The process of selecting suitable concrete ingredients and determining their relative quantities is called the concrete mix design with the aim of producing as economically as possible a concrete of the required, strength, durability and workability. The proportioning of the concrete components in 2 materials, namely the plastic and the hardened states, is controlled by the necessary concrete quality. It can not be properly placed and compacted if the acrylic cement is not workable. Then, the property of workability is important.
The compressive strength of reinforced concrete, which is generally regarded as a measure of its other attributes, depends on many factors, such as the quality and quantity of asphalt, water, and aggregates; batching and mixing; position, compaction, and healing. Concrete costs are made up of materials, plant and labor costs. The difference in material cost is due to the fact that the concrete is several times more expensive than the aggregate, so the goal is to produce as lean a combination as possible.
Requirements of Concrete Mix Design
The requirements which form the basis of selection and proportioning of mix ingredients are
(a) the minimum compressive strength required by structural consideration.
(b) the adequate workability required for full compaction with the available compacting equipment.
(c) Maximum water-cement ratio and/or cement content to provide adequate durability for specific site conditions.
(d) Maximum cement content to avoid cracking due to the temperature cycle in mass concrete.
Types of Mixes
- Nominal Mixes
- Standard Mixes
- Designed Mixes
Nominal Mixes
In the past, concrete specifications prescribed cement, fine and coarse aggregates proportions. These mixes are called nominal mixes of fixed cement-aggregate ratio that ensures adequate strength. They give convenience and have a strong margin above that stated in normal circumstances. However, the nominal concrete for given workability varies widely in strength due to the variability of mixing ingredients.
Standard mixes
The marginal blend of defined cement aggregate ratio (by volume) varies widely in intensity and may result in combinations that are under- or over-rich. For this reason, in many configurations, the necessary compressive strength was included. Such mixes are referred to as normal mixes.
IS 456-2000 classified concrete mixtures as M10, M15, M20, M25, M30, M35 and M40 in a variety of levels. The letter M refers to the mix in this category and the number refers to the defined mix intensity of the 28-day cube in N / mm2. M10, M15, M20 and M25 class blends refer to the ratios of the product (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2) respectively.
Designed Mixes
The manufacturer determines the concrete quality in these blends, but the mixing ratios are decided by the concrete supplier, except that the required cement content can be fixed. This is the most rational approach to choosing ratios of blends of specific materials in mind that have more or less unique features. The solution results in the most economically efficient development of concrete with the necessary materials. The designed mix, however, does not serve as a guide as this does not guarantee the correct mix proportions for the performance prescribed.
Concrete mix ratio with undemanding quality marginal or regular mixes (prescribed by amounts of dry ingredients per cubic meter and a slump in the codes) can only be used for very small jobs if the concrete intensity of 28 days does not reach 30 N/mm2. No control testing is required to depend on the component masses.
Concrete mix design is the process of finding the right proportions of asphalt, sand and concrete aggregates to reach desired strength in frameworks. For example, concrete mix layout can be defined as Concrete Mix = Asphalt: Sand: Aggregates.
Different steps, calculations, and laboratory tests are involved in the concrete mix design to find the right mix proportions. Usually, this process is adopted for structures requiring higher concrete grades such as M25 and above and large construction projects where there is a huge amount of concrete consumption.
The advantages of concrete mix engineering are that it provides the right ratios of components, rendering concrete building cost-effective in obtaining the required strength for structural members. As the amount of concrete needed for large buildings is immense, the economy in the number of materials such as cement makes the design of the project economical.