and retardation required. Site trials should be carried out to determine optimum dosage. If used for cement reduction without loss in strength the dosage is normally 0.15 litres / 50 kg cement. Dispensing The correct quantity of PLAST- PR 462 should be measured by means of an accurate and recommended dispenser. The measured quantity of the admixture should be added directly to the mixer at the same time as the mixing water. Under no circumstances should PLAST- PR 462 be added to the dry mix. If mixing water is added in more than one stage, add PLAST- PR 462 in the last stage. Overdosing An overdose of double the recommended measure of PLAST-RP 464 will result in increased retardation but the ultimate strength of the concrete will not be reduced and could be increased if advantage is taken of the increased workability. Estimating Packaging PLAST- PR 462 is supplied in 5, 20 and 200 litre containers. Storage Minimum shelf life of 12 months provided the temperature has not exceeded 2OC to 50OC. If this range is exceeded in any respect, advice should be sought from the supplier. Precautions Health & Safety PLAST- PR 462 is non-toxic, non-inflammable, any splashes should be washed well with water. If contact with eyes occur it shall be washed immediately with water and medical advice sought immediately.
Test Results Mix: Sand Zone 2 (I.S.383) 35%, Aggregate 20-5 mm (I.S. 383) 65%, Cement OPC (I.S. 269)
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Test
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Dosage of PlastR 464 Litre/50 kg cement
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W/C Ratio
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Slump (mm)
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Compressive strength N/mm2
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Density Kg/m3
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Control
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None
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0.65
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60
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10.2
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13.1
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16.7
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2368
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Workability increased
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0.15
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0.65
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130
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10.5
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13.5
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17.1
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2348
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Strength Increase
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0.15
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0.57
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65
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16.1
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19.3
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25.7
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2378
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Retardation Observed
- With no water reduction= 3 hours over control
- With water reduction= 2 hours over control
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