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?
Results and Conclusions
From the experiments carried out on the key phases of concrete, the following results relating to saturation dosages, mortar flow, concrete slumps and finally concrete compressive strength were assessed and discussed. This section represents the outcome from the experimental methods, supplying the relevant data used for discussion.
For each case, for the ease of comparison, the different mixes were broken down into categories as follows:
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Control: 100% Cement & Water to Powder ratio = 0.50,
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Class 1: 25% Cement Reduction, Water to Cement ratio = 0.67 & Water to Powder ratio = 0.50,
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Class 2: 50% Cement Reduction, Water to Cement ratio = 1.00 & Water to Powder ratio = 0.50.
Note:
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The notations KB02, KB05 and KB10 refers to the limestone fillers with increasing grades of ultrafine, fine and coarse respectively. The ultrafine is much finer than the cement particles, the fine is still finer than the cement but coarser than the ultrafine and the coarse had the same fineness as the cement particles.
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The mixes are denoted using ratios. The name '75C:25KB02' for instance, represents a mix whereby 25% of the cement is substituted by the limestone filler 'KB02' by weight.
Results
1. Saturated Superplasticizer Dosages for Cement Pastes
The saturation dosage for each cement paste was determined and was compared with that of the Control Mix which contained cement without any partial substitution.
2. Mortar Flow
The flow spread of each mortar was determined and was compared with that of the Control Mix.
3. Concrete Slump
The different mixes were prepared using different superplasticizer dosages to achieve a target slump of 100±20 mm. The slump aquired together with the superplasticizer dosage used in a particular mix were compared with the Control Mix.
4. Concrete Compressive Strength
The compressive strength of the cubes were evaluated after 7 and 28 days of water curing and the influence of the limestone fillers on strengths were assessed with respect to a Control Mix
General Conclusions
The research aims were successfully met, whereby cement can be partially replaced by limestone fines without negatively affecting the rheological (flow) properties and the compressive strength of concrete.
Most structures are commonly designed using concretes having a compressive strength of about 30 MPa. It was found that the strength achieved by the control after 28 days of water curing was about twice (62 MPa) as much. It was also noted that at a cement reduction of as high as 50%, compressive strengths ranging from 27.0 MPa to 38.0 MPa after 28 days of water curing were achieved. It should be noted that even at such a high reduction in cement content, the workability was not compromised.
Hence, it can be concluded that a concrete mix can be designed with reduced cement content, for the desired compressive strength without compromising the workability of the mix.
Reducing the cement content in concrete, will allow the ease for cement production companies to comply with policies and regulations in regards to the lowering of the CO2 emissions. In addition, the reduction of cement content will also render the production of a more economical concrete, which will in turn benefit construction companies as well as clients.
