Cement & Concrete Basics Faqs

By 1897, Sears Roebuck was selling 50-gallon drums of imported Portland cement for $3.40 each. Although in 1898 cement manufacturers were using more than 90 different formulas, by 1900, basic testing — if not manufacturing methods — had become standardized. It wasn’t until 1793 that the technology took a big leap forward when John Smeaton discovered a more modern method for producing hydraulic lime for cement. He used limestone containing clay that was fired until it turned into clinker, which was then ground it into powder. He used this material in the historic rebuilding of the Eddystone Lighthouse in Cornwall, England.

But there is only so much concrete you can usefully lay without ruining the environment. The ever-diminishing returns were made apparent in the 1990s, when even the most creative politicians struggled to justify the government’s stimulus spending packages. Concrete is a thirsty behemoth, sucking up almost a 10th of the world’s industrial water use.

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Built by Rome’s Emperor Hadrian and completed in 125 AD, the Pantheon has the largest un-reinforced concrete dome ever built. The dome is 142 feet in diameter and has a 27-foot hole, called an oculus, at its peak, which is 142 feet above the floor.

Nominal mixes are a simple, fast way of getting a basic idea of the properties of the finished concrete without having to perform testing in advance. Carbon products have been added to make concrete electrically conductive, for deicing purposes. Redistribution of aggregates after compaction often creates inhomogeneity due to the influence of vibration. and the first reinforced concrete house was built by François Coignet in 1853. The first concrete reinforced bridge was designed and built by Joseph Monier in 1875. Perhaps the greatest step forward in the modern use of concrete was Smeaton’s Tower, built by British engineer John Smeaton in Devon, England, between 1756 and 1759. This third Eddystone Lighthouse pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate.

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That is why it serves as the foundation of modern life, holding time, nature, the elements and entropy at bay. When combined with steel, it is the material that ensures our dams don’t burst, our tower blocks don’t fall, our roads don’t buckle and our electricity grid remains connected. By one calculation, we may have already passed the point where concrete outweighs the combined carbon mass of every tree, bush and shrub on the planet. Our built environment is, in these terms, outgrowing the natural one.

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The original batter has changed, while the fruit and nuts are pretty much the same—just suspended and held together by the cake. Today, it seems as if we define civilization in terms of the small things, like decoded strands of DNA, splitting atoms and microscopic bumps on plastic compact discs. With a focus so fine, it’s easy to forget the bigger, simpler things that got us here and continue to define our lives.

  • Fly ash and slag can enhance some properties of concrete such as fresh properties and durability.
  • The concrete solidifies and hardens through a chemical process called hydration.
  • Other cementitious materials, such as fly ash and slag cement, are sometimes added—either pre-blended with the cement or directly as a concrete component—and become a part of the binder for the aggregate.
  • For cementitious binders, water is mixed with the dry powder and aggregate, which produces a semi-liquid slurry that can be shaped, typically by pouring it into a form.
  • The water reacts with the cement, which bonds the other components together, creating a robust, stone-like material.

The placement consisted of 10,251 cubic yards of concrete placed in 58.5 hours using two concrete pumps and two dedicated concrete batch plants. The world record for largest continuously poured concrete floor was completed 8 November 1997, in Louisville, Kentucky by design-build firm EXXCEL Project Management. The monolithic placement consisted of 225,000 square feet of concrete placed in 30 hours, finished to a flatness tolerance of FF 54.60 and a levelness tolerance of FL 43.83.

According to the watchdog group Transparency International, construction is the world’s dirtiest business, far more prone to graft than mining, real estate, energy or the arms market. No country is immune, but in recent years, Brazil has revealed most clearly the jawdropping scale of bribery in the industry. Yu has been consulted by government officials, who are increasingly aware of the brittleness of the current Chinese model of growth. The initial momentum of a concrete economy is always followed by inertia in concrete politics. Instead, China is doing what countless other nations have done, exporting its environmental stress and excess capacity overseas. Which made the devastating 2011 Tohoku earthquake and tsunami all the more shocking.

The minimum strength before exposing concrete to extreme cold is 500 psi (3.5 MPa). CSA A 23.1 specified a compressive strength of 7.0 MPa to be considered safe for exposure to freezing. More than 55,000 miles of highways in the United States are paved with this material. Reinforced concrete, prestressed concrete and precast concrete are the most widely used types of concrete functional extensions in modern days. The proper treatment of the surface of concrete, and therefore its characteristics, is an important stage in the construction and renovation of architectural structures. Other finishes can be achieved with chiseling, or more conventional techniques such as painting or covering it with other materials.

A relatively dry sample slumps very little, having a slump value of one or two inches out of one foot . A relatively wet concrete sample may slump as much as eight inches.

Wet methods involve the application of water or specific chemicals according to the nature of the stain. The chemical treatment either dissolves the staining substance so it can be blotted up from the surface of the concrete or bleaches the staining substance so it will not show. Stains can be removed from concrete with dry or mechanical methods, or by wet methods using chemical or water. Status of acceptance of portland-limestone cement in state DOT specifications. This type of cement has been common internationally for decades but is relatively new to North America. Type V cement resists chemical attack by soil and water high in sulfates. Type III cement provides high strength at an early state, usually in a week or less.

Slump can be increased by addition of chemical admixtures such as plasticizer or superplasticizer without changing the water-cement ratio. Some other admixtures, especially air-entraining admixture, can increase the slump of a mix. Workability can be measured by the concrete slump test, a simple measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN test standards. Slump is normally measured by filling an “Abrams cone” with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity.

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This often strains supplies for drinking and irrigation, because 75% of this consumption is in drought and water-stressed regions. In cities, concrete also adds to the heat-island effect by absorbing the warmth of the sun and trapping gases from car exhausts and air-conditioner units – though it is, at least, better than darker asphalt. At times an unyielding ally, at times a false friend, concrete can resist nature for decades and then suddenly amplify its impact. Solidity is a particularly attractive quality at a time of disorientating change. But – like any good thing in excess – it can create more problems than it solves.

Raw concrete surfaces tend to be porous and have a relatively uninteresting appearance. Many finishes can be applied to improve the appearance and preserve the surface against staining, water penetration, and freezing. Concrete strength values are usually specified as the lower-bound compressive strength of either a cylindrical or cubic specimen as determined by standard test procedures. Traditional conditions for curing involve spraying or ponding the concrete surface with water. The adjacent picture shows one of many ways to achieve this, ponding—submerging setting concrete in water and wrapping in plastic to prevent dehydration. Additional common curing methods include wet burlap and plastic sheeting covering the fresh concrete.

Larger earthquakes can generate very large shear loads on structures. These shear loads subject the structure to both tensile and compressional loads. Concrete structures without reinforcement, like other unreinforced masonry structures, can fail during severe earthquake shaking.

At coastal towns such as Ishinomaki, Kamaishi and Kitakami, huge sea walls that had been built over decades were swamped in minutes. Almost 16,000 people died, a million buildings were destroyed or damaged, town streets were blocked with beached ships and port waters were filled with floating cars. It was a still more alarming story at Fukushima, where the ocean surge engulfed the outer defences of the Fukushima Daiichi nuclear plant and caused a level 7 meltdown.

Like Baking A Cake To understand the nature of concrete, it might help to think of a cake—a fruitcake. To make one, you mix up some flour, baking powder, butter and eggs, add dried fruit and nuts and pour the whole thing into a cake pan. Apply heat for a while, and presto—that unappetizing paste is suddenly something new.

It was built in place, probably by starting above the outside walls and building up increasingly thin layers while working toward the center. By about 5600 BC along the Danube River in the area of the former country of Yugoslavia, homes were built using a type of concrete for floors. One problem with concrete is a tendency for freeze/thaw cycles to cause cracks. These admixtures create a dispersion of very fine air bubbles that cushion the concrete against the effects of freezing water.

In there with wood, steel and glass you’ll find another material quietly holding it all up. The finishing operations should not begin until the water sheen on the surface is gone and excess bleed water on the surface has had a chance to evaporate. If this excess water is worked into the concrete because the finishing operations are begun too soon, the concrete on the surface will have too high a water content and will be weaker and less durable. Portland cement is a hydraulic cement which means that it sets and hardens due to a chemical reaction with water. It is concrete that is strong enough to carry a compressive stress of 3,000 psi at 28 days. Conventional concrete has strengths of 7,000 psi or less; concrete with strengths between 7,000 and 14,500 psi is considered high-strength concrete.

This surpassed the previous record by 50% in total volume and 7.5% in total area. The Polavaram dam works in Andhra Pradesh on 6 January 2019 entered the Guinness World Records by pouring 32,100 cubic metres of concrete in 24 hours. The world record for the largest continuously poured concrete raft was achieved in August 2007 in Abu Dhabi by contracting firm Al Habtoor-CCC Joint Venture and the concrete supplier is Unibeton Ready Mix. The pour (a part of the foundation for the Abu Dhabi’s Landmark Tower) was 16,000 cubic meters of concrete poured within a two-day period. Concrete is used to create hard surfaces that contribute to surface runoff, which can cause heavy soil erosion, water pollution, and flooding, but conversely can be used to divert, dam, and control flooding. Concrete dust released by building demolition and natural disasters can be a major source of dangerous air pollution. As discussed above, concrete is very strong in compression, but weak in tension.

Instead, its chief quality is to harden and then degrade, extremely slowly. The record for the largest continuously placed underwater concrete pour was completed 18 October 2010, in New Orleans, Louisiana by contractor C.

Unreinforced masonry structures constitute one of the largest earthquake risks globally. These risks can be reduced through seismic retrofitting of at-risk buildings, (e.g. school buildings in Istanbul, Turkey). Concrete buildings are more resistant to fire than those constructed using steel frames, since concrete has lower heat conductivity than steel and can thus last longer under the same fire conditions. Concrete is sometimes used as a fire protection for steel frames, for the same effect as above. Concrete as a fire shield, for example Fondu fyre, can also be used in extreme environments like a missile launch pad. Boston City Hall is a Brutalist design constructed largely of precast and poured in place concrete.

During placement, the concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycombs and air pockets. A report last year by Chatham House calls for a rethink in the way cement is produced. It also puts a crushing weight on the ecosystems that are essential for human wellbeing. Chatham House predicts urbanisation, population growth and economic development will push global cement production from 4 to 5bn tonnes a year.

During the late 19th century, the use of steel-reinforced concrete paver molds was being developed more or less simultaneously by a German, G.A. Wayss, a Frenchman, Francois Hennebique, and an American, Ernest L. Ransome. Ransome started building with steel-reinforced concrete in 1877 and patented a system that used twisted square rods to improve the bond between steel and concrete.

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During the curing period, concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during curing, concrete slabs are often sprayed with “curing compounds” that create a water-retaining film over the concrete. Typical films are made of wax or related hydrophobic compounds. After the concrete is sufficiently cured, the film is allowed to abrade from the concrete through normal use. After mixing, concrete is a fluid and can be pumped to the location where needed. High-flow concrete for concrete paver molds, like self-consolidating concrete, is tested by other flow-measuring methods. One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted.

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