What Considerations Should Be Made Before Selecting Concrete Additives?
There are many things that should be considered when selecting concrete additives. They are:
- Comprehensive Strength
This is one of the most important properties of concrete as it can influence various other desirable properties of hardened concrete. The mean compressive strength needed at a specific age is generally 28 days determines the water-cement ratio of the mix. The other factor which affects the strength of concrete is the degree of compaction. According to Abraham’s law, the strength of fully compacted concrete is inversely proportional to the water-cement ratio.
The degree of workability required depends on three factors-the sizes of the material to be concreted, the number of concrete additives and the method of compaction. For narrow sections with many corners or inaccessible parts, the concrete must have high workability so that full compaction can be achieved with the least effort. This applies to embedded steel sections as well. The desired workability depends on the equipment used at the site.
The durability of concrete refers to its resistance to environmental conditions. High-strength concrete is considered to be more durable than low-strength concrete. In situations where high strength is not needed but the conditions of exposure necessitate high durability, the durability requirement determines the water-cement ratio.
- Maximum Nominal Size Of Aggregate
Generally, the larger the size of the concrete admixture, the smaller the cement requirement for the water-cement ratio. This is because the workability of concrete improves with an increase in the maximum size of the aggregate. Vice versa, the compressive strength tends to increase with a decrease in the size of the aggregate.
- Grading And Type Of Aggregate
The grading of aggregate directly influences the mix proportions for workability and water-cement ratio. The coarser the grading, the learner will be the concrete admixture. A lean mix is generally not desirable as it does not have enough fine material to make the concrete cohesive.
The type of aggregate also strongly influences the aggregate-cement ratio for desired workability and water-cement ratio. An important feature of a satisfactory aggregate mix is the uniformity of the grading which can be easily achieved by mixing fractions of different sizes.
- Quality Control
The degree of control can be predicted by the variations in test results. The variation in strength results can be either due to variations in the properties of concrete additives or a lack of control in batching, mixing, placing, curing and testing. The lower the difference between the mean and minimum strengths of the mix, the less cement will be required. This is known as quality control.
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