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Concrete Manufacturing Process 101: A Comprehensive Overview

Concrete

Overview

Concrete is a very Important material for the construction industry; We all know it is the backbone of this modern infrastructure. From Skyscrapers to sturdy bridges, concrete plays a crucial role in construction projects of all scales. Understanding the concrete manufacturing process is essential for engineers, Architects and construction professionals must ensure the quality and durability of their structures. In this article, we will take a detailed look at each step involved in the concrete manufacturing process.

  • Batching
  • Mixing
  • Transportation
  • Placing

Batching

Batching is an initial stage in the concrete manufacturing process, whereas aggregates (such as sand, gravel, or crushed stone), cement, and water should be measured with an accuracy of ±3 percent of the batch quantity and the admixtures with 5 percent of the batch quantity.

These are the two Methods of batching material are

  • Volume mixing
  • weight Mixing

Volume mixing

In volume mixing, the proportions of the raw material are calculated based on volume rather than weight. Using measurement instruments like buckets or drums, the volume of each substance is calculated, including that of cement, aggregates, and water. While using sophisticated weighing equipment is not possible or while working on small-scale projects, volume mixing is frequently employed. It is excellent for straightforward building work due to its functionality and simplicity.

Volume mixing does, however, have some restrictions. Because the density of materials might fluctuate, it could not be as accurate as weight batching. For instance, the precision of the mix may be impacted by variations in the density of sand from one batch to the next.

Inconsistencies in the concrete mix might result from differences in material density and handling. impacting its strength and durability.

weight mixing

Weight batching entails weighing the raw components and measuring and dividing them accordingly. With the use of weight cells or weighing scales, each item is precisely weighed, giving the mix proportions exact control. In large-scale concrete production and for projects where the mix’s quality and uniformity are critical, weigh batching is frequently employed. It is preferred because it is more accurate and can provide the appropriate mix design with little variations.

The mix proportions can be modified as necessary to produce certain concrete qualities by weighing the ingredients, guaranteeing the greatest performance for the desired purpose.

Weigh batching reduces the possibility of material differences and guarantees a more consistent and dependable concrete mix.

Complete batching process, the initial stages laid the foundation for the quality and performance of the structure.

Selection of raw material

Before a batching can begins is very important to to select a precise and quality raw material Cement, aggregates, water, and any supplementary cementitious materials (SCMs) must meet the necessary standards and specifications to ensure the desired concrete properties.

Proportions and Mix Design

After the selection of raw materials, engineers and other professionals must determine the appropriate proportions of each item to produce concrete with the necessary properties. This method, called as mix design, takes into account factors as per the IS codes such as the concrete’s intended use, the environment, and the required strength. 

Batching Equipment

Typically, batching is done with the use of specialized machinery like volumetric mixers or batch plants. Bins, hoppers, and conveyors are included in these machines in order to store and move the raw ingredients to the mixing area.

Weighing and measurement

 Accurate weighing and measurement of each raw material in accordance with the mix design are required throughout the batching process. The possibility of inconsistencies is minimized by the sophisticated weighing devices that are included in modern batch facilities.

Sequential Addition

The elements are added progressively in the predetermined sequence to achieve a homogeneous mixture. A typical order of addition is cement first, then aggregates, water, then any SCMs or admixtures. Depending on the type of batching equipment being utilized, the order could change.

Quality control

Throughout the batching procedure, quality control tests are made to ensure that the right ratios are being utilized and the mixture complies with the necessary criteria. Regular testing guarantees that any deviations or consistency issues are quickly found and fixed.

Batching Tolerance

Certain tolerances that govern batching specify the amount of permissible deviance from the prescribed mix design. These tolerances are set up to preserve the consistency of the concrete while taking into consideration the actual constraints of the batching process.

Records and documentation

When batching, accurate record-keeping is crucial. To keep track of the materials used, the ratios, and any modifications made throughout the process, batch tickets or electronic logs are kept.

Environmental Considerations

Wind, temperature, and humidity are just a few examples of the environmental conditions that should be taken into account for batching operations since they can affect the concrete’s workability and setting time. The right steps are taken to guarantee constant quality despite shifting circumstances.

Mixing Concrete: Ensuring Homogeneity and Quality

Concrete mixing is the second stage of the manufacturing process, where the various raw materials—aggregates (such as sand, gravel, or crushed stone), cement, and water—are combined to create a homogeneous and consistent concrete mix. The proper Mixing of cement aggregates and water and any supplementary cementitious materials (SCMs) is essential to ensuring the concrete’s strength, durability, and overall performance in construction projects. Let’s discussed the same in detailed

Mixing Methods

 Concrete mixing can be achieved through different methods, depending on the scale of the project and the equipment used. The two most common methods are

Hand Mixing

Hand mixing is adopted for a small job only where the quality of the concrete involved is small, and the approximate time is 2 minutes and should never exceed 3 minutes.

Machine mixing (mixture)

  • When a large quantity of concrete of the desired quality is to be produced, the machine mixing becomes necessary so that the concrete can be produced at a faster rate with better quality.
  • Concrete mixers are classified by the volume of mixed concrete discharged after mixing each batch, expressed in m3 , such as 0.25, 0.38, 0.57, 1.5, 2.25, and 3m3 
  • Sometimes the total volume of the unmixed ingredients in m3 is given as prefix 1.0/0.75 mixers takes 1 m3 of unmixed material and gives 0.75 m3 of mixed concrete in each batch.

Mixing Equipment

Concrete mixers come in various types, such as

Tilting Drum Mixers: Commonly used for small to medium-scale projects, tilting drum mixers are versatile and easy to operate. They tilt to discharge the concrete mix.

Non-Tilting Drum Mixers: Suitable for larger projects, non-tilting drum mixers have a fixed drum that rotates to mix the materials. A chute is used to discharge the concrete.

Pan Mixers: Pan mixers have a stationary mixing pan and rotating blades that blend the materials effectively. They are suitable for dry or semi-dry mixes.

Twin-Shaft Mixers: Twin-shaft mixers are high-capacity mixers used for large projects and are known for their fast and efficient mixing

Transportation

According to the specification, mixing, moving, placing, and compacting the concrete shouldn’t take longer than the cement’s initial setting time (30 minutes when using OPC).It must also ensure that segregation not takes place.

The Transportation of concrete can be done by the following methods:

  • Pans: only suitable for little tasks
  • Power buggies may reach speeds of 24 km/h.
  • Concrete can be released through a steel shaft known as a chute when it needs to be deposited farther underground.
  • When the concrete slump volume ranges from 50 mm to 100 mm and the pipes used in the concrete pump have a diameter of 10 mm to 20 mm, concrete pumps are frequently employed for tunnel construction and in difficult-to-reach regions.
    Transit mixture: When concrete needs to be moved constantly to an inaccessible location, a belt conveyer is used.

Placing

Concrete placement is a crucial step in the building process that calls for meticulous attention to detail and expert execution. It entails the exact placement of newly mixed concrete in the designated spot so that it may serve as the foundation for the structural components of a building or infrastructure. The integrity and durability of the finished construction are directly influenced by the effectiveness of the concrete placing. Here is a detailed explanation of the pouring of concrete

As per is 456 maximum free falls of concrete may be taken as 1.5 m

Compaction

To eliminate air voids and ensure maximum strength, the freshly placed concrete must undergo compaction. Vibrators are commonly used to achieve this, as they help the concrete settle into all the nooks and crannies within the formwork.

The presence of even 5% and 10% voids in hardened concrete left due to incomplete compaction may result in a decrease in compressive strength by about 30% and 60% respectively  

Types of vibrators

Internal (Immersion) Vibrators

These are often referred to as poker or needle vibrators. Freshly poured concrete is compacted and consolidated using internal vibrators. The vibrations they cause when they are put into the concrete mix help to release trapped air bubbles and ensure that the concrete is distributed evenly inside the formwork. Slabs, columns, and other concrete components frequently employ internal vibrators.

Key Points
  • These vibrators consist of metals which is inserted in fresh of concrete.
  • Skilled and experienced men should handle internal vibrators. These vibrators are more efficient than other vibrators
  • These vibrators can compact up to 450mm from the face but have to be moved from one place to another as concrete progress.
  • The frequency of vibration is about 4000 to 12000rpm
  • The needle diameter varies from 20mm to 75mm and its length 25cm to 90cm
External Vibrators (Formwork Vibrators):

External vibrators are fastened to the outside of Molds or formwork used in the building of concrete. They cause the formwork to vibrate, which compacts the concrete and eliminates air spaces. For complex or significantly reinforced concrete constructions, these vibrators are very helpful.

Surface Vibrators (Plate Vibrators):

Surface vibrators, also called plate vibrators or compaction plates, are used to compact granular soils and asphalt surfaces. They are ideal for compacting roadways, pavements, and other large areas. Surface vibrators work by applying vibrations directly to the surface of the material to achieve compaction

Key Points
  • These vibrators are mounted on platform or screeds.
  • They are used to finish concrete such as bridge floor, Road slabs, station platform etc.
  • It is placed directly on concrete mass for the compaction of shallow elements (where internal vibrators cannot be applied) depth > 150mm. Ex, Road surface, plain concrete floor etc.
Screed Vibrators

Screed vibrators are used in concrete flatwork applications, such as sidewalks, driveways, and floors. They are used to level and smooth the surface of freshly poured concrete. The screed vibrator is pulled across the surface, and the vibrations help in settling and finishing the concrete.

These are just a few examples of the many types of vibrators available, each serving specific purposes in construction, material handling, and industrial processes. The choice of vibrator depends on the material being handled and the desired outcome

Curing

For sturdy and long-lasting constructions, concrete must be cured. Following the rules outlined by the Indian Standards (IS) code is essential to guaranteeing the finest outcomes. Simple information regarding curing concrete in accordance with the IS code is provided below

Objectives of curing

  • To prevent the loss of moisture from concrete due to evaporation or any other reason, supply additional moisture or heal-end moisture to accelerate the gain of strength.
  • To keep capillary pores saturated to ensure hydration of cement, increase the durability and impermeability of concrete, and reduce shrinkage.
  • As per IS 456, concrete members shall be kept under curing for a minimum period of 7 days for OPC at 90% humidity and at least 10 days where mineral admixtures and blended cements are used.

Note

Lower temperatures reduce the rate of setting and higher temperatures reduce the ultimate strength; therefore, the curing temperature needs to be within 5 to 30 C.

Important key points

Duration of Curing
  1. Minimum 7 days for Ordinary Portland Cement (OPC).
  2. 10 to 14 days for blended cements.
  3. Longer curing may be needed for specific projects.
Curing Methods
  1. Water Curing: Keep concrete continuously wet with ponding or sprinkling.
  2. Membrane Curing: Apply liquid curing compound to retain moisture.
  3. Steam Curing: For precast elements, use steam with controlled temperature.
Curing Temperature
  1. Maintain concrete temperature between 10°C to 27°C.
  2. Avoid extreme temperature fluctuations.
Protection from External Factors
  1. Shield concrete from rain, direct sunlight, strong winds, and extreme temperatures.

Finishing

Finishing is defined as the process of levelling and smoothing the top surfaces of freshly placed concrete to achieve the desired appearance. It is done as follows:

  1. Screeding: striking off the excess concrete to bring the top surfaces up to the lower garde is called Screeding.
  2. Trowelling: The final operation of finishing is to be done after all excess water has evaporated by a steel float in a conical shape, giving a very smooth finish.

Maturity of concrete

  • The strength of concrete depends on both the period of curing (age) and the temperature during curing.
  • The product (period x temperature) is called the maturity of concrete.
  • It is measured in °C hours and °C days.

Frequently Asked Questions

Concrete is composed of cement, aggregates (such as sand and gravel), water, and sometimes supplementary cementitious materials like fly ash.

 The curing period for concrete typically lasts for at least 28 days to achieve maximum strength.

Materials, such as crushed concrete, is an environmentally friendly practice that can enhance concrete sustainability.

Proper compaction ensures the removal of air voids, preventing potential weak spots and enhancing the concrete’s strength and durability.

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This Post Has 10 Comments

  5. Karan Sharma October 24, 2023

    Thankyou for this information I like to read it

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