Concrete mix design and Factors influencing mix design in English

 Concrete mix design and Factors influencing mix design

The concrete mix design could be a process of choosing suitable ingredients for concrete and determining their proportions which might produce, as economically as possible, a concrete that satisfies the task requirements, i.e. concrete having a particular minimum compressive strength, workability, and durability.

basic
The proportioning of concrete mixes is accomplished by the utilization of certain empirical relations that afford a reasonably accurate guide to pick the most effective combination of the ingredients so on achieve the specified properties. the planning of plastic concrete of medium strengths will be.

The compressive strength of concrete is governed by its water-cement ratio.

For the given aggregate characteristics the workability of concrete is governed by its water content.

For high-performance concrete mixed of low workability, considerable interaction occurs between the above two criteria and also the validity of such assumptions may become limited.

There are various factors that affect the properties of concrete, E.g. water and aggregates, Mixing, placing, compaction curing, techniques used for batching, the quality and quantity of cement.

The cost of materials, labor, and plant are three main factors contributing to the price of concrete. (Concrete mix design)

Cement is costlier than aggregate. Therefore the lean mixes i.e. mix containing less cement are desirable. The lean mixes evolve less heat of hydration and hence reduce cracking in mass concrete.

Rich mixes may cause high shrinkage and cracking in structural concrete. Therefore the employment of lean mixed of required strength and durability are desirable from technical still as cost considerations.

Concrete mix design ratio
The common method of expressing the proportions of the materials in a very concrete mix is within the varieties of pars, of rations of cement, the fine and coarse aggregates with cement being taken as unity.

For example, a 1:3:6 mix contains one a part of cement, three parts of fine aggregates, and 6 parts of coarse aggregates. The proportion should indicate whether it's by volume or by mass.

One purpose of mix proportioning is an obtain a product that may perform consistent with certain predetermined requirements. Conventionally, the 2 most essential requirements are the workability of fresh concrete and therefore the strength of hardened concrete at a special age.

Workability is that the property that determines the benefit with which a concrete mixture is placed, compacted, and finished. Durability is another important property, but it's satisfactory if the concrete mixture develops the mandatory strength. Of course, under severe conditions, like freeze-thaw cycles or exposure to sulfate water, the proportioning of the concrete mixture would require special attention.

Another purpose of mix proportioning is to get a concrete mixture satisfying the performance requirement at eh lowest possible cost.

This involves decisions regarding the choice of ingredients that aren't only suitable but also available at reasonable prices.

The overall objective of proportioning concrete mixtures can, therefore, be summarized as selecting the acceptable ingredients among the available materials the determining the foremost economical combination that may produce concrete with certain minimum perforation characteristics.

Quality control in mix design refers to the supervision exercise on the materials, the procedure of handling concrete, testing a taking of necessary corrective action so on make sure that the standard of the hardened concrete confirms with the planning requirements.

Factors influencing concrete mix design
They have lots of influencing to design mix

Water cement ratio
Quality of Cement and chemical constituents
Storage of Cement
Aggregate
Water
moisture of aggregate
Slump
Degree of compaction
Curing Efficiency
Curing Temperature
Duration of Loading
Moisture Content at the time of Cube tests
Water cement ratio of concrete mix design
The water-cement ratio is that the main factor affecting the compressive strength of concrete in any respect ages. Every increase of 0.01 within the water-cement ratio decreases the strength by 1-1.5.

Storage of Cement

The quality of cement stored in bags in godowns gradually deteriorates because of hydration. The losses in strength for various periods of storages are 15% in 3 Months, 30% in 6 months and 50% in an exceedingly year.

Aggregate of concrete mix design

The efficiency of cement increases with the utilization of aggregates with larger maximum sizes, especially for leaner mixes. Well graded natural gravel or natural sand gives practically the identical strength as well-graded crushed aggregates and natural sand concrete.

Water

Every extra liter of water added over the required quantity in a very 50-kg bag batch alters the water-cement ratio by 0.02-0.03 and affects the strength of concrete by 1-2N/mm2. The accuracy of batching water should maintain within 1%.

Moisture in aggregate in concrete mix design

The moisture within the sand can cause a variation of the maximum amount as 20% within the quantities of materials batched by volume.

Slump of concrete mix design

A 3% change in water content can cause a range of 20mm in an exceedingly slump, and would generally affect the concrete strength by 2 N/mm2.

Degree of compaction

The presence of 1% voids within the mix reduces the strength of concrete by 5%. Thus, with improper compaction and 5% voids, a well-proportioned concrete of strength 20 N/mm2 would actually exhibit strength of 15 N/mm2 only.

Curing Efficiency

Concrete develops its full strength when kept wet continuously for 28 days. The drying of concrete at some intermediated stage will, within the future, lower its strength below that of a completely wet-cured specimen.

Curing Temperature

At very low temperatures, concrete gets frozen and should not hydrate. At temperatures above 10 C, a awfully small change in temperature causes a variation of 0.2-0.4 N/mm2 within the strength of concrete.

Duration of concrete mix design

Constant or continuous loading of a structure may cause fatigue and reduce the strength of concrete to 50% of its ultimate strength. Under a sustained load, failure may occur at a strength of 90% for a 1-hour loading, 80% for a 2-month loading, and 70% for a 30-year loading.

The moisture content at the time of cube tests

Concrete cubes must be tested in an exceedingly moist condition as soon as possible after removal from a curing tank. Oven-dried cubes are likely to indicate a better strength by up to 80%.