Term: Reinforced concrete
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**Reinforced Concrete Overview:**
– Description of reinforcing schemes to resist tensile stresses.
– Use of varied materials like steel and polymers for reinforcement.
– Importance of permanent stress for better structure behavior.
– Properties required for reinforcement: high strength, good bond to concrete, etc.
– Common methods in the US: pre-tensioning and post-tensioning.
**History and Innovations:**
– Contributions of François Coignet, Joseph Monier, Thaddeus Hyatt, Ernest L. Ransome, and G. A. Wayss in reinforced concrete.
– Evolution of iron and steel concrete construction techniques.
**Design and Behavior of Reinforced Concrete:**
– Use of reinforced concrete elements in various structures.
– Importance of designing efficient floor systems for optimal building structures.
– Understanding the behavior of reinforced concrete elements under external loads.
– Various stresses like tension, compression, bending, shear, and torsion experienced by elements.
**Materials and Mechanisms:**
– Composition of concrete and steel in reinforced concrete.
– Key characteristics like thermal expansion coefficients and protection against corrosion.
– Mechanism of composite action of reinforcement and concrete.
– Anchorage codes and anticorrosion measures for reinforced concrete.
**Innovations and Challenges in Reinforced Concrete:**
– Techniques like prestressed concrete to increase load-bearing strength.
– Common failure modes, including mechanical failure and carbonation.
– Challenges like alkali silica reaction, sulfate attack, and use of non-steel reinforcement materials.
– Advantages of plastic reinforcement like FRP and GRP in concrete applications.
Reinforced concrete, also called ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel bars (rebar) and is usually embedded passively in the concrete before the concrete sets. However, post-tensioning is also employed as a technique to reinforce the concrete. In terms of volume used annually, it is one of the most common engineering materials. In corrosion engineering terms, when designed correctly, the alkalinity of the concrete protects the steel rebar from corrosion.
Reinforced concrete | |
---|---|
Material type | Composite material |
Mechanical properties | |
Tensile strength (σt) | Stronger than concrete |
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- Glossary: ConcreteDefinition and Composition of Concrete - Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. - It is the second-most-used substance in the world after water. - Concrete is the most widely used building material. - Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined. - When aggregate is mixed with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape. Hydration Process, Additives, and Reinforced Concrete - The cement reacts with the water through a process called concrete hydration that hardens it over several hours. - The hydration process is exothermic, meaning ambient temperature affects the setting time of concrete. - Additives like pozzolans or superplasticizers are included to improve the physical properties of the wet mix. - Additives can also delay or accelerate the curing time of concrete. - The finished material can be modified by adding additives to change its properties. - Most concrete is poured with reinforcing materials, such as steel rebar, embedded to provide tensile strength. - Reinforced concrete is a combination of concrete and reinforcement materials. - The addition of reinforcement allows concrete to withstand tensile forces. - Reinforced concrete is widely used in construction due to its strength and durability. - It is commonly used in structures like bridges, buildings, and infrastructure. Types of Concrete and Historical Significance - Lime-based cement binders, such as lime putty, were used in the past. - Portland cement concrete is a common type of concrete that uses Portland cement as a binder. - Non-cementitious types of concrete exist, such as asphalt concrete with a bitumen binder. - Polymer concretes use polymers as a binder. - Concrete is distinct from mortar, which is a bonding agent used to hold masonry units together. - Concrete floors were found in ancient structures like the royal palace of Tiryns, Greece. - The Assyrian Jerwan Aqueduct (688 BC) made use of waterproof concrete. - Mayan concrete at the ruins of Uxmal (850-925 A.D.) is referenced in historical accounts. - The Nabateans pioneered small-scale production of concrete-like materials. - The Romans extensively used concrete from 300 BCE to 476 CE, revolutionizing architecture. Cement, Water, Aggregates, and Admixtures - Portland cement is the most common type of cement, patented by Joseph Aspdin in 1824. - Cement consists of calcium silicates, aluminates, and ferrites. - Water combines with cementitious material to form a cement paste. - Lower water-to-cement ratio yields stronger, more durable concrete. - Impure water can cause problems in concrete setting and structure failure. - Fine and coarse aggregates make up the bulk of a concrete mixture. - Sand, natural gravel, and crushed stone are commonly used aggregates. - Recycled aggregates from construction, demolition, and excavation waste are increasingly used. - Admixtures are materials added to concrete to give it certain characteristics. - Common admixtures include retarders, accelerators, air entraining agents, and bonding agents. Use of Alternative Materials, Concrete Enhancements, and Production - Alternative materials can lower costs, improve concrete properties, and recycle wastes. - Limestone, fly ash, blast furnace slag, and other materials are being tested and used. - These developments aim to minimize the impacts of cement use on greenhouse gas emissions. - Alternative materials contribute to circular economy aspects of the construction industry. - Crystalline admixtures, pigments, plasticizers, superplasticizers, and retarders are used to enhance concrete. - Concrete production is the process of mixing water, aggregate, cement, and additives to produce concrete. - Concrete production takes place in concrete plants, either ready mix plants or central mix plants. - Design mix ratios, mixing techniques, and curing methods are important factors in concrete production.
- Glossary: Concrete sawBlade choice - Consider the diamond saw blades' features and the type of concrete/asphalt being cut - Take into account the presence of steel bars in reinforced concrete - Differentiate between pebbles and crushed rocks in concrete stone aggregate - Account for the curing time of the concrete (long or short) - Ensure the diamond saw blades are designed to fit the specific concrete and asphalt Wet or dry cutting - Diamond saw blades for concrete are usually designed for wet cutting - Inadequate water during dry cutting can cause the diamond segment or steel core to break - Dry cutting should be intermittent and shallow to keep the blade cool - Choose sharper diamond blades for dry cutting if water source is not available - Dry cutting should be done in several passes to achieve a deep cut Faster cutting or longer lifespan - Determine the basic cutting speed of the diamond saw blades - Select a blade with faster cutting speed or longer lifespan based on the determined speed - Consider the specific cutting requirements for the task at hand - Evaluate the trade-off between cutting speed and lifespan - Choose a blade that meets the desired balance between speed and lifespan Power output of the concrete saw - Higher power output requires a higher diamond concentration or a harder bond - Lower power output requires a lower diamond concentration or a softer bond - Diamond concentration and bond hardness affect the blade's sharpness - Consider the impact on the diamonds when cutting with high power output - Ensure the blade can achieve the necessary cutting speed based on the saw's power output Dust control - Cutting materials like stones, rocks, sands, and clays can produce airborne dust containing fine respirable crystalline silica (RCS) particles - RCS particles can cause serious health effects such as lung cancer or silicosis - Wet cutting with adequate water supply helps control dust - Diamond saw blades are preferable to abrasive blades for faster cutting with less water - Local exhaust ventilation (LEV) systems can capture the majority of dust emitted during cutting operations
- Glossary: Ready-mix concreteHistory and Growth of Ready-Mix Concrete - First ready-mix delivery made in Baltimore in 1913 - Over 100 plants operating in the United States by 1929 - Significant industry expansion in the 1960s - Continued growth since the 1960s - Dispute over the first factory built Design and Usage of Ready-Mix Concrete - Batch plants combine gravel, sand, water, and cement by weight - Wide range of uses in building, especially in large projects - Long lifespan compared to other products - Used when construction site cannot mix concrete on-site - Cost and time benefits for small to medium projects - Ready-mix concrete delivered finished, on demand, in specific quantity and mix design - Cost and time savings compared to on-site mixing - Environmental concerns with on-site mixing - Outsourcing concrete production for large projects - Bought and sold by volume (cubic meters) Testing, Quality Control, and Advantages of Ready-Mix Concrete - Ready-mixed concrete specified by weight or volume - Laboratory testing and field testing for verification - Admixtures used to modify concrete mix performance - Limited lifespan between batching/mixing and curing - Various methods of transportation and placement at the site - Controlled conditions in ready-mix concrete plants ensure quality - Use of admixtures and additives to slow hydration process - Steady supply for large forms to prevent cold joints - Sophisticated equipment and consistent methods for quality control - Strict testing of materials and continuous monitoring of key practices - Improved control over the manufacturing process - Increased speed in construction practices - Reduction in cement consumption by 10-12% - Decreased environmental pollution - Reduced dependency on human labor Challenges and Comparison of Ready-Mix Concrete - Cracking and shrinkage issues - Weight limitations for access roads and sites - Need for specialized mini mix trucks in weight-restricted areas - Limited range of mix designs in centralized batch systems - Continuous loading and mixing capabilities of volumetric mixers - Transit Mixed Ready Mix vs. Volumetric Mixed Ready Mix - Site-mix trucks can serve remote locations - Volumetric trucks have lower water demand and higher compressive strength - Centralized batch systems offer a greater range of mix designs - Volumetric mixers can change mix designs on-site - Centralized batching provides predictable and consistent results - Advantages of Centralized Batching - Tighter tolerances for mixes - Centralized lab for designing and verifying mixes - Ability to scale quickly with less movement - Consistent large-scale pours across a site - Reduced traffic and fuel consumption for small loads Additional Information on Ready-Mix Concrete - Types of concrete - Reinforced concrete - References for further reading - Industry market research and statistics - Importance of controlling hazardous substances in construction - Properties of Ready-mix Concrete - ASTM C 94 and AASHTO M 157 standards govern ready-mix concrete - Time limit between placing fresh concrete layers is important - Nano-silica incorporating polymer-modified cement pastes affect the fresh properties of ready-mix concrete - Chemical admixtures can be used in ready-mix concrete - Cold joints can occur in ready-mix concrete - Manufacturing of Ready-mix Concrete - Fosroc, Akona India, and Major 3000 Concrete Batching are manufacturers of ready-mix concrete - Precision and quality are important factors in manufacturing ready-mix concrete - Design and control of concrete mixtures play a crucial role in the manufacturing process - Structural Properties of Ready-mix Concrete - Ready-mix concrete is used as a structural material - Density of concrete affects its weight - ASTM provides standard test methods for measuring the density of concrete - The book 'Structural Materials' provides insights into the properties of ready-mix concrete - Ready-mix concrete contributes to the strength and stability of structures - Applications of Ready-mix Concrete - Ready-mix concrete is widely used in construction projects - It is commonly used for building foundations - Ready-mix concrete is suitable for paving roads and highways - It is used in the construction of bridges and tunnels - Ready-mix concrete is also used in the production of precast concrete elements - Importance of Quality Control in Ready-mix Concrete - Quality control is crucial in the production of ready-mix concrete - Adhering to ASTM standards ensures quality control - Proper testing and monitoring of fresh properties of ready-mix concrete are essential - Quality control measures prevent issues like cold joints and ensure uniformity - Ready-mix concrete suppliers should prioritize quality control to meet customer expectations
- Glossary: RebarDefinition, Purpose, and History of Rebar - Rebar is short for reinforcing bar, used to strengthen and support concrete and masonry structures. - It is made of steel and increases the tensile strength of the structure. - Rebar has a ribbed surface to enhance bonding with concrete and prevent slippage. - Carbon steel is the most common type of rebar, but other options like stainless steel and composite bars are available. - Coatings like zinc or epoxy resin can be applied to protect against corrosion. - Rebar has been used since ancient times, with iron or wooden rods in arch construction. - In the 19th century, steel bars were embedded in concrete, leading to the development of modern reinforced concrete. - Notable figures in the invention and popularization of reinforced concrete include Joseph Monier and Ernest L. Ransome. - Twisted iron rebar was initially met with skepticism but was used in the first reinforced concrete bridge in the United States. - Different reinforcing systems, such as the mushroom system and diamond-shaped rebar, were experimented with but faced criticism and were eventually replaced. Use and Benefits of Rebar - Rebar is used in concrete to provide tensile strength, compensating for its weakness in tension. - Primary reinforcement ensures the overall resistance needed to support design loads. - Secondary reinforcement, also known as distribution or thermal reinforcement, limits cracking and resists stresses caused by temperature changes and shrinkage. - Rebar can also be embedded in masonry walls for added strength and stability. - Rebar significantly increases the tensile strength of concrete structures, making them more durable and resistant to cracking. - It enhances the structural integrity and stability of buildings, bridges, and other reinforced concrete elements. - The use of rebar allows for the construction of larger and more complex structures. - Different types of rebar, such as stainless steel or composite bars, offer specific performance advantages in certain construction projects. - Coatings like zinc or epoxy resin protect rebar from corrosion, extending its lifespan in harsh environments. Standards and Specifications for Rebar - Deformations on steel bar reinforcement were standardized in the US construction industry around 1950. - ASTM A305-49 established the requirements for deformations, including rib height and spacing. - Current specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, maintain the same deformation requirements as ASTM A305-49. - These standards ensure the quality and performance of rebar in reinforced concrete structures. - Compliance with these specifications is essential for the safety and longevity of the construction projects. Physical Characteristics, Corrosion Prevention, and Sizes of Rebar - Steel has a thermal expansion coefficient similar to modern concrete. - Rebar can be pulled out of concrete under high stresses, leading to collapse. - Rebar is deeply embedded or bent and hooked to prevent failure. - Unfinished tempered steel rebar is susceptible to rusting. - Concrete cover must provide a pH value higher than 12 to avoid corrosion. - Uncoated steel rebars can be prone to rusting. - Corrosion-resistant materials like epoxy-coated, galvanized, or stainless steel rebars are used in saltwater or marine applications. - Epoxy-coated rebar provides better corrosion resistance than uncoated rebar. - Damage to epoxy-coated rebar reduces its long-term corrosion resistance. - Stainless steel rebar with low magnetic permeability is used to avoid magnetic interference. - US/Imperial bar sizes are given in units of 1/8 inch. - The cross-sectional area of a bar is calculated using the formula (bar size/9)^2. - Bar sizes larger than #8 follow the 1/8-inch rule and skip certain sizes due to historical convention. - Sizes smaller than #3 are not recognized as standard sizes. - US/Imperial bar sizes can be converted to metric sizes, but it may result in physically different sized bars. - Fiber-reinforced plastic (FRP) rebar is used in high-corrosion environments. - FRP rebar is available in various forms like spirals, rods, and meshes. - Most commercially available FRP rebar is made from unidirectional fibers set in a thermoset polymer resin. - Glass fiber types of FRP rebar have low electrical conductivity and are non-magnetic. Rebar Sizes in Different Countries - Metric bar designations represent the nominal bar diameter in millimeters. - Preferred bar sizes in Europe comply with Table 6 of the standard EN 10080. - Various national standards still remain in force, such as BS 4449 in the United Kingdom. - Reinforcement for concrete construction in Australia follows the requirements of Australian Standards AS3600 and AS/NZS4671. - Reinforcement for concrete construction in New Zealand complies with the requirements of AS/NZS4671. - Rebars in India are available in different grades such as FE 415, FE 415D, FE 415S, FE 500, FE 500D, FE 500S, FE 550, FE 550D, and FE 600. - Very large format rebar sizes are available from specialty manufacturers. - Jumbo bars are commonly used as anchor rods for large structures in the tower and sign industries. - Fully threaded rebar with coarse threads is produced to satisfy rebar deformation standards and allow for custom nuts and couplers.