Concrete is the most commonly used building material, and it is made up of fine and coarse aggregate bound together with a cement paste that hardens over time. There have been a few older blogs about the reinforcement for concrete and the curing of concrete. This article discusses the different concrete mixing methods as well as some crucial factors to remember when concreting.
But, before that let us first know how to check the quality of concrete for a site.
1. Quality Control In Concrete
Slump cone test- It should be carried out on the site before concreting. Concrete slump tests are performed from batch to batch to ensure that the quality of the concrete is consistent during construction. The slump test is the simplest basic workability test for concrete since it is inexpensive and offers rapid results. It requires filling a clean mould with newly prepared concrete and removing the mould as soon as it is full. The slump is defined as the difference in height between the mould and the highest point of the sample being tested.
Concrete Cube Test- A minimum of three concrete cubes should be cast on the site and tested on a regular basis to see whether the required compressive strength is achieved.
A test for the moisture content and bulkage of sand should also be done at the site before doing concreting.
2. Types of Concrete Mixing
Mixing concrete is an elaborate procedure. Concrete mixing is the process of combining ingredients such as cement, sand, aggregate, water, and admixtures to produce concrete of an appropriate grade. To achieve the necessary strength of concrete, the mixing of concrete components should be done properly according to the grade of concrete. There are two types of concrete mixing as given below:
Concrete Hand Mixing
Machine Concrete Mixing
2.1 How Is Machine Mixing Of Concrete Done?
About 10 per cent of the water required for mixing shall be poured into the mixing drum before the dry materials are added.
Water shall then be added along with the dry materials continuously, except for about 10 per cent that can be added after all the dry materials have been fed into the concrete mixer.
Mixing shall be continued until there is a uniform distribution of the materials and the mass is uniform in colour and consistency.
In no case shall mixing be done for less than two minutes.
The concrete shall be discharged from the mixer quickly in one operation.
Generally, the amount of water required for concrete per bag of cement is 20-28 litres of water. If the sand and the aggregate are wet, then it will be even less.
During machine mixing of concrete, ensure that the water is measured and added.
Once water is added, concrete should be used within 45 minutes.
2.2 How Is Hand Mixing Of Concrete Done?
Hand mixing is adopted where the quantity of concrete is very small. Cement and sand are mixed dry, on a clean, hard and impermeable platform. The mixing of the dry materials is continued until the mixture has reached a uniform colour. This is again mixed with the coarse aggregate to attain a uniform colour. A hollow in the middle is made, and 75% of the required quantity of water is added. Mixing is done, and the remaining quantity of water is added to acquire uniform workability.
There are many chemicals called admixtures that can be added to cement water and aggregate during mixing in order to modify or improve the properties of concrete for a required application. Adding them does not mean that the quality of workmanship can be reduced. Please remember that there is no shortcut to good quality concrete and workmanship.
3. Placing of Concrete- Points To Be Remembered
Concreting shall be done continuously and finished in one stretch.
The concrete shall be placed in position gently and not thrown from a height. It should not be dropped from a height while placing. This is to prevent the segregation of aggregates.
Concrete shall be deposited as near as practicable to its final position.
Concrete shall be laid in layers not exceeding 15 cm in thickness, and thoroughly compacted before the next layer is laid.
Do not mix more concrete than can be laid in twenty minutes to ensure that the setting action has not commenced.
Do not mix concrete in the rain.
4. Conclusion
This blog focused on two methods of concrete mixing: hand mixing and machine mixing. It also included some suggestions to keep in mind during the concrete placing process. Following mixing, the next steps are pouring, compacting, and finishing, which will be explored in future posts.
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