Term: Demolition

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.