How to Control Concrete Quality when Mixing with Mixture Machine

Concrete quality depends on several factors. Major factors are quality of concrete ingredients, mixing process, carrying, placing, water-cement ratio etc. For large volume of concrete we generally order ready-mix concrete. But For small quantity concrete we always depend on mixture machine. Now-a-days, producing ready-mix concrete in plant is controlled digitally. But in job site, when we produce concrete with mixture machine we have to control that manually. The question is -

How to control concrete quality when mixing with mixture machine?

Spraying water on stone
For controlling concrete quality with mixture machine you have to control following things -

Material quality: Of course, you need quality material for producing quality concrete. For this purpose choose best quality materials as per design requirement. Ensure aggregates are free from dust or other foreign material. Select sharp edge aggregate. See "How to Identify Best Quality Material on Site" for better understanding.
Spray water on coarse aggregate before put into mixture machine. Use fresh drinking water in concrete mix.

Mixing proportion: Select how you'll measure the material quantity. We use a steel box for measuring materials which is called Fera. The volume of a Fera is 0.625 cubic feet. That's equal to half bag of cement. Suppose you will mix concrete at 1:1.5:3 ratio. Therefore, you need one bag cement, three fera fine aggregate (sand) and six fera coarse aggregate (stone chips) for a batch. Employ one person to tally the materials. There are many idle men you'll find on construction site. Such as guard, curing man etc. Employ one of them for counting concrete ingredients and marking on a piece of paper as put into mixture machine's drum. Determine the needed water content for one bag cement. Find this article to know “How to Calculate Concrete Ingredients”.

Mixing: Now start the mixture machine. Put one-third of required materials and one-third of required water into the drum. Then put a bag of cement. After that put the rest of materials and water into the drum. Mix the content properly. Spin the drum for at least 120 sec for properly mixing concrete ingredients after putting all ingredients into the drum.

Test: To check the water content in the mix do slump test. If the slump is higher than specified in the structural notes, reduce slump by mixing extra ingredients into the mixture drum. To increase the slump mix water. To do the slump test follow these procedure described in "This Article".

You also should make concrete cube or cylinder to test the concrete compressive strength. See "How to Make Concrete Cylinder Specimen". If 28 days cylinder test result meets required compressive strength then you made no mistake during mixing concrete and the concrete quality is perfect. If you cube test result doesn't meet design requirement then you should remake the structure.

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