Category Archives: CONCRETE

Reinforced cement concrete is a topic you will need to familiarize at some point, if you are into civil engineering field. The category explicitly presents it. Reinforced cement concrete (RCC), a composite material has been accepted worldwide as a construction material, bridges, retaining walls, docks and harbour, airfield pavements, flyovers,multi-storey building,complexes and simple houses etc., Concrete is good in resisting compression but is very weak in resisting tension. Hence reinforcement is provided in the concrete wherever tensile stress is expected. The best reinforcement is steel since the tensile strength of steel is quite high and the bond between steel and concrete is good. As the elastic modulus of steel is high, for the same extension the force resisted by steel is high compared to concrete. However in tensile zone, hair cracks in concrete are unavoidable. Reinforcements are usually in the form of mild steel or ribbed steel bars of 6 mm to 32 mm diameter. A cage of reinforcements is prepared as per the design requirements, kept in a formwork and then green concrete is poured. After the concrete hardens, the formwork is removed. The composite material of steel and concrete now called R.C.C. acts as a structural member and can resist tensile as well as compressive stresses very well. Aggregates are the inert or chemically inactive materials which form the bulk of cement concrete. These aggregates are bound together by means of a cement. They can be classified into two. The selection of aggregate is based on the purpose and its maximum size.

civil engineering, quality tests on concrete

Non-destructive Testing Meets Nanotechnology: Exploring Innovations and Applications

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Introduction

Non-destructive testing (NDT) has long been a cornerstone in ensuring the integrity and safety of structures, components, and materials across various industries. As technology advances, the integration of nanotechnology into NDT has opened up new frontiers, offering unprecedented levels of precision, sensitivity, and efficiency. This article provides an overview of the convergence of non-destructive testing and nanotechnology, exploring the innovative techniques, applications, and potential impact on diverse sectors.

Non-destructive Testing (NDT)

Non-destructive testing encompasses a range of techniques designed to evaluate the properties of materials without causing damage. These methods are crucial for identifying defects, assessing structural integrity, and ensuring the reliability of critical components. Traditional NDT methods include ultrasonic testing, radiography, magnetic particle testing, and eddy current testing. While these methods have proven effective, the marriage of NDT and nanotechnology is poised to revolutionize the field.

Non Destructive Testing

Nanotechnology in NDT

Nanotechnology involves manipulating materials at the nanoscale, typically at dimensions of less than 100 nanometers. When applied to NDT, nanotechnology brings a wealth of advantages, including enhanced sensitivity, improved resolution, and the ability to detect defects at a microscopic level. Here are key ways in which nanotechnology is making an impact in non-destructive testing.

Enhanced Imaging Resolution

Nanomaterials, such as nanoparticles and nanocomposites, enable the development of advanced imaging agents. These agents, when incorporated into NDT methods like radiography or magnetic resonance imaging, enhance resolution and provide detailed insights into the internal structure of materials.

Sensitivity Improvement

Nanoscale sensors and probes enhance the sensitivity of NDT techniques. For instance, nano sensors can be employed in ultrasonic testing to detect minute defects or irregularities that may go unnoticed with conventional sensors. This heightened sensitivity contributes to early defect detection and prevention.

Functional Nanomaterials

Functional nanomaterials, like carbon nanotubes or quantum dots, are employed to tailor specific properties for NDT applications. Carbon nanotubes, for example, can be used in sensors to improve conductivity and responsiveness, making them valuable for detecting flaws in materials.

Smart Coatings

Nanotechnology enables the development of smart coatings that respond to external stimuli, such as changes in temperature or stress. These coatings, when applied to surfaces, can reveal hidden defects or structural changes, providing real-time data during operation without disrupting the material’s integrity.

Smart coating - Nano Technology

    Applications of Nanotechnology in NDT

    The incorporation of nanotechnology into non-destructive testing has resulted in a myriad of applications across diverse industries. Some notable areas where this synergy is making a significant impact include:

    Aerospace Industry

    In the aerospace sector, where the demand for lightweight yet robust materials is critical, nanotechnology aids in identifying defects at the nanoscale. This ensures the integrity of components like aircraft wings and fuselage, contributing to overall safety and efficiency.

    Medical Imaging

    In the field of medical imaging, the use of nanomaterials enhances the resolution of diagnostic tools. Nanoparticles can be employed as contrast agents in techniques like magnetic resonance imaging (MRI) or ultrasound, allowing for more accurate and detailed medical assessments.

    Materials Science and Manufacturing

    Nanotechnology plays a pivotal role in materials science and manufacturing, where the detection of microscopic defects is crucial. Whether assessing welds in construction materials or inspecting microelectronics in manufacturing processes, nanotechnology-driven NDT ensures the quality and reliability of products.

    Oil and Gas Industry

    In the oil and gas sector, nanotechnology aids in the inspection of pipelines and critical infrastructure. Nano sensors can detect corrosion or structural weaknesses in real-time, preventing potential disasters and optimizing maintenance schedules.

      Challenges and Future Directions

      While the integration of nanotechnology into NDT holds immense promise, there are challenges that researchers and industries must address. Ensuring the scalability and cost-effectiveness of nanotechnology-driven NDT methods, as well as addressing potential environmental and health concerns related to nanomaterials, are crucial aspects.

      The future of NDT with nanotechnology is likely to witness further innovations, including the development of autonomous nanorobots for in-situ inspections and the application of artificial intelligence to analyze complex nanoscale data. As research progresses, the synergy between non-destructive testing and nanotechnology will continue to redefine the boundaries of material inspection and quality assurance.

      Conclusion

      The convergence of non-destructive testing and nanotechnology represents a paradigm shift in how we assess the integrity of materials and structures. Nanotechnology’s ability to operate at the molecular and atomic levels brings unprecedented precision and sensitivity to NDT methods, ensuring early defect detection and contributing to enhanced safety across industries. As research and development in this field advance, the innovative applications of nanotechnology in NDT are poised to reshape industry standards, making material inspection more reliable, efficient, and technologically sophisticated.

      Fiber reinforced concrete

      Fiber Reinforced Concrete (FRC) – Types and Advantages

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      Fiber-reinforced concrete (FRC), an advanced form of Reinforced Cement Concrete is finding wide applications these days. Fiber-reinforced concrete (FRC) is a versatile and durable composite material consisting of a cementitious matrix with uniformly dispersed fibers. The addition of discontinuous, discrete fibers to cement, mortar or concrete mixes can enhance the concrete properties. Ever thought why do we add different kinds of fibres to the Reinforced Cement Concrete and what are the different types of fibres that we add? Stay with me till the end of this blog and we will find answers to all these questions.

      Before proceeding further, make sure you check out our blog, Reinforced Cement Concrete (RCC)|Definition|Advantages to have your concepts clear.

      First, let’s have a look at the basics of fiber-reinforced concrete and its applications.

      What is Fiber-reinforced concrete?

      Fiber-reinforced concrete (FRC) is a versatile and durable composite material consisting of a cementitious matrix with uniformly dispersed fibers. The addition of discontinuous, discrete fibers to cement, mortar or concrete mixes can enhance the concrete properties. These fibers act as reinforcement throughout the concrete matrix, and control cracking due to plastic shrinkage and drying shrinkage. Fiber-reinforced concrete reduces the permeability of concrete and reduces water bleeding.

      Fiber reinforced concrete finds extensive applications in various infrastructure works, industrial flooring works and other construction works that demand enhanced durability and crack control. FRC improves the flexural and impact resistance and hence we prefer it for structures subjected to dynamic or heavy loads.

      Now, let’s discuss the reason behind the addition of fibres to the reinforced concrete.

      Principle of Fiber-reinforced concrete

      Fibre-reinforced concrete uses discrete fibres to improve its mechanical properties, making it stronger, more durable, and resistant to cracking. Fiber is a small piece of circular or flat reinforcing material possessing certain characteristics and properties. These fibers are of steel, glass, synthetic polymer fibers and natural fibers like jute or hemp.

      Fibers are available in various sizes ranges from a few millimeters to a few centimetres. They are uniformly distributed throughout the concrete matrix. The features of Fiber reinforced concrete depends on the character and percentage, diameter and length of fibers and water-cement ratios. Typically fiber reinforced concrete is used in shotcrete but can also be used in normal concrete.

      The addition of fibres to concrete controls the shrinkage cracking, lower permeability, and reduce water bleeding. Some fibers enhance impact, abrasion, and shatter resistance. However, they do not increase flexural strength or replace structural steel reinforcement.

      We measure the amount of fiber as a percentage of total volume (Vf) and typically ranges from 0.1 to 3%. Aspect ratio (l/d) affects strength and toughness, but long fibers can hinder workability. Recent research shows limited impact resistance improvement, with microfibers performing better than longer fibers.

      Types of Fiber-reinforced concrete

      The type of fiber-reinforced concrete depends on the nature of the structure and applications. Let us have a look at the most common types of fibre reinforced concretes commonly used in construction.

      • Steel Fiber Reinforced Concrete
      • Polypropylene Fiber Reinforced (PFR) Concrete
      • GFRC Glass Fiber Reinforced Concrete
      • Asbestos Fibers
      • Polyester fiber
      • Carbon Fibers
      • Macro synthetic fibers
      • Organic Fibers
      • Cellulose fibers
      • Micro-synthetic fibers
      • Synthetic Fiber Reinforced Concrete (SFRC)Natural Fiber Reinforced Concrete (NFRC)Carbon Fiber Reinforced Concrete (CFRC)Basalt Fiber Reinforced Concrete (BFRC)Nylon Fiber Reinforced Concrete (NyFRC)Polyvinyl Alcohol Fiber Reinforced Concrete (PVAFRC)High-Performance Fiber Reinforced Concrete (HPFRC)

      Steel fiber-reinforced concrete

      SFRC is a composite material that includes a certain amount of steel fibers in the concrete mix. These fibres can change the properties of concrete and thereby enhance the performance of concrete. The typical diameter lies in the range of 0.25 to 0.75mm. Steel fibers having a rectangular c/s are produced by silting the sheets about 0.25mm thick.

      Steel fibre reinforced Concrete

      SFRC offers numerous advantages, including improved tensile strength, crack resistance, impact resistance, and durability. The steel fibers act as reinforcement, effectively bridging cracks and enhancing the concrete’s structural integrity. The steel fiber types are as per ASTM A.820 Type I: cold-drawn wire, Type II; cut sheet, Type III: melt-extracted, Type IV: mill cut and Type V: modified cold-drawn wire.

      SFRC finds applications in industrial floors, pavements, tunnels, and precast elements, where increased toughness and load-bearing capacity are required. It is also widely used in applications prone to dynamic loading, such as blast-resistant structures and earthquake-resistant buildings.

      Glass fiber-reinforced concrete

      Glass Fiber Reinforced Concrete (GFRC) is a composite material incorporating fine glass fibers into the concrete mix. These fibers, typically around 3-12 mm in length, enhance the concrete’s strength, durability, and flexibility. GFRC is commonly used in architectural applications, such as cladding, facades, and decorative elements, due to its lightweight nature and ability to create intricate designs.

      Glass fiber reinforced concrete

      You can get the full details about glass fiber-reinforced concrete here. Glass Fiber Reinforced Concrete – GFRC Ingredients and Uses

      Polypropylene Fiber Reinforced Concrete (PFRC)

      Polypropylene Fiber Reinforced Concrete (PFRC) is a composite material that combines polypropylene fibers with concrete. One of the cheapest & abundantly available synthetic fiber/ polymer is polypropylene. They are resistant to most chemicals and only the cementitious matrix will deteriorate first. These discrete fibers, typically ranging from 6 to 30 mm in length uniformly dispersed in concrete will control cracking due to plastic and drying shrinkage.

      We usually use these fibers in concrete to control cracking due to plastic shrinkage and drying shrinkage. The fibers act as reinforcement and reduce the permeability of concrete and thus reducing the bleeding of water and improving crack resistance, impact resistance, and durability. Polypropylene fibers being hydrophobic can be easily mixed as they do not need lengthy contact during mixing and only need to be evenly distressed in the mix.

      Polyester fiber reinforced concrete

      Polyester fiber-reinforced concrete is a composite material that incorporates polyester fibers into the concrete mix. These fibers, typically short and discrete, improve the concrete’s toughness, crack resistance, and impact resistance. Polyester fibers due to the high tensile strength and resistance to alkalis make them suitable for various construction applications that demand enhanced durability.

      Carbon fibers

      Carbon fiber reinforced concrete (CFRC) is a composite material that combines concrete with carbon fibers about 5-10 microns in diameter having carbon atoms. The carbon fibers, known for their exceptional tensile strength and stiffness, low weight, high chemical resistance, high-temperature tolerance and low thermal expansion impart their qualities to the concrete.

      We manufacture carbon fibers by baking plastic resins. They have high strength-to-weight ratio. Carbon fibers form the most recent and probably the most spectacular addition to the range of fiber available for commercial use. Since they are more vulnerable to damage than even glass fiber, we generally treat them with resin coating.

      Macro synthetic fibers

      Macro synthetic fibers are synthetic fibers used as reinforcement in concrete. These fibers, typically longer and thicker than traditional fibers, are manufactured from a blend of polymers. These fibers are developed for shot create or sprayed concrete. But they find extensive applications in floor slabs for enhancing the concrete’s toughness, crack resistance, and impact resistance.

      They offer improved durability and control of plastic shrinkage cracking. This makes them suitable for various construction applications in marine and coastal structures which require enhanced performance and reduced maintenance.

      Advantages of fibre-reinforced concrete

      1. Enhanced Durability: FRC increases the impact, fatigue, and abrasion resistance of concrete structures while minimising cracking. It increases the tensile strength and durability of the concrete.
      2. Crack prevention: The use of fibres reduces the spread and enlargement of cracks by controlling plastic and drying shrinkage cracking.
      3. Permeability Reduction: Fibres make concrete less permeable, which reduces water bleeding and improves resistance to moisture infiltration.It reduces the air voids and water voids and the inherent porosity of gel.
      4. Improved Impact Resistance: Certain types of fibres enhance the impact resistance of concrete, making it more resilient against sudden loads and external forces.
      5. Increased Toughness: The bridging action of the fibres, which absorbs energy and prevents abrupt failure, gives FRC an improved level of toughness.
      6. Design Flexibility: Using fibres in concrete allows for design flexibility, enabling the creation of complicated shapes and architectural freedom.
      7. Simplicity: Using fibre reinforcement instead of or less frequently than standard steel reinforcement simplifies construction operations.
      8. Better Workability: Fibres can make concrete mixes more workable and cohesive, making placement and compaction easier.
      9. Corrosion Resistance: In some circumstances, fibre reinforcement can reduce the likelihood that concrete buildings will corrode.
      10. Sustainable: Fibre-reinforced concrete is a sustainable solution since it can increase the longevity of structures and lessen the reliance on non-renewable resources.
      11. Creep Resistance: Fibres such as graphite and glass have excellent resistance to creep, while the same is not true for most resins. Therefore, the orientation and volume of fibres have a significant influence on the creep performance of rebars/tendons.

      Shall we wrap up?

      Conclusion

      In this blog, we saw the properties, uses, types and advantages of fiber-reinforced concrete. If you have any queries please feel free to ask in the comments.

      CONCRETE, quality tests on concrete

      Ultrasonic pulse velocity test || UPV Test – Types and Methodology

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      The ultrasonic pulse velocity test, or UPV test, is an example of a non-destructive concrete test. Generally, hardened concrete is subjected to non-destructive testing (NDT) and destructive tests (DT). Concrete is the world’s oldest and most significant construction material. Therefore, concrete testing is crucial for assessing the stability, strength, durability, and condition of structures.

      Non-destructive testing of concrete is a way of analysing concrete structures without causing damage. This aids in ensuring the structural quality and condition. The strength of the concrete is also influenced by various characteristics, including hardness, density, curing circumstances, ingredient quality, workability and water-to-cement ratio, etc.

      This article discusses the UPV test, which is one of the most well-liked and reliable non-destructive tests carried out on concrete structures.

      1. Ultra sonic Pulse Velocity test (UPV Test)
      2. Relevant IS code for Ultrasonic Pulse Velocity Test (UPV Test)
      3. Ultrasonic Pulse Velocity tester
      4. Principles of Ultrasonic Pulse Velocity test
      5. Objective of UPV tests
      6. Factors affecting Ultrasonic pulse velocity test
      7. Methodology of Ultrasonic Pulse velocity tests
        1. Direct method
        2. Indirect method
      8. Result interpretation of UPV testing
      9. Conclusion

      Also read : Bitumen tests – 9 tests for flexible pavements

      Ultra sonic Pulse Velocity test (UPV Test)

      The most efficient and fast method of testing concrete is through ultrasonic pulse velocity tests, or UPV tests. The quality of concrete is assessed using the results of UPV tests, which evaluate the period of travel of ultrasonic pulse waves. A 50–55 kHz range must be maintained for the ultrasonic pulse wave’s frequency. The pulses are generated by the UPV tester’s pulse generator and are allowed to travel through the concrete. By monitoring the traversing distance and the duration, the pulse velocity can be determined. Higher velocity indicates that the density and elastic modulus of the concrete are higher.

      Cracks and defects in the structure are detected using UPV tests. Significant variations in pulse velocity values are indicative of broken and degraded concrete. The concrete’s density and wave velocity are related. Therefore, this test has a tremendous potential for evaluating the quality of concrete.

      Relevant IS code for Ultrasonic Pulse Velocity Test (UPV Test)

      IS-13311 (Part 1):1992 (Reaffirmed- May 2013) “Non-Destructive Testing of Concrete- Methods of Test (Ultrasonic Pulse Velocity)”

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      Ultrasonic Pulse Velocity tester

      The UPV tester is the name of the type of equipment used to measure ultrasonic pulse velocity. The following accessories are included in ultrasonic pulse velocity tester.

      • Electrical Pulse generator
      • Pair of Transducers (probes)
      • Amplifier
      • Electronic timing device
      Ultrasonic Pulse Velocity Tester
      Ultrasonic Pulse Velocity Tester

      Principles of Ultrasonic Pulse Velocity test

      The electrical pulse generator generates pulses that are sent through the UPV tester’s transducer. Through the concrete surfaces, the pulse generates many reflections. Using the formula shown below, the pulse velocity is calculated.

      Pulse velocity, V = L/T

      where L is the traverse distance, T is the time for the receiver to receive the pulse

      The geometry of the material is unrelated to the UPV test. Better concrete strength is associated with higher velocity and vice versa. One of the dynamic tests for concrete is the ultrasonic pulse velocity test.

      Objective of UPV tests

      The main objectives of the ultrasonic pulse velocity test or UPV tests are

      • To learn the homogeneity of the concrete.
      • Determines the presence of cracks, voids and imperfections. 
      • To calculate the elastic modulus of concrete. 
      • Finds the quality of concrete relative to the standard requirements. 
      • To determine the age of concrete. 

      Factors affecting Ultrasonic pulse velocity test

      The UPV test detects cracks and assists in structure development. However, a number of factors influence how pulse velocity is measured. As a result, compressive strength cannot generally be approximated from the pulse velocity. The following are the elements that impact the UPV test.

      • Presence of reinforcement
      • Water content
      • Mix proportion
      • Temperature of concrete
      • Concrete age
      • Stress level of concrete

      Methodology of Ultrasonic Pulse velocity tests

      Piezoelectric and magneto strictive types of transducers are suitable for use with the UPV test. Additionally, its frequency range should be between 20 and 150 kHz. The electronic timing device monitors time with an accuracy of 0.1 microseconds.

      The transducer transmits the waves that travel through the concrete surface. The receiver transducer detects the electric signals that are generated once the pulse waves are transformed to them. The traversal length will be displayed as ( L). The electronic timing device calculates how long it takes for signals to arrive. Time is shown as (T).


      The Electronic timing device measures the receiving time of the signals. The time is denoted as (T).

      Pulse velocity (v) = L/T

      There are three common methods for doing UPV tests. They are direct method and indirect method.

      • Direct Method of UPV Testing
      • Indirect Method of UPV Testing
      Methodology of UPV test
      Methodology of UPV test

      Direct method

      The maximum energy is transmitted at right angles to the face of the transmitter. As a result, to achieve the greatest results, the receiving transducer must be placed on the side of the transmitting transducer. This is referred to as the direct approach or cross probing.

      Ultrasonic pulse velocity test
      Ultrasonic Pulse velocity test -Types

      Indirect method

      In some circumstances, the opposite side of the structure may be inaccessible. The receiving and transmitting transducers are installed on the same face of the concrete members in this scenario. This is known as the indirect method or surface probing. This approach is less effective than the direct approach. The test findings are mostly influenced by the surface concrete, which has different properties from the structural components’ core concrete.

      Result interpretation of UPV testing

      The density and elastic modulus of concrete are correlated with the ultrasonic pulse velocity. This in turn depends on the components, mixing processes, placement techniques, concrete compaction and curing, casting temperature, etc.

      The main causes of internal cracks and pockets in concrete are lack of compaction and concrete segregation. Lower pulse velocity values are a result of these concrete defects. However, the laboratory tests might have confirmed a well-designed concrete.

      The range of pulse velocity in the direct method is as shown below.

      1. Above 4.5 Excellent
      2. 3.5 to 4.5 Good
      3. 3.0 to 3.5 Medium
      4. Below 3.0 Doubtful

      Conclusion

      The final assessment of compressive strength from UPV is not the sole criterion used to determine concrete strength. The strength is confirmed by comparing it to a compressive strength estimate derived from the same ingredient mix and conditions. The results of the UPV test and site tests conducted using similar ingredients may be correlated. When compared to actual UPV intensities, the numbers may change by about 20%.

      CONCRETE

      Concrete Mixing || Mixing concrete – Objectives and types

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      Concrete Mixing or Mixing of concrete is the complete blending of the ingredients necessary for the production of a homogeneous concrete. In the previous blogs, we saw different types of concrete and their quality tests. Today, let me walk you through the details of it.

      To begin with, let’s try to understand the objectives of mixing concrete and concrete mixing types

      1. Objectives of Concrete Mixing
      2. Concrete Mixing Types
        1. Hand Mixing of concrete
          1. Process – Hand Mixing of concrete
        2. Machine Mixing of Concrete
          1. Concrete Mixing Machine
          2. Machine Mixing Process
        3. Ready Mix Concrete
        4. Mixing Ratios
      3. Conclusion

      Objectives of Concrete Mixing

      How many of you have wondered why we mix concrete? Read on to find the answers.

      • To manufacture high-quality fresh concrete, proper mixing of materials is critical. 
      • The surface of all aggregate particles is coated with cement paste during the mixing phase.
      • For the desired workability and performance of concrete in both the fresh and hardened states.
      • To avoid segregation and bleeding.

      In the next section, we will learn the types of concrete mixing

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      Concrete Mixing Types

      There are three methods to produce efficient and high-quality concrete.

      • Hand Mixing – Mixing concrete manually without a mixer machine.
      • Machine Mixing – Mixing using a mixer machine.
      • Ready Mix Concrete – Mixing is done in an automatic or semi-automatic batch plant.

      Let’s dig deeper into each of them.

      Hand Mixing of concrete

      • Method of manually mixing the concrete materials without the use of a mixer machine. 
      • Hand mixing is done only for small jobs where the concrete demand is low and quality control is not critical. 
      • Uniformity of mixing is difficult to achieve by hand mixing. It necessitates extra caution and effort. 
      • In the case of hand mixing, 10% more cement should be applied to the nominal mix concrete proportion.
      Hand mixing of concrete
      Hand mixing of concrete

      Process – Hand Mixing of concrete

      • Hand mixing is done on a flat iron sheet plate base that is hard, clean, and non-porous.
      • On the platform, a measured amount of sand is placed.
      • Then the cement is poured over the sand.
      • In a dry state, the sand and cement are thoroughly combined with shovels several times until the mixture achieves an even colour.
      • The coarse aggregates are then spread out on top of the above mixture and thoroughly mixed. 
      • The whole mixture is properly mixed by twisting it from centre to side, back to centre, and then to the sides several times.
      • After that, depression is rendered in the mixed materials’ nucleus.
      • 75 per cent of the necessary amount of water is then poured into the depression and mixed with shovels.
      • Finally, the remaining water is applied, and the mixing process is repeated until the concrete has a uniform colour and consistency. 

      The total time for concrete mixing does not exceed 3 minutes.

      Let’s move on to the next method ie mechanised concrete mixing.

      Machine Mixing of Concrete

      • The method of combining concrete materials with a concrete mixer system is known as machine mixing. 
      • It meets the demands of fast mixing times, optimal consistency, and homogeneous concrete efficiency. 
      • Since it ensures uniform homogeneity, machine mixing of concrete is best suited for large projects requiring large quantities. 

      Concrete Mixing Machine

      It is also known as a concrete mixer is a machine that mixes cement, aggregate (such as sand or gravel), and water in a uniform manner to shape concrete. A rotating drum is used to combine the components in a traditional concrete mixer. Concrete mixers powered by gasoline, diesel, or electricity are now widely available. The mixer machine is mostly used for mixing ingredients by volume. They are also used for mixing ingredients by weight by providing weigh batcher.

      Mixer machine in action
      Mixer machine in action

      Machine Mixing Process

      • Wet the inner surfaces of the concrete mixer drum first.
      • The coarse aggregates are added first, followed by sand, and finally cement, in the mixer.
      • In a mixing machine, combine the products in a dry state. In most cases, 1.5 to 3 minutes should suffice.
      • While the machine is running, slowly add the appropriate amount of water after the dry materials have been thoroughly mixed. 
      • Don’t use any extra water.
      • Concrete must be mixed in the drum for at least two minutes after adding water.

      We have seen the details of machine mixing. How about getting an idea about ready-mix concrete?

      Ready Mix Concrete

      • Ready Mix Concrete (RMC) is a specialised material in which the cement, aggregates, and other materials are weighed and batched at a central location, then mixed either in a central mixer or in truck mixers. Then it is shipped to construction sites.
      • The consistency of the resulting concrete is much superior to that of site-mixed concrete.
      • Useful on congested sites or in road construction where space for a mixing plant or aggregate storage is limited or nonexistent. 
      • Quality control of concrete is simple in this process.

      So far, I have showed you the types of concrete mixing and its procedures. Now its time to throw some light on concrete mixing ratios.

      Ready Mix concrete plant
      Ready Mix concrete plant

      Mixing Ratios

      The proportions of concrete components such as cement, sand, aggregates, and water are known as concrete mix ratios. The method of building and mix designs are used to determine these ratios. In comparison to other mixing processes, the water/cement ratio in RMC can be easily managed.

      Conclusion

      To summarise,

      • Hand blending of concrete is the cheapest method.
      • It is only recommended for very limited projects requiring a small amount of concrete since consistent concrete consistency is difficult to achieve with this method. 
      • It ensures proper material mixing.
      • When compared to site mixing (both hand and machine mixing), RMC takes less time and produces a higher quality product.
      • It’s also very handy when you need a large amount of concrete per day.
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      Waffle Slab or Ribbed slab details and Construction, Advantages

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      Waffle slabs are ribbed reinforced concrete slabs. A waffle slab often referred to as a ribbed slab, is a structural component that is plain on top and has a grid pattern on the bottom. A waffle slab also called a two-way joist slab got ribs running perpendicular to each other in two directions on the underside. This slab resembles pockets of waffles because of its grid pattern. Hence they are named Waffle slab systems.

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      For spans longer than 40 feet (12 metres), waffle slabs are chosen because they are stronger than flat slabs, flat slabs with drop panels, two-way slabs, one-way slabs, and one-way joist slabs. These are more expensive than other slabs but in turn, are more rigid and stable. Waffle slabs are apt for both ceiling and floor slabs. Slabs are one of the important structural components of a building. They provide a flat surface and help in transferring load. This article is about what is waffle slabs, the Construction process, Advantages and Disadvantages. 

      1. What is a waffle slab – Details and construction
      2. Waffle slab construction details
        1. In situ construction
        2. Precast
        3. Prefabricated
      3. Advantages of Waffle slab 
      4. Disadvantages of Waffle slab

      What is a waffle slab – Details and construction

      A waffle slab is a type of slab that is appropriate for industrial and commercial buildings. Waffle slabs are also referred to as two-way joist slabs or ribbed slabs. They have a flat top and grids on the underside. It has greater strength than flat slabs and hence is suited for longer spans. It enables both distributed and point vertical actions. The bottom layer of concrete reinforcement in waffle slabs is replaced by concrete ribs running in two orthogonal directions. Additionally, the rib depth should range from 135mm to 235mm. Because the overall depth of the floor increases as the depth of the ribs does. The structure’s lateral loading is impacted by this.

      Waffle slab - supports and pods

      Waffle slab construction details

      The waffle slabs need only 70% of concrete and 80% of steel from the concrete and steel used for the construction of the raft slab. The construction stages of the waffle slab include the following

      • The first step is to create the forms
      • Place the formwork components in place.
      • Position your waffle pods or moulds on the shuttering. Generally, the pods are typically constructed of plastic, and they come in a variety of sizes and shapes. The size of the pod is determined by the requirements and span length. A significant number of pods are necessary for greater spans. Accordingly, the same size pods should be used for the entire slab.
      waffle pods and beam supports
      • Place the support components horizontally and vertically according to the connectors.
      • Lay out the waffle pods and spacer within the formwork in a grid pattern beginning at one corner, following the instructions in the design.
      waffle slab grid supports
      Waffle slab supports
      • Fix the pod corners to the framework using cube joints.
      • Position reinforcement bars on the spacers between the waffle Pods.
      • Reinforcement is added in the two directions after the formwork has been fixed.
      • Lay the top mesh out according to the design specifications, then secure it where necessary.
      • Making sure connecting ribs are filled, pour the concrete and give it a good vibrating.
      • After the setting of the concrete, remove the frames into which the waffles are embedded. Then slowly remove the waffle forms. 

      The construction of a waffle slab can be done in three ways

      In situ construction

      This process entails placing formwork and pouring concrete over it. A slab is cast on-site in the desired size and according to the design.

      Waffle slab
      waffle slab (https://styrofoamindustries.com.au/

      Precast

      Using this technique, the casting of the slab panel is done elsewhere, and it is then placed, connected, and reinforced with concrete.

      Prefabricated

      In this procedure, reinforcement is built into the slab panels using prefabricated steel bars. Slabs are manufactured elsewhere and brought to the location to be erected.

      Advantages of Waffle slab 

      • It is suitable for large-span structures and can be achieved with less concrete and rebar than similar conventional slabs
      • They require only a fewer number of columns.
      • It possesses a higher load-carrying capacity
      • It has higher structural stability
      • They have a good aesthetic appearance. 
      • Waffle slabs are suitable for roof slabs and floor slabs.
      • Waffle slabs have high vibration control capacity
      • The construction of this slab can be done faster and easier.
      • They are light weighted 
      • They require low construction costs, Hence they are economical when compared to other conventional slabs of the same span
      • It requires only less amount concrete and can be reinforced with mesh or rebars.

      Disadvantages of Waffle slab

      • Requires Expensive formwork
      • Requires skilled workmen and supervision for the construction of waffle slabs. 
      • Higher maintenance cost
      • The increase in the depth of ribs leads to an increase in the floor height.
      • This type of slab is not suitable for windy and slope areas.
      CONCRETE, curing

      Curing of Concrete – Concrete Curing Methods explained

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      Curing concrete is the process of preserving the requisite moisture and temperature in hardened concrete for continued hydration. Concrete’s curing is crucial for sustaining the material’s longevity and design strength. This article discusses the importance of curing and the various concrete curing methods prevailing on construction sites.

      1. Curing of concrete methods
      2. Why Curing of concrete is important?
      3. Concrete Curing time as per IS 456-2000
      4. Concrete curing methods
        1. Water Curing method
        2. Membrane Curing method
        3. Steam curing method
      5. Conclusion

      Curing of concrete methods

      Curing is the process of retaining moisture to allow fresh concrete to reach its intended strength in a predetermined manner through a hydration reaction. Concrete is a mixture of cement, aggregates, and water in fixed designed proportions calculated based on specific strength requirements. The water to cement ratio is the most important factor in these proportions (Water cement ratio). In order to facilitate the hydration reaction, the water-cement ratio must be maintained. If the water evaporates quickly, there will not be enough water available for the hydration process. Because of this curing of concrete is required.

      Curing assists in the retention of moisture until the hydration process is complete and it reaches the required strength. The American Concrete Institute (ACI) Committee 301 recommends a minimum cure duration equal to 70% of the required compressive strength. According to IS 456-2000 standards and construction norms, the curing period of 7 days/10 days is the time required to achieve at least 70% of the intended compressive strength. That is why concrete is cured for 7-10 days.

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      Why Curing of concrete is important?

      Perfect curing is necessary for the following reasons in order to achieve good strength and serviceability:

      • Curing prevents concrete from drying and maintains the acceptable temperature range by preventing moisture loss.
      • Curing increases the strength and decreases the permeability of hardened concrete.
      • Curing prevents the formation of cracks caused by thermal and plastic shrinkage.
      • Concrete curing maintains a strong link between the components and the reinforcement.
      • Curing can provide the desired strength and a durable concrete free of cracks.
      • Concrete curing assists in achieving high serviceability performance by improving abrasion resistance.

      Also Read : Concrete Pumps Types – Application and advantages

      Concrete Curing time as per IS 456-2000

      According to the Indian Standard IS 456 – 2000, concrete should be allowed to cure for a minimum of seven days while using ordinary Portland cement and for a minimum of ten days while using blended cement or concrete with mineral admixtures. Additionally, it suggests that the curing time should not be less than 10 days for structures exposed to hot, dry weather and 14 days in case for or blended cement or cement with mineral admixtures.

      OPC cement = 7 Days (Normal conditions) and 14 Days ( Hot and dry weather)

      Concrete with mineral admixture or blended cement (PPC cement) = 7 Days (Normal conditions) and 14 Days ( Hot and dry weather)

      Concrete curing methods

      The curing method and time primarily depend on structure type, site conditions, and ingredient parameters. Some of the curing methods adopted in constructions sites are as follows.

      • Water curing
      • Membrane Curing
      • Steam curing

      Water Curing method

      Water curing is the most popular and common method adopted in construction sites. Basically, this method maintains or retains water on the concrete surface by various methods. This includes ponding, sprinkling and fogging, and saturated wet coverings or left-in-place forms.
      Similarly, these methods prevent water loss from the concrete surface by continuous wetting of the exposed surface of the concrete.

      Water curing
      Water curing

      Membrane Curing method

      The basic concept of membrane curing is reducing the loss of water from the surface of the concrete. Generally, membrane curing methods uses curing compounds or impervious plastic sheets. Curing compounds are available in water-based and acrylic-based types. They form an impermeable membrane and reduces the loss of moisture.

      Membrane curing /Curing compound
      Membrane curing /Curing compound

      Steam curing method

      The steam curing process accelerates the process of strength gaining by using heat and providing additional moisture. Generally, this speeds up the early hardening process. Basically, these methods are familiar in prefabricated structures and factory-made precast components for the speedy recovery of form works.
      Accordingly, Steam curing keeps the surface moist and raises the concrete temperature to speed up the strength achievement rate.

      Steam curing - Precast factory
      Precast factory

      Conclusion

      Now a days curing activity is not taken seriously and this hampers the strength and quality. Likewise, this is an activity to be done with utmost care to ensure design strength and serviceability of structures.