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Kurdish language

Kurdish (Kurdî, کوردی) is a Northwestern Iranian language or group of languages spoken by Kurds in the region of Kurdistan, namely in Turkey, northern Iraq, northwest and northeast Iran, and Syria.

Kurdish varieties constitute a dialect continuum, with some mutually unintelligible varieties, and collectively have 26 million native speakers. The main varieties of Kurdish are Kurmanji, Sorani, and Southern Kurdish (Xwarîn). The majority of the Kurds speak Kurmanji, and most Kurdish texts are written in Kurmanji and Sorani. Kurmanji is written in the Hawar alphabet, a derivation of the Latin script, and Sorani is written in the Sorani alphabet, a derivation of the Arabic script.

A separate group of non-Kurdish Northwestern Iranian languages, the Zaza–Gorani languages, are also spoken by several million ethnic Kurds.

The classification of Laki as a dialect of Southern Kurdish or as a fourth language under Kurdish is a matter of debate, but the differences between Laki and other Southern Kurdish dialects are minimal.

The literary output in Kurdish was mostly confined to poetry until the early 20th century, when more general literature became developed. Today, the two principal written Kurdish dialects are Kurmanji and Sorani. Sorani is, along with Arabic, one of the two official languages of Iraq and is in political documents simply referred to as "Kurdish".

Classification and origin
The Kurdish varieties belong to the Iranian branch of the Indo-European family. They are generally classified as Northwestern Iranian languages, or by some scholars as intermediate between Northwestern and Southwestern Iranian. Martin van Bruinessen notes that "Kurdish has a strong South-Western Iranian element", whereas "Zaza and Gurani [...] do belong to the north-west Iranian group".

Ludwig Paul concludes that Kurdish seems to be a Northwestern Iranian language in origin, but acknowledges that it shares many traits with Southwestern Iranian languages like Persian, apparently due to longstanding and intense historical contacts.

Windfuhr identified Kurdish dialects as Parthian, albeit with a Median substratum. Windfuhr and Frye assume an eastern origin for Kurdish and consider it as related to eastern and central Iranian dialects.

The present state of knowledge about Kurdish allows, at least roughly, drawing the approximate borders of the areas where the main ethnic core of the speakers of the contemporary Kurdish dialects was formed. The most argued hypothesis on the localisation of the ethnic territory of the Kurds remains D.N. Mackenzie's theory, proposed in the early 1960s (Mackenzie 1961). Developing the ideas of P. Tedesco (1921: 255) and regarding the common phonetic isoglosses shared by Kurdish, Persian, and Baluchi, Mackenzie concluded that the speakers of these three languages may once have been in closer contact.

Varieties
Kurdish varieties are divided into three or four groups, with varying degrees of mutual intelligibility.

 * Kurmanji is the largest dialect group, spoken by an estimated 15 to 20 million Kurds in Turkey, Syria, northern Iraq, and northwest and northeast Iran.
 * Sorani is spoken by an estimated 6 to 7 million Kurds in much of Iraqi Kurdistan and the Iranian Kurdistan Province. Sorani is a written standard of Central Kurdish developed in the 1920s (named after the historical Soran Emirate) and was later adopted as the standard orthography of Kurdish as an official language of Iraq.
 * Southern Kurdish (Pehlewani) is spoken in the Kermanshah, Ilam and Lorestan provinces of Iran and in the Khanaqin District of eastern Iraq. Laki and Kordali (Palai) are often included in Southern Kurdish, but they have some distinct features.

In historical evolution terms, Kurmanji is less modified than Sorani and Pehlewani in both phonetic and morphological structure. The Sorani group has been influenced by among other things its closer cultural proximity to the other languages spoken by Kurds in the region including the Gorani language in parts of Iranian Kurdistan and Iraqi Kurdistan.

Philip G. Kreyenbroek, an expert writing in 1992, says: "Since 1932 most Kurds have used the Roman script to write Kurmanji.... Sorani is normally written in an adapted form of the Arabic script.... Reasons for describing Kurmanji and Sorani as 'dialects' of one language are their common origin and the fact that this usage reflects the sense of ethnic identity and unity among the Kurds. From a linguistic or at least a grammatical point of view, however, Kurmanji and Sorani differ as much from each other as English and German, and it would seem appropriate to refer to them as languages. For example, Sorani has neither gender nor case-endings, whereas Kurmanji has both.... Differences in vocabulary and pronunciation are not as great as between German and English, but they are still considerable."

According to Encyclopaedia of Islam, although Kurdish is not a unified language, its many dialects are interrelated and at the same time distinguishable from other Western Iranian languages. The same source classifies different Kurdish dialects as two main groups, northern and central. The average Kurmanji speaker does not find it easy to communicate with the inhabitants of Sulaymaniyah or Halabja.

Some linguistic scholars assert that the term "Kurdish" has been applied extrinsically in describing the language the Kurds speak, whereas some ethnic Kurds have used the word term to simply describe their ethnicity and refer to their language as Kurmanji, Sorani, Hewrami, Kermanshahi, Kalhori or whatever other dialect or language they speak. Some historians have noted that it is only recently that the Kurds who speak the Sorani dialect have begun referring to their language as Kurdî, in addition to their identity, which is translated to simply mean Kurdish.

The Mokriani variety of Sorani is widely spoken in Mokrian. Piranshahr and Mahabad are two principal cities of the Mokrian area.

Zazaki and Gorani
Zaza–Gorani languages, which are spoken by communities in the wider area who identify as ethnic Kurds, are not linguistically classified as Kurdish. Zaza-Gorani is classified as adjunct to Kurdish, although authorities differ in the details. groups Kurdish with Zaza Gorani within a "Northwestern I" group, while Glottolog based on Encyclopædia Iranica prefers an areal grouping of "Central dialects" (or "Kermanic") within Northwest Iranic, with Kurdish but not Zaza-Gorani grouped with "Kermanic".

Gorani is distinct from Northern and Central Kurdish, yet shares vocabulary with both of them and there are some grammatical similarities with Central Kurdish. The Hawrami dialects of Gorani includes a variety that was an important literary language since the 14th century, but it was replaced by Central Kurdish in the 20th century.

European scholars have maintained that Gorani is separate from Kurdish and that Kurdish is synonymous with the Northern Kurdish group, whereas ethnic Kurds maintain that Kurdish encompasses any of the unique languages or dialects spoken by Kurds that are not spoken by neighbouring ethnic groups.

Gorani is classified as part of the Zaza–Gorani branch of Indo-Iranian languages. The Zaza language, spoken mainly in Turkey, differs both grammatically and in vocabulary and is generally not understandable by Gorani speakers but it is considered related to Gorani. Almost all Zaza-speaking communities, as well as speakers of the closely related Shabaki dialect spoken in parts of Iraqi Kurdistan, identify themselves as ethnic Kurds.

Geoffrey Haig and Ergin Öpengin in their recent study suggest grouping the Kurdish languages into Northern Kurdish, Central Kurdish, Southern Kurdish, Zaza, and Gorani, and avoid the subgrouping Zaza–Gorani.

The notable professor Zare Yusupova has carried out a lot of work and research into the Gorani dialect (as well as many other minority/ancient Kurdish dialects).

History
During his stay in Damascus, historian Ibn Wahshiyya came across two books on agriculture written in Kurdish, one on the culture of the vine and the palm tree, and the other on water and the means of finding it out in unknown ground. He translated both from Kurdish into Arabic in the early 9th century AD.

Among the earliest Kurdish religious texts is the Yazidi Black Book, the sacred book of Yazidi faith. It is considered to have been authored sometime in the 13th century AD by Hassan bin Adi (b. 1195 AD), the great-grandnephew of Sheikh Adi ibn Musafir (d. 1162), the founder of the faith. It contains the Yazidi account of the creation of the world, the origin of man, the story of Adam and Eve and the major prohibitions of the faith. According to The Cambridge History of the Kurds, "the first proper 'text'" written in Kurdish is a short Christian prayer. It was written in Armenian characters, and dates from the fifteenth century. From the 15th to 17th centuries, classical Kurdish poets and writers developed a literary language. The most notable classical Kurdish poets from this period were Ali Hariri, Ahmad Khani, Malaye Jaziri and Faqi Tayran.

The Italian priest Maurizio Garzoni published the first Kurdish grammar titled Grammatica e Vocabolario della Lingua Kurda in Rome in 1787 after eighteen years of missionary work among the Kurds of Amadiya. This work is very important in Kurdish history as it is the first acknowledgment of the widespread use of a distinctive Kurdish language. Garzoni was given the title Father of Kurdology by later scholars. The Kurdish language was banned in a large portion of Kurdistan for some time. After the 1980 Turkish coup d'état until 1991 the use of the Kurdish language was illegal in Turkey.

Current status

Today, Sorani is an official language in Iraq. In Syria, on the other hand, publishing materials in Kurdish is forbidden, though this prohibition is not enforced any more due to the Syrian civil war.

Before August 2002, the Turkish government placed severe restrictions on the use of Kurdish, prohibiting the language in education and broadcast media. In March 2006, Turkey allowed private television channels to begin airing programming in Kurdish. However, the Turkish government said that they must avoid showing children's cartoons, or educational programs that teach Kurdish, and could broadcast only for 45 minutes a day or four hours a week. The state-run Turkish Radio and Television Corporation (TRT) started its 24-hour Kurdish television station on 1 January 2009 with the motto "we live under the same sky". The Turkish prime minister sent a video message in Kurdish to the opening ceremony, which was attended by Minister of Culture and other state officials. The channel uses the X, W, and Q letters during broadcasting. However, most of these restrictions on private Kurdish television channels were relaxed in September 2009. In 2010, Kurdish municipalities in the southeast began printing marriage certificates, water bills, construction and road signs, as well as emergency, social and cultural notices in Kurdish alongside Turkish. Also Imams began to deliver Friday sermons in Kurdish and Esnaf price tags in Kurdish. Many mayors were tried for issuing public documents in Kurdish language. The Kurdish alphabet is not recognized in Turkey, and prior to 2013 the use of Kurdish names containing the letters X, W, and Q, which do not exist in the Turkish alphabet, was not allowed. In 2012, Kurdish-language lessons became an elective subject in public schools. Previously, Kurdish education had only been possible in private institutions.

In Iran, though it is used in some local media and newspapers, it is not used in public schools. In 2005, 80 Iranian Kurds took part in an experiment and gained scholarships to study in Kurdish in Iraqi Kurdistan.

In Kyrgyzstan, 96.21% of the Kurdish population speak Kurdish as their native language. In Kazakhstan, the corresponding percentage is 88.7%.

title: Kurdish language


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UTF-16

UTF-16 (16-bit Unicode Transformation Format) is a character encoding capable of encoding all 1,112,064 valid code points of Unicode (in fact this number of code points is dictated by the design of UTF-16). The encoding is variable-length, as code points are encoded with one or two 16-bit code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding now known as "UCS-2" (for 2-byte Universal Character Set), once it became clear that more than 216 (65,536) code points were needed, including most emoji and important CJK characters such as for personal and place names.

UTF-16 is used by systems such as the Microsoft Windows API, the Java programming language and JavaScript/ECMAScript. It is also sometimes used for plain text and word-processing data files on Microsoft Windows. It is used by more modern implementations of SMS.

UTF-16 is the only encoding (still) allowed on the web that is incompatible with ASCII and never gained popularity on the web, where it is declared by under 0.004% of web pages. UTF-8, by comparison, accounts for over 98% of all web pages. The Web Hypertext Application Technology Working Group (WHATWG) considers UTF-8 "the mandatory encoding for all [text]" and that for security reasons browser applications should not use UTF-16.

History
In the late 1980s, work began on developing a uniform encoding for a "Universal Character Set" (UCS) that would replace earlier language-specific encodings with one coordinated system. The goal was to include all required characters from most of the world's languages, as well as symbols from technical domains such as science, mathematics, and music. The original idea was to replace the typical 256-character encodings, which required 1 byte per character, with an encoding using 65,536 (216) values, which would require 2 bytes (16 bits) per character.

Two groups worked on this in parallel, ISO/IEC JTC 1/SC 2 and the Unicode Consortium, the latter representing mostly manufacturers of computing equipment. The two groups attempted to synchronize their character assignments so that the developing encodings would be mutually compatible. The early 2-byte encoding was originally called "Unicode", but is now called "UCS-2".

When it became increasingly clear that 216 characters would not suffice, IEEE introduced a larger 31-bit space and an encoding (UCS-4) that would require 4 bytes per character. This was resisted by the Unicode Consortium, both because 4 bytes per character wasted a lot of memory and disk space, and because some manufacturers were already heavily invested in 2-byte-per-character technology. The UTF-16 encoding scheme was developed as a compromise and introduced with version 2.0 of the Unicode standard in July 1996. It is fully specified in RFC 2781, published in 2000 by the IETF.

UTF-16 is specified in the latest versions of both the international standard ISO/IEC 10646 and the Unicode Standard. "UCS-2 should now be considered obsolete. It no longer refers to an encoding form in either 10646 or the Unicode Standard." UTF-16 will never be extended to support a larger number of code points or to support the code points that were replaced by surrogates, as this would violate the Unicode Stability Policy with respect to general category or surrogate code points. (Any scheme that remains a self-synchronizing code would require allocating at least one Basic Multilingual Plane (BMP) code point to start a sequence. Changing the purpose of  a code point is disallowed.)

Description
Each Unicode code point is encoded either as one or two 16-bit code units. Code points less than 216 ("in the BMP") are encoded with a single 16-bit code unit equal to the numerical value of the code point, as in the older UCS-2. Code points greater than or equal to 216 ("above the BMP") are encoded using two 16-bit code units. These two 16-bit code units are chosen from the UTF-16 surrogate range which had not previously been assigned to characters. Values in this range are not used as characters, and UTF-16 provides no legal way to code them as individual code points. A UTF-16 stream, therefore, consists of single 16-bit codes outside the surrogate range, and pairs of 16-bit values that are within the surrogate range.

U+0000 to U+D7FF and U+E000 to U+FFFF
Both UTF-16 and UCS-2 encode code points in this range as single 16-bit code units that are numerically equal to the corresponding code points. These code points in the Basic Multilingual Plane (BMP) are the only code points that can be represented in UCS-2. As of Unicode 9.0, some modern non-Latin Asian, Middle-Eastern, and African scripts fall outside this range, as do most emoji characters.

Code points from U+010000 to U+10FFFF
Code points from the other planes are encoded as two 16-bit code units called a surrogate pair. The first code unit is a high surrogate and the second is a low surrogate (These are also known as "leading" and "trailing" surrogates, respectively, analogous to the leading and trailing bytes of UTF-8. ):

 * 0x10000 is subtracted from the code point (U), leaving a 20-bit number (U') in the hex number range 0x00000–0xFFFFF.
 * The high ten bits (in the range 0x000–0x3FF) are added to 0xD800 to give the first 16-bit code unit or high surrogate (W1), which will be in the range 0xD800–0xDBFF.
 * The low ten bits (also in the range 0x000–0x3FF) are added to 0xDC00 to give the second 16-bit code unit or low surrogate (W2), which will be in the range 0xDC00–0xDFFF.

Illustrated visually, the distribution of U' between W1 and W2 looks like: Since the ranges for the high surrogates (0xD800–0xDBFF), low surrogates (0xDC00–0xDFFF), and valid BMP characters (0x0000–0xD7FF, 0xE000–0xFFFF) are disjoint, it is not possible for a surrogate to match a BMP character, or for two adjacent code units to look like a legal surrogate pair. This simplifies searches a great deal. It also means that UTF-16 is self-synchronizing on 16-bit words: whether a code unit starts a character can be determined without examining earlier code units (i.e. the type of code unit can be determined by the ranges of values in which it falls). UTF-8 shares these advantages, but many earlier multi-byte encoding schemes (such as Shift JIS and other Asian multi-byte encodings) did not allow unambiguous searching and could only be synchronized by re-parsing from the start of the string. UTF-16 is not self-synchronizing if one byte is lost or if traversal starts at a random byte.

Because the most commonly used characters are all in the BMP, handling of surrogate pairs is often not thoroughly tested. This leads to persistent bugs and potential security holes, even in popular and well-reviewed application software (e.g. ).

U+D800 to U+DFFF (surrogates)
The official Unicode standard says that no UTF forms, including UTF-16, can encode the surrogate code points. Since these will never be assigned a character, there should be no reason to encode them. However, Windows allows unpaired surrogates in filenames and other places, which generally means they have to be supported by software in spite of their exclusion from the Unicode standard.

UCS-2, UTF-8, and UTF-32 can encode these code points in trivial and obvious ways, and a large amount of software does so, even though the standard states that such arrangements should be treated as encoding errors.

It is possible to unambiguously encode an unpaired surrogate (a high surrogate code point not followed by a low one, or a low one not preceded by a high one) in the format of UTF-16 by using a code unit equal to the code point. The result is not valid UTF-16, but the majority of UTF-16 encoder and decoder implementations do this when translating between encodings.

Examples
To encode U+10437 (𐐷) to UTF-16:

 * Subtract 0x10000 from the code point, leaving 0x0437.
 * For the high surrogate, shift right by 10 (divide by 0x400), then add 0xD800, resulting in 0x0001 + 0xD800 = 0xD801.
 * For the low surrogate, take the low 10 bits (remainder of dividing by 0x400), then add 0xDC00, resulting in 0x0037 + 0xDC00 = 0xDC37.

To decode U+10437 (𐐷) from UTF-16:

 * Take the high surrogate (0xD801) and subtract 0xD800, then multiply by 0x400, resulting in 0x0001 × 0x400 = 0x0400.
 * Take the low surrogate (0xDC37) and subtract 0xDC00, resulting in 0x37.
 * Add these two results together (0x0437), and finally add 0x10000 to get the final code point, 0x10437.

The following table summarizes this conversion, as well as others. The colors indicate how bits from the code point are distributed among the UTF-16 bytes. Additional bits added by the UTF-16 encoding process are shown in black.

Byte-order encoding schemes
UTF-16 and UCS-2 produce a sequence of 16-bit code units. Since most communication and storage protocols are defined for bytes, and each unit thus takes two 8-bit bytes, the order of the bytes may depend on the endianness (byte order) of the computer architecture.

To assist in recognizing the byte order of code units, UTF-16 allows a byte order mark (BOM), a code point with the value U+FEFF, to precede the first actual coded value. (U+FEFF is the invisible zero-width non-breaking space/ZWNBSP character.) If the endian architecture of the decoder matches that of the encoder, the decoder detects the 0xFEFF value, but an opposite-endian decoder interprets the BOM as the value U+FFFE reserved for this purpose. This incorrect result provides a hint to perform byte-swapping for the remaining values.

If the BOM is missing, RFC 2781 recommends that big-endian (BE) encoding be assumed. In practice, due to Windows using little-endian (LE) order by default, many applications assume little-endian encoding. It is also reliable to detect endianness by looking for null bytes, on the assumption that characters less than U+0100 are very common. If more even bytes (starting at 0) are null, then it is big-endian.

The standard also allows the byte order to be stated explicitly by specifying UTF-16BE or UTF-16LE as the encoding type. When the byte order is specified explicitly this way, a BOM is specifically not supposed to be prepended to the text, and a U+FEFF at the beginning should be handled as a ZWNBSP character. Most applications ignore a BOM in all cases despite this rule.

For Internet protocols, IANA has approved "UTF-16", "UTF-16BE", and "UTF-16LE" as the names for these encodings (the names are case insensitive). The aliases UTF_16 or UTF16 may be meaningful in some programming languages or software applications, but they are not standard names in Internet protocols.

Similar designations, UCS-2BE and UCS-2LE, are used to show versions of UCS-2.

Size
A "character" may use any number of Unicode code points. For instance an emoji flag character takes 8 bytes, since it is "constructed from a pair of Unicode scalar values" (and those values are outside the BMP and require 4 bytes each). UTF-16 in no way assists in "counting characters" or in "measuring the width of a string".

UTF-16 is often claimed to be more space-efficient than UTF-8 for East Asian languages, since it uses two bytes for characters that take 3 bytes in UTF-8. Since real text contains many spaces, numbers, punctuation, markup (for e.g. web pages), and control characters, which take only one byte in UTF-8, this is only true for artificially constructed dense blocks of text. A more serious claim can be made for Devanagari and Bengali, which use multi-letter words and all the letters take 3 bytes in UTF-8 and only 2 in UTF-16.

In addition the Chinese Unicode encoding standard GB 18030 always produces files the same size or smaller than UTF-16 for all languages, not just for Chinese (it does this by sacrificing self-synchronization).

Usage
UTF-16 is used for text in the OS API of all currently supported versions of Microsoft Windows (and including at least all since Windows CE/2000/XP/2003/Vista/7 ) including Windows 10. In Windows XP, no code point above U+FFFF is included in any font delivered with Windows for European languages. Older Windows NT systems (prior to Windows 2000) only support UCS-2. Files and network data tend to be a mix of UTF-16, UTF-8, and legacy byte encodings.

While there's been some UTF-8 support for even Windows XP, it was improved (in particular the ability to name a file using UTF-8) in Windows 10 insider build 17035 and the May 2019 update. As of May 2019, Microsoft recommends software use UTF-8, on Windows and Xbox, instead of other 8-bit encodings. It is unclear if they are recommending usage of UTF-8 over UTF-16, though they do state "UTF-16 [..] is a unique burden that Windows places on code that targets multiple platforms."

The IBM i operating system designates CCSID (code page) 13488 for UCS-2 encoding and CCSID 1200 for UTF-16 encoding, though the system treats them both as UTF-16.

UTF-16 is used by the Qualcomm BREW operating systems; the .NET environments; and the Qt cross-platform graphical widget toolkit.

Symbian OS used in Nokia S60 handsets and Sony Ericsson UIQ handsets uses UCS-2. iPhone handsets use UTF-16 for Short Message Service instead of UCS-2 described in the 3GPP TS 23.038 (GSM) and IS-637 (CDMA) standards.

The Joliet file system, used in CD-ROM media, encodes file names using UCS-2BE (up to sixty-four Unicode characters per file name).

Python version 2.0 officially only used UCS-2 internally, but the UTF-8 decoder to "Unicode" produced correct UTF-16. There was also the ability to compile Python so that it used UTF-32 internally, this was sometimes done on Unix. Python 3.3 switched internal storage to use one of ISO-8859-1, UCS-2, or UTF-32 depending on the largest code point in the string. Python 3.12 drops some functionality (for CPython extensions) to make it easier to migrate to UTF-8 for all strings.

Java originally used UCS-2, and added UTF-16 supplementary character support in J2SE 5.0. Recently they have encouraged dumping support for any 8-bit encoding other than UTF-8 but internally UTF-16 is still used.

JavaScript may use UCS-2 or UTF-16. As of ES2015, string methods and regular expression flags have been added to the language that permit handling strings from an encoding-agnostic perspective.

UEFI uses UTF-16 to encode strings by default.

Swift, Apple's preferred application language, used UTF-16 to store strings until version 5 which switched to UTF-8.

Quite a few languages make the encoding part of the string object, and thus store and support a large set of encodings including UTF-16. Most consider UTF-16 and UCS-2 to be different encodings. Examples are the PHP language and MySQL.

A method to determine what encoding a system is using internally is to ask for the "length" of string containing a single non-BMP character. If the length is 2 then UTF-16 is being used. 4 indicates UTF-8. 3 or 6 may indicate CESU-8. 1 may indicate UTF-32, but more likely indicates the language decodes the string to code points before measuring the "length".

In many languages, quoted strings need a new syntax for quoting non-BMP characters, as the C-style  syntax explicitly limits itself to 4 hex digits. The following examples illustrate the syntax for the non-BMP character :
 * The most common (C++, C#, D, and several other languages) is an upper-case 'U' with 8 hex digits such as.
 * Java 7 regular expressions, ICU, and Perl, use.
 * ECMAScript 2015 (JavaScript) uses.
 * In many other cases (such as Java outside of regular expressions), the only way to get non-BMP characters is to enter the surrogate halves individually:.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: UTF-16


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Portland cement

Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th century by Joseph Aspdin, and is usually made from limestone. It is a fine powder, produced by heating limestone and clay minerals in a kiln to form clinker, and then grinding the clinker with the addition of several percent (often around 5%) gypsum. Several types of portland cement are available. The most common, historically called ordinary portland cement (OPC), is grey, but white portland cement is also available. Its name is derived from its resemblance to Portland stone which is quarried on the Isle of Portland in Dorset, England. It was named by Joseph Aspdin who obtained a patent for it in 1824. His son William Aspdin is regarded as the inventor of "modern" portland cement due to his developments in the 1840s.

The low cost and widespread availability of the limestone, shales, and other naturally occurring materials used in portland cement make it a relatively cheap building material. Its most common use is in the production of concrete, a composite material consisting of aggregate (gravel and sand), cement, and water.

History
Portland cement was developed from natural cements made in Britain beginning in the middle of the 18th century. Its name is derived from its similarity to Portland stone, a type of building stone quarried on the Isle of Portland in Dorset, England.

The development of modern portland cement (sometimes called ordinary or normal portland cement) began in 1756, when John Smeaton experimented with combinations of different limestones and additives, including trass and pozzolanas, intended for the construction of a lighthouse, now known as Smeaton's Tower. In the late 18th century, Roman cement was developed and patented in 1796 by James Parker. Roman cement quickly became popular, but was largely replaced by portland cement in the 1850s. In 1811, James Frost produced a cement he called British cement. James Frost is reported to have erected a manufactory for making of an artificial cement in 1826. In 1811 Edgar Dobbs of Southwark patented a cement of the kind invented 7 years later by the French engineer Louis Vicat. Vicat's cement is an artificial hydraulic lime, and is considered the "principal forerunner" of Portland cement.

The name portland cement is recorded in a directory published in 1823 being associated with a William Lockwood and possibly others. In his 1824 cement patent, Joseph Aspdin called his invention "portland cement" because of its resemblance to Portland stone. Aspdin's cement was nothing like modern Portland cement, but a first step in the development of modern portland cement, and has been called a "proto-portland cement".

William Aspdin had left his father's company, to form his own cement manufactury. In the 1840s William Aspdin, apparently accidentally, produced calcium silicates which are a middle step in the development of portland cement. In 1848, William Aspdin further improved his cement. Then, in 1853, he moved to Germany, where he was involved in cement making. William Aspdin made what could be called "meso-portland cement" (a mix of portland cement and hydraulic lime). Isaac Charles Johnson further refined the production of "meso-portland cement" (middle stage of development), and claimed to be the real father of portland cement.

In 1859, John Grant of the Metropolitan Board of Works, set out requirements for cement to be used in the London sewer project. This became a specification for portland cement. The next development in the manufacture of portland cement was the introduction of the rotary kiln, patented by Frederick Ransome in 1885 (U.K.) and 1886 (U.S.); which allowed a stronger, more homogeneous mixture and a continuous manufacturing process. The Hoffmann "endless" kiln which was said to give "perfect control over combustion" was tested in 1860 and shown to produce a superior grade of cement. This cement was made at the Portland Cementfabrik Stern at Stettin, which was the first to use a Hoffmann kiln. The Association of German Cement Manufacturers issued a standard on Portland cement in 1878.

Portland cement had been imported into the United States from Germany and England, and in the 1870s and 1880s, it was being produced by Eagle Portland cement near Kalamazoo, Michigan. In 1875, the first portland cement was produced in the Coplay Cement Company Kilns under the direction of David O. Saylor in Coplay, Pennsylvania. By the early 20th century, American-made portland cement had displaced most of the imported portland cement.

Composition
ASTM C150 defines portland cement as:

"hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers which consist essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulphate as an inter ground addition." The European Standard EN 197-1 uses the following definition:

"Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, (3 CaO·SiO2, and 2 CaO·SiO2), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass."

(The last two requirements were already set out in the German Standard, issued in 1909).

Clinkers make up more than 90% of the cement, along with a limited amount of calcium sulphate (CaSO4, which controls the set time), and up to 5% minor constituents (fillers) as allowed by various standards. Clinkers are nodules (diameters, 0.2 –) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature. The key chemical reaction distinguishing portland cement from other hydraulic limes occurs at these high temperatures (>1300 C) as belite (Ca2SiO4) combines with calcium oxide (CaO) to form alite (Ca3SiO5).

Manufacturing
Portland cement clinker is made by heating, in a cement kiln, a mixture of raw materials to a calcining temperature of above 600 C and then a fusion temperature, which is about 1450 C for modern cements, to sinter the materials into clinker.

The materials in cement clinker are alite, belite, tricalcium aluminate, and tetracalcium alumino ferrite. The aluminium, iron, and magnesium oxides are present as a flux allowing the calcium silicates to form at a lower temperature, and contribute little to the strength. For special cements, such as low heat (LH) and sulphate resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3 CaO·Al2O3) formed.

The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Secondary raw materials (materials in the raw mix other than limestone) depend on the purity of the limestone. Some of the materials used are clay, shale, sand, iron ore, bauxite, fly ash, and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.

Cement grinding

To achieve the desired setting qualities in the finished product, a quantity (2–8%, but typically 5%) of calcium sulphate (usually gypsum or anhydrite) is added to the clinker, and the mixture is finely ground to form the finished cement powder. This is achieved in a cement mill. The grinding process is controlled to obtain a powder with a broad particle size range, in which typically 15% by mass consists of particles below 5 μm diameter, and 5% of particles above 45 μm. The measure of fineness usually used is the 'specific surface area', which is the total particle surface area of a unit mass of cement. The rate of initial reaction (up to 24 hours) of the cement on addition of water is directly proportional to the specific surface area. Typical values are 320–380 m2·kg−1 for general purpose cements, and 450–650 m2·kg−1 for 'rapid hardening' cements. The cement is conveyed by belt or powder pump to a silo for storage. Cement plants normally have sufficient silo space for one to 20 weeks of production, depending upon local demand cycles. The cement is delivered to end users either in bags, or as bulk powder blown from a pressure vehicle into the customer's silo. In industrial countries, 80% or more of cement is delivered in bulk.

Setting and hardening
Cement sets when mixed with water by way of a complex series of chemical reactions still only partly understood. The different constituents slowly crystallise, and the interlocking of their crystals gives cement its strength. Carbon dioxide is slowly absorbed to convert the portlandite (Ca(OH)2) into insoluble calcium carbonate. After the initial setting, immersion in warm water will speed up setting. Gypsum is added as an inhibitor to prevent flash (or quick) setting.

Use

The most common use for portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Concrete can be used in the construction of structural elements like panels, beams, and street furniture, or may be cast-in situ for superstructures like roads and dams. These may be supplied with concrete mixed on site, or may be provided with 'ready-mixed' concrete made at permanent mixing sites. Portland cement is also used in mortars (with sand and water only), for plasters and screeds, and in grouts (cement/water mixes squeezed into gaps to consolidate foundations, road-beds, etc.).

When water is mixed with portland cement, the product sets in a few hours, and hardens over a period of weeks. These processes can vary widely, depending upon the mix used and the conditions of curing of the product, but a typical concrete sets in about 6 hours and develops a compressive strength of 8 MPa in 24 hours. The strength rises to 15 MPa at 3 days, 23 MPa at 1 week, 35 MPa at 4 weeks, and 41 MPa at 3 months. In principle, the strength continues to rise slowly as long as water is available for continued hydration, but concrete is usually allowed to dry out after a few weeks and this causes strength growth to stop.

ASTM C150
Five types of portland cements exist, with variations of the first three according to ASTM C150.

Type I Portland cement is known as common or general-purpose cement. It is generally assumed unless another type is specified. It is commonly used for general construction, especially when making precast, and precast-prestressed concrete that is not to be in contact with soils or ground water. The typical compound compositions of this type are:

55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% ignition loss, and 1.0% free CaO (utilizing cement chemist notation).

A limitation on the composition is that the (C3A) shall not exceed 15%.

Type II provides moderate sulphate resistance, and gives off less heat during hydration. This type of cement costs about the same as type I. Its typical compound composition is:

51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 0.8% ignition loss, and 1.0% free CaO.

A limitation on the composition is that the (C3A) shall not exceed 8%, which reduces its vulnerability to sulphates. This type is for general construction exposed to moderate sulphate attack, and is meant for use when concrete is in contact with soils and ground water, especially in the western United States due to the high sulphur content of the soils. Because of similar price to that of type I, type II is much used as a general purpose cement, and the majority of Portland cement sold in North America meets this specification.

Note: Cement meeting (among others) the specifications for types I and II has become commonly available on the world market.

Type III has relatively high early strength. Its typical compound composition is:

57% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 0.9% ignition loss, and 1.3% free CaO.

This cement is similar to type I, but ground finer. Some manufacturers make a separate clinker with higher C3S and/or C3A content, but this is increasingly rare, and the general purpose clinker is usually used, ground to a specific surface area typically 50–80% higher. The gypsum level may also be increased a small amount. This gives the concrete using this type of cement a three-day compressive strength equal to the seven-day compressive strength of types I and II. Its seven-day compressive strength is almost equal to 28-day compressive strengths of types I and II. The only downside is that the six-month strength of type III is the same or slightly less than that of types I and II. Therefore, the long-term strength is sacrificed. It is usually used for precast concrete manufacture, where high one-day strength allows fast turnover of molds. It may also be used in emergency construction and repairs, and construction of machine bases and gate installations.

Type IV Portland cement is generally known for its low heat of hydration. Its typical compound composition is:

28% (C3S), 49% (C2S), 4% (C3A), 12% (C4AF), 1.8% MgO, 1.9% (SO3), 0.9% ignition loss, and 0.8% free CaO.

The percentages of (C2S) and (C4AF) are relatively high and (C3S) and (C3A) are relatively low. A limitation on this type is that the maximum percentage of (C3A) is seven, and the maximum percentage of (C3S) is thirty-five. This causes the heat given off by the hydration reaction to develop at a slower rate. Consequently, the strength of the concrete develops slowly. After one or two years the strength is higher than the other types after full curing. This cement is used for very large concrete structures, such as dams, which have a low surface to volume ratio. This type of cement is generally not stocked by manufacturers, but some might consider a large special order. This type of cement has not been made for many years, because Portland-pozzolan cements and ground granulated blast furnace slag addition offer a cheaper and more reliable alternative.

Type V is used where sulphate resistance is important. Its typical compound composition is:

38% (C3S), 43% (C2S), 4% (C3A), 9% (C4AF), 1.9% MgO, 1.8% (SO3), 0.9% ignition loss, and 0.8% free CaO.

This cement has a very low (C3A) composition which accounts for its high sulphate resistance. The maximum content of (C3A) allowed is 5% for type V Portland cement. Another limitation is that the (C4AF) + 2(C3A) composition cannot exceed 20%. This type is used in concrete to be exposed to alkali soil and ground water sulphates which react with (C3A) causing disruptive expansion. It is unavailable in many places, although its use is common in the western United States and Canada. As with type IV, type V portland cement has mainly been supplanted by the use of ordinary cement with added ground granulated blast furnace slag or tertiary blended cements containing slag and fly ash.

Types Ia, IIa, and IIIa have the same composition as types I, II, and III. The only difference is that in Ia, IIa, and IIIa, an air-entraining agent is ground into the mix. The air-entrainment must meet the minimum and maximum optional specification found in the ASTM manual. These types are only available in the eastern United States and Canada, only on a limited basis. They are a poor approach to air-entrainment which improves resistance to freezing under low temperatures.

Types II(MH) and II(MH)a have a similar composition as types II and IIa, but with a mild heat.

EN 197 norm
The European norm EN 197-1 defines five classes of common cement that comprise Portland cement as a main constituent. These classes differ from the ASTM classes.

 * Constituents that are permitted in Portland-composite cements are artificial pozzolans (blast furnace slag (in fact a latent hydraulic binder), silica fume, and fly ashes), or natural pozzolans (siliceous or siliceous aluminous materials such as volcanic ash glasses, calcined clays and shale).

CSA A3000-08
The Canadian standards describe six main classes of cement, four of which can also be supplied as a blend containing ground limestone (where a suffix L is present in the class names).

White Portland cement
White Portland cement or white ordinary Portland cement (WOPC) is similar to ordinary, grey, Portland cement in all respects, except for its high degree of whiteness. Obtaining this colour requires high purity raw materials (low Fe2O3 content), and some modification to the method of manufacture, among others a higher kiln temperature required to sinter the clinker in the absence of ferric oxides acting as a flux in normal clinker. As Fe2O3 contributes to decrease the melting point of the clinker (normally 1450 °C), the white cement requires a higher sintering temperature (around 1600 °C). Because of this, it is somewhat more expensive than the grey product. The main requirement is to have a low iron content which should be less than 0.5 wt.% expressed as Fe2O3 for white cement, and less than 0.9 wt.% for off-white cement. It also helps to have the iron oxide as ferrous oxide (FeO) which is obtained via slightly reducing conditions in the kiln, i.e., operating with zero excess oxygen at the kiln exit. This gives the clinker and cement a green tinge. Other metallic oxides such as Cr2O3 (green), MnO (pink), TiO2 (white), etc., in trace content, can also give colour tinges, so for a given project it is best to use cement from a single batch.

Safety issues
Bags of cement routinely have health and safety warnings printed on them, because not only is cement highly alkaline, but the setting process is also exothermic. As a result, wet cement is strongly caustic and can easily cause severe skin burns if not promptly washed off with water. Similarly, dry cement powder in contact with mucous membranes can cause severe eye or respiratory irritation. The reaction of cement dust with moisture in the sinuses and lungs can also cause a chemical burn, as well as headaches, fatigue, and lung cancer.

The production of comparatively low-alkalinity cements (pH<11) is an area of ongoing investigation.

In Scandinavia, France, and the United Kingdom, the level of chromium(VI), which is considered to be toxic and a major skin irritant, may not exceed 2 parts per million (ppm).

In the US, the Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for portland cement exposure in the workplace as 50 mppcf (million particles per cubic foot) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday. At levels of 5000 mg/m3, portland cement is immediately dangerous to life and health.

Environmental effects
Portland cement manufacture can cause environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust; gases; noise and vibration when operating machinery and during blasting in quarries; consumption of large quantities of fuel during manufacture; release of from the raw materials during manufacture, and damage to countryside from quarrying. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used, and equipment to trap and separate exhaust gases are coming into increased use. Environmental protection also includes the re-integration of quarries into the countryside after they have been closed down by returning them to nature or re-cultivating them.

Portland cement is caustic, so it can cause chemical burns. The powder can cause irritation or, with severe exposure, lung cancer, and can contain a number of hazardous components, including crystalline silica and hexavalent chromium. Environmental concerns are the high energy consumption required to mine, manufacture, and transport the cement, and the related air pollution, including the release of the greenhouse gas carbon dioxide, dioxin, NO_{x}, SO2, and particulates. Production of portland cement contributes about 10% of world carbon dioxide emissions. The International Energy Agency has estimated that cement production will increase by between 12 and 23% by 2050 to meet the needs of the world's growing population. There are several ongoing researches targeting a suitable replacement of portland cement by supplementary cementitious materials.

Epidemiologic Notes and Reports Sulfur Dioxide Exposure in Portland Cement Plants, from the Centers for Disease Control, states:

"Workers at portland cement facilities, particularly those burning fuel containing sulfur, should be aware of the acute and chronic effects of exposure to [sulfur dioxide], and peak and full-shift concentrations of should be periodically measured."

An independent research effort of AEA Technology to identify critical issues for the cement industry today concluded the most important environment, health and safety performance issues facing the cement industry are atmospheric releases (including greenhouse gas emissions, dioxin, NO_{x},, and particulates), accidents, and worker exposure to dust.

The associated with portland cement manufacture comes mainly from four sources:

Overall, with nuclear or hydroelectric power, and efficient manufacturing, generation can be reduced to  per kg cement, but can be twice as high. The thrust of innovation for the future is to reduce sources 1 and 2 by modification of the chemistry of cement, by the use of wastes, and by adopting more efficient processes. Although cement manufacturing is clearly a very large emitter, concrete (of which cement makes up about 15%) compares quite favourably with other modern building systems in this regard.. Traditional materials such as lime based mortars as well as timber and earth based construction methods emit significantly less.

Cement plants used for waste disposal or processing
Due to the high temperatures inside cement kilns, combined with the oxidising (oxygen-rich) atmosphere and long residence times, cement kilns are used as a processing option for various types of waste streams; indeed, they efficiently destroy many hazardous organic compounds. The waste streams also often contain combustible materials which allow the substitution of part of the fossil fuel normally used in the process.

Waste materials used in cement kilns as a fuel supplement:

 * Car and truck tires – steel belts are easily tolerated in the kilns
 * Paint sludge from automobile industries
 * Waste solvents and lubricants
 * Meat and bone meal – slaughterhouse waste due to bovine spongiform encephalopathy contamination concerns
 * Waste plastics
 * Sewage sludge
 * Rice hulls
 * Sugarcane waste
 * Used wooden railroad ties (railway sleepers)
 * Spent cell liner from the aluminium smelting industry (also called spent pot liner)

Portland cement manufacture also has the potential to benefit from using industrial byproducts from the waste stream. These include in particular:
 * Slag
 * Fly ash (from power plants)
 * Silica fume (from steel mills)
 * Synthetic gypsum (from desulphurisation)

title: Portland cement


text:
Sarah Hughes

Sarah Elizabeth Hughes (born May 2, 1985) is an American former competitive figure skater. She is the 2002 Olympic Champion and the 2001 World bronze medalist in ladies' singles.

Personal life
Hughes was born in Great Neck, New York, a suburb on Long Island. Her father, John Hughes, was a Canadian of Irish descent and was one of the captains of the undefeated and untied NCAA champion 1969–70 Cornell University ice hockey team. Her mother, Amy Pastarnack, is Jewish and is a breast cancer survivor. This led Hughes to become an advocate for breast cancer awareness. She appeared in a commercial for General Electric promoting breast cancer awareness and research. Hughes stated, "I always said that if I can get one person to get a mammogram, I've accomplished something." Among the other causes Hughes supports is Figure Skating in Harlem, which provides free ice skating lessons and academic tutoring for girls in the Harlem community in New York City. Hughes has supported this program for over ten years.

Hughes attended Great Neck North High School. In 2003, she began her studies at Yale University where she was in Timothy Dwight College. On May 25, 2009, Hughes graduated from Yale and received a bachelor's degree in American studies with a concentration in U.S. politics and communities. She graduated from the University of Pennsylvania Law School on May 15, 2018. As of May 2023, Hughes was pursuing a business degree at Stanford University.

Hughes had previously dated former New York City Mayor Rudy Giuliani's son Andrew Giuliani in 2011, whom she befriended in 2005.

Hughes is the fourth of six children. One of her younger sisters, Emily, is also a figure skater and competed at the 2006 Winter Olympics. She is the cousin of Gregg "Opie" Hughes, from the Opie and Anthony radio show.

Skating career
Hughes began skating at the age of three. Robin Wagner, who also choreographed for her from 1994, became her head coach in January 1998.

Hughes won the junior title at the 1998 U.S. Championships in the 1997–1998 season. The following season, she competed on the ISU Junior Grand Prix and won the silver medal at the 1998–1999 Junior Grand Prix Final. She also took silver at the 1999 World Junior Championships held in November 1998. At the 1999 U.S. Championships, Hughes won the pewter medal in her senior-level debut. As the fourth-place finisher, Hughes would not normally have received one of the three spots for U.S. ladies at the 1999 World Championships, however, Naomi Nari Nam, the silver medalist, was not age-eligible for the event according to ISU rules. Hughes was likewise not age-eligible, but at the time a loophole existed for skaters who had medaled at Junior Worlds. Hughes was sent to senior Worlds and finished 7th in her debut.

In the 1999–2000 season, Hughes made her Grand Prix debut, winning the bronze medal at the 1999 Trophée Lalique. She won the bronze medal at the 2000 U.S. Championships and was credited with a triple-salchow-triple-loop combination. She placed 5th at the 2000 World Championships.

On September 7, 2001, at the age of 16, Hughes was invited to meet United States National Security Advisor Condoleezza Rice.

In the 2000–2001 season, Hughes won three medals on the Grand Prix circuit and won the bronze medal at the 2000–2001 Grand Prix of Figure Skating Final. She won the silver medal at the 2001 U.S. Championships. At the 2001 World Championships, she won the bronze medal.

In the 2001–2002 season, Hughes again competed on the Grand Prix, winning the 2001 Skate Canada International while placing second at her other two events. She won her second consecutive bronze medal at the Grand Prix Final and won the bronze medal at the 2002 U.S. Championships to qualify for the 2002 Winter Olympics.

The week before the opening of the 2002 Olympics, Hughes appeared on the cover of Time magazine.

At the 2002 Olympics, Hughes won the gold medal in what was widely considered one of the biggest upsets in figure skating history. She was the youngest skater in the competition, and was not expected to seriously challenge the favorites, teammate Michelle Kwan and Russia's Irina Slutskaya. Hughes became the first woman in Olympic history to land two triple jump-triple jump combinations in a 4-minute free skate. Kwan, Slutskaya, and Sasha Cohen (the three skaters that finished ahead of Hughes in the short program), all made significant mistakes in the free skate, clearing the way for Hughes to win gold. Her Lutz jump was flawed, but her difficult and successful jump combinations made up for it. Her artistry, above-average edge quality, and ice coverage combined to establish her as a "strong all-around skater" and ensured her gold-medal win.

After her Olympic win, Hughes was honored with a parade in her hometown of Great Neck, attended by U.S. Senators Hillary Clinton and Chuck Schumer, as well as Governor of New York George Pataki. Clinton spoke at the event and declared it Sarah Hughes Day. She received the James E. Sullivan Award as the top amateur athlete in the U.S., becoming the third figure skater to win this award after Dick Button (1949) and Michelle Kwan (2001).

Hughes did not compete at the 2002 World Championships. In the 2002–2003 season, she won the silver medal at the 2003 U.S. Championships, and placed sixth at the 2003 World Championships.

Hughes took the 2004–2005 year off from college and skated professionally with the Smuckers Stars on Ice tour company. She was inducted into the International Jewish Sports Hall of Fame in 2005.

Richard Krawiec wrote a biography about her, Sudden Champion: The Sarah Hughes Story (2002).

Skating technique
Hughes employed a variety of triple-triple jump combinations, including a triple loop-triple loop, triple salchow-triple loop, and a triple toe-triple loop. She would also perform the triple loop jump which she often completed out of and following a back spiral. She was known for her camel spin with a change of edge as well as her spiral position. Unlike most skaters, she executed jumps and spins clockwise.

Politics
On May 15, 2023, Hughes filed paperwork to run for Congress as a Democrat in New York's 4th congressional district. She withdrew from the race on September 9.

Results
GP: Grand Prix; JGP: Junior Grand Prix

title: Sarah Hughes