Influence of Limestone Fillers on the Properties of Concrete
Can cement in concrete be reduced without having any adverse effects on the properties of concrete?
Concrete Compressive Strength
7-day Compressive Strength
1. Class 1 Strength (25% Cement Reduction)
The following observations were made:
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Some of the mixes exceeded the strength of the control and others had slightly lower strength.
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During the water curing phase, the strength gained is governed by a process called hydration. Hence, the hydration reaction was higher in some cases and lower in other cases.
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The limestone filler act as nucleation sites for the hydration reaction to occur (filler effect).
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In the cases where the strengths were found to be lower, the packing density could have been low. A low packing density tends to decrease the hydration rate and hence yielding lower strengths.
2. Class 2 Strength (50% Cement Reduction)
The following observations were made:
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The strengths were much lower in this case when compared to the Class 1 case. Since the water to cement ratio was higher in Class 2, lower strengths were recorded as the water to cement ratio is one of the governing factors for the compressive strength. Another possible explanation for the low strength could be due to the dilution effect since the cement content in this case was lower and hence less potential cementing materials were available for the hydration process.
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It was found that all the mixes containing limestone fillers had strengths exceeding that of the control. This again shows that the filler effect influences the strength of the resulting concrete.
28-day Compressive Strength
1. Class 1 Strength (25% Cement Reduction)
The following observations were made:
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After 28 days of water curing, the strength of the control exceeded the strengths of the concrete mixes containing the limestone fillers. This could have been due to the dilution effect. Since the potential cementing materials were higher in the control, a higher strength gained was observed. Moreover, at the later ages, it was found that the dilution effect is more pronounced than the filler effect.
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There was a variation in strengths among the limestone-cement blends. Hence, it can be concluded that the particle sizes and the types of combinations used had an effect on the strength gained.
2. Class 2 Strength (50% Cement Reduction)
The following observations were made:
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The strengths were much lower in this case when compared to the Class 1 case. Again, this was mainly due to the water to cement ratio being higher in this case and also due to the dilution effect.
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The mixes were found to have lower compressive strengths when compared to that of the Control Mix, which is again a consequence of the dilution effect. The potential cementing materials for the hydration process was higher in the control.
Concluding Remarks
The limestone fillers have an effect on the compressive strength of concrete. At the early ages (7 days), an increase in strength was found due to the filler effect. However, at the later ages (28 days), a loss in strength was found due to the dilution effect which tends to be more pronounced at the later ages.