DEAR BRUDERS DEAR SISTERS DEAR KIDS EASTER WORLD GOSPEL PIPLE NATIONE, Oxford Кembridg United Kingdom England - Новости

The mission of Jesus Christ Gospel Jesus Politic Party Direction in the UN

Безусловно, Иисус Христос является величайшей Личностью в истории человечества. Несмотря на то, что Он прожил совсем недолгую жизнь, всего 33 года. Причем, общественной деятельностью Он занимался...

Адрес: Израиль, 7958500, Oxford Кembridg United Kingdom England, , Jerusalem The Temple Mount is the Armenian quarter with Oxford Venue Contact Christian Church United Kingdom England Washington Mosque The Al-Aqsa Jerusalem Joanna Malton Christian Сhurch United Kingdom Oxford Universitet

Телефон: +7(953)270-90-00

E-mail адрес: serzh.yakunoff@yandex.ru

Сообщение

zoomНажмите на картинку для увеличения

DEAR BRUDERS DEAR SISTERS DEAR KIDS EASTER WORLD GOSPEL PIPLE NATIONE

24:45 CANDIDATKA GOSPEL SELF MENEGER

24:46

24:47железнодорожный

прил

railway

railroad

train

rail

поездной,

рельсовыйforeign trade

external trade

international trade

foreign commerce

overseas trade

внешнеэкономическая деятельность,

международная торговля

foreign trading внутренняя торговля

сущ

domestic trade

internal trade

domestic commerce

home trade рынок

сущ мужской род

market

marketplace

базар,

базарная площадь

mart

emporiumэтнический

прил

ethnic

ethnical

национальный

ethic

нравственны

торговый цен

24:48 CANDIDAT GOSPEL SELF MENEGER CONSTRUCTIONE BUSNES IMPORT EXPORT MARCET

24:49

24:50

24:51

24:52

24:53

Английский (NKJV)

Языки

Now on the first day of the week, very early in the morning, they, and certain other women with them, came to the tomb bringing the spices which they had prepared.

But they found the stone rolled away from the tomb.

Then they went in and did not find the body of the Lord Jesus.

And it happened, as they were greatly perplexed about this, that behold, two men stood by them in shining garments.

Then, as they were afraid and bowed their faces to the earth, they said to them, «Why do you seek the living among the dead?

He is not here, but is risen! Remember how He spoke to you when He was still in Galilee,

saying, «The Son of Man must be delivered into the hands of sinful men, and be crucified, and the third day rise again.»́

And they remembered His words.

Then they returned from the tomb and told all these things to the eleven and to all the rest.

It was Mary Magdalene, Joanna, Mary the mother of James, and the other women with them, who told these things to the apostles.

And their words seemed to them like idle tales, and they did not believe them.

But Peter arose and ran to the tomb; and stooping down, he saw the linen cloths lying by themselves; and he departed, marveling to himself at what had happened.

Now behold, two of them were traveling that same day to a village called Emmaus, which was seven miles from Jerusalem.

And they talked together of all these things which had happened.

So it was, while they conversed and reasoned, that Jesus Himself drew near and went with them.

But their eyes were restrained, so that they did not know Him.

And He said to them, «What kind of conversation is this that you have with one another as you walk and are sad?»

Then the one whose name was Cleopas answered and said to Him, «Are You the only stranger in Jerusalem, and have You not known the things which happened there in these days?»

And He said to them, «What things?» So they said to Him, «The things concerning Jesus of Nazareth, who was a Prophet mighty in deed and word before God and all the people,

and how the chief priests and our rulers delivered Him to be condemned to death, and crucified Him.

But we were hoping that it was He who was going to redeem Israel. Indeed, besides all this, today is the third day since these things happened.

Yes, and certain women of our company, who arrived at the tomb early, astonished us.

When they did not find His body, they came saying that they had also seen a vision of angels who said He was alive.

And certain of those who were with us went to the tomb and found it just as the women had said; but Him they did not see.»

Then He said to them, «O foolish ones, and slow of heart to believe in all that the prophets have spoken!

Ought not the Christ to have suffered these things and to enter into His glory?»

And beginning at Moses and all the Prophets, He expounded to them in all the Scriptures the things concerning Himself.

Then they drew near to the village where they were going, and He indicated that He would have gone farther.

But they constrained Him, saying, «Abide with us, for it is toward evening, and the day is far spent.» And He went in to stay with them.

Now it came to pass, as He sat at the table with them, that He took bread, blessed and broke it, and gave it to them.

Then their eyes were opened and they knew Him; and He vanished from their sight.

And they said to one another, «Did not our heart burn within us while He talked with us on the road, and while He opened the Scriptures to us?»

So they rose up that very hour and returned to Jerusalem, and found the eleven and those who were with them gathered together,

saying, «The Lord is risen indeed, and has appeared to Simon!»

And they told about the things that had happened on the road, and how He was known to them in the breaking of bread.

Now as they said these things, Jesus Himself stood in the midst of them, and said to them, «Peace to you.»

But they were terrified and frightened, and supposed they had seen a spirit.

And He said to them, «Why are you troubled? And why do doubts arise in your hearts?

Behold My hands and My feet, that it is I Myself. Handle Me and see, for a spirit does not have flesh and bones as you see I have.»

When He had said this, He showed them His hands and His feet.

But while they still did not believe for joy, and marveled, He said to them, «Have you any food here?»

So they gave Him a piece of a broiled fish and some honeycomb.

And He took it and ate in their presence.

Then He said to them, «These are the words which I spoke to you while I was still with you, that all things must be fulfilled which were written in the Law of Moses and the Prophets and the Psalms concerning Me.»

And He opened their understanding, that they might comprehend the Scriptures.

Then He said to them, «Thus it is written, and thus it was necessary for the Christ to suffer and to rise from the dead the third day,

and that repentance and remission of sins should be preached in His name to all nations, beginning at Jerusalem.Евангелие от Луки

…

24:6. Его нет здесь: Он воскрес; вспомните, как Он

говорил вам, когда был еще в Галилее,

24:7. сказывая, что Сыну Человеческому надлежит быть

предану в руки человеков грешников, и быть

Читать полностью

Автор: Библия, Новый ЗаветIn the UK Easter is one of the major Christian festivals of the year. It is traditionally about Jesus Christ’s resurrection from death, according to Christian belief. However, Easter in Britain has its beginnings long before the arrival of Christianity. Many theologians believe Easter itself is named after the Anglo-Saxon goddess of the dawn and spring — Eostre.Евангелие от Луки

включенный

прич

included

внесенный

incorporated

integrated

объединенный

involved…

2:28. он взял Его на руки, благословил Бога и сказал:

2:29. Ныне отпускаешь раба Твоего, Владыко, по слову

Твоему, с миром,

2:30. ибо видели очи мои спасение Твое,

Читать полностьюincluded

внесенный

incorporated

integrated

объединенныйПасха в Соединенном королевстве - один из главных религиозных праздников в году. По христианской традиции в этот день отмечается воскресение Иисуса Христа. Между тем, в Великобритании этот день начали отмечать задолго до прихода Христианства. Многие теологи полагают, что английское название Пасхи “Easter” происходит от имени англо-саксонской богини рассвета и весны Eostre.

Пасху в Великобритании принято отмечать в первое полнолунное воскресенье после весеннего равноденствия. Это означает, что праздник может наступить в любое воскресенье с 22 марта по 25 апреля. Пасха знаменует собой не только конец зимы, но и окончание традиционного для христианского календаря Великого поста. А значит это время для веселья и праздника!

DEAR FRIENDLY DEAR KIDS Листья безропотно дарят свою красоту людям !успешный

прил

successful

prosperous

удачный,

благополучный

success

рост

сущ мужской род

height

stature

высота,

статус

growth

development

gain

upgrowth

прирост,

развитие

increase

growing

увеличение,

растущийчистая прибыль

сущ

net profit

net income

clear profit

чистый доход

net gain

net earnings

чистый доход

earningsвыплата зарплаты

сущ

salary payment

wage payment

payment of wagesвыплата налогов

сущ

payment of taxes

уплата налоговкачество

сущ средний род

quality

property

свойство

capacity

потенциал

characteristic

trait

характеристика,

черт

выплата заработной платы

прибыль

succeed

РАСПРОСТРАНИТЕ EASTER DEAR FRIENDS WORLD GLOBAL PIPLE GOSPEL NATIONE JERUSALEM THREE CHRA NEWS TV JURNALISTICS MASS MEDIA TELEVISION PABLIC NEWS TV телевизор

сущ мужской род

television Here are the Most Popular TV Channels in the World 2023:

FOX TV Channel

Disney Channel

Star World

BBC Food

Channel V

CW Channel

HBO

ESPN

CNN

BBC News

television set

telly

телевидение,

телик

set

набор

box

благословение сущ ср START BUSSNESS MENEDGMENT INDUSTRY FRIENDLY NATURAL CEMENT+REGISTR CRISTAL PROECT MENEDGMENT+IT DEVELOPMENT MASS MEDIA CONFERENSE+media tv internet+SELF MENEDGMENT+каталог сущ м

RED DIPLOMA MGIMO St. Petersburg State University

cataloguebrit, catalogamerвключенный причOXFORD KEMBRIDG HARWARD MOSKOW LOMONOSOW UNIVERSITY YALE LAW ECONOMIC

WESNA LETO REGISTRATIONE BUSSNESS COMPANY PIC DEVELOPMENT BUSNESS CONSTRUCTIONE COMPANY CANDIDTE DEVELOPMENT INVESTMENTS 252 CONTRY MEGAPOLISE REGIONE 2000% при предл индивидуальный прил

individual, personal, private, separate

(отдельный, личный, частный)

unique, specific, particular, special, peculiar

(уникальный, конкретный, специальный, своеобразный)

custom

(пользовательский)

by, near, of

(возле, близко к, у)

with, on, about

(с, у)

in front of, before

(в присутствии, перед)

(перечень)Catholic, roman

(вселенский)

сообщить об ошибке

Примеры

всеиндивидуальный предприниматель сущ

individual entrepreneur, individual businessman, private entrepreneur, sole proprietor, sole trader, private businessman

(частный предприниматель, единоличный торговец)

independent entrepreneur

(независимый предприниматель)

sole proprietorship

(индивидуальное предприятие)

Catholic geographical map of the world политолог

сущ мужской род

political scientist

politologist

political expert

политический эксперт

political analyst

policy analyst

политический аналитик

pundit

эксперт цвет

сущ мужской род

color

colour

colors

colored

colouring

dye

краска,

тон,

окраска

flower

blossom

bloom

цветок,

цветение

cream

крем Мы оба знаем, что существуют женщины, которых по природе своей привлекает власть.

We both know that there are women out there that are naturally attracted to power.

По мере этого изменяется природа самой власти.

As упаковка

сущ женский род

packaging

packing

container

фасовка,

контейнер

package

pack

пакет

wrapping

wrap

wrapper

обе

Пятница перед Пасхальным воскресеньем (которую также называют Страстной пятницей) и понедельник после него в Великобритании официально считаются выходными днями. Кроме того, на Пасху обычно выпадают двухнедельные школьные каникулы.

involvedNow you release your servantHistory of cement

The origin of hydraulic cements goes back to ancient Greece and Rome. The materials used were lime and a volcanic ash that slowly reacted with it in the presence of water to form a hard mass. This formed the cementing material of the Roman mortars and concretes of more than 2,000 years ago and of subsequent construction work in western Europe. Volcanic ash mined near what is now the city of Pozzuoli, Italy, was particularly rich in essential aluminosilicate minerals, giving rise to the classic pozzolana cement of the Roman era. To this day the term pozzolana, or pozzolan, refers either to the cement itself or to any finely divided aluminosilicate that reacts with lime in water to form cement. (The term cement, meanwhile, derives from the Latin word caementum, which meant stone chippings such as were used in Roman mortar—not the binding material itself.)

Eddystone Lighthouse: Sir James N. Douglass's version

Portland cement is a successor to a hydraulic lime that was first developed by John Smeaton in 1756 when he was called in to erect the Eddystone Lighthouse off the coast of Plymouth, Devon, England. The next development, taking place about 1800 in England and France, was a material obtained by burning nodules of clayey limestone. Soon afterward in the United States, a similar material was obtained by burning a naturally occurring substance called “cement rock.” These materials belong to a class known as natural cement, allied to portland cement but more lightly burned and not of controlled composition.

The invention of portland cement usually is attributed to Joseph Aspdin of Leeds, Yorkshire, England, who in 1824 took out a patent for a material that was produced from a synthetic mixture of limestone and clay. He called the product “portland cement” because of a fancied resemblance of the material, when set, to portland stone, a limestone used for building in England. Aspdin’s product may well have been too lightly burned to be a true portland cement, and the real prototype was perhaps that produced by Isaac Charles Johnson in southeastern England about 1850. The manufacture of portland cement rapidly spread to other European countries and North America. During the 20th century, cement manufacture spread worldwide. By 2019 China and India had become the world leaders in cement production, followed by Vietnam, the United States, and Egypt.

Raw materials

Composition

Portland cement consists essentially of compounds of lime (calcium oxide, CaO) mixed with silica (silicon dioxide, SiO2) and alumina (aluminum oxide, Al2O3). The lime is obtained from a calcareous (lime-containing) raw material, and the other oxides are derived from an argillaceous (clayey) material. Additional raw materials such as silica sand, iron oxide (Fe2O3), and bauxite—containing hydrated aluminum, Al(OH)3—may be used in smaller quantities to get the desired composition.

The commonest calcareous raw materials are limestone and chalk, but others, such as coral or shell deposits, also are used. Clays, shales, slates, and estuarine muds are the common argillaceous raw materials. Marl, a compact calcareous clay, and cement rock contain both the calcareous and argillaceous components in proportions that sometimes approximate cement compositions. Another raw material is blast-furnace slag, which consists mainly of lime, silica, and alumina and is mixed with a calcareous material of high lime content. Kaolin, a white clay that contains little iron oxide, is used as the argillaceous component for white portland cement. Industrial wastes, such as fly ash and calcium carbonate from chemical manufacture, are other possible raw materials, but their use is small compared with that of the natural materials.

The magnesia (magnesium oxide, MgO) content of raw materials must be low because the permissible limit in portland cement is 4 to 5 percent. Other impurities in raw materials that must be strictly limited are fluorine compounds, phosphates, metal oxides and sulfides, and excessive alkalies.

Another essential raw material is gypsum, some 5 percent of which is added to the burned cement clinker during grinding to control the setting time of the cement. Portland cement also can be made in a combined process with sulfuric acid using calcium sulfate or anhydrite in place of calcium carbonate. The sulfur dioxide produced in the flue gases on burning is converted to sulfuric acid by normal processes.

Extraction and processing

Raw materials employed in the manufacture of cement are extracted by quarrying in the case of hard rocks such as limestones, slates, and some shales, with the aid of blasting when necessary. Some deposits are mined by underground methods. Softer rocks such as chalk and clay can be dug directly by excavators.

The excavated materials are transported to the crushing plant by trucks, railway freight cars, conveyor belts, or ropeways. They also can be transported in a wet state or slurry by pipeline. In regions where limestones of sufficiently high lime content are not available, some process of beneficiation can be used. Froth flotation will remove excess silica or alumina and so upgrade the limestone, but it is a costly process and is used only when unavoidable.

Manufacture of cement

Hachinohe: cement factory

There are four stages in the manufacture of portland cement: (1) crushing and grinding the raw materials, (2) blending the materials in the correct proportions, (3) burning the prepared mix in a kiln, and (4) grinding the burned product, known as “clinker,” together with some 5 percent of gypsum (to control the time of set of the cement). The three processes of manufacture are known as the wet, dry, and semidry processes and are so termed when the raw materials are ground wet and fed to the kiln as a slurry, ground dry and fed as a dry powder, or ground dry and then moistened to form nodules that are fed to the kiln.

It is estimated that around 4–8 percent of the world’s carbon dioxide (CO2) emissions come from the manufacture of cement, making it a major contributor to global warming. Some of the solutions to these greenhouse gas emissions are common to other sectors, such as increasing the energy efficiency of cement plants, replacing fossil fuels with renewable energy, and capturing and storing the CO2 that is emitted. In addition, given that a significant portion of the emissions are an intrinsic part of the production of clinker, novel cements and alternate formulations that reduce the need for clinker are an important area of focus.

Crushing and grinding

All except soft materials are first crushed, often in two stages, and then ground, usually in a rotating, cylindrical ball, or tube mills containing a charge of steel grinding balls. This grinding is done wet or dry, depending on the process in use, but for dry grinding the raw materials first may need to be dried in cylindrical, rotary dryers.

Soft materials are broken down by vigorous stirring with water in wash mills, producing a fine slurry, which is passed through screens to remove oversize particles.

Blending

A first approximation of the chemical composition required for a particular cement is obtained by selective quarrying and control of the raw material fed to the crushing and grinding plant. Finer control is obtained by drawing material from two or more batches containing raw mixes of slightly different composition. In the dry process these mixes are stored in silos; slurry tanks are used in the wet process. Thorough mixing of the dry materials in the silos is ensured by agitation and vigorous circulation induced by compressed air. In the wet process the slurry tanks are stirred by mechanical means or compressed air or both. The slurry, which contains 35 to 45 percent water, is sometimes filtered, reducing the water content to 20 to 30 percent, and the filter cake is then fed to the kiln. This reduces the fuel consumption for burning.

Burning

The earliest kilns in which cement was burned in batches were bottle kilns, followed by chamber kilns and then by continuous shaft kilns. The shaft kiln in a modernized form is still used in some countries, but the dominant means of burning is the rotary kiln. These kilns—up to 200 metres (660 feet) long and six metres in diameter in wet process plants but shorter for the dry process—consist of a steel, cylindrical shell lined with refractory materials. They rotate slowly on an axis that is inclined a few degrees to the horizontal. The raw material feed, introduced at the upper end, moves slowly down the kiln to the lower, or firing, end. The fuel for firing may be pulverized coal, oil, or natural gas injected through a pipe. The temperature at the firing end ranges from about 1,350 to 1,550 °C (2,460 to 2,820 °F), depending on the raw materials being burned. Some form of heat exchanger is commonly incorporated at the back end of the kiln to increase heat transfer to the incoming raw materials and so reduce the heat lost in the waste gases. The burned product emerges from the kiln as small nodules of clinker. These pass into coolers, where the heat is transferred to incoming air and the product cooled. The clinker may be immediately ground to cement or stored in stockpiles for later use.

In the semidry process the raw materials, in the form of nodules containing 10 to 15 percent water, are fed onto a traveling chain grate before passing to the shorter rotary kiln. Hot gases coming from the kiln are sucked through the raw nodules on the grate, preheating the nodules.

Dust emission from cement kilns can be a serious nuisance. In populated areas it is usual and often compulsory to fit cyclone arrestors, bag-filter systems, or electrostatic dust precipitators between the kiln exit and the chimney stack. More than 50 percent of the emissions from cement production are intrinsically linked to the production of clinker and are a by-product of the chemical reaction that drives the current process. There is potential to blend clinker with alternative materials to reduce the need for clinker itself and thus help reduce the climate impacts of the cement-making process.

Modern cement plants are equipped with elaborate instrumentation for control of the burning process. Raw materials in some plants are sampled automatically, and a computer calculates and controls the raw mix composition. The largest rotary kilns have outputs exceeding 5,000 tons per day.

Grinding

The clinker and the required amount of gypsum are ground to a fine powder in horizontal mills similar to those used for grinding the raw materials. The material may pass straight through the mill (open-circuit grinding), or coarser material may be separated from the ground product and returned to the mill for further grinding (closed-circuit grinding). Sometimes a small amount of a grinding aid is added to the feed material. For air-entraining cements (discussed in the following section) the addition of an air-entraining agent is similarly made.

Finished cement is pumped pneumatically to storage silos from which it is drawn for packing in paper bags or for dispatch in bulk containers.

The major cements: composition and properties

Portland cement

Chemical composition

Portland cement is made up of four main compounds: tricalcium silicate (3CaO · SiO2), dicalcium silicate (2CaO · SiO2), tricalcium aluminate (3CaO · Al2O3), and a tetra-calcium aluminoferrite (4CaO · Al2O3Fe2O3). In an abbreviated notation differing from the normal atomic symbols, these compounds are designated as C3S, C2S, C3A, and C4AF, where C stands for calcium oxide (lime), S for silica, A for alumina, and F for iron oxide. Small amounts of uncombined lime and magnesia also are present, along with alkalies and minor amounts of other elements.

Hydration

The most important hydraulic constituents are the calcium silicates, C2S and C3S. Upon mixing with water, the calcium silicates react with water molecules to form calcium silicate hydrate (3CaO · 2SiO2 · 3H2O) and calcium hydroxide (Ca[OH]2). These compounds are given the shorthand notations C–S–H (represented by the average formula C3S2H3) and CH, and the hydration reaction can be crudely represented by the following reactions:

2C3S + 6H = C3S2H3 + 3CH

2C2S + 4H = C3S2H3 + CH

During the initial stage of hydration, the parent compounds dissolve, and the dissolution of their chemical bonds generates a significant amount of heat. Then, for reasons that are not fully understood, hydration comes to a stop. This quiescent, or dormant, period is extremely important in the placement of concrete. Without a dormant period there would be no cement trucks; pouring would have to be done immediately upon mixing.

Following the dormant period (which can last several hours), the cement begins to harden, as CH and C–S–H are produced. This is the cementitious material that binds cement and concrete together. As hydration proceeds, water and cement are continuously consumed. Fortunately, the C–S–H and CH products occupy almost the same volume as the original cement and water; volume is approximately conserved, and shrinkage is manageable.

Although the formulas above treat C–S–H as a specific stoichiometry, with the formula C3S2H3, it does not at all form an ordered structure of uniform composition. C–S–H is actually an amorphous gel with a highly variable stoichiometry. The ratio of C to S, for example, can range from 1:1 to 2:1, depending on mix design and curing conditions.

Structural properties

The strength developed by portland cement depends on its composition and the fineness to which it is ground. The C3S is mainly responsible for the strength developed in the first week of hardening and the C2S for the subsequent increase in strength. The alumina and iron compounds that are present only in lesser amounts make little direct contribution to strength.

Set cement and concrete can suffer deterioration from attack by some natural or artificial chemical agents. The alumina compound is the most vulnerable to chemical attack in soils containing sulfate salts or in seawater, while the iron compound and the two calcium silicates are more resistant. Calcium hydroxide released during the hydration of the calcium silicates is also vulnerable to attack. Because cement liberates heat when it hydrates, concrete placed in large masses, as in dams, can cause the temperature inside the mass to rise as much as 40 °C (70 °F) above the outside temperature. Subsequent cooling can be a cause of cracking. The highest heat of hydration is shown by C3A, followed in descending order by C3S, C4AF, and C2S.

Types of portland cement

Five types of portland cement are standardized in the United States by the American Society for Testing and Materials (ASTM): ordinary (Type I), modified (Type II), high-early-strength (Type III), low-heat (Type IV), and sulfate-resistant (Type V). In other countries Type II is omitted, and Type III is called rapid-hardening. Type V is known in some European countries as Ferrari cement.

There also are various other special types of portland cement. Coloured cements are made by grinding 5 to 10 percent of suitable pigments with white or ordinary gray portland cement. Air-entraining cements are made by the addition on grinding of a small amount, about 0.05 percent, of an organic agent that causes the entrainment of very fine air bubbles in a concrete. This increases the resistance of the concrete to freeze-thaw damage in cold climates. The air-entraining agent can alternatively be added as a separate ingredient to the mix when making the concrete.

Low-alkali cements are portland cements with a total content of alkalies not above 0.6 percent. These are used in concrete made with certain types of aggregates that contain a form of silica that reacts with alkalies to cause an expansion that can disrupt a concrete.

Masonry cements are used primarily for mortar. They consist of a mixture of portland cement and ground limestone or other filler together with an air-entraining agent or a water-repellent additive. Waterproof cement is the name given to a portland cement to which a water-repellent agent has been added. Hydrophobic cement is obtained by grinding portland cement clinker with a film-forming substance such as oleic acid in order to reduce the rate of deterioration when the cement is stored under unfavourable conditions.

Oil-well cements are used for cementing work in the drilling of oil wells where they are subject to high temperatures and pressures. They usually consist of portland or pozzolanic cement (see below) with special organic retarders to prevent the cement from setting too quickly.

Slag cements

The granulated slag made by the rapid chilling of suitable molten slags from blast furnaces forms the basis of another group of constructional cements. A mixture of portland cement and granulated slag, containing up to 65 percent slag, is known in the English-speaking countries as portland blast-furnace (slag) cement. The German Eisenportlandzement and Hochofenzement contain up to 40 and 85 percent slag, respectively. Mixtures in other proportions are found in French-speaking countries under such names as ciment portland de fer, ciment métallurgique mixte, ciment de haut fourneau, and ciment de liatier au clinker. Properties of these slag cements are broadly similar to those of portland cement, but they have a lower lime content and a higher silica and alumina content. Those with the higher slag content have an increased resistance to chemical attack.

Another type of slag-containing cement is a supersulfated cement consisting of granulated slag mixed with 10 to 15 percent hard-burned gypsum or anhydrite (natural anhydrous calcium sulfate) and a few percent of portland cement. The strength properties of supersulfated cement are similar to those of portland cement, but it has an increased resistance to many forms of chemical attack. Pozzolanic cements are mixtures of portland cement and a pozzolanic material that may be either natural or artificial. The natural pozzolanas are mainly materials of volcanic origin but include some diatomaceous earths. Artificial materials include fly ash, burned clays, and shales. Pozzolanas are materials that, though not cementitious in themselves, contain silica (and alumina) in a reactive form able to combine with lime in the presence of water to form compounds with cementitious properties. Mixtures of lime and pozzolana still find some application but largely have been superseded by the modern pozzolanic cement. Hydration of the portland cement fraction releases the lime required to combine with the pozzolana.

High-alumina cement

High-alumina cement is a rapid-hardening cement made by fusing at 1,500 to 1,600 °C (2,730 to 2,910 °F) a mixture of bauxite and limestone in a reverberatory or electric furnace or in a rotary kiln. It also can be made by sintering at about 1,250 °C (2,280 °F). Suitable bauxites contain 50 to 60 percent alumina, up to 25 percent iron oxide, not more than 5 percent silica, and 10 to 30 percent water of hydration. The limestone must contain only small amounts of silica and magnesia. The cement contains 35 to 40 percent lime, 40 to 50 percent alumina, up to 15 percent iron oxides, and preferably not more than about 6 percent silica. The principal cementing compound is calcium aluminate (CaO · Al2O3).

High-alumina cement gains a high proportion of its ultimate strength within 24 hours and has a high resistance to chemical attack. It also can be used in refractory linings for furnaces. A white form of the cement, containing minimal proportions of iron oxide and silica, has outstanding refractory properties.

Expanding and nonshrinking cements

Expanding and nonshrinking cements expand slightly on hydration, thus offsetting the small contraction that occurs when fresh concrete dries for the first time. Expanding cements were first produced in France about 1945. The American type is a mixture of portland cement and an expansive agent made by clinkering a mix of chalk, bauxite, and gypsum.

Gypsum plasters

Gypsum plasters are used for plastering, the manufacture of plaster boards and slabs, and in one form of floor-surfacing material. These gypsum cements are mainly produced by heating natural gypsum (calcium sulfate dihydrate, CaSO4 · 2H2O) and dehydrating it to give calcium sulfate hemihydrate (CaSO4 · 1/2H2O) or anhydrous (water-free) calcium sulfate. Gypsum and anhydrite obtained as by-products in chemical manufacture also are used as raw materials.

The hemihydrate, known as plaster of Paris, sets within a few minutes on mixing with water; for building purposes a retarding agent, normally keratin, a protein, is added. The anhydrous calcium sulfate plasters are slower-setting, and often another sulfate salt is added in small amounts as an accelerator. Flooring plaster, originally known by its German title of Estrich Gips, is of the anhydrous type.

Cement testing

Various tests to which cements must conform are laid down in national cement specifications to control the fineness, soundness, setting time, and strength of the cement. These tests are described in turn below.

Fineness

Fineness was long controlled by sieve tests, but more sophisticated methods are now largely used. The most common method, used both for control of the grinding process and for testing the finished cement, measures the surface area per unit weight of the cement by a determination of the rate of passage of air through a bed of the cement. Other methods depend on measuring the particle size distribution by the rate of sedimentation of the cement in kerosene or by elutriation (separation) in an airstream.

Soundness

After it has set, a cement must not undergo any appreciable expansion, which could disrupt a mortar or concrete. This property of soundness is tested by subjecting the set cement to boiling in water or to high-pressure steam. Unsoundness can arise from the presence in the cement of too much free magnesia or hard-burned free lime.

Setting time

The setting and hardening of a cement is a continuous process, but two points are distinguished for test purposes. The initial setting time is the interval between the mixing of the cement with water and the time when the mix has lost plasticity, stiffening to a certain degree. It marks roughly the end of the period when the wet mix can be molded into shape. The final setting time is the point at which the set cement has acquired a sufficient firmness to resist a certain defined pressure. Most specifications require an initial minimum setting time at ordinary temperatures of about 45 minutes and a final setting time no more than 10 to 12 hours.

Strength

The tests that measure the rate at which a cement develops strength are usually made on a mortar commonly composed of one part cement to three parts sand, by weight, mixed with a defined quantity of water. Tensile tests on briquettes, shaped like a figure eight thickened at the centre, were formerly used but have been replaced or supplemented by compressive tests on cubical specimens or transverse tests on prisms. The American Society for Testing and Materials (ASTM) specification requires tensile tests on a 1:3 cement-sand mortar and compressive tests on a 1:2.75 mortar. The British Standards Institution (BSI) gives as alternatives a compressive test on a 1:3 mortar or on a concrete specimen. An international method issued by the International Organization for Standardization (ISO) requires a transverse test on a 1:3 cement-sand mortar prism, followed by a compressive test on the two halves of the prism that remain after it has been broken in bending. Many European countries have adopted this method. In all these tests the size grading of the sand, and usually its source, is specified.

In the testing of most cements, a minimum strength at 3 and 7 days and sometimes 28 days is specified, but for rapid-hardening portland cement a test at 1 day also is sometimes required. For high-alumina cement, tests are required at 1 and 3 days.

Strength requirements laid down in different countries are not directly comparable because of the differences in test methods. In actual construction, to check the strength of a concrete, compressive tests are made on cylinders or cubes made from the concrete being placed.

Frederick M. Lea

The Editors of Encyclopaedia Britannica

gypsum plaster

Home

Technology

Engineering

Civil Engineering

gypsum plaster

building material

Written and fact-checked by

Last Updated: Article History

Julius Caesar

See all media