Etymology and History
– The word ‘concrete’ comes from the Latin word ‘concretus’ meaning compact or condensed.
– The term ‘concrete’ signifies the process of materials bonding together.
– Concrete floors were found in the royal palace of Tiryns, Greece, dating back to 1400-1200 BC.
– The Assyrian Jerwan Aqueduct (688 BC) utilized waterproof concrete.
– The Nabatean traders in the 4th century BC pioneered the production of concrete-like materials.
– Ancient Egyptians and Romans discovered the pozzolanic reaction by adding volcanic ash to lime.
– Roman concrete, known as ‘opus caementicium,’ revolutionized architecture with its structural complexity.
– The Colosseum and the Pantheon are notable examples of Roman structures made of concrete.
– After the decline of the Roman Empire, the use of concrete diminished.
– The knowledge of Roman concrete was preserved in some structures, such as the Baths of Caracalla.
– Many Roman aqueducts and bridges had masonry cladding on a concrete core.
– The use of concrete resurged during the Renaissance and became more prominent in modern construction.
Composition
– Concrete is an artificial composite material.
– It consists of a matrix of cementitious binder and a dispersed phase or filler of aggregate.
– The binder glues the filler together to form a synthetic conglomerate.
– Different formulations of binders and types of aggregate determine the strength, density, and resistance of the finished concrete.
– Construction aggregates consist of large chunks of material, such as coarse gravel or crushed rocks, along with finer materials like sand.
– Portland cement is the most common type of cement used in concrete.
– Portland cement is made by heating limestone with clay or shale and grinding the resulting clinker with a source of sulfate.
– Water combined with cementitious material forms a cement paste through hydration.
– The water-to-cement ratio affects the strength and flow of concrete.
– Fine and coarse aggregates make up the bulk of a concrete mixture.
– Sand, natural gravel, and crushed stone are commonly used aggregates.
Admixtures and Blended Cements
– Admixtures are materials added to concrete to give it specific characteristics.
– Common admixtures include retarders and accelerators.
– Mineral admixtures are fine-grained materials added to improve concrete properties.
– Blended cements replace Portland cement and incorporate useful materials.
– Fly ash is a by-product of coal-fired plants and can replace up to 60% of cement.
– Ground granulated blast furnace slag can replace up to 80% of cement.
– Silica fume has a smaller particle size and requires superplasticizers for workability.
Production and Types of Admixtures
– Concrete production involves mixing water, aggregate, cement, and additives.
– Production usually takes place in a concrete plant or batch plant.
– Concrete must be placed before it hardens.
– Accelerators speed up the hardening of concrete.
– Air entraining agents reduce damage during freeze-thaw cycles.
– Bonding agents create a bond between old and new concrete.
– Corrosion inhibitors minimize corrosion of steel in concrete.
– Crystalline admixtures lower permeability and provide waterproof protection.
Environmental Considerations and Concrete Plants
– Alternative materials can lower costs and improve concrete properties.
– Cement production is a significant contributor to greenhouse gas emissions.
– Fly ash is a by-product of coal-fired plants and can be used as a cement replacement.
– Ground granulated blast furnace slag is a by-product of steel production and can replace cement.
– Recycled materials, such as washed and dried diapers, can be used in concrete production.
– Two main types of concrete plants: ready mix plants and central mix plants.
– Ready-mix plant mixes all ingredients except water, while central mix plant mixes all ingredients including water.
– Central-mix plant offers more accurate control of concrete quality.
– Concrete plant consists of storage hoppers, machinery, and facilities for dispensing mixed concrete.
– Concrete is usually poured into forms to give it the desired shape.
– Forms can be prepared through slip forming or steel plate construction.
– Proper formwork preparation is crucial to avoid cold joints between batches.
– Design mix ratios are decided by an engineer and custom-designed mix meets specific site requirements.
– Thorough mixing is essential for uniform, high-quality concrete.
– Workability is the ability of fresh concrete mix to fill the form properly.
– Concrete must be kept moist during curing for optimal strength and durability. Source: https://en.wikipedia.org/wiki/Concrete
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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.
