Robert Estes Kennington


Image by Robert of Fairfax
The Story of Jackson

Biographical sketches of the builders of the capital of Mississippi

Volume II

J. F. Hyer Publishing Company

Jackson, Mississippi, 1953

[brackets are annotations by RGK]

Robert Estes Kennington

[page 15, The Story of Jackson]

Ranking foremost among the business civic, church and social leaders of his city and state, Robert Estes Kennington is one whose life story is in the great American tradition. His success in building what is indisputably Mississippi’s "finest and largest" department store did not come as the result of inherited properties and money, but from a far greater legacy of thrift, determination, expert judgment, courage and vision.

Orphaned at an early age and deprived of formal schooling by the necessity of earning his own livelihood, young Robert Kennington surmounted obstacles which would have downed a less sturdy character at the outset and rose to be one of the ablest and most highly respected men in his field in the nation. The word failure was not in Robert Kennington’s vocabulary. Destined for great things, he displayed at an early age the intelligence, stamina and will to succeed, and the magnificent department store in the heart of downtown Jackson, capital city of a state toward which the eyes of the nation are turned, is a monument to his unerring judgment, his keen sense of business, his meticulous attention to detail and his concern for the welfare of others.

Born March 19, 1876, in Columbus, Georgia [other records indicate Phenix City, Alabama which is adjacent and to the west of Columbus], young Kennington complet4d four grades in public school in Camilla, Georgia, before he was forced to quit his formal studies and go to work. In his own words, Robert Estes Kennington was educated in the "school of hard knocks." At ten years of age, he began helping on of his uncles in the latter’s store in Camilla, Georgia, sweeping out and performing odd jobs. He earned his first dollar delivering soda samples in Camilla when he was 11 years old. Later, he went to Pelham, Georgia, to work in another uncle’s store, and his wages here were five dollars a month and board.

Both of the uncles moved to Mississippi to establish mercantile and general stores in Yazoo city and Jackson, and when Robert was 14 years old, he joined them, becoming associated with the Jackson store. Displaying the farsightedness which carried him far in the business world, young Kennington at 15 took a six-month business course, and at 16, was keeping books in his uncle’s mercantile establishment. His talent for merchandising became evident at this time, and when he was 17, he was made manager o the Yazoo City store, which he was eventually able to purchase.

Later, his interest a Yazoo City was transferred to Jackson, the Jones Brothers became the Jones Brothers Company, building two stores in Jackson located on South State and Pearl Streets, the general merchandise store having entrances on South State, and the grocery and general supply store facing on Pearl Street.

Business establishments at that period in Jackson’s history depended largely on the wagon trade with neighboring counties, and when in about 1900, the Gulf and Ship Island Rail Road was built through to Jackson, many of the merchants felt that the wagon trade was doomed and their own financial ruin impending. This was not so with R. E. Kennington. His faith in the future was secure, and with the clear vision which has always been apparent in his business ventures, he predicted that while the wagon trade would largely disappear, it would be replaced by a bigger and better volume of business from an extended trade area.

He prophesied: "We won’t lose anything–on the contrary, we will get the cream of the trade." He was right, although the change in mode of travel proved revolutionary in more ways than one for the merchants. They found it necessary to change their stocks and adopt more modern business methods. Gone was the old supply business, and gone was the practice of bartering bales of cotton for groceries and other necessities.

It was at this period in Mr. Kennington’s business career that he and his uncles, differing in opinion concerning methods of handling the trade, agreed that the young nephew was to take charge of the general merchandise store on South State Street while the uncles were to continue operating the wholesale grocery and supply store on South State Street. The Jones-Kennington Dry Goods Company was incorporated and continued in existence for several years.

In 1905, Mr. Kennington saw that business was swinging from South State Street to Capitol Street, and once more displaying the keen vision and the courage which have been part of his most successful transactions, he decided to build a modern department store on the corner of Capitol and Congress Streets. This site had been occupied for years by the old St. Andrew’s Episcopal Church, and at the time, the church was erecting a new building on the corner of West and Capitol Streets. The old site of the church was bought and on April 7, 1906, the Kennington Dry Goods Company opened for business in its present home.

In 1906, the new corporation was under Mr. Kennington’s complete control. At that time, however, he owned only one-third interest in the corporation and the capital sock of ,000 consisted entirely of merchandise and accounts. In 1911, Mr. Kennington bought out the Jones’ shares in the store, and the R. E. Kennington Company, as we know it today, was on its way. Major expansions came in 1925, 1941 and another 25 percent increase in the store’s physical plant in 1948.

Over all the years, Mr. Kennington kept his finger on the pulse of the buying public and anticipated needs before they presented themselves. By keeping his own books in the early days of the store, Mr. Kennington knew exactly what was happening and what to expect in the business day by day. He opened the store in the mornings and closed it late at nights, and of all the people in the store, "the boss" was always the busiest man on the premises.

As an employer he has always been kind, courteous and considerate. He has demanded and received the best of his employees and they in turn have been rewarded. As a younger man, he would never ask an employee to do more than he would do himself, and he, too, was rewarded by the loyal devotion of his workers to himself and their painstaking attention to the business.

Mr. Kennington pioneered in many ways in the business field. His store was one of the first to take advantage of the radical shift in location from South State to Capitol Street; the first in the state to boast an elevator; the first to depart from the barter and dicker system and fix a uniform price on merchandise; a leader in shorter working hours for employees; and the first to air-condition its building in Mississippi. All Kennington employees today are covered by a variety of all-inclusive benefit plans.

While in his late teens and before transferring his interests to Jackson, Mr. Kennington married Miss Bethunia Battaile, a member of a fine old Yazoo City family. Their union was blessed with four children: Robert George Kennington, Marian Kennington (now deceased [she died in 1924, see Gordin, page 390]), who became the wife of Dr. Archie Ewing Gordin; John Andrew Kennington and Cordelia Kennington, who is now Mrs. Thomas Burkett [census and ship records indicate his name may have been spelled Burkitt, he died by a stroke of lightening on the golf course]. There are two grandchildren: Robert Kennington Gordon, now married and the father of three; and Marian (Kennington) Stevens whose little son bears her father’s name, John Kennington Stevens.

In addition to his family and store, Mr. Kennington has demonstrated a genuine and broad interest in community, state, and national affairs. A great traveler, Mr. Kennington is familiar with the large cities of the country but is unswerving in his loyalty to Jackson. He has been interested from time to time in a large number of other business enterprises. He organized the predecessor of the Jackson Chamber of Commerce and the Mississippi State Fair, and was a charter member of the Jackson Rotary Club, serving one year as its president, and now holding an honorary membership. He was chairman of the committee that established Belhaven College, a girls’ school of his own Presbyterian denomination, and assisted in organizing the Mississippi Cotton Co-op Association in 1930.

Mr. Kennington organized and was president of the Mississippi Rehabilitation Corporation, 1927-28, for financial relief of flood sufferers; served as a member of the executive committee of the State Board of Welfare, appointed by Governor Mike Conner; was vice-president and director of the National Retail Dry Goods Association; served as a member of the Domestic Distribution Committee of the United States Chamber of Commerce; was Mississippi chairman of the R.F.C. in Jackson, Mississippi, Office; and organized the Regional Agricultural Corporation of Jackson and served as its president until August 1, 1933.

In addition to being president and director of R. E. Kennington Company, Mr. Kennington is also vice president and director of the Kennington Investment Company, Jackson; vice-president and director, Kennington-Saenger Theatres, Jackson.

Mr. Kennington has led in fund-raising campaigns for almost every worthwhile project in the city. During World War I, his public services were on statewide and national levels as well as local. He served as state chairman of the Red Cross Campaign Fund, was State Merchants representative in Food Administration; served as Hinds County Food Administrator; was a member of the Hinds County Liberty Loan Committee, and district chairman of the Fourth Liberty Loan. During World War II, his elder son, Robert G. Kennington, performed similar services to the community, the state and the nation.

Now, having labored long and contentedly, Mr. Kennington is enjoying the fruits of his toil. With more leisure, and leaving the management of his business affairs largely in the capable hands of his splendid son, J.[John, but nicknamed Jack] A. Kennington, his other son, Robert G., having suffered a serious heart attack four years ago and upon advice of his physician retired from active participation in the business.

A man whose spirit of adventure never led him astray but was guided in all his pioneering and business dealing by the principles of honesty, tolerance and industry, Robert Estes Kennington is a Jackson leader of whom not only his fellow citizens may be well proud, but his nation as well. His influence upon the growth and progress of his adopted city is evident upon all sides and will be felt by the generations to com.

… Read further about Archie Ewing Gordon who married Robert Estes Kennington’s daughter Marion about 1921.

Archie Ewing Gordin, M.D.

[page 390, The Story of Jackson]

Descended from pioneer Jackson families, Dr. Archie Ewing Gordin is an eminent surgeon whose ability is recognized by other medical men and surgeons throughout the country. Actively engaged in the practice of surgery in Jackson since 1920, he has made many valuable contributions to his profession and has added materially to the progress of the city through his civic activities as well.

Dr. Archie Ewing Gordin was born in Jackson on September 11, 1892, the son of James Archie and Frances (Ewing) Gordin. His father, James Archie Gordin, who was born at Vaiden, Carroll County, Mississippi, is a retired railroad man and real estate operator, now living in retirement at the age of ninety-one in Jackson. Frances (Ewing) Gordin, who died in 1946, was a member of one of the old pioneer families of Jackson. She was a woman who had a genuine affection and regard for humankind and especially for the unfortunate. She went about her acts of charity quietly, and her kindness, generosity and understanding had far-reaching effects on the lives of those she helped. The oldest circle of the King’s Daughters and Sons, an international philanthropic order, bears her name.

Archie Ewing Gordin was educated in the public schools of Jackson, Bingham Military School in Asheville, North Carolina, and graduated from the University of Virginia with the [an] M.D. Degree in 1915. His period of internship was spent as house surgeon at the University of Virginia, in the New York Lying-In Hospital and German Hospital in New York City. With the rank of First Lieutenant he served in the Medical Corps of the United States Army from 1917-1918 in World War I.

Following his period of army service, Doctor Gordin was on the surgical staffs of San Mateo Hospital, San Mateo, California. Returning to Jackson in 1920, he entered into general practice of surgery and for several years following was associate surgeon in operating the old Jackson Infirmary which later became St. Dominic’s Hospital. Since then he has continued in the general practice of surgery with offices at 121 North President Street. He is a member of the surgical staffs of both St. Dominic’s and Mississippi Baptist Hospital, has served as a member of the attending surgical staff of the Mississippi State Charity Hospital, and as a consulting surgeon, Mississippi State Tuberculosis Sanatorium. For the past twenty-five years he has been surgeon for the Mississippi Power and Light Company.

A close student of his profession, Doctor Gordin always has kept in touch with the trends and progress in medicine and surgery, attending clinics in various medical centers, reading and studying, and through his membership in the American Medical Association, the Southern Medical Association, the Southeastern Surgical Congress, the Mississippi State Medical Society, Central Medical Society and Tri-State Medical Society.

He was made a Fellow in the American College of Surgeons in 1924 and a Fellow in the International College of Surgeons in 1950. He is the author of numerous articles on surgery, a month them being: Pancreatic Cysts, published in Annals of Surgery; Bone Grafts, in Southern Surgical Journal; Fracture of the Spine, in American Journal of Surgery; Herniated Nucleus Pulposis, in Journal of Industrial Surgery; Surgical Treatment of Electrical Burns, Journal of Industrial Surgery; Plaster Casts and Surgery, Gynecology and Obstetrics (both of these papers being reprinted in the Year Book of Orthopedic Surgery); Surgery of Gallbladder, Journal of Medical Association; The Misuses of Caesarean Section, Mississippi State Medical Journal; Post-Operative Intestinal Obstruction, Journal of Central Medical Society; Local Anesthesia in Major Surgery, Journal of Central Medical Association, and many others.

As a college student, Doctor Gordin belonged to Alpha Tau Omega and Phi Rho Sigma Fraternities. He is also a member and past president of the Jackson Exchange Club, a member of the P.P.O.E. Elks; a 32nd degree Scottish Rite Mason and a Shriner; a member of the American Legion, the Executives Club and the Jackson Country Club. He is a Presbyterian.

In the midst of his busy and useful life, Doctor Gordin occasionally finds a leisure hour. He enjoys deep-sea fishing, horseback riding and a game of golf. He and his wife are fond of their friends and are known for their gracious hospitality.

Dr. Gordin first married [must be about 1921 just before his son was born] Miss Marian Kennington, daughter of R. E. Kennington [1875 - 1969], prominent Jackson merchant. Marion (Kennington) Gordin died in 1924, leaving one son, Robert Kennington Gordin [1922 - 1999], who was educated at Central High School, Gulfport Military Academy and was graduated from the University of Virginia with the Class of 1947, obtaining his B.A. degree. He served in World War II with the rank of captain, seeing active duty in the European Theatre with the 101st Paratroop Battalion, United States Army. He was wounded and subsequently was decorated with eh Purple Heart.

As a member of the United States Army Reserve Officers, Robert Kennington Gordin recently reentered the service and is now stationed at Fort Devens, Massachusetts. His wife is the form Barbara Pitt of Charlottesville, Virginia. They are the parents of three children: Marian Kennington Gordin, Robert Kennington Gordin, Jr., and Elizabeth Ewing Gordin.

Doctor Gordin married for the second time on May 17, 1942. His wife is the former Margaret Gray of Gulfport, Mississippi, daughter of the late Andrew and Alice (Highlands) Gray. A graduate of Mississippi State College, Mrs. Archie Ewing Gordin is member of Ralph Humphreys Chapter, Daughters of the American Revolution, the Jackson country Club, the Women’s Auxiliary to the Central Medical Society, a member of the Board of Managers of the Old Ladies Home and a Presbyterian. She is particularly active in her work for the Old Ladies Home, give unstintingly of herself to make the twilight years of these aged women happy and contented ones. She frequently visits the Home, not only to attend the board meetings, but to pay persona calls on the ladies and to assist in the hospital ward. Her gentleness and kindness have greatly enriched the last years of these frail, aged women, and their faces reflect their joy in her presence. Mrs. Gordin has taken a prominent part in the civic and social life of the city, and during World War II, rendered outstand service the Red Cross and in bond-selling drives.

An attractive, energetic woman, possessing a fine mind and pleasing personality, Mrs. Gordin is a perfect complement to her busy and brilliant husband. Her skill in the management of both minor and major affairs greatly lightens the self-imposed burden her husband shoulders as he follows his heavy schedule. With her help, he free to fill the professional demands which claim a major portion of his time and keeps at peak the highly developed powers which have brought him to a point of leadership in his professional field.

Concrete


Image by Joost J. Bakker IJmuiden
Concrete
Concrete is a composite construction material, composed of cement (commonly Portland cement) and other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravel or crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures.

The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to grow).

Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a robust stone-like material. Concrete is used to make pavements, pipe, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles.

Concrete is used more than any other man-made material in the world. As of 2006, about 7.5 cubic kilometres of concrete are made each year—more than one cubic metre for every person on Earth.

Concrete powers a US billion industry, employing more than two million workers in the United States alone.[citation needed] More than 55,000 miles (89,000 km) 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.

History

Concrete has been used for construction in various ancient structures. An analysis of ancient Egyptian pyramids has shown that concrete may have been employed in their construction, although its composition would have differed from modern concrete.

During the Roman Empire, Roman concrete (or opus caementicium) was made from quicklime, pozzolana, and an aggregate of pumice. Its widespread use in many Roman structures, a key event in the history of architecture termed the Roman Architectural Revolution, freed Roman construction from the restrictions of stone and brick material and allowed for revolutionary new designs in terms of both structural complexity and dimension.

Hadrian’s Pantheon in Rome is an example of Roman concrete construction.Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that trouble the builders of similar structures in stone or brick.

Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (ca. 200 kg/cm2). However, due to the absence of steel reinforcement, its tensile strength was far lower and its mode of application was also different:

Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.

The widespread use of concrete in many Roman structures has ensured that many survive to the present day. The Baths of Caracalla in Rome are just one example. Many Roman aqueducts and bridges have masonry cladding on a concrete core, as does the dome of the Pantheon.

Some have stated that the secret of concrete was lost for 13 centuries until 1756, when the British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. However, the Canal du Midi was built using concrete in 1670.[11] Likewise there are concrete structures in Finland that date back to the 16th century. Portland cement was first used in concrete in the early 1840s.

Additives

Concrete additives have been used since Roman and Egyptian times, when it was discovered that adding volcanic ash to the mix allowed it to set under water. Similarly, the Romans knew that adding horse hair made concrete less liable to crack while it hardened, and adding blood made it more frost-resistant.

Recently the use of recycled materials as concrete ingredients has been gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a byproduct of coal-fired power plants. This use reduces the amount of quarrying and landfill space required, and, as the ash acts as a cement replacement, reduces the amount of cement required.

In modern times, researchers have experimented with the addition of other materials to create concrete with improved properties, such as higher strength or electrical conductivity. Marconite is one example.

Composition

There are many types of concrete available, created by varying the proportions of the main ingredients below. In this way or by substitution for the cemetitious and aggregate phases, the finished product can be tailored to its application with varying strength, density, or chemical and thermal resistance properties.

The mix design depends on the type of structure being built, how the concrete will be mixed and delivered, and how it will be placed to form this structure.

Cement
Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar, and plaster. English masonry worker Joseph Aspdin patented Portland cement in 1824; it was named because of its similarity in colour to Portland limestone, quarried from the English Isle of Portland and used extensively in London architecture. It consists of a mixture of oxides of calcium, silicon and aluminium. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum).

Water

Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and allows it to flow more freely.

Less water in the cement paste will yield a stronger, more durable concrete; more water will give an freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.

Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles, and other components of the concrete, to form a solid mass.

Reaction:

Cement chemist notation: C3S + H → C-S-H + CH
Standard notation: Ca3SiO5 + H2O → (CaO)·(SiO2)·(H2O)(gel) + Ca(OH)2
Balanced: 2Ca3SiO5 + 7H2O → 3(CaO)·2(SiO2)·4(H2O)(gel) + 3Ca(OH)2

Aggregates

Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition and excavation waste) are increasingly used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.

Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.

The presence of aggregate greatly increases the robustness of concrete above that of cement, which otherwise is a brittle material, and thus concrete is a true composite material.

Redistribution of aggregates after compaction often creates inhomogeneity due to the influence of vibration. This can lead to strength gradients.

Reinforcement

Concrete is strong in compression, as the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail. Reinforced concrete solves these problems by adding either steel reinforcing bars, steel fibers, glass fiber, or plastic fiber to carry tensile loads. Thereafter the concrete is reinforced to withstand the tensile loads upon it.
Chemical admixtures

Chemical admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. In normal use, admixture dosages are less than 5% by mass of cement, and are added to the concrete at the time of batching/mixing. The common types of admixtures are as follows.

Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are CaCl2, Ca(NO3)2 and NaNO3. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that nitrates may be favored.
Retarders slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.
Air entrainments add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles, thereby increasing the concrete’s durability. However, entrained air entails a tradeoff with strength, as each 1% of air may result in 5% decrease in compressive strength.
Plasticizers increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability, and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics. Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects, and can be used to increase workability more than is practical with traditional plasticizers. Compounds used as superplasticizers include sulfonated naphthalene formaldehyde condensate, sulfonated melamine formaldehyde condensate, acetone formaldehyde condensate, and polycarboxylate ethers.
Pigments can be used to change the color of concrete, for aesthetics.
Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
Bonding agents are used to create a bond between old and new concrete.
Pumping aids improve pumpability, thicken the paste, and reduce separation and bleeding.

Mineral admixtures and blended cements

There are inorganic materials that also have pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements).

Fly ash: A by product of coalfired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, siliceous fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties.
Ground granulated blast furnace slag (GGBFS or GGBS): A by-product of steel production is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties.[18]
Silica fume: A by-product of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability.[19]
High reactivity Metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume. While silica fume is usually dark gray or black in color, high-reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important.
Concrete production

The processes used vary dramatically, from hand tools to heavy industry, but result in the concrete being placed where it cures into a final form. Wide range of technological factors may occur during production of concrete elements and their influence to basic characteristics may vary

When initially mixed together, Portland cement and water rapidly form a gel, formed of tangled chains of interlocking crystals. These continue to react over time, with the initially fluid gel often aiding in placement by improving workability. As the concrete sets, the chains of crystals join and form a rigid structure, gluing the aggregate particles in place. During curing, more of the cement reacts with the residual water (hydration).

This curing process develops physical and chemical properties. Among these qualities are mechanical strength, low moisture permeability, and chemical and volumetric stability

Mixing concrete

Thorough mixing is essential for the production of uniform, high quality concrete. For this reason equipment and methods should be capable of effectively mixing concrete materials containing the largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work.

Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete.[21] The paste is generally mixed in a high-speed, shear-type mixer at a w/cm (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, plasticizers, pigments, or silica fume. The premixed paste is then blended with aggregates and any remaining batch water, and final mixing is completed in conventional concrete mixing equipment.

High-energy mixed (HEM) concrete is produced by means of high-speed mixing of cement, water, and sand with net specific energy consumption of at least 5 kilojoules per kilogram of the mix. A plasticizer or a superplasticizer is then added to the activated mixture, which can later be mixed with aggregates in a conventional concrete mixer. In this process, sand provides dissipation of energy and creates high shear conditions on the surface of cement particles. This results in the full volume of water interacting with cement. The liquid activated mixture can be used by itself or foamed (expanded) for lightweight concrete. HEM concrete hardens in low and subzero temperature conditions and possesses an increased volume of gel, which drastically reduces capillarity in solid and porous materials.
Workability

Main article: Concrete slump test
Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete’s quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration), and can be modified by adding chemical admixtures, like superplasticizer. Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increased bleeding (surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. The use of an aggregate with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot be readily made more workable by addition of reasonable amounts of water.

Workability can be measured by the concrete slump test, a simplistic measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 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 in order to consolidate the layer. When the cone is carefully lifted off, the enclosed material will slump a certain amount due to gravity. A relatively dry sample will slump very little, having a slump value of one or two inches (25 or 50 mm). A relatively wet concrete sample may slump as much as eight inches. Workability can also be measured by using the Flow table test.

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.

High-flow concrete, 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.

After mixing, concrete is a fluid and can be pumped to the location where needed.

Curing

In all but the least critical applications, care needs to be taken to properly cure concrete, to achieve best strength and hardness. This happens after the concrete has been placed. Cement requires a moist, controlled environment to gain strength and harden fully. The cement paste hardens over time, initially setting and becoming rigid though very weak, and gaining in strength in the weeks following. In around 3 weeks, typically over 90% of the final strength is reached, though strengthening may continue for decades. The conversion of calcium hydroxide in the concrete into calcium carbonate from absorption of CO2 over several decades further strengthen the concrete and making it more resilient to damage. However, this reaction, called carbonation, lowers the pH of the cement pore solution and can cause the reinforcement bars to corrode.

Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. Strength of concrete changes (increases) up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation.

During this period concrete needs to be kept under controlled temperature and humid atmosphere. In practice, this is achieved by spraying or ponding the concrete surface with water, thereby protecting the concrete mass from ill effects of ambient conditions. The pictures to the right show two of many ways to achieve this, ponding – submerging setting concrete in water, and wrapping in plastic to contain the water in the mix.

Properly curing concrete leads to increased strength and lower permeability, and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing, or overheating due to the exothermic setting of cement (the Hoover Dam used pipes carrying coolant during setting to avoid damaging overheating). Improper curing can cause scaling, reduced strength, poor abrasion resistance, and cracking.

Properties

Main article: Properties of concrete
Concrete has relatively high compressive strength, but much lower tensile strength, and for this reason is usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete has a very low coefficient of thermal expansion, and shrinks as it matures. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete that is subjected to long-duration forces is prone to creep.

Tests can be made to ensure the properties of concrete correspond to specifications for the application.
Environmental concerns

Carbon dioxide emissions and climate change

The cement industry is one of two primary producers of carbon dioxide (CO2), creating up to 5% of worldwide man-made emissions of this gas, of which 50% is from the chemical process, and 40% from burning fuel. The embodied carbon dioxide (ECO2) of one tonne of concrete is around 100 kg/tonne. The CO2 emission from the concrete production is directly proportional to the cement content used in the concrete mix. Indeed, 900 kg of CO2 are emitted for the fabrication of every ton of cement. Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide, and also through the use of energy, particularly from the combustion of fossil fuels. However, some companies have recognized the problem and are envisaging solutions to counter their CO2 emissions. The principle of carbon capture and storage consists of directly capturing the CO2 at the outlet of the cement kiln in order to transport it and to store the captured CO2 in an adequate and deep geological formation.

Surface runoff

Surface runoff, when water runs off impervious surfaces, such as non-porous concrete, can cause heavy soil erosion. Urban runoff tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from sidewalks, roadways and parking lots. The impervious cover in a typical urban area limits groundwater percolation and causes five times the amount of runoff generated by a typical woodland of the same size. A 2008 report by the United States National Research Council identified urban runoff as a leading source of water quality problems.

Urban heat

Both concrete and asphalt are the primary contributors to what is known as the urban heat island effect.
Using light-colored concrete has proven effective in reflecting up to 50% more light than asphalt and reducing ambient temperature. A low albedo value, characteristic of black asphalt, absorbs a large percentage of solar heat and contributes to the warming of cities. By paving with light colored concrete, in addition to replacing asphalt with light-colored concrete, communities can lower their average temperature.

In many U.S. cities, pavement covers about 30-40% of the surface area. This directly affects the temperature of the city, and contributes to the urban heat island effect. Paving with light-colored concrete would lower temperatures of paved areas and improve nighttime visibility. The potential of energy saving within an area is also high. With lower temperatures, the demand for air conditioning decreases, saving energy.

Atlanta has tried to mitigate the heat-island effect. City officials noted that when using heat-reflecting concrete, their average city temperature decreased by 6 °F The Design Trust for Public Space found that by slightly raising the albedo value in in New York City, beneficial effects such as energy savings could be achieved.[citation needed] It was concluded that this could be accomplished by the replacement of black asphalt with light-colored concrete.

However, in winter this may be a disadvantage as ice will form more easily and remain longer on the light colored surfaces as they will be colder due to less energy absorbed from the reduced amount of sunlight in winter.

Concrete dust

Building demolition and natural disasters such as earthquakes often release a large amount of concrete dust into the local atmosphere. Concrete dust was concluded to be the major source of dangerous air pollution following the Great Hanshin earthquake

Health concerns

The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns. Natural radioactive elements (K, U and Th) can be present in various concentration in concrete dwellings, depending on the source of the raw materials used. Toxic substances may also be added to the mixture for making concrete by unscrupulous makers. Dust from rubble or broken concrete upon demolition or crumbling may cause serious health concerns depending also on what had been incorporated in the concrete.

Concrete handling/safety precautions

Handling of wet concrete must always be done with proper protective equipment. Contact with wet concrete can cause skin chemical burns due to the caustic nature of the mixture of cement and water. Indeed, the pH of fresh cement water is highly alkaline due to the presence of free potassium and sodium hydroxides in solution (pH ~ 13.5). Eyes, hands and feet must be correctly protected to avoid any direct contact with wet concrete and washed without delay if necessary.
Damage modes

Main article: Concrete degradation

Concrete spalling caused by the corrosion of reinforcement bars after that carbonation of cement decreased the pH below the passivation threshold for steel.Concrete can be damaged by many processes, such as the expansion of corrosion products of the steel reinforcement bars, freezing of trapped water, fire or radiant heat, aggregate expansion, sea water effects, bacterial corrosion, leaching, erosion by fast-flowing water, physical damage and chemical damage (from carbonation, chlorides, sulfates and distillate water)

Concrete repair

Concrete pavement preservation (CPP) and concrete pavement restoration (CPR) are techniques used to manage the rate of pavement deterioration on concrete streets, highways and airports. Without changing concrete grade, this non-overlay method is used to repair isolated areas of distress. CPP and CPR techniques include slab stabilization, full- and partial-depth repair, dowel bar retrofit, cross stitching longitudinal cracks or joints, diamond grinding and joint and crack resealing. CPR methods, developed over the last 40 years, are utilized in lieu of short-lived asphalt overlays and bituminous patches to repair roads. These methods are often less expensive[citation needed]than an asphalt overlay but last three times longer and provide a greener solution.[38]

CPR techniques can be used to address specific problems or bring a pavement back to its original quality. When repairing a road, design data, construction data, traffic data, environmental data, previous CPR activities and pavement condition, must all be taken into account. Pavements repaired using CPR methods usually last 15 years. The methods are described below.

Slab stabilization restores support to concrete slabs by filling small voids that develop underneath the concrete slab at joints, cracks or the pavement edge.
Full-depth repairs fixes cracked slabs and joint deterioration by removing at least a portion of the existing slab and replacing it with new concrete.
Partial-depth repairs corrects surface distress and joint-crack deterioration in the upper third of the concrete slab. Placing a partial-depth repair involves removing the deteriorated concrete, cleaning the patch area and placing new concrete.
Dowel bar retrofit consists of cutting slots in the pavement across the joint or crack, cleaning the slots, placing the dowel bars and backfilling the slots with new concrete. Dowel bar retrofits link slabs together at transverse cracks and joints so that the load is evenly distributed across the crack or joint.
Cross-stitching longitudinal cracks or joints repairs low-severity longitudinal cracks. This method adds reinforcing steel to hold the crack together tightly.
Diamond grinding, by removing faulting, slab warping, studded tire wear and unevenness resulting from patches, diamond grinding creates a smooth, uniform pavement profile. Diamond grinding reduces road noise by providing a longitudinal texture, which is quieter than transverse textures. The longitudinal texture also enhances surface texture and skid resistance in polished pavements.
Joint and crack sealing minimizes the infiltration of surface water and incompressible material into the joint system. Minimizing water entering the joint reduces sub-grade softening, slows pumping and erosion of the sub-base fines, and may limit dowel-bar corrosion caused by de-icing chemicals
Concrete recycling

Concrete recycling is an increasingly common method of disposing of concrete structures. Concrete debris was once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws, and economic benefits.

Concrete, which must be free of trash, wood, paper and other such materials, is collected from demolition sites and put through a crushing machine, often along with asphalt, bricks, and rocks.

Reinforced concrete contains rebar and other metallic reinforcements, which are removed with magnets and recycled elsewhere. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. Smaller pieces of concrete are used as gravel for new construction projects. Aggregate base gravel is laid down as the lowest layer in a road, with fresh concrete or asphalt placed over it. Crushed recycled concrete can sometimes be used as the dry aggregate for brand new concrete if it is free of contaminants, though the use of recycled concrete limits strength and is not allowed in many jurisdictions. On March 3, 1983, a government funded research team (the VIRL research.codep) approximated that almost 17% of worldwide landfill was by-products of concrete based waste.

Recycling concrete provides environmental benefits, conserving landfill space and use as aggregate reduces the need for gravel mining.

World records

The world record for the largest concrete pour in a single project is the Three Gorges Dam in Hubei Province, China by the Three Gorges Corporation. The amount of concrete used in the construction of the dam is estimated at 16 million cubic meters over 17 years. The previous record was 3.2 million cubic meters held by Itaipu hydropower station in Brazil.

Concrete pumping

The world record was set at on 7 August 2009 during the construction of the Parbati Hydroelectric Project, near the village of Suind, Himachal Pradesh, India, when the concrete mix was pumped through a vertical height of 715 m (2,346 ft).
Continuous pours

The world record for largest continuously poured concrete raft was achieved in August 2007 in Abu Dhabi by contracting firm Al Habtoor-CCC Joint Venture. 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.[44] The previous record (close to 10,500 cubic meters) was held by Dubai Contracting Company and achieved March 23, 2007.

The world record for largest continuously poured concrete floor was completed November 8, 1997, in Louisville, Kentucky by design-build firm EXXCEL Project Management. The monolithic placement consisted of 225,000 square feet (20,900 m2) of concrete placed within a 30 hour period, finished to a flatness tolerance of FF 54.60 and a levelness tolerance of FL 43.83. This surpassed the previous record by 50% in total volume and 7.5% in total area.

The record for the largest continuously placed underwater concrete pour was completed October 18, 2010, in New Orleans, Louisiana by contractor C. J. Mahan Construction Company, LLC of Grove City, Ohio. The placement consisted of 10,224 cubic yards of concrete placed in a 58 hour period using two concrete pumps and two dedicated concrete batch plants. Upon curing, this placement will allow the 50,180-square-foot (4,662 m2) cofferdam to be dewatered approximately 26 feet (7.9 m) below sea level to allow the construction of the IHNC GIWW Sill & Monolith Project to be completed in the dry

Use of concrete in infrastructure

Mass concrete structures

These include gravity dams such as the Hoover Dam, the Itaipu Dam, and the Three Gorges Dam and large breakwaters. Concrete that is poured all at once in one block (so that there are no weak points where the concrete is "welded" together) is used for tornado shelters.

Reinforced concrete structures

Reinforced concrete contains steel reinforcing that is designed and placed in the structure at specific positions to cater for all the stress conditions that the structure is required to accommodate.
Prestressed concrete structures

Prestressed concrete is a form of reinforced concrete that builds in compressive stresses during construction to oppose those found when in use. This can greatly reduce the weight of beams or slabs, by better distributing the stresses in the structure to make optimal use of the reinforcement. For example a horizontal beam will tend to sag down. If the reinforcement along the bottom of the beam is prestressed, it can counteract this.

In pre-tensioned concrete, the prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.

Concrete textures

When one thinks of concrete, the image of a dull, gray concrete wall often comes to mind. With the use of form liner, concrete can be cast and molded into different textures and used for decorative concrete applications. Sound/retaining walls, bridges, office buildings and more serve as the optimal canvases for concrete art. For example, the Pima Freeway/Loop 101 retaining and sound walls in Scottsdale, Arizona, feature desert flora and fauna, a 67-foot (20 m) lizard and 40-foot (12 m) cacti along the 8-mile (13 km) stretch. The project, titled "The Path Most Traveled," is one example of how concrete can be shaped using elastomeric form liner.

Building with concrete

Concrete is one of the most durable building materials. It provides superior fire resistance compared with wooden construction, can gain strength over time. Structures made of concrete can have a long service life. Concrete is the most widely used construction material in the world with annual consumption estimated at between 21 and 31 billion tonnes
Environmentally sustainable

With its 100-year service life, concrete conserves resources by reducing the need for reconstruction. Its ingredients are cement and readily available natural materials: water, aggregate (sand and gravel or crushed stone). Concrete does not require any CO2 absorbing trees to be cut down. The land required to extract the materials needed to make concrete is only a fraction of that used to harvest forests for lumber.

The Baths of Caracalla, Rome, Italy, in 2003.Concrete absorbs CO2 throughout its lifetime through carbonation, helping reduce its carbon footprint. A recent study [48] indicates that in countries with the most favorable recycling practices, it is realistic to assume that approximately 86% of the concrete is carbonated after 100 years. During this time, the concrete will absorb approximately 57% of the CO2 emitted during the original calcination. About 50% of the CO2 is absorbed within a short time after concrete is crushed during recycling operations.

Concrete consists of between 7% and 15% cement, its only energy-intensive ingredient. A study [49] comparing the CO2 emissions of several different building materials for construction of residential and commercial buildings found that concrete accounted for 147 kg of CO2 per 1000 kg used, metals accounted for 3000 kg of CO2 and wood accounted for 127 kg of CO2. The quantity of CO2 generated during the cement manufacturing process can be reduced by changing the raw materials used in its manufacture.

A new environmentally friendly blend of cement known as Portland-limestone cement (PLC) is gaining ground all over the world. It contains up to 15% limestone, rather than the 5% in regular Portland cement and results in 10% less CO2 emissions from production with no impact on product performance. Concrete made with PLC performs similarly to concrete made with regular cement and thus PLC-based concrete can be widely used as a replacement. In Europe, PLC-based concrete has replaced about 40% of general use concrete. In Canada, PLC will be included in the National Building Code in 2010. The approval of PLC is still under consideration in the United States
Energy efficiency

Energy requirements for transportation of concrete are low because it is produced locally from local resources, typically manufactured within 100 kilometers of the job site. Once in place, concrete offers significant energy efficiency over the lifetime of a building.[50] Concrete walls leak air far less than those made of wood-frames. Air leakage accounts for a large percentage of energy loss from a home. The thermal mass properties of concrete increase the efficiency of both residential and commercial buildings. By storing and releasing the energy needed for heating or cooling, concrete’s thermal mass delivers year-round benefits by reducing temperature swings inside and minimizing heating and cooling costs. While insulation reduces energy loss through the building envelope, thermal mass uses walls to store and release energy. Modern concrete wall systems use both insulation and thermal mass to create an energy-efficient building. Insulating Concrete Forms (ICFs) are hollow blocks or panels made of either insulating foam or rastra that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.

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