Speaker 1: Welcome to the I Can't Sleep Podcast, where I help
Speaker 1: you drift off one fact at a time. I'm your host,
Speaker 1: Benjamin Boster, and today's episode is about concrete. Concrete is
Speaker 1: a composite material composed of aggregate bound together with a
Speaker 1: fluid cement that cures to a solid. It is the
Speaker 1: second most used substance after water, the most widely used
Speaker 1: building material, and the most manufactured material in the world.
Speaker 1: When aggregate is mixed with dry Portland cement and water,
Speaker 1: the mixture forms a fluid slurry that can be poured
Speaker 1: and molded into shape. The cement reys with the water
Speaker 1: through a process called hydration, which hardens it after several
Speaker 1: hours to form a solid matrix that binds the materials
Speaker 1: together into a durable, stone like material with various uses.
Speaker 1: This time allows concrete to not only be cast in forms,
Speaker 1: but also to have a variety of tooled processes performed.
Speaker 1: The hydration process is exocermic, which means that ambient temperature
Speaker 1: plays a significant role in how long it takes concrete
Speaker 1: to set. Often, additives are included in the mixture to
Speaker 1: improve the physical properties of the wet mix, delay or
Speaker 1: accelerate the curing time, or otherwise the finished material. Most
Speaker 1: structural concrete is poured with reinforcing materials such as steel
Speaker 1: rebar embedded to provide tensile strength yielding reinforced concrete. Before
Speaker 1: the invention of Portland cement in the early eighteen hundreds,
Speaker 1: lime based cement binders such as lime putty were often used.
Speaker 1: The overwhelming majority of concretes are produced using Portland cement,
Speaker 1: but sometimes with other hydraulic cements such as calcium luminate cement.
Speaker 1: Many other non cementitious types of concrete exist with other
Speaker 1: methods of binding aggregate together, including asphalt concrete with a
Speaker 1: bitumen binder, which is frequently used for road surfaces, and
Speaker 1: polymer concretes that use polymers as a binder. Concrete is
Speaker 1: distinct from mortar. Whereas concrete is itself a building material
Speaker 1: and contains both coarse, large and fine small aggregate particles,
Speaker 1: mortar contains only fine aggregates and is mainly used as
Speaker 1: a bonding agent to hold bricks, tiles, and other masonry
Speaker 1: units together. Grout is another material associated with concrete and cement.
Speaker 1: It also does not contain coarse aggregates and is usually
Speaker 1: either poorable or a sixotropic and is used to fill
Speaker 1: gaps between masonry components or coarse aggregate which has already
Speaker 1: been put in place. Some methods of concrete manufacture and
Speaker 1: repair involve pumping grout into the gaps to make up
Speaker 1: a solid mass in situ. The word concrete comes from
Speaker 1: the Latin word concretis, meaning compact or condensed. The perfect
Speaker 1: passive participle of concrescere from cone together and cressere to grow.
Speaker 1: Concrete floors were found in the Royal Palace of Tirans, Greece,
Speaker 1: which dates roughly to fourteen hundred to twelve hundred BC.
Speaker 1: Lime mortars were used in Greece, such as in crete
Speaker 1: and cip press. In eight hundred b C. The Assyrian
Speaker 1: Jiwan Aqueduct six eighty eight b C made use of
Speaker 1: waterproof concrete. Concrete was used for construction in many ancient structures.
Speaker 1: Small scale production of concrete like materials was pioneered by
Speaker 1: the Nebataean traders, who occupied and controlled a series of
Speaker 1: oaysees and developed a small empire in the regions of
Speaker 1: southern Syria and northern Jordan from the fourth century b C.
Speaker 1: They discovered the advantages of hydraulic lime with some self
Speaker 1: cementing properties. By seven hundred b C. They built kilns
Speaker 1: to supply mortar for the construction of rubble masonry houses,
Speaker 1: concrete floors, and underground waterproof cisterns. They kept the cistern secret,
Speaker 1: as these enabled the Naboteans to thrive in the desert.
Speaker 1: Some of these structures survived to this day. The Romans
Speaker 1: used concrete extensively from three hundred b C to eighty
Speaker 1: four seventy six during the Roman Empire. Roman concrete was
Speaker 1: made from quicklime, pozzolana and an aggregate of pumice. Its
Speaker 1: widespread use in many Roman structures, a key event in
Speaker 1: the history of architecture, termed the Roman architectural Revolution, freed
Speaker 1: Roman construction from the restrictions of stone and brick materials.
Speaker 1: It enabled revolutionary new ideas in terms of both structural
Speaker 1: complexity and dimension. The Colosseum in Rome was built largely
Speaker 1: of concrete, and the Pantheon was the world's largest unreinforced
Speaker 1: concrete dome. Concrete, as the Romans knew it, was a
Speaker 1: new and revolutionary material, laid in the shape of arches, vaults,
Speaker 1: and domes. It quickly hardened into a rigid mass, free
Speaker 1: from many of the internal thrusts and strains that troubled
Speaker 1: the builders of similar structures in stone or brick. Modern
Speaker 1: tests show that OPA's sementissium had a similar compressive strength
Speaker 1: to modern Portland cement concrete. However, due to the absence
Speaker 1: of reinforcement, its tensile strength was far lower than modern
Speaker 1: reinforced concrete, and its mode of application also differed. Modern
Speaker 1: structural concrete differs from Roman concrete in two important details. First,
Speaker 1: its mixed consistencies fluid and homogeneous, allowing it to be
Speaker 1: poured into forms rather than requiring hand layering, together with
Speaker 1: the replacement of aggregate, which in Roman practice often consisted
Speaker 1: of rubble. Second, integral reinforcing steel gives modern concrete assemblies
Speaker 1: great strengths and tension, whereas Roman concrete could depend only
Speaker 1: upon the strength of the concrete bonding to resist tension.
Speaker 1: The long term durability of Roman concrete structures was found
Speaker 1: to be due to the presence of pyroclastic volcanic rock
Speaker 1: and ash in a concrete mix. The crystallization of stretlinge
Speaker 1: during the formation of the concrete, and its merging with
Speaker 1: similar calcium aluminum silicate hydrate structures helped gives a Roman
Speaker 1: concrete a greater degree of fracture resistance compared to modern concrete.
Speaker 1: In addition, Roman concrete is significantly more resistant to erosion
Speaker 1: by sea water than modern concrete. The aforementioned pyroclastic materials
Speaker 1: react with sea water to form aluminium to bermeerite crystals
Speaker 1: over time. The use of hot mixing in preparation of concrete,
Speaker 1: leading to the formation of light class in the final product,
Speaker 1: has been proposed to give the Roman concrete a self
Speaker 1: healing ability. The widespread use of concrete in many Roman
Speaker 1: structures ensured that many survive to the present day. The
Speaker 1: baths of Caracalla and Rome are just one example. Many
Speaker 1: Roman aqueducts and bridges, such as the magnificent Pont Nouguer
Speaker 1: and Southern France, have masonry cladding on a concrete core,
Speaker 1: as does the dome in the Pantheon In Britannia. After
Speaker 1: the Roman Empire, there is evidence of the continued use
Speaker 1: of burned lime, and remains of an eighth century mortar
Speaker 1: mill have been found in Northamptonshire, but it is thought
Speaker 1: that low kiln temperatures in the burning of lime, lack
Speaker 1: of pozzolana, poor mixing, and an Anglo Saxon culture of
Speaker 1: timber construction all contributed to a decline in the quality
Speaker 1: of concrete and mortar there, but it did not become
Speaker 1: a lost art. From the eleventh century in England, the
Speaker 1: increased use of stone and church in castle construction led
Speaker 1: to an increased demand for mortar. Quality began to improve
Speaker 1: in the twelfth century threw better grinding and seeving. Medieval
Speaker 1: lime mortars and concretes were non hydraulic and were used
Speaker 1: for binding masonry, parting, binding rubble masonry, cores and foundations.
Speaker 1: Bartolomeus Anglicu, in his De Proprietatibus Rerum twelve forty describes
Speaker 1: the making of mortar. In an English translation from thirteen
Speaker 1: ninety seven, it reads, lime is a stone brind by
Speaker 1: meddling thereof with sand and water cements made. From the
Speaker 1: fourteenth century the quality of mortar was again excellent, but
Speaker 1: only from the seventeenth century was potsolana commonly added. Mayan
Speaker 1: concrete at the ruins of Ushmaal A d. Eight fifty
Speaker 1: to nine twenty five is referenced in incidents of travel
Speaker 1: in the Yucatan by John L. Stephens. The roof is
Speaker 1: flat and had been covered with cement. The floors were
Speaker 1: cemented in some places harred but by law exposure, broken
Speaker 1: and now crumbling under the feet. But throughout the wall
Speaker 1: was solid and consisting of large stones embedded in mortar
Speaker 1: almost as hard as rock. Medieval hydraulic mortars were made
Speaker 1: from the addition of pozzolans such as crushed ceramics, volcanic soils,
Speaker 1: or metamorphosed soils from specific deposits was known bodzolonic properties
Speaker 1: like trass or non crystalline opal hydraulic mortar was used
Speaker 1: in medieval crete. The use of specific sands containing volcanic
Speaker 1: ash and tents in eleven centuries South Italian mortars may
Speaker 1: indicate a knowledge of its properties them An architectural treatise
Speaker 1: De Architectura by Vitruvius contained a description of Roman cement
Speaker 1: and a copy at the Scriptorium of Charlemagne produced many
Speaker 1: of the medieval copies that subsequently survived. A copy at
Speaker 1: Saint Gile Abbey was found by Poggio Bracciolini in fourteen fourteen.
Speaker 1: The first printed edition was published in fourteen eighty six
Speaker 1: by fra Giovanni Sulpicius, and versions in Italian, German, French,
Speaker 1: Spanish and English were published between fifteen twenty and sixteen
Speaker 1: ninety two. The sixteenth century dockyard in Venice used hydraulic
Speaker 1: lime mortars in foundations. Hydraulic mortar was also though used
Speaker 1: in Ottoman Baths and Budapest from the same period. The
Speaker 1: Canal du Mede was built using concrete in sixteen seventy.
Speaker 1: Trass from the Rhineland was added to Lyme in England
Speaker 1: in the seventeenth century, including for the mole of English Tangier,
Speaker 1: which also used Italian podzolana, recommended and supplied by the
Speaker 1: Genoese engineers at the port of Toulon. Concrete foundations were
Speaker 1: built using podzolana or trass, quicklime, sand, pebbles, and slag
Speaker 1: or cinder. The seventeen fifty two reconstruction of the foundations
Speaker 1: of Essex Bridge by George Semple included a mixture of
Speaker 1: small stones, sand and powdered lime. Perhaps the greatest stab
Speaker 1: forward in the modern use of concrete was Smeaden's Tower,
Speaker 1: built by British engineer John Smeaton in Devon, England between
Speaker 1: seventeen fifty six and seventeen fifty nine. This third Eddystone
Speaker 1: Lighthouse pioneered the use of hydraulic lime and concrete using
Speaker 1: pebbles and powdered brick as aggregate. A method for producing
Speaker 1: Portland cement was developed in England and patented by Joseph
Speaker 1: Aspden in eighteen twenty four. Aspden chose the name for
Speaker 1: its similarity to Portland stone, which was quarried on the
Speaker 1: Isle of Portland in Dorset, England. His son William continued
Speaker 1: developments into the eighteen forties, earning him the recognition for
Speaker 1: the development of modern Portland cemen. Reinforced concrete was invented
Speaker 1: in eighteen forty nine by Josephe Monier, and the first
Speaker 1: reinforced concrete house was built by Francois Coigner in eighteen
Speaker 1: fifty three. The first concrete reinforced bridge was designed and
Speaker 1: built by Joseppe Monier in eighteen seventy five. Prestress concrete
Speaker 1: and post tension concrete were pioneered by Eugen Fresnay, a
Speaker 1: French structural and civil engineer. Concrete components or structures are
Speaker 1: compressed by tendon cables during or after their fabrication in
Speaker 1: order to strengthen them against tensile forces developing when put
Speaker 1: in service. Presina patented the technique on October second, nineteen
Speaker 1: twenty eight. Concrete is an artificial composite material comprising a
Speaker 1: matrix of sementitious binder, typically Portland cement, paste or asphalt,
Speaker 1: and a dispersed phase or filler of aggregate, typically a
Speaker 1: rocky material loose stones and sand. The binder glues the
Speaker 1: filler together to form a synthetic conglomerate. Many types of
Speaker 1: concrete are available, determined by the formulations of binders and
Speaker 1: the types of aggregate used to suit the application of
Speaker 1: the engineered material. These variables determine strength and density, as
Speaker 1: well as chemical and thermal resistance of the finished product.
Speaker 1: Construction aggregates consist of large chunks of material in a
Speaker 1: concrete mix, generally a coarse gravel or crushed rocks such
Speaker 1: as limestone or granite, along with finer materials such as sand.
Speaker 1: Cement paste, most commonly made of Portland cement, is the
Speaker 1: most prevalent kind of concrete binder. Poor sementitious binders water
Speaker 1: is mixed with the dry cement powder and aggregate, which
Speaker 1: produces a semi liquid slurry that can be shaped, typically
Speaker 1: by pouring it into a form. The concrete solidifies and
Speaker 1: hardens through a mical process called hydration. The water reacts
Speaker 1: with the cement, which bonds the other components together, treating
Speaker 1: a robust, stone like material. Other sementitious materials, such as
Speaker 1: fly ash and slag cement are sometimes added, either pre
Speaker 1: blended with the cement or directly as a concrete component
Speaker 1: and become a part of the binder for the aggregate.
Speaker 1: Fly Ash and slag can enhance some properties of concrete,
Speaker 1: such as fresh properties and durability. Alternatively, other materials can
Speaker 1: also be used as a concrete binder. The most prevalent
Speaker 1: substitute is asphalt, which is used as the binder and
Speaker 1: asphalt concrete admixtures are added to modify the cure rate
Speaker 1: or properties of the material. Mineral admixtures use recycled materials
Speaker 1: as concrete ingredients. Conspicuous materials include fly ash, a byproduct
Speaker 1: of coal fired power plants, ground granulated blast furnace slag,
Speaker 1: a byproduct of steel making, and silica fume, a byproduct
Speaker 1: of industrial electric arc furnaces. Structures employing Portland cement concrete
Speaker 1: usually include steel reinforcement because this type of concrete can
Speaker 1: be formulated with high compressive strength, but always has lower
Speaker 1: tensile strength. Therefore, it is usually reinforced with materials that
Speaker 1: are strong in tension, typically steel rebar. The mixed design
Speaker 1: depends on the type of structure being built, how the
Speaker 1: concrete is mixed and delivered, and how it is placed
Speaker 1: to form the structure. Portland cement is the most common
Speaker 1: type of cement in general usage. It is a basic
Speaker 1: ingredient of concrete, mortar, and many plasters. It consists of
Speaker 1: a mixture of calcium, silicates, illuminates, and ferrites, compounds which
Speaker 1: will react with water. Portland cement and similar materials are
Speaker 1: made by heating limestone, a source of calcium, with clay
Speaker 1: or shale a source of silicon, aluminium and iron, and
Speaker 1: grinding this product called clinker with a source of sulfate,
Speaker 1: most commonly gypsum. Cement kilns are extremely large, complex, and
Speaker 1: inherently dusty industrial installations. Of the various ingredients used to
Speaker 1: produce a given quantity of concrete, The cement is the
Speaker 1: most energetically expensive. Combining water with a cementitious material forms
Speaker 1: a cement paste by the process of hydration. The cement
Speaker 1: paste glues the aggregate together, fills voids within it, and
Speaker 1: makes it flow more freely. As stated by Abram's law,
Speaker 1: a lower water to cement ratio yields as stronger, more
Speaker 1: durable concrete, whereas more water gives of freer flowing concrete
Speaker 1: with a higher slump. The hydration of cement involves many
Speaker 1: concurrent reactions. The process involves polymerization, the interlinking of the
Speaker 1: silicids and alumina components, as well as their bonding to
Speaker 1: sand and gravel particles to form a solid mass. Fine
Speaker 1: and coarse aggregates make up the bulk of a concrete mixture. Sand,
Speaker 1: natural gravel, and crushed stone are used mainly for this purpose.
Speaker 1: Recycled aggregates from construction, demolition and excavation waste are increasingly
Speaker 1: used as partial replacements for natural aggregates, while a number
Speaker 1: of manufactured aggregates, including air cooled blast, furnace slag, and
Speaker 1: bottom ash, are also permitted. The size distribution of the
Speaker 1: aggregate determines how much binder is required. Aggregate with a
Speaker 1: very even sized distribution has the biggest gaps whereas adding
Speaker 1: aggregate with smaller particles tends to fill these gaps. The
Speaker 1: binder must fill the gaps between the aggregate as well
Speaker 1: as paste the surfaces of the aggregate together, and is
Speaker 1: typically the most expensive component. Thus variation and sizes of
Speaker 1: the aggregate reduces the cost of concrete. The aggregate is
Speaker 1: nearly always stronger than the binder, so its use does
Speaker 1: not negatively affect the strength of the concrete. Redistribution of
Speaker 1: aggregates after compaction often creates non homogeneity due to the
Speaker 1: influence of vibration. This can lead to strength gradients. Decorative
Speaker 1: stones such as quartzite, small river stones, or crushed glass
Speaker 1: are sometimes added to the surface of concrete for a
Speaker 1: decorative exposed aggregate finish, popular among landscape designers. Admixtures are
Speaker 1: materials in the form of powder or fluids that are
Speaker 1: added to the concrete to give it certain characteristics not
Speaker 1: obtainable with plain concrete mixes. Admixtures are defined as additions
Speaker 1: made as the concrete mix is being prepared. In normal use,
Speaker 1: admixture dosages are less than five percent by mass of
Speaker 1: cement and are added to the concrete at the time
Speaker 1: of batch mixing. In organic materials that have podzolanic or
Speaker 1: latent hydraulic properties. These very fine grain materials are added
Speaker 1: to the concrete mix to improve the properties of concrete
Speaker 1: or as a replacement for Portland cement products which incorporate limestone,
Speaker 1: fly ash, blast, furnace slag and other useful materials with
Speaker 1: podzolanic properties into the mix are being tested and used.
Speaker 1: These developments are ever growing in relevance to minimize the
Speaker 1: impacts caused by cement use. The use of alternative materials
Speaker 1: also is capable of lowering costs and recycling wastes, the
Speaker 1: latest being relevant for circular economy aspects of the construction industry,
Speaker 1: whose demand is ever growing with greater impacts on raw
Speaker 1: material extraction, waste generation and landfill practices.