The Constructor

A Beginner’s Guide to Concrete Mixes [PDF]

Beginners Guide to Concrete Mixes

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A concrete mix is a proportionate mixture of components such as cement, sand, aggregates, and water. The mix ratios are determined based on the type of construction and mix designs. However, building codes provide nominal and standard concrete mix ratios for various construction works based on experience and testing. This article acts as a guide for beginners wanting to learn more about the various aspects of concrete mixes such as safety, concrete mixing ratios, mixing the fundamental ingredients, sunlight, and curing speed.

Fig 1: Components of Concrete Mix

1. Safety

The most critical thing a beginner should know about concrete is that it is acidic. Cement is capable of causing chemical burns on exposed skin, and even through clothing if wet concrete is not washed away. Care should be taken when working with concrete to avoid its ingress into the eyes. It is recommended to wear safety goggles while mixing, placing, or finishing concrete. One may also want to wear a breathing mask when dealing with concrete to avoid inhalation of toxic particles. The paper dust mask is most widely used when handling concrete, but the full-breather mask with cartridge filters is ideal.

2. Concrete Mixing Ratios

When working with concrete, one should know that the correct mixing proportions are very significant. If not followed, the consistency will get weakened, and the final product will yield volatile and undesirable results. The most common mistake that a beginner may make would be the addition of excess water to the mixture. The mixture with the consistency of damp sand insinuates that the quantity of water is more than enough to prepare concrete. With any significant volume of water over the amount of concrete required, the ultimate strength would be drastically reduced. When a wet mix with high concentration is needed, water reducers are applied to concrete to help achieve a workable slump without losing the strength of the mixture.

3. Mixing the Fundamental Ingredients

The more you mix the concrete, the stronger it will be, which is also essential to the mixing phase. Once the concrete is mixed, it will result in gaps where the cement and aggregates have not been thoroughly blended, creating weak points in the finished product. In the worst-case scenario, you might end up with a whole section of concrete that isn't built up and stays wet.

4. Sunlight and Curing Speed

Make sure that the surrounding is conducive to the production of concrete. The amount of heat and direct sunlight in the working environment must be within a limit. Direct sunlight may expedite the setting up of concrete, but if exposed for too long may result in its deterioration due to UV rays.

5. Don't Remix the Concrete

A significant error made by beginners is to add water to the concrete for a second time after it has begun to set, just so they could finish the concrete easily. It should be noted that the required quantity of water should be added at once i.e., during the preparation of concrete. Adding water again would only compromise the integrity of the structure and may prevent it from attaining the requisite strength. However, this is only true when the concrete begins to set and does not apply for the next 30 days after it has hardened.

6. Concrete Curing Fundamentals

Concrete takes a whole month to attain full strength, and it is essential to keep the concrete moist during this period. Water is the catalyst that allows concrete to harden by nullifying the effect of the heat of hydration in concrete. Continuing to moisten or dampen the concrete over the next 30 days can help ensure that the concrete achieves the highest possible strength. Read More: 1. Effects of Excess Water in Concrete Mix 2. What is the Basis for Selection of Concrete Mix Proportions? 3. Concrete Mix Design Calculation for M15 Grade as per IS 10262-2009  
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