Concrete Mix Design represents the whole process of selecting ingredients of concrete and determining their relative proportion with the aim of producing concrete of the required durability, strength and work ability.
Relative amount of concrete is maintained by required performance of concrete in two states. If plastic concrete doesn’t work, you can’t place it directly and compact it. The compressive strength of hardened concrete which is mainly recognized as index of other properties depends upon factors like water and aggregates, quality and quantity of cement, compaction and curing, batching and mixing.
Requirements of Concrete Mix Design
Requirements include the basis of proportioning and selecting mix ingredients. It is summarized as:-
- The least compressive strength needed from structural consideration
- The sufficient workability required for full compaction with the availability of compacting equipment
- Maintain the ratio of maximum water-cement ratio or maximum cement content to give enough strength
- Sufficient cement content is maintained to prevent shrinkage cracking due to temperature cycle in mass concrete.
Let us discuss now the types of Mixes:
Amount of cement, coarse and fine aggregates mixes of fixed cement aggregate ratio ensures optimum strength. Due to variation of mix ingredients the normal concrete for a given workability differ extensively in strength.
Nominal mixes of fixed cement aggregate ratio differs in strength and may result in under or over rich mixes. Due to this reason, the minimum compressive strength has been added in many specifications. These mixes are known as standard mixes.
In designed mix, the level of performance of concrete is measured by the designer and the mix proportions are specified by producer of concrete. It is most normal approach to the selection of mix proportions along with specific materials having unique characteristics. This is most economical method in the production of concrete.
Nominal or standard mixes may be used only for small jobs.
Factors Influencing Choice of Mix Proportions
Various factors that affect the mix design are:-
Compressive strength is the important property of the concrete that affects the other properties of hardened concrete. It is required at particular age, typically 28 days, denotes the nominal water-cement ratio of the mix. Other factors that affects the strength of concrete at given time and treated at a prescribed temperature is degree of compaction.
It depends on 3 factors: the size of section to be concreted, the method of compaction to be used and the amount of reinforcement. Concrete must have maximum workability for narrow and complicated sections with unreachable parts. Workability depends on compacting equipment available at the site.
>>Maximum nominal size of Aggregate
Size of aggregate is inversely proportional to cement requirement for water-cement ratio because workability is directly proportional to size of aggregate. Compressive strength increases with decrease in size of aggregate.
>>Grading Type of Aggregate
The grading of aggregate is affected by water-cement ratio and workability. Aggregate cement ratio for particular workability and water –cement ratio is affected by the type of aggregate.
Degree of control is measured by variation in test results. Difference in strength occurs due to differences in the properties of the mix ingredients and shortage of control of accuracy in batching, placing, mixing and testing. Minimum the difference between the mean and minimum strengths of the mix, minimum will be the cement-content needed. The factor that controls this variation is termed as quality control.
To know more about concrete mix design and other concrete pumping services and equipments, feel free to contact our Maple experts at: 647 529 PUMP. Maple Concrete Pumping will provide you well maintained equipments and quality service at affordable range.