Definition 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.
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Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and 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. The cement reacts with the water through a process called concrete hydration that hardens it over several hours to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. This time allows concrete to not only be cast in forms, but also to have a variety of tooled processes performed. The hydration process is exothermic, which means ambient temperature plays a significant role in how long it takes concrete to set. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix, delay or accelerate the curing time, or otherwise change the finished material. Most concrete is poured with reinforcing materials (such as steel rebar) embedded to provide tensile strength, yielding reinforced concrete.
In the past, lime based cement binders, such as lime putty, were often used but sometimes with other hydraulic cements, (water resistant) such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (named for its visual resemblance to Portland stone). Many other non-cementitious types of concrete exist with other methods of binding aggregate together, including asphalt concrete with a bitumen binder, which is frequently used for road surfaces, and polymer concretes that use polymers as a binder. Concrete is distinct from mortar. Whereas concrete is itself a building material, mortar is a bonding agent that typically holds bricks, tiles and other masonry units together. Grout is another material associated with concrete and cement. It does not contain coarse aggregates and is usually either pourable or thixotropic, and is used to fill gaps between masonry components or coarse aggregate which has already been put in place. Some methods of concrete manufacture and repair involve pumping grout into the gaps to make up a solid mass in situ.