Difference between nominal mix and design mix of concrete
Concrete is the most extensive material consisting of cement, sand, coarse aggregate and fine aggregate, and it hardens when mixed with water. During the formation of the concrete mix ratio, we can add whether the plasticizer is an accelerating/retarding plasticizers, which depends on the consideration of the design mix ratio. In addition, temperature is an important factor affecting concrete, and the mix design should have good quality and high performance. Concrete is the most widely used mixture achieve the expected structural characteristics.
There are two methods to prepare the concrete mix.
- Nominal mix
- Design mix
Nominal Mix:
In the nominal mix concrete, all the components and their ratios are specified in the standard specification. These ratios are specified in the ratio of cement to aggregate to obtain a certain strength. In the weight approximation method, the amount of sand and aggregate is directly calculated by the weight (kg) per 50 kg cement bag.
The mix ratios of 1:1.5:3, 1:2:4, and 1:3:6 are the nominal mix ratios of concrete used based on previous empirical research without any scientific basis. Therefore, it is suitable for ordinary concrete, or it can be said that for simpler, relatively unimportant and smaller concrete, the nominal mix ratio is preferred.
The ratio of various grade of concrete is being given below:
M-5- 1:5:10
M-7.5- 1:4:8
M-10- 1:3:6
M-15- 1:2:4
M-20- 1:1.5:3
1. Nominal mixture is the volume of all volume ratios in the case of changes in the strength and cost of concrete.
2. Used for ordinary concrete, including concrete grade not exceeding M-20.
3. No quality control is required.
4. This type of concrete mix ratio is generally used in occasions with a small amount or low load.
5. The ratio of water cement to stability is determined based on quality, experience and actual tests.
6. The water content can be changed at a slow cost (field test).
7. Mixing time-The concrete mixer rotates at a minimum speed of 15 rpm, and the mixing time required to produce one batch of concrete is 2 minutes.
Design Mix:
In the design mix ratio concrete, the proportion of ingredients and their relative proportions are appropriately determined to achieve the required strength of concrete. Not only must the required strength be considered, but also the characteristics of fresh concrete, such as workability or the performance of specific specifications of concrete, must be considered in detail. All materials are tested before use, and the whole process is discovered based on trial and error of various options from the available materials designated for work.
There are many grade of design mix concrete like M-25, M-30, M-35 andM-40 etc.
M-25- 1:1:2
M-30- 1:0.75:1.5
M-35- 1:0.5:1
M-40- 1:0.25:0.5
1. The design mix ratio is a mix ratio in which all mix ratios are considered based on weight, which can reduce the stability cost of concrete.
2. Performance-oriented concrete.
3. For high-grade concrete.
4. It has quality control.
5. The ratio of water grade based on concrete grade to 28-day compressive strength and concrete strength of concrete. The water content can be modified according to the compressibility value (laboratory test).
6. According to aggregate, it is considered to be the largest size material.
7. When pumping concrete in the mixing station, plasticizers can also be used to obtain good workability.
8. The mixing time can be kept standard, and if necessary, it can be changed due to the influence of temperature.
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