Which batching is good for concrete?

What is batching and its methods?

Batching of concrete refers to the process of measuring and combining the ingredients required to produce concrete in the desired proportions.

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What are the types of batching plants?

The two types of concrete batching plants are ready Mix Concrete batching Plant, Dry Mix Concrete Batching Plant, Continuous Concrete Batching Plant, Mobile Concrete Batching Plant and Compact Concrete Batching Plant.

What is weight and volume batching?

Weight and Volume batching are the two types of concrete batching. Weight batching is a method of measuring the ingredients of concrete by their weight.Volume batching, on the other hand, is a method of measuring the ingredients of concrete by their volume.

What is the formula for Weight Batching?

Batch Weight = (Weight of Cement + Weight of Fine Aggregates + Weight of Coarse Aggregates + Weight of Water + Weight of Admixtures).

What is volume batching?

Volume batching is a method of measuring the ingredients of concrete by their volume rather than their weight.

In the construction industry, volume batching of concrete remains a fundamental practice. It is especially suitable for small-scale projects with a focus on simplicity. Despite increasing automation in batching, many regions still rely on volume batching. The main reason is its cost-effectiveness and low initial investment setup.

Precision in material proportioning is essential for successful volume batching. Consistency is key to preventing discrepancies in values and ratios. The construction industry is striving to blend traditional methods with technology, leading to the evolution of volume batching practices.

What is Volume Batching of Concrete?

The volume batching of concrete is a method that includes measuring the ingredients by volume before mixing. The ingredients include sand, coarse aggregate, and water. The main purpose of this is to ensure the correct proportion of materials during the concrete formation.  It is commonly used on small-scale construction sites.

Volume batching involves certain attributes, which include 

• Measurement of ingredients 
• Proportioning
• Moisture Content

Measurement of Ingredients:

• Cement

Cement is typically measured by volume rather than weight in volume batching. However, this measurement can be inaccurate.

• Aggregates

Fine and coarse aggregates are measured using a gauge box. The gauge box should be filled and levelled using a straightedge. 

• Water

Water is typically measured in liters but is represented in kilogrammes (kg) for volume batching. Therefore, the density of water is 1 kg/L.

2. Proportioning:
   • The ingredients are specified in volume proportions. The water-cement ratio is crucial for maintaining the mix design to ensure the desired strength and workability.

3. Moisture Content:
   • The moisture content in aggregates must be valued and monitored. It affects the volume and weight of the aggregates. The surface moisture can vary based on the condition of the aggregates.

How is Volume Batching Done in the Field?

Step 1: Batching of cement

Batching of cement refers to the process of measurement and combining the raw materials. Cement materials are measured using gauge boxes, also known as 'farmas or forms' in volume batching. Volume batching is less accurate when compared to weight batching. 

The gauge boxes are typically made of timber, steel, or iron. One pack of cement, which is 50 kg, is considered 35 liters. The gauge box has a volume of 0.035 cubic meters(m³). This is equivalent to one bag of cement. The cement should be ideally measured by weight to ensure accuracy. This is because the volume can vary based on compaction and moisture content.

Step 2: Batching of aggregate (by volume)

Aggregates, such as fine and coarse aggregate, are measured using the gauge box. It should be filled to the top and level with straight heads to ensure consistent volume. These gauge boxes are designed to match the volume of one bag of cement. The gauge box has a dimension of 0.40 m × 0.25 m × 0.25 m with a volume of 0.025 m³, which is equivalent to a volume of 25 litres.

Step 3: Batching of water

The water-cement ratio is essential and commonly measured in kilograms. If the water-cement ratio is 0.5, then 1 cement bag of 50 kg or 35 litres will require 17.5 l of water.

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Volume Batching of Concrete Ratio

Concrete mixes are typically mixed with a specific proportion of their materials. Its ratio is often represented by cement: sand:  aggregate. This ratio indicates the amount of each ingredient to be used. This helps to achieve the desired concrete properties and strength when mixed. Here are some common ratios:

1. M10 (1:3:6)
   • Cement: 1 part
   • Sand: 3 parts
   • Coarse Aggregate: 6 parts
2. M15 (1:2:4)
   • Cement: 1 part
   • Sand: 2 parts
   • Coarse Aggregate: 4 parts
3. M20 (1:1.5:3)
   • Cement: 1 part
   • Sand: 1.5 parts
   • Coarse Aggregate: 3 parts
4. M25 (1:1:2)
   • Cement: 1 part
   • Sand: 1 part
   • Coarse Aggregate: 2 parts

Advantages and Disadvantages

Advantages:

• The volume batching is simple and quick for small projects.
• It does not need sophisticated equipment.

Disadvantages:

• Volume batching is less accurate when compared to weight batching.
• It is not suitable for large or critical structures.
• Variability in material properties can affect the mix quality.

Volume Batching of Concrete Formula

For a concrete mix of 1:2:4 (cement:sand: coarse aggregate), which is an M15 grade:

• Cement: 

1 bag of cement=50 kg 

 In volume= 35 liters

• Sand

2 gauge boxes are required 

2 x 35 liters = 70 liters

(1 bag of cement= 35 litres)

• Coarse Aggregate: 

4 gauge boxes are used

4 x 35 liters = 140 liters

• Water

Water: cement= 0.5

If the water-cement ratio is 0.5, then 17.5 litres of water is required for 35 litres of cement( = 1 bag of cement).

Technical Considerations

1. Accuracy:
   • When compared to weight batching, volume batching is less accurate. Thus, the volume of each material can vary due to factors like moisture content and compaction.
   • It is essential to consider the moisture content in aggregates. For example, take very wet sand. It can contain up to 7.5% surface moisture by weight, which can greatly impact the mix proportions.
2. Suitability:
   • Volume batching is suitable for small-scale construction works. In these types, precision is not critical.
   • It is highly not recommended for reinforced concrete structures or large-scale projects. This is mainly due to the potential for variability in mix proportions.
3. Economy:
   • While volume batching is economical and straightforward, it may not be cost-effective in the long run. It is due to potential inconsistencies in the concrete mix, which leads to reduced strength and durability.

Common Mistakes in Volume Batching

• Improper proportions of the materials can lead to the weakening of the concrete.

• Ignoring the moisture content can affect the ratio of water to cement. 

• Using inaccurate measurement tools leads to inconsistent batching. 

• Inadequate mixing can often result in non-uniform concrete with lumps found. 

• Overloading the gauge or mixer can cause incomplete mixing and underloading can cause inefficient mixing. 

• Adding water inconsistently can affect the strength and workability of the concrete. 

• Ignoring the temperature effect can cause an impact on the setting time and the strength of the concrete. 

• Improper calibration of equipment can lead to inaccuracy during the batching. 

• Using the wrong size of aggregate can affect the concrete mix. 

Conclusion

Volume batching of concrete remains a pivotal method in construction. It ensures the consistency and accuracy required for high-quality concrete. From a technical standpoint, volume batching can lead to several variations. This makes precision critical. Therefore, current industry standards increasingly advocate for the use of computerized batching systems. Ensuring awareness of its limitations and ongoing development is essential in its advocacy in the construction industry. 

Ultimately volume batching serves a specific purpose in the industry. While moving towards smart systems and sustainable practices, the method's relevance depends on its advancement. 

This balanced perspective reminds the industry that while volume batching has its merit, the future lies in adapting it with technological precision. This helps to meet the growing demand for quality and sustainability in the construction industry.

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