Concrete Mixture Design - Basic Ideas

The proportions of concrete mixes determine the amount of various concrete-forming materials required to produce concrete that has a 28-day compressive strength of concrete for a particular grade of concrete and concrete and durability requirements. The emphasis is on making the most economical use of available materials so as to produce concrete of required characteristics at minimum cost.

Concrete should be satisfactory in both fresh and hardened state. The proportion of concrete mixes is accomplished by use of some established relationship from experimental data which provides reasonably accurate guidance for selecting the best combination of materials to achieve the desired properties of fresh and hardened concrete. Of all the physical characteristics of concrete compressive strength is often taken as an index. Therefore, mix design is generally done for a particular compressive strength of concrete with sufficient workability to allow fresh concrete to be properly placed and compacted. In addition the mix ratio is also checked against the requirement of sufficient stability for the type of risk condition anticipated in service. The following basic assumptions are made in the design of medium strength concrete mixes:

  1. For given composite characteristics, the workability of concrete is dependent on its water content.
  2. The compressive strength of concrete is related to its water-cement ratio.

For high strength concrete mixes, there is considerable interaction between these two criteria and the validity of such assumptions may be limited. In addition, there are many other factors that affect the properties of concrete such as the quality and quantity of cement, water, aggregates and admixtures (if used); Processes of batching, mixing, placement, compaction and curing etc. Therefore, the specific relation used in the proportion of concrete mix should be considered only as the basis of trial mix.

Concrete mix design based on the recommended guidelines is actually a process of making a preliminary estimate on the optimum combination of ingredients and the final mix ratio is worked out only on the basis of further test mixes.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.