Youtube video, cool 🙂
For most people concrete conjures up images of a cold, grey and boring construction material but two women from Northern Ireland want to change your mind.
Textile designer, Trish Belford and architect, Ruth Morrow, have come up with an award-winning concrete idea called ‘Girli Concrete’ which blends rough and smooth materials.
“We like to encourage people to touch the pieces and feel them,” designer,” Trish Belford said.
Their current commission, a 7.5-metre-long frieze will be installed in the newly refurbished Derry Playhouse next week.
The frieze is made up of four undulating sections of concrete, out of which embroidered and fabric flowers and leaves seem to grow.
Trish Belford said the original features such as fireplaces and fanlights were copied from the Playhouse and incorporated in the design.
“We wanted to look at the indigenous industries of Ireland, the architecture, arts, crafts and textiles and put them together.”
The textiles used were embedded or built into the concrete and some of them were woven with steel thread.
It has taken Trish Belford and Ruth Morrow three years to perfect their technique which they are keeping secret whilst they apply for a patent.
Apparently it is all down to the consistency of the concrete, which is poured into moulds over a period of weeks.
As a textile designer, Trish has worked with designers, Vivienne Westwood and Jasper Conran but this is the first time she’s teamed up with an architect.
Both she and Ruth were keen to produce an innovative building material, bringing together the two Ulster traditions of construction and textiles.
“We have also created the ‘Tactility Factory’ to open ourselves up to the use of other hard and soft construction materials.”
The design duo also want to test and develop the material in terms of its insulation and acoustic properties and are even looking at building textiles into exterior walls.
Trish said the unusual name ‘Girli Concrete’ came about from an off-the-cuff remark when a man walked into their studio and asked what they were doing up to their arms in concrete.
“Ruth just turned round to him and said- ‘girly concrete, what does it look like!”
And since then it has stuck, Trish added: “some people love it and some people hate it, but at least they always remember it.”
The is frieze is part of the Fabrication exhibition which runs until March 14 at Place on Fountain Street.
Water-cement ratio is the ratio of weight of water to the weight of cement used in a concrete mix. It has an important influence on the quality of concrete produced. A lower water-cement ratio leads to higher strength and durability, but may make the mix more difficult to place. Placement difficulties can be resolved by using plasticizer. The water-cement ratio is independent of the total cement content (and the total water content) of a concrete mix.
After concrete is placed, a satisfactory moisture content and temperature (between 50°F and 75°F) must be maintained, a process called curing. Adequate curing is vital to quality concrete.
Curing has a strong influence on the properties of hardened concrete such as durability, strength, watertightness, abrasion resistance, volume stability, and resistance to freezing and thawing and deicer salts. Exposed slab surfaces are especially sensitive to curing. Surface strength development can be reduced significantly when curing is defective.
Curing the concrete aids the chemical reaction called hydration. Most freshly mixed concrete contains considerably more water than is required for complete hydration of the cement; however, any appreciable loss of water by evaporation or otherwise will delay or prevent hydration. If temperatures are favorable, hydration is relatively rapid the first few days after concrete is placed; retaining water during this period is important. Good curing means evaporation should be prevented or reduced.
Curing is the process of keeping concrete under a specific environmental condition until hydration is relatively complete. Because the cement used in concrete requires time to fully hydrate before it acquires strength and hardness, concrete must be cured once it has been placed.
Good curing is typically considered to use a moist environment which promotes hydration, since increased hydration lowers permeability and increases strength, resulting in a higher quality material. Allowing the concrete surface to dry out excessively can result in tensile stresses, which the still-hydrating interior cannot withstand, causing the concrete to crack. Also, the amount of heat generated by the chemical process of hydration can be problematic for very large placements.
Allowing the concrete to freeze in cold climates before the curing is complete will interrupt the hydration process, reducing the concrete strength and leading to scaling and other damage or failure.
The effects of curing are primarily a function of specimen geometry, the permeability of the concrete, curing length, and curing history
Reinforced concrete is concrete in which steel reinforcement bars (“rebars”) or fibers have been incorporated to strengthen a material that would otherwise be brittle. In industrialised countries, nearly all concrete used in construction is reinforced concrete.
Concrete is a mixture of cement (usually Portland cement) and stone aggregate. When mixed with a small amount of water, the cement hydrates form microscopic opaque crystal lattices encapsulating and locking the aggregate into a rigid structure. Typical concrete mixes have high resistance to compressive stresses (about 4,000 psi (27.5 MPa)); however, any appreciable tension (e.g. due to bending) will break the microscopic rigid lattice resulting in cracking and separation of the concrete. For this reason, typical non-reinforced concrete must be well supported to prevent the development of tension.
If a material with high strength in tension, such as steel, is placed in concrete, then the composite material, reinforced concrete, resists compression but also bending, and other direct tensile actions. A reinforced concrete section where the concrete resists the compression and steel resists the tension can be made into almost any shape and size for the construction industry.
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What is Good Concrete?
A good concrete is one which has workability in the fresh state and develops adequate strength. Maximum strength of concrete can only be obtained, if the concrete has adequate degree of workability in relation to the method of compaction to be used. Concrete which is to be compacted by mechanical vibrator, will need 15% less water and 15% less cement as compared to the one which has to be compacted by hand
What is the difference between cement and concrete?
Although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. Concrete gets stronger as it gets older. Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. Cement comprises from 10 to 15 percent of the concrete mix, by volume. Through a process called hydration, the cement and water harden and bind the aggregates into a rocklike mass. This hardening process continues for years meaning that concrete gets stronger as it gets older.
What does it mean to “cure” concrete?
Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process. new concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.
Can it be too hot or too cold to place new concrete?
What are recommended mix proportions for good concrete?
Good concrete can be obtained by using a wide variety of mix proportions if proper mix design procedures are used. A good general rule to use is the rule of 6’s:
A minimum cement content of 6 bags per cubic yard of concrete,
A maximum water content of 6 gallons per bag of cement,
A curing period (keeping concrete moist) a minimum of 6 days, and
An air content of 6 percent (if concrete will be subject to freezing and thawing).
What are the most common tests for fresh concrete?
Slump, air content, unit weight and compressive strength tests are the most common tests.
Slump is a measure of consistency, or relative ability of the concrete to flow. If the concrete can’t flow because the consistency or slump is too low, there are potential problems with proper consolidation. If the concrete won’t stop flowing because the slump is too high, there are potential problems with mortar loss through the formwork, excessive formwork pressures, finishing delays and segregation.
Air content measures the total air content in a sample of fresh concrete, but does not indicate what the final in-place air content will be, because a certain amount of air is lost in transportation, consolidating, placement and finishing. Three field tests are widely specified: the pressure meter and volumetric method are ASTM standards and the Chace Indicator is an AASHTO procedure.
Unit weight measures the weight of a known volume of fresh concrete.
Compressive strength is tested by pouring cylinders of fresh concrete and measuring the force needed to break the concrete cylinders at proscribed intervals as they harden. According to Building Code Requirements for Reinforced Concrete (ACI 318), as long as no single test is more than 500 psi below the design strength and the average of three consecutive tests equals or exceed the design strength then the concrete is acceptable. If the strength tests don’t meet these criteria, steps must be taken to raise the average.
How do you remove stains from concrete?
Stains can be removed from concrete with dry or mechanical methods, or by wet methods using chemical or water.
Common dry methods include sandblasting, flame cleaning and shotblasting, grinding, scabbing, planing and scouring. Steel-wire brushes should be used with care because they can leave metal particles on the surface that later may rust and stain the concrete.
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.
To remove blood stains, for example, wet the stains with water and cover them with a layer of sodium peroxide powder; let stand for a few minutes, rinse with water and scrub vigorously. Follow with the application of a 5 percent solution of vinegar to neutralize any remaining sodium peroxide
What is 3,000 pound concrete?
It is concrete that is strong enough to carry a compressive stress of 3,000 psi (20.7 MPa) at 28 days. Concrete may be specified at other strengths as well. 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.
How do you control the strength of concrete?
The easiest way to add strength is to add cement. The factor that most predominantly influences concrete strength is the ratio of water to cement in the cement paste that binds the aggregates together. The higher this ratio is, the weaker the concrete will be and vice versa. Every desirable physical property that you can measure will be adversely effected by adding more water.
Flaking Good Concrete.
Concrete, now so much used in forming the foundations of buildings of every description, and even the walls themselves, is a mixture of cement and sand, gravel, broken stones, brick rubbish, or similiar materials in the proportion of one part of cement to five or six parts of any of the other ingredients that are used in its manufacture. Good lime is often used instead of cement, but the amateur, if he uses lime at all, is advised to use cement with it in equal parts. The cement, being the substance that binds the gravel ballast, etc., together into a solid mass impervious to water, is technically called the matrix, and the substance that is added to the lime is called the aggregate.
It may be said that any waste material of a hard nature may be used as aggregate in making concrete, sand and gravel of all kinds, including pea or fine gravel, pit gravel, river gravel, ashes, cinders, and coke, lime chippings, flints, old stones and bricks, especially when broken, broken earthenware and stoneware, and rubbish from the brickyard may all be used. Slag, too, the refuse of the iron furnaces, can be made available whenever it can be obtained. It should not be used in too large sizes. Pieces about the size of stones ordinarily used for mending roads, or such as will pass through a ring of 2½ inches in diameter, are best suited for the purpose when the material is broken up on purpose for making concrete.
Any of the various cements in general use may be used in the manufacture of concrete, but the amateur is recommended in all cases to use Portland cement.
At the height of the U.S. housing boom, when building materials were in short supply, American construction companies used millions of pounds of Chinese-made drywall because it was abundant and cheap.
Now that decision is haunting hundreds of homeowners and apartment dwellers who are concerned that the wallboard gives off fumes that can corrode copper pipes, blacken jewelry and silverware, and possibly sicken people.
Shipping records reviewed by The Associated Press indicate that imports of potentially tainted Chinese building materials exceeded 500 million pounds during a four-year period of soaring home prices. The drywall may have been used in more than 100,000 homes, according to some estimates, including houses rebuilt after Hurricane Katrina.
“This is a traumatic problem of extraordinary proportions,” said U.S. Rep. Robert Wexler, a Florida Democrat who introduced a bill in the House calling for a temporary ban on the Chinese-made imports until more is known about their chemical makeup. Similar legislation has been proposed in the Senate.
The drywall apparently causes a chemical reaction that gives off a rotten-egg stench, which grows worse with heat and humidity.
Researchers do not know yet what causes the reaction, but possible culprits include fumigants sprayed on the drywall and material inside it. The Chinese drywall is also made with a coal byproduct called fly ash that is less refined than the form used by U.S. drywall makers.
Dozens of homeowners in the Southeast have sued builders, suppliers and manufacturers, claiming the very walls around them are emitting smelly sulfur compounds that are poisoning their families and rendering their homes uninhabitable.
“It’s like your hopes and dreams are just gone,” said Mary Ann Schultheis, who has suffered burning eyes, sinus headaches, and a general heaviness in her chest since moving into her brand-new, 4,000-square foot house in this tidy South Florida suburb a few years ago.
She has few options. Her builder is in bankruptcy, the government is not helping and her lender will not give her a break.
“I’m just going to cry,” she said. “We don’t know what we’re going to do.”
Builders have filed their own lawsuits against suppliers and manufacturers, claiming they unknowingly used the bad building materials.
The Consumer Product Safety Commission is investigating, as are health departments in Virginia, Louisiana, North Carolina, Florida and Washington state.
Companies that produced some of the wallboard said they are looking into the complaints, but downplayed the possibility of health risks.
“What we’re trying to do is get to the bottom of what is precisely going on,” said Ken Haldin, a spokesman for Knauf Plasterboard Tianjin, a Chinese company named in many of the lawsuits.
The Chinese ministries of commerce, construction and industry and the Administration of Quality Supervision Inspection and Quarantine did not respond to repeated requests for comment. Chinese news reports have said AQSIQ, which enforces product quality standards, was investigating the complaints but people in the agency’s press office said they could not confirm that.
Meanwhile, governors in Louisiana and Florida are asking for federal assistance, and experts say the problem is only now beginning to surface.
“Based on the amount of material that came in, it’s possible that just in one year, 100,000 residences could be involved,” said Michael Foreman, who owns a construction consulting firm. The company has performed tests on some 200 homes in the Sarasota area and has been tracking shipments of the drywall.
Federal authorities say they are investigating just how much of the wallboard was imported. Shipping records analyzed by the AP show that more than 540 million pounds of plasterboard — which includes both drywall and ceiling tile panels — was imported from China between 2004 and 2008, although it’s unclear whether all of that material was problematic or only certain batches.
Most of it came into the country in 2006, following a series of Gulf Coast hurricanes and a domestic shortage brought on by the national housing boom.
The Chinese board was also cheaper. One homeowner told AP he saved $1,000 by building his house with it instead of a domestic product.
In 2006, enough wallboard was imported from China to build some 34,000 homes of roughly 2,000 square feet each, according to AP’s analysis of the shipping records and estimates supplied by the nationwide drywall supplier United States Gypsum.
Experts and advocates say many homes may have been built with a mixture of Chinese and domestic drywall, potentially raising the number of affected homes much higher.
So far, the problem appears to be concentrated in the Southeast, which blossomed with new construction during the housing boom and where the damp climate appears to cause the gypsum in the building material to degrade more quickly. In Florida alone, more than 35,000 homes may contain the product, experts said.
In Louisiana, the state health department has received complaints from at least 350 people in just a few weeks. Many of the affected homeowners rebuilt after Hurricane Katrina only to face the prospect of tearing down their houses and rebuilding again.
In another cruel twist, some of the very communities that have been hit hardest by the collapse of the housing market and skyrocketing foreclosure rates are now at the epicenter of the drywall problem.
Foreman warns of a “sleeping beast” in the thousands of bank-owned condos and houses across the country, with no one in them to complain.
Outside the South, it’s harder to pinpoint the number of affected homes. And in drier climates such as California and Nevada, it may be years before homeowners begin to see — and smell — what may be lurking inside their walls.
The drywall furor is the latest in a series of scares over potentially toxic imports from China. In 2007, Chinese authorities ratcheted up inspections and tightened restrictions on exports after manufacturers were found to have exported tainted cough syrup, toxic pet food and toys decorated with lead paint.
Scientists hope to understand the problem by studying the chemicals in the board. Drywall consists of wide, flat boards used to cover walls. It is often made from gypsum, a common mineral that can be mined or manufactured from the byproducts of coal-fired power plants.
Plaintiffs in the lawsuits, as well as U.S. wallboard manufacturers, say the tainted drywall was made with fly ash, a residue of coal combustion more commonly used in concrete mixtures.
Fly ash can be gathered before it ever reaches the smokestack, where technology is used to remove sulfur dioxide from the emissions. The process of “scrubbing” the smokestack emissions creates calcium sulfate, or gypsum, which can then used to make wallboard, experts say.
Haldin, the Knaupf Tianjin spokesman, says some domestic drywall is also made from the less-refined fly ash.
But Michael Gardner, executive director of the U.S. Gypsum Association, said American manufacturers gather the gypsum from the smokestacks after the scrubbing, which produces a cleaner product.
The Consumer Product Safety Commission has dispatched teams of toxicologists, electrical engineers and other experts to Florida to study the phenomenon. The commission is also working with the Environmental Protection Agency and the Centers for Disease Control and Prevention to determine whether there is a health hazard.
A Florida Department of Health analysis found the Chinese drywall emits “volatile sulfur compounds,” and contains traces of strontium sulfide, which can produce the rotten-egg odor and reacts with air to corrode metals and wires.
But the agency says on its Web site that it “has not identified data suggesting an imminent or chronic health hazard at this time.”
“We’re continuing to test,” said Susan Smith, a spokeswoman for the department, which has logged 230 complaints from homeowners.
Dr. Patricia Williams, a University of New Orleans toxicologist hired by a Louisiana law firm that represents plaintiffs in some of the cases, said she has identified highly toxic compounds in the drywall, including hydrogen sulfide, sulfuric acid, sulfur dioxide and carbon disulfide.
Prolonged exposure to the compounds, especially high levels of carbon disulfide, can cause breathing problems, chest pains and even death; and can affect the nervous system, according to the CDC.
“It is absolutely shocking what is happening,” Williams said.
Dr. Phillip Goad, a toxicologist hired by Knaupf Plasterboard Tianjin, sampled drywall from 25 homes, some that contained the company’s wallboard and some that did not.
“The studies we have performed to date have identified very low levels of naturally occurring compounds,” Goad said. “The levels we have detected do not present a public health concern. The chemicals are naturally occurring. They’re produced in ocean water, in salt marsh air, in estuaries.”
But those who are living with it are convinced that something is making them sick, including dozens of homeowners in a single subdivision in Parkland, about 50 miles north of Miami. They are now faced with a daunting choice: Tear down and rebuild, or move out and be stuck with a mortgage and a home they cannot sell.
“We are particularly concerned about the safety and well-being of our children,” said Holly Krulik, who lives down the street from Mary Ann Schultheis.
She and her husband, Doug, are suffering sinus problems and respiratory ailments, and their young daughter has repeated nose bleeds.
“If a shiny copper coil can turn absolutely black within a matter of months, it certainly can’t be good for human beings,” Krulik said.
Neighbor John Willis is moving out, even though he can hardly afford to walk away from a house he’s owned for just three years. He cries as he speaks of his 3-year-old son’s respiratory infection, which eventually required surgery.
“They basically took out a substance that looked like rubber cement out of my 3-year-old son’s sinuses,” he said. “My wife and I are now faced with the choice between our children’s health and our financial health. My children are always going to win on that.”
The subdivision’s builder, WCI Communities, is in Chapter 11 bankruptcy restructuring and can do little more than log complaints, said spokeswoman Connie Boyd.
The federal government does not regulate the chemical ingredients of imported drywall.
Plasterboard Tianjin said it has been making drywall for 10 years in accordance with U.S. and international standards.
Another Chinese company facing lawsuits, Taishan Gypsum Ltd., also insists that it meets all U.S. standards.
Determining what is causing the problems could take months. Researchers will try to recreate in a lab the conditions that caused the sulfur compounds normally found in drywall to give off noxious gases.
Meanwhile, people like Lisa Sich, 43, are left with more questions than answers. Sich has not felt well since moving into the Henderson, Nev., apartment she rents less than a year ago, and her silverware quickly tarnished.
“I can hear myself wheezing,” said Sich, who is having environmental experts test the apartment, built in 2007. “My eyes are constantly itchy, extreme fatigue.”
And while Sich is not even certain she’s got the bad wallboard, she has not felt like herself in months. She’s missed five weeks of work just since Thanksgiving.
“I’m just tired all the time,” she said. “It doesn’t make sense.”
Associated Press Writer Joe McDonald in Beijing contributed to this report. Burdeau reported from New Orleans.
(Massachusetts Institute of Technology) — MIT civil engineers have for the first time identified what causes the most frequently used building material on earth — concrete — to gradually deform, decreasing its durability and shortening the lifespan of infrastructures such as bridges and nuclear waste containment vessels.
In a paper published in the Proceedings of the National Academy of Sciences (PNAS) online Early Edition the week of June 15, researchers say that concrete creep (the technical term for the time-dependent deformation that occurs in concrete when it is subjected to load) is caused by the rearrangement of particles at the nano-scale.
“Finally, we can explain how creep occurs,” said Professor Franz-Josef Ulm, co-author of the PNAS paper. “We can’t prevent creep from happening, but if we slow the rate at which it occurs, this will increase concrete’s durability and prolong the life of the structures. Our research lays the foundation for rethinking concrete engineering from a nanoscopic perspective.”
This research comes at a time when the American Society of Civil Engineers has assigned an aggregate grade of D to U.S. infrastructure, much of which is made of concrete. It likely will lead to concrete infrastructure capable of lasting hundreds of years rather than tens, which will bring enormous cost-savings and decreased concrete-related CO2 emissions. An estimated 5 to 8 percent of all human-generated atmospheric CO2 worldwide comes from the concrete industry.
Ulm, who has spent nearly two decades studying the mechanical behavior of concrete and its primary component, cement paste, has in the past several years focused on its nano-structure. This led to his publication of a paper in 2007 that said the basic building block of cement paste at the nano-scale — calcium-silicate-hydrates, or C-S-H — is granular in nature. The paper explained that C-S-H naturally self-assembles at two structurally distinct but chemically similar phases when mixed with water, each with a fixed packing density close to one of the two maximum densities allowed by nature for spherical objects (64 percent for the lower density and 74 percent for high).
In the new research revealed in the PNAS paper, Ulm and co-author Matthieu Vandamme explain that concrete creep comes about when these nano-meter-sized C-S-H particles rearrange into altered densities: some looser and others more tightly packed.
They also explain that a third, more dense phase of C-S-H can be induced by carefully manipulating the cement mix with other minerals such as silica fumes, a waste material of the aluminum industry. These reacting fumes form additional smaller particles that fit into the spaces between the nano-granules of C-S-H, spaces that were formerly filled with water. This has the effect of increasing the density of C-S-H to up to 87 percent, which in turn greatly hinders the movement of the C-S-H granules over time.
“There is a search by industry to find an optimal method for creating such ultra-high-density materials based on packing considerations in confined spaces, a method that is also environmentally sustainable,” said Ulm. “The addition of silica fumes is one known method in use for changing the density of concrete; we now know from the nanoscale packing why the addition of fumes reduces the creep of concrete. From a nanoscale perspective, other means now exist to achieve such highly packed, slow-creeping materials.”
“The insight gained into the nanostructure puts concrete on equal footing with high-tech materials, whose microstructure can be nanoengineered to meet specific performance criteria: strength, durability and a reduced environmental footprint,” said Vandamme, who earned a PhD from MIT’s Department of Civil and Environmental Engineering in 2008 and is now on the faculty of the Ecole des Ponts ParisTech, Université Paris-Est.
In their PNAS paper, the researchers show experimentally that the rate of creep is logarithmic, which means slowing creep increases durability exponentially. They demonstrate mathematically that creep can be slowed by a rate of 2.6. That would have a truly remarkable effect on durability: a containment vessel for nuclear waste built to last 100 years with today’s concrete could last up to 16,000 years if made with an ultra-high-density (UHD) concrete.
Ulm stressed that UHD concrete could alter structural designs, as well as have enormous environmental implications, because concrete is the most widely produced man-made material on earth: 20 billion tons per year worldwide with a 5 percent increase annually. More durable concrete means that less building material and less frequent renovations will be required.
“The thinner the structure, the more sensitive it is to creep, so up until now, we have been unable to build large-scale lightweight, durable concrete structures,” said Ulm. “With this new understanding of concrete, we could produce filigree: light, elegant, strong structures that will require far less material.”
Ulm and Vandamme achieved their research findings using a nano-indentation device, which allows them to poke and prod the C-S-H (or to use the terminology of civil engineering, apply load) and measure in minutes creep properties that are usually measured in year-long creep experiments at the macroscopic scale.
This work was funded in part by the Lafarge Group, a French building materials producer.
By: Denise Brehm
Portland cement is the most common type of cement in general use around the world, because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate which controls the set time, and up to 5% minor constituents (as allowed by various standards).
As defined by the European Standard EN197.1, “Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3CaO.SiO2 and 2CaO.SiO2), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium content (MgO) shall not exceed 5.0% by mass.” (The last two requirements were already set out in the German Standard, issued in 1909).
Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a sintering temperature, which is about 1450 °C for modern cements. The aluminium oxide and iron oxide are present as a flux and contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3CaO.Al2O3) formed. The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Second raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the second raw materials used are: clay, shale, sand, iron ore, bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.
How is portland cement made?
Materials that contain appropriate amounts of calcium compounds, silica, alumina and iron oxide are crushed and screened and placed in a rotating cement kiln. Ingredients used in this process are typically materials such as limestone, marl, shale, iron ore, clay, and fly ash.
The kiln resembles a large horizontal pipe with a diameter of 10 to 15 feet (3 to 4.1 meters) and a length of 300 feet (90 meters) or more. One end is raised slightly. The raw mix is placed in the high end and as the kiln rotates the materials move slowly toward the lower end. Flame jets are at the lower end and all the materials in the kiln are heated to high temperatures that range between 2700 and 3000 Fahrenheit (1480 and 1650 Celsius). This high heat drives off, or calcines, the chemically combined water and carbon dioxide from the raw materials and forms new compounds (tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite). For each ton of material that goes into the feed end of the kiln, two thirds of a ton the comes out the discharge end, called clinker. This clinker is in the form of marble sized pellets. The clinker is very finely ground to produce portland cement. A small amount of gypsum is added during the grinding process to control the cement’s set or rate of hardening.
What is air-entrained concrete?
Air-entrained concrete contains billions of microscopic air cells per cubic foot. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. Air-entrained concrete is produced through the use of air-entraining portland cement, or by the introduction of air-entraining agents, under careful engineering supervision as the concrete is mixed on the job. The amount of entrained air is usually between 4 percent and 7 percent of the volume of the concrete, but may be varied as required by special conditions.
Why does concrete crack?
Concrete, like all other materials, will slightly change in volume when it dries out. In typical concrete this change amounts to about 500 millionths. Translated into dimensions-this is about 1/16 of an inch in 10 feet (.4 cm in 3 meters). The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes due to shrinkage
Keeping its tradition of innovation alive, Lafarge has announced the launching of a new range of insulating ready-mix concretes: Thermedia.
The product is a result of four years of research in Lafarge’s laboratories and several social housing sites.
For the development and testing of Thermedia 0.6 B in France, Lafarge has combined its scientific expertise with Bouygues Construction. Bouygues Construction carried out building engineering studies and carried out the implementation as well as the acceptance tests for all its characteristics.
This concrete is in keeping with the guidelines of the French Grenelle Environment Forum. It is intended for building envelope applications and introduces a new performance feature to concrete in construction systems.
Thermedia 0.6 B is a product made for the French market and meets an environmental and financial requirement. This concrete actively improves construction systems that integrate interior thermal insulation (ITI) by contributing to heat loss reductions through the building’s envelope.
Thermedia 0.6 B is the only structural ready-mix concrete that will combine strength and lightness, mechanical performances and thermal properties.
Thermedia 0.6 B’s specific mix design, patented by Lafarge, significantly limits heat losses in buildings.
Therefore, in cases of interior thermal insulation, this new concrete reduces the impact between building facades and intermediate floor by 35% in terms of thermal bridges.
Thermedia 0.6 B is produced at a batching plant and then cast on-site. The product’s fluidity and workability make it a material that is easy to use in traditional construction methods.
By: Rashmi Kalia (ARI-C NEWS)
“In Recent Earthquakes, Buildings Have Acted as Weapons of Mass Destruction”
“When you build strong buildings, as an earthquake engineer would certainly be doing in Chile, and have done, you use a very angular kind of aggregate. If you use rounded pebbles, the pebbles don’t grab on the cement, and they just fall to pieces.” – Earthquake expert Roger Bilham.
(Denver, Colroado) — The earthquake that struck Chile was 500 times more powerful than the earthquake that struck Haiti, but it caused a fraction of the casualties.
AMY GOODMAN: In Chile, rescue workers are searching for survivors under the rubble following Saturday’s massive 8.8 earthquake, one of the strongest in recorded history. More than 700 people were killed, with the number expected to rise.
Chilean President Michelle Bachelet has announced emergency measures to deal with the destruction. She said one-and-a-half million people have been affected by the earthquake and declared a “state of catastrophe.” A curfew has been put in place in some areas.
The quake heavily damaged many of the country’s roads, airports and ports. It also triggered a tsunami that killed at least four people and caused serious damage to at least one port town.
Concepción, Chile’s second largest city, about 300 miles south of Santiago, one the hardest hit of the cities. The mayor has said food is running out and the situation is getting out of control. Thousands of people remain homeless. The army has been sent in to support local police. Security officials used tear gas and water cannons to disperse crowds who took food and supplies from a supermarket in Concepción. But according to the New York Times, law enforcement authorities, heeding the cries of residents that they lacked food and water, eventually settled on a system that allowed staples to be taken but not televisions and other electronic goods.
Even as the people of southern Chile continue to grapple with the death toll and the devastation wrought by the massive earthquake, many seismologists believe the wreckage could have been far worse. The 8.8-magnitude earthquake that struck Chile early Saturday morning was 500 times more powerful than the 7.0-magnitude quake that struck Haiti on January 12th, but it caused only a fraction of the casualties in comparison with the 300,000 people estimated to have died in Haiti.
Seismologists suggest one reason for the difference in scale is that Chile enforced building codes for earthquake-resistant structures after the experience of a 9.0-magnitude earthquake fifty years ago in 1960. Earthquake expert Roger Bilham argues it is quality of building construction and not simply the strength of the tremor that poses the most danger during an earthquake. He warns some of the fastest growing cities in the global south are also those facing significant seismic hazards, and the rapid pace of haphazard construction in these cities puts some 400 million people at risk.
Bilham was among the first seismologists to visit Haiti after the earthquake and in a recent article in Nature magazine calls for the enforcement of earthquake-resistant construction guidelines. University of Colorado professor of geology and co-author with Susan Elizabeth Hough of After the Earth Quakes: Elastic Rebound on an Urban Planet, Roger Bilham joins me now from Denver, Colorado.
We welcome you to Democracy Now! It’s very good to have you with us.
ROGER BILHAM: Good Morning.
AMY GOODMAN: Roger, can you start off by explaining the magnitude of the earthquake that has hit Chile and the scope of the damage?
ROGER BILHAM: Yes, a magnitude-8.8 earthquake is one of the biggest that you can have on the planet. In fact, the very largest we know about also happened in Chile in 1960, as you rightly point out. It had a magnitude of 9.5, much bigger than the one that’s just occurred. However, the death toll in Chile during that earthquake was only 1,600 people.
We may reach four figures in this earthquake, but we have to think of this as a tremendous success story. Earthquake-resistant construction prevails throughout Chile. They have an intelligent government that enforces these regulations. And they have constant reminders of what earthquakes can do. So, although a tremendous number of buildings have been damaged, the buildings are damaged to the point that people can walk out of them.
In Haiti, this did not occur. The buildings were shaken violently and completely pancaked, in many cases, because there was no earthquake resistance at all. And although Haiti has a history of earthquakes, stretching back to the same period of time — Christopher Columbus obviously arrived 1492, we don’t know about earthquakes before then — although Haiti has this extraordinary long history of earthquakes, the local government was completely unaware of the potential effects of bad building practices.
AMY GOODMAN: And when you talk about bad building practices, what exactly do you mean? What did Chile have that Haiti didn’t have?
ROGER BILHAM: Well, first of all, there are various things that earthquake engineers insist on. The survival of certain critical structures, like hospitals, schools, fire stations and so on, those have to survive earthquakes intact and operate the next, you know, few minutes after the shaking has stopped. It turns out that some of these hospitals have been damaged, but probably not as many as could have.
Now, what do you do to make a building safe from earthquakes? You need good quality foundations. Most buildings now going up are known as concrete skeleton designs. They have a structure of steel embedded in concrete. And you have to make sure you have the right kind of steel. If you use brittle steel, for example, the steel will simply snap during an earthquake. What you need is ductile steel. It costs a little bit more.
In Haiti, it was all brittle steel, steel without ribbing, even, in terms of little corrugations that hold the concrete together when shaking commences. There are little structural members that look as though they’re in place simply to hold the steel in place during pouring of the cement, those things called stirrups. In fact, the stirrups used in Haiti were very weak, almost chicken wire-type strength, whereas in Chile, I’m sure, they applied the appropriate strength and thickness. And what these little pieces of metal do is stop the columns from exploding during the violent vertical shaking in an earthquake.
Then the quality of the concrete (1) matters. If you mix three parts of sand to one part of cement, which is something they’ll never tell you in school, but which most construction people know, you get good quality concrete that doesn’t fall to pieces in an earthquake. However, if you go down the beach and shovel beach sand into a wheelbarrow and take it back to your building site without washing it or without checking, you know, exactly what it’s got in it — it might have dirt or soil, or it might have salt in — you finish up with a very weak concrete (1). And it’s all too tempting, if you’re building your own house, as must have occurred frequently in Haiti, to take four parts of sand or five parts of sand, making an extremely weak concrete (1).
Another thing is the addition of aggregate. When you build strong buildings, as an earthquake engineer would certainly be doing in Chile, and have done, you use a very angular kind of aggregate. If you use rounded pebbles, the pebbles don’t grab on the cement, and they just fall to pieces.
So there are a number of very obvious things that can be done, and unfortunately, people are not told how to do this. You know, very frequently, the lowest-paid workers turn up at a construction site, and they’re told to, you know, mix some cement, follow what that man is doing over there, and assemble it. Well, if there’s an engineer on board, it gets done right. If the man does it on his own, he may well be copying incorrect practices. And as a result, Haiti has duplicated a series of catastrophic designs that are weak from the foundations up and consequently fell down.
AMY GOODMAN: Professor Bilham, are there an increased number of earthquakes? I mean, this weekend you have what happened in Chile. Also, wasn’t there a small one in Pakistan? And then, of course, you had the horror in Haiti on January 12th. If you could talk about these, and beyond, in China, in Pakistan, in the past, in the United States.
ROGER BILHAM: Of course, yes. Earthquakes are happening all the time. They’ve been happening for the last several billion years on our planet, and there’s no change in their frequency. It looks like large earthquakes are happening suddenly now, a kind of conspiracy effect. No, it’s just a statistical fluctuation.
We have to worry about earthquakes that actually occur near population centers. We don’t need to worry about earthquakes that happen in the middle of the ocean. Nobody is there, just a few fish. So, what really matters is where our populations are.
And one of the most unexpected things is if you make a map of the world and plop down all the cities that you know about, the very largest of them, probably half of them, are located on plate boundaries. Plate boundaries is where earthquakes occur. Now, supposing you were coming in from a distant galaxy and you wanted to just populate the planet, you would try to avoid those places. But we have grown up on this planet, and we found that plate boundaries are in fact very desirable places to live. They’re on the seashore. There’s usually a good trading arrangement, even inland, near mountain belts, which are plate boundaries, like the Himalaya and parts of Iran, and so on. Cities are often located near sources of water, and these sources of water come out at range fronts. In other words, all the most desirable places on our planet appear to be populated by very, very large cities.
Now, if you wind the clock back 150 years, you find that these were only villages. The population of the world has increased tenfold in the repeat time of most damaging earthquakes on our planet. And so, we have set up a disaster waiting to happen in probably a hundred cities with populations more than a million people. And one could list — one could list these hundred cities, and probably two or three of these will be damaged in the next two or three decades. A completely unacceptable prediction. It should not be possible for us to say that we’re going to lose another 500,000 people. Six hundred and fifty thousand people have died from earthquakes just since 2000. That’s up almost fourfold since the previous two decades.
And you could ask, well, why is this? Well, it’s partly a statistical fluctuation in the locations of large earthquakes that are occurring, and it’s partly a recurrence of these big earthquakes to cities that were former villages only 200 years ago. We know their history of earthquakes, and we know they will have a future of earthquakes. And so, many of these cities, mostly in the developing nations, are slated for demolition by earthquakes.
And it’s — a well-known phrase is that earthquakes don’t kill people, buildings do. And we are now seeing that buildings are in fact weapons of mass destruction. And in fact, it’s, to me, completely unacceptable that we should live in a world where you can shake the ground a little bit, and the building will fall down. It’s just nonsense. We know how to do it right. It’s just that we haven’t done it right. It will take a long while, maybe —
AMY GOODMAN: How does that kind of building get enforced, Roger Bilham? How does that kind of building get enforced, the kind of building regulations you’re talking about?
ROGER BILHAM: Building inspectors are designed to come and watch every stage of a building’s assembly in the U.S.. You can’t put a building up in California, or in Colorado, even, without someone watching over your shoulder every step of a moment. You can’t go to the next step until you’ve received your certificate.
In a place like Karachi or Tehran, building codes are now being enforced, and that’s something that’s happening officially. However, in some parts of the world, it’s possible to talk to your building inspector and say, “Why don’t to come tomorrow, after I pour the concrete? Here’s, you know, a few hundred dollars to look the other way.”
And you might think, well, how can anyone be so stupid as to assemble a building without sufficient strength? The answer is, you can save money. And in the developing nations, there is this battle between what should be done and human nature, trying to either overtly make profits or covertly just to save money for the builders. You know, very often these —
AMY GOODMAN: And also the issue of poverty.
ROGER BILHAM: Yes. In Haiti, seismologists, my colleagues, told the Haitians that, in fact, large earthquakes were overdue, and they had happened a few hundred years ago, and there was enough strain now developed at the plate boundary to repeat a sequence of events that happened in the 1700s. Well, this knowledge is like kind of “dream on.” There are so many problems that Haiti had that even if they had started to act on retrofitting these buildings, it would have taken two, three decades. And there was no money for this. There are much more pressing issues.
AMY GOODMAN: Finally, are there manmade situations or phenomena that are increasing the number of earthquakes? Does anything human beings do on earth have an effect on earthquakes, the number of earthquakes or their intensity?
ROGER BILHAM: Not really. I can’t say that it doesn’t happen at all. If you build a very large dam, you sometimes trigger an earthquake. But what we’re watching is just the relentless movement of the plates. And what the earth has in store for us are usually a hundred magnitude-7.0 earthquakes a year. Our future disasters depend whether those earthquakes occur close to cities that are vulnerable to shaking, or whether they occur away from these cities. And it’s a hit-or-miss problem.
But I forecast that it is possible now to have something that has never happened in earth’s history: an earthquake killing perhaps a million people. And how can you make such a ridiculous prediction? The answer is that never before have we had such large populations at risk from earthquakes, cities of 12 million. And there are many cities like this, and several of them, like Istanbul and Tehran, have a history of damaging earthquakes, and we may well see the effects of corruption and bad building practices revealed only after these earthquakes have struck.
AMY GOODMAN: Finally, do you predict an earthquake in the United States anytime soon?
ROGER BILHAM: Well, we’re very careful not to predict earthquakes. We tried that with a harmless earthquake in a field of cows at Parkfield a few years ago and failed miserably.
What we can do, though, is forecast earthquakes, meaning that we know earthquakes will occur in something like a thirty-year window. And on the San Andreas Fault, of course, there are a couple of large earthquakes overdue, one near Palm Springs. It might reach up into the LA region through Palmdale and so on. That earthquake is known to be ripe, sufficiently mature to happen any day. It may not happen for a hundred years, but it’s certainly something they’re expecting. And, of course, earthquake resistance is pretty good in LA. I mean, the houses are made of wood, and earthquake-resistant design prevails throughout.
But there is a much larger earthquake that could occur, and that is from Cape Mendocino northwards through Oregon, up to Washington state. We are expecting in this country a magnitude-9.0 earthquake. This may — this, again, could occur now; it may not occur for a hundred years. But occur, it will. And when it does, it will test those building regulations that have been put into effect in places like Seattle. There is a large building stock that hasn’t had the benefit of earthquake-resistant construction from the start. One can think of a lot of masonry buildings that will be damaged. There will also be a very large tsunami. And yeah, this is something that is definitely going to occur in our future, or the next generation. And I think we are more or less ready for it, certainly much better prepared than Haiti and as well-prepared as Chile.
AMY GOODMAN: Roger Bilham, I want to thank you for being with us, professor of geology at the University of Colorado in Boulder, co-author with Susan Elizabeth Hough of After the Earth Quakes: Elastic Rebound on an Urban Planet.
(1) Corrections made from original article regarding the terminology of ‘cement’ and ‘concrete’.
Cement is an ingredient of concrete, like flour is to bake a cake.
There’s been a stir in the British construction industry lately over the development of a new building material that holds out the promise of greatly reducing cement use while delivering high fire ratings and great load-bearing strength.
It was developed by Pal Mangat, director of the Centre for Infrastructure Management at Sheffield Hallam University, and despite early successes in the application of his material, he’s keeping pretty quiet about what’s in it.
From what we know so far, the product, dubbed Liquid Granite, is a powder made up of between 30 and 70 per cent industrial waste. It also contains less than one-third of the cement usually used for precast concrete. And, no, that isn’t a typographical error. Liquid Granite is a powder.
“It replaces most of the cement in standard concrete with a secret formula of products to change the basic properties of the material,” Mangat says. “I believe it has great potential for the future.”
Concrete made with the material has high compressive strength and a high level of fire resistance.
So far, it’s available only in the United Kingdom, supplied by a firm called Liquid Granite Ltd. But, despite the name, it is not related to the “liquid granite” used in North America as a sealant with a wide range of applications, from industrial floors to kitchen countertops. That means there will be a name change somewhere along the way before the new British product is available over here.
In England it is being used, so far, for fire-resistant members in construction of the Olympic Village which is being built for the London Summer Olympics in 2012, and in a shopping mall, also in London.
Mangat says that, so far, he’s been able to replace more than two-thirds of the Portland cement when making concrete, thus saving the associated carbon emissions.
“One of the biggest culprits of carbon footprint is cement, which we use in making concrete,” he says. “Liquid Granite does away with most of the use of cement. The amount used is pretty small.”
“Potentially, by the time we’re finished with this developmental technology, it’ll be close to zero.”
He’s especially keen on the material’s fire-resistant properties. It can withstand temperatures of up to 1,100°C while maintaining its structural properties. Thus, it has already been granted a four-hour fire rating.
That means, Mangat says, that it should find uses wherever fire safety is crucial, “such as around power stations, and in domestic and commercial buildings, where it can offer added time for evacuation in case of emergency.”
Beyond that, he won’t say much — with good reason.
The world uses about two billion tonnes of cement every year, and there are estimates that by 2020, demand will be 50 per cent higher than it is today.
Each tonne of cement manufactured results in the release of about 400 kg of carbon dioxide, and the industry is responsible for roughly five per cent of the world’s carbon emissions, so huge rewards await anyone who can come up with a carbon-free material to replace it.
Indeed, a British firm called Novacem has created a new cement that has a negative carbon footprint over its lifetime. It uses magnesium silicates, which emit no carbon dioxide when heated, and the process is carried out at much lower temperatures than used in the manufacture of Portland cement. As well, the magnesium-based product absorbs carbon dioxide as it hardens. It has been estimated that over its lifetime, a tonne of the material could remove about 600 kg of the gas.
As climate agreements are written, and begin to bite, it’s a safe bet that the race to reduce carbon emissions will get tighter and tighter.
The payoff for the winner will be immense.
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