text:
Talk:Portland cement

picture shows Portland-composite cement, not (Ordinary) Portland cement
The first picture in the article shows 'CEM II/B-M' cement, which is strictly speaking not Portland cement, but Portland-composite-cement (EN 197-1) and has a clinker content <79%. This might be confusing because the picture is placed beside the statement that Portland cement has more than 90% clinker. However, the name 'Portland cement' is sometimes used for Ordinary Portland cement only or for all cements with some Portland cement content, including blended cements/composite cements. CEM I is Portland cement with >90% clinker (so called 'Ordinary Portland cement' in the USA). —Preceding unsigned comment added by 129.132.211.56 (talk) 15:24, 9 June 2010 (UTC)

physical properties
"The physical properties of concrete depend on the chemical properties and the proportions of the constituent materials. Compressive strength is usually between 2,000 and 15,000 psi, tensile strength between 100 and 4,000 psi, and shear strength between 1,000 and 10,000 psi."

I have not verified the correctness of these numbers. They are off the top of my head. If anyone can verify, please do so.

The strength of concrete depends mainly on the water to cement ratio. For a footpath concrete with a 28day compressive strength of 20 MPa is can be used particularly if the concrete contains flyash which will give added strength beyond 90 days or the cement is a blended cement containing slag which has a slower strength growth. For a driveway or garage floor one should specify a minimum 28 day strength of 30 Mpa and ensure a maximum slump of 80mm. 50-60 Mpa concrete is normally used with high rise concrete building where the concrete is pumped. Water reducing additives are used with these concretes. I have seen 120 MPa (at 28 day) concrete put down at a truck weighbridge so that it could be used after 2 days when the strength was over 40Mpa. This concrete contained a blended cement with a high proportion of ground slag and a superplastiser to reduce the water.

NPOV lacking in this article
I believe this article lacks neutrality and requires some restructuring. The disputed second paragraph in the article reads as follows:

"Manufacture of portland cement requires the burning of large quantities of fuel, typically coal or natural gas, which along with impurities contained in the limestone can result in significant emissions of pollutants regulated in many countries, including greenhouse gases such as nitrogen oxides (NOx) and sulfur dioxide, as well as particulates (PM 10, PM 2.5), volatile organic compounds (VOCs), and carbon monoxide. Cement plants emit substantial quantities of arsenic, lead and mercury."

This paragraph initiates a discussion of pollution at the outset of the article, which is pejorative and atypical of other wikipedia articles dealing with global industries (see: Petroleum and Steel, for examples). The paragraph is factually incorrect, listing oxides of nitrogen and sulfur dioxide as greenhouse gases; they are not. The final sentence declares that "cement plants emit substantial quantities of arsenic, lead and mercury" which is not supported by fact. See the discussion of cement chemistry later in the article and note that none of these elements play any part in the manufacturing process, nor are such heavy metals typical of the limestone and shale that comprise the essential raw materials in production.

The disputed third paragraph under "Safety and health" is similarly pejorative. It reads:

"Living near a portland cement plant can have serious health consequences due to the large quantity of pollutants released by the manufacturing process, as well as fugitive emissions from related on-site activities (such as haul roads, blasting, and truck traffic). The pollutants released by portland cement industry are known to contribute to lung and circulatory problems, including asthma, bronchitis, and heart attacks, as well as cancers. Hovever, many residents in these communities consider these risks to be acceptable in view of the economic benefits. For instance, polls show the residents of Ste. Genevieve County, Missouri to be overwhelmingly in favor of the cement plant being built there beginning in 2005. This plant will be the largest cement plant in the United States."

The statement "living near a portland cement plant can have serious health consequences" is an allegation lacking any source, certainly not a statement from NPOV. Looking to the article on Oil refineries as an example, public  health concerns voiced by environmental groups should be cited as such, with appropriate links. The environmental concerns must be cast as topics of public debate with the article taking a strictly neutral position.

Following the example of the articles on Petroleum and Steel, I propose to retitle the "Safety and health" heading as "Safety and Environmental Effects" and relocate the discussion of fuel usage, impurities, and pollution under that heading. I have collected some data on typical cement plant emissions to place as a data table under that heading, but for the sake of balance some examples of emissions control technology as applied to cement production might be appropriate as well.

I invite informed, objective debate on these issues…please speak here before deleting or reverting. Thanks JJackson8 20:02, 2 November 2005 (UTC)

--- Its sensationalist, delete it. The lights in a concete building would use 1000 times more electricity over the building lifetime, than electricity used in construction. The pollutants a re no worse than any other industrial process, and I dont see a pollution section on every manufacturing article. There is also the sentence: "For instance, polls show the residents of Ste. Genevieve County, Missouri to be overwhelmingly in favor of the cement plant being built there beginning in 2005." (My comment: There's a cement plant near me opposite an ice cream factory. Nobody cares less about either, including pollutants.)

Gtoomey 02:46, 3 November 2005 (UTC) First, I am not an expert on the enviromental side (only on the material) and thus can't tell what's "correct" for this - but as like other ppl I am of the opinnion that I can make up my own decissions based on the presentation of documented facts. Second, the "exhaust gasses" from a cement plant will pollute alot if not cleansed - but major cleansing prosesses are used (and pollution regulated) for many countries. This is the same as for metal production, oil refining etc. I vote for the creation of an Safety and enviromental effects section. Oyvind 09:18, 4 November 2005 (UTC) Noted today that WAS 4.250 moved the disputed sections without any contribution the discussion here. I have now deleted the disputed text (shown above in entirety). Based on comments here and attempted edits by several others (look to the history) there is a consensus that this text is not appropriate. I believe the burden now belongs to those who wish to insert such text to discuss it here and provide proper documentation. To consider any "data" as fact, it must be supported as being true. It is not correct to argue that we must disprove it. I will be proposing text and data to insert under the "Safety and environmental effect" heading here for discussion and improvement prior to any further edit of the article. This is the Wiki way...please participate! JJackson8 18:04, 6 November 2005 (UTC)

The environmental effects section needs a rework. As it reads at the moment, CO2 isn't a special problem of cement as compared to any other industry - the criticism is generic and noone reading the article would realise that the cement industry is a particularly significant CO2 emitter. I propose

1) a concise and factual addition to the first paragraph that underlines the specific problem that CO2 poses for the cement industry. Its the industry with the second largest CO2 emissions worldwide, and its well known for being so. 2) splitting the first paragraph (and the section itself) into problems and mitigation techniques. Its an industry that has a large environmental impact, which is mitigated to some extent. The split emphasises the size of both the environmental impact and the diversity of ways that are used to mitigate them. more importantly, it makes the structure of the whole section less choppy...it now progresses from a list of problems to a description and analysis of CO2 emission to mitigation, rather than mixing them all together due to previous editing spats. The way it reads at the moment is a testament to generations of opposing POV rather than proper consensus. 3) cutting back on the section on SO2/worker hazards. its far too large, and could be summarised in a sentence 4) cleaning up the language a bit...my cement future doesn't include thrusts of any sort, even of innovation ;) I don't know what to do with the references. Do we need as many SO2 references as we've got, now that the section is gone? what does everyone think? Where we do need references is when the article first mentions the scale of CO2 emissions (e.g. an IPCC report or peer reviewed paper), and we need at least one for the whole CO2 source analysis. The numerical section corresponds nicely to the data found at arjournals.annualreviews.org/doi/abs/10.1146/annurev.energy.26.1.303 - this paper is old now, but the data corresponds well to that already in this WP article, and its east to read. It also demonstrates the difference between efficient and inefficient production nicely. Here's my proposed rewrite: -- 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 CO2 from the raw materials during manufacture, and damage to countryside from quarrying. Fuel consumption and CO2 release from raw materials make cement manufacture the second largest manmade source of CO2 after power generation. In the absence of well-implemented mitigating practices worker safety may be impaired, in particular by airborne pollution. The CO2 associated with Portland cement manufacture falls into 3 categories: (1) CO2 derived from decarbonation of limestone, (2) CO2 from kiln fuel combustion, (3) CO2 produced by vehicles in cement plants and distribution. Source 1 is fairly constant: minimum around 0.47 kg CO2 per kg of cement, maximum 0.54, typical value around 0.50 world-wide. Source 2 varies with plant efficiency: efficient precalciner plant 0.24 kg CO2 per kg cement, low-efficiency wet process as high as 0.65, typical modern practice averaging around 0.30. Source 3 is almost insignificant at 0.002-0.005. So average total CO2 is around 0.80 kg CO2 per kg finished cement. This leaves aside the CO2 associated with electric power consumption, since this varies according to the local generation type and efficiency. Typical electrical energy consumption is of the order of 90-150 kWh per tonne cement, equivalent to 0.09-0.15 kg CO2 per kg finished cement if the electricity is coal-generated. Overall, CO2 generation ranges from a minimum of 0.7 kg per kg cement with nuclear- or hydroelectric power and efficient manufacturing to twice this amount. Research focuses on the reduction of sources 1 and 2 by modification of the chemistry of cement, by the use of wastes, and by adopting more efficient processes. Although cement manufacture is a very large CO2 emitter, concrete (of which cement makes up about 15%) compares quite favorably with other building systems in this regard. See also cement kiln emissions. 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 in developed countries. 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.

I'll edit the article to this in three days. As most of the text is straight from the existing article, i don't anticipate much objection. i think it presents cement as it is: a great product with an annoying CO2 side effect which can be exacerbated or mitigated depending on the production method. Cool? Hardcoeur 6 September 2007

 * Cool by me!! If there are other parts of the article you want to have a go at, there's plenty of scope for improvement. . . .LinguisticDemographer 14:56, 6 September 2007 (UTC)

== photo sensitive elements ==

Apart from that it Could be photo-electric/photo sensitive

possible mistake?
Shouldn't the raw material be calcium carbonate (44%) not calcium oxide (44%) ? Portland clinker (at least in N europe) consists of 45-65% (% by weight) Tricalcium silicate C3S. The finished product (cement) consist of 62-67% calcium oxide. Oyvind 09:52, 27 October 2005 (UTC)

Formula mistake?
Shouldn't "dicalcium and tricalcium silicates (C2S C3S)" be "(Ca2S Ca3S)" - i.e., symbol for calcium, not carbon?
 * No, see cement chemist notation Dave 23:07, 19 August 2005 (UTC)

 * It doesn't matter. Some screwball, idiosyncratic jargon of a narrow field should not be used in Wikipedia without including normal, general usage as well.  Gene Nygaard 23:44, 19 August 2005 (UTC)

 * While I'm in agreement that the more mainstream notation should also be used, if the original CCN formulations C2S, C3S were correct, then the translations done above, and the ones done on the entry in July are wrong. C2S in CCN would be 2 CaO • SiO2 in normal mainstream notation. (see the CCN entry.)

 * Cement production is a global industry, hardly a "narrow field."  I agree that the shorthand cement notation is idiosyncratic, but it is in no way "screwball".  This notation is used worldwide; I know of no cement plants that do NOT use this notation.  A reader seeking understanding of cement production needs to be aware of this notation in addition to the formal chemistry.

 * The cement manufacturing industry may be worldwide, but it is a narrow field. And even educated persons worldwide will not understand such jargonlike notation as C2S. (PeacePeace (talk) 04:23, 31 May 2018 (UTC))

Global warming?
"...The high energy requirements and the release of significant amounts of carbon dioxide makes cement production a concern for global warming...."

This is an opinion - the author's - and is inappropriate in this context.

Agreed. Delete it. Gtoomey 02:47, 3 November 2005 (UTC)

I have worked in construction for many years and have formulated a variety of products with PC and with other cements as well, such as calcium alumina. For every ton of PC made, you produce a ton of CO2. Think about that for a moment. A ton of PC fits on a skid. How much room does a ton of CO2 gas take up? Everybody in the business knows it. However, nobody (the public that is) cares enough to change. There are alterante inorganic binders out there. Pyrament was such an experiment. Worked great, cured fast, reliable, all that. However, it was more expensive and thus an economic failure. This sort of thing requires governmental backing and in order for government to back it, it must be an election issue for voters, which it is not. Most people will not reserve any attention span as soon as the word cement is uttered. Nobody cares, even if the alternative is THAT much better, let alone perhaps pay more in taxes to fund public highway projects? Are you kidding? Everybody wants a bargain and alternatives to great pollution are as popular and Green parties are in general elections. They don't even appear on the radar screen. So, the issue is not nearly controversial The cement industry REALLY TRIED and offered an alternative and nobody cared enough to make the alternative economically viable. The only thing controversial here is showing a generally apathetic public a mirror. That is not a sexy thing to do in politics and there the matter will rest - until we have, in the words of Captain Jean-Luc Picard: "evolved beyond the need for money".--Achim 22:17, 15 April 2006 (UTC)

What I do not understand: when the cement is cured, doesn't it absorb the released CO2 again, with Ca(OH)2 + CO2 -> CaCO3 + H2O ? It seems I have a misconception there, but I could not find a definite answer anywhere. Oku 00:32, 12 May 2006 (UTC)

That is very simplified but correct chemical equation. Ca(OH)2 + CO2 --> CaCO3 + H2O However there are two important points to consider why this reaction does not negate all of cement's CO2 emissions. 1st: Half of the total CO2 emitted from cement production is from fossil fuel combustion to produce the heat required to pyrolize limestone (CaCO3) feedstock. This CO2 is not recaptured in the first hydration reaction. CaCO3 + Heat --> CO2 + CaO 2nd: CO2 reactions with concrete mainly occur on the surface layer. Thus all of the interior material is not carbonated and thus, will not reabsorb CO2.

Together these two points explain why concrete does not reabsorb all of the CO2 released during its production. The cement industry is the second largest CO2 polluting industry behind power generation. See the latest IPCC report.

There is third reason why it is impossible for concrete to reabsorb all of the CO2 evolved during the cement-making process. Ca(OH)2 is only one reaction product of cement hydration, the rest of the calcium is tied up in calcium silicate hydrates. For example when C3S reacts fully with water the reaction is;-

2(3CaO.SiO2) +7H2O --> 3CaO.2SiO2.4H2O + 3Ca(OH)2

So, at best, only half of the CaO in C3S can ever be converted to Ca(OH)2. For C2S, this ratio is even smaller... only one quarter of the CaO in C2S can be converted into calcuim hydroxide during hydration. Ted Krapkat [Cement Australia] 203.161.131.164 (talk) 03:13, 26 July 2010 (UTC)

Possible mistake?
Under "Types of Portland Cement" the comment "Note: Type II cement is not really used any more in industry." appears under the heading for Type IV. Is it out of place, or should it be referring to Type IV?

Eitherway, type II cement is used almost exclusively in Northern California. And if the comment is referring to Type II it is a definite mistake.

In the US, rather more than half Portland cement consumption is Type II. On the other hand, no Type IV has been made in the last 30 years or so, because low heat concrete is normally now made with Type II and a large addition of ground granulated blastfurnace slag (ggbs).LinguisticDemographer 15:33, 27 September 2006 (UTC)

Regarding composition, Standards and emision
Oyvind 09:41, 2 November 2005 (UTC)
 * 1) ASTM C150 and EN 197 are the two major standards for Portland Cement - ASMT used in America+ and EN used in Europe+. Both are definitly notable ;) and just covering one of them is a one-sided and "protectionistic".
 * 2) As there are more than one standard the composition of cement and clinker differs - there is a larger span for the composition. To give the composition with aproximate 44% etc is to "coarse" as the spread is larger than can be coverded by the word "Aproximate"
 * 3) As to emmisions - lets settle that on this page and try to stay avay from an revert-war between different POV's. Keep it clean and simple, pleace.

I agree -- and yet, I see that emmisions is indeed an issue here and if it's an issue, it's an issue. There is no issue about whether paddling a canoe and greenhouse gasses. Whereas to create Portland cement one must use lots of fuel. I find that to be a fact and therefor worth mentioning. I find it a kind of political motive to want to Not mention it.

I don't feel it's neutral to say "there is debate about mentioning greenhouse gasses in relation to Portland cement production." I feel that if this debate should be mentioned at all, it would be "there is debate about mentioning facts or instead letting political viewpoints gloss over the fact that this production uses sufficient energy to question it's use by many."

Another way to share my view is that "there is discussion on the Talk Page to gloss over the high fuel/energy usage under the guise of NPV." *smile*

Michael Walsh 09:41, 2 November 2005 (UTC)

The picture is inaccurate.
The picture is wrong, as it shows two men making 6"x12" compressive strength TEST CYLINDERS.

Test cylinders are used to test CONCRETE, not CEMENT (cement is used to MAKE concrete)

2x2 TEST CUBES are used to test CEMENT.

Type Ia etc. Poor choice.
Not sure what the author means niggers with the statement that the grinding of cement with an air entraining agent is a poor choice. Please elaborate on this statement. I believe that if it is infact a poor choice either this product would have been replaced by better choices or would have disappeared from the market.

=* This logic doesn't work for me ("neoliberal" logic?)-- following this logic, heroin is a "good choice" since even armies can't stop it's use. I LOVE the NPV being most important here -- some day all these industries will have comments regarding the fuel/energy/greenhousegas usage. Whereas some are here advocating deletion of comments because other industries don't have greenhouse gas comments. Fact is, if indeed the generation of a ton of portland cement creates a ton of CO2, then yes, this ought be mentioned here. This is not "topical" it is as relevant as the formulii or ecomonies -- the greenhouse gas facts are indeed important.

History

 * Would a history of the invention of Portland Cement be appropriate in this article?

I think the history is appropriate, the name says it too, and where did you say it comes from? Gregorydavid 08:09, 30 March 2006 (UTC)

 * Indeed it is appropriate. I failed to see it and looked for it at the bottom of the page. I made no statement other than my question, which unfortunately gave the impression that I was questioning the inclusion as it stands.

 * Very complete and well written article as it stands.

Cement plants as alternatives to conventional waste disposal or processing
This section was obviously written by a shill for the cement industry. Cement is one of the most energy intensive products in the world, and manufacturers are seeking out any means of reducing their energy costs. The practice of incinerating hazardous and nonhazardous waste is extremely controversial. For example, one Lafarge plant at St. Constant in Quebec, Canada is producing stratospheric (and increasing) amounts of dioxins as a result of incinerating scrap tires.

All I'm saying is that this particular section is far from neutral. It reads like propaganda from the cement industry.

I agree - there is on-going opposition to the use of wastes in cement kilns, which were not designed for the job, and much data which suggests that they are not as good at burning everything up with no emmissions than is suggested by the industry. In addition, cement companies are not properly set up for the collection and storage of such wastes, and this introduces further complication. Even burning normal fuels, such as coal, results in dangerous emmissions of mercury, and of green-house gases.JaneH 13:00, 5 July 2006 (UTC)

History of cement
The section on the history of Portland cement duplicates thatin the "Portland cement" article, but has a different emphasis, giving greater credit to the Aspdins. Ideally the general history should be in the cement article, and the complicated evolution of modern Portland cement in the more specialised article. I missed an explanation of how cement sets at the microscopic level.

very confusing usage
Wait, so portland cement was invented by a guy who didn't invent portland cement? I think what the article is trying to say is that the cement originally named "portland cement" is not the stuff which is today called "portland cement" (sort of like the concept that tinfoil is actually aluminum and pencil leads are made of graphite) but I'm not entirely sure. Someone who knows should fix here, and in the Aspdin article... -- Akb4 05:20, 31 August 2006 (UTC)

Joseph Aspdin (the father) coined (and patented) the term "Portland Cement" because, when set, it looked like Portland stone. However, his product was a hydraulic lime, and not the product recognized today. Portland cement, as currently understood, is characterized by containing substantial amounts of alite ("C3S") and Joseph Aspdin's cement contained none of this. William Aspdin (the son) noted that by increasing lime content, and burning hotter, a slow-setting but high-strength product was produced. This is "Portland cement as we know it", and differs in application from his father's product: the earlier cements were used primarily for fast-setting stuccos, whereas the new product could be used for (relatively) high-strength concrete. Modern concrete production starts at this point. He subsequently set up in business on his own, and in 1842, produced the modern product commercially for the first time at Northfleet, Kent. This is much earlier than the date given in the article. He subsequently moved to Germany and commenced production at Lagerdorf in 1863. The cited source "A J Francis" describes this sequence of events although it is poor on technical detail. The latter can be supplemented with R.G.Blezard "The History of Calcareous Cements" in "Lea's Chemistry of Cement and Concrete: 4th Ed" Arnold 1998. The question arises; why did William Aspdin not give his new product a new name? It would appear that WA believed, probably correctly, that if he brought out a new patent, and disclosed his manufacturing techniques, the patent would be infringed by all and sundry almost immediately, and he would spent years fruitlessly suing his competitors. He therefore decided to claim that his product was his father's product - and protected by his father's patent - and resorted to various bizarre measures to prevent his secrets being stolen. This bought him about 2 years free from competition, until I C Johnson (at Swanscombe, Kent) found out how to emulate the product.LinguisticDemographer 15:02, 27 September 2006 (UTC)

CO2
CO2 production - people keep saying that 1 unit of CO2 is produced for every unit of PC (in the chemical reaction). Do they mean "about 1 unit"? Rich Farmbrough, 17:43 20 September 2006 (GMT).

I have pasted my initial respose to this into the Environmental section, since it appears to read OK.LinguisticDemographer 17:38, 30 September 2006 (UTC)

"Overall, with nuclear- or hydroelectric power and efficient manufacturing, CO2 generation can be as little as 0.7 kg per kg cement" What is the correct amount of CO2 generated, in the context of this passage? 0.07kg maybe? Kibblesnbits (talk) 22:32, 11 October 2008 (UTC)

Introduction: Use of Clay
In the introduction, it is stated that the wet process is no longer used, and that as a consequence clay is no longer used, because (among other reasons) it contributes too much alumina. This is all incorrect. (1) The wet process, although much less used, is still in operation. Wet and semi-wet process still accounts for more than 10% of UK production. In the US it's still around 20%. In some countries it's 100%. (2) Clay usage is not restricted to wet process: many dry process plants use clays. (3) Clays are in no way chemically distinct from shales; high-alumina shale are just as common as high-alumina clays.LinguisticDemographer 16:28, 27 September 2006 (UTC)

 * Please feel free to make the appropriate edits, particularly if you have references for your assertions. See WP:BOLD Argyriou 16:42, 27 September 2006 (UTC)

Description of ASTM C 150 Cements
This section appears to be based on texts written 50 or more years ago. The typical composition data is out of date. There was a survey of North American portland cements in the mid 1990s (Gebhardt, R. F., "Survey of North American Portland Cements: 1994," Cement, Concrete, and Aggregates, December 1995, 145-189). The following mean compositions come from this: Type I: 55% (C3S), 18% (C2S), 8% (C3A), 9% (C4AF), 2.0% MgO, 2.8% (SO3), 1.3% Ignition loss, and 1.0% free CaO. Type II: 54% (C3S), 20% (C2S), 6% (C3A), 11% (C4AF), 2.2% MgO, 2.7% (SO3), 1.2% Ignition loss, and 1.0% free CaO. Type III: 55% (C3S), 17% (C2S), 9% (C3A), 8% (C4AF), 2.2% MgO, 3.5% (SO3), 1.3% Ignition loss, and 1.3% free CaO. Type V: 55% (C3S), 20% (C2S), 4% (C3A), 13% (C4AF), 2.5% MgO, 2.3% (SO3), 1.0% Ignition loss, and 0.8% free CaO. The description of Type III states that it is made by raising the C3S and C3A in the mix. This was the practice in the 1930s, but nowadays, very few manufacturers deliberately make a different mix for Type III, and this fact is born out by the above data - Type III is typically almost identical to Type I in chemistry. Type III is differentiated from Type I by finer grinding: typical Blaine fineness (m2/kg): Type I: 377 Type II: 374 Type III: 547 Type V: 370 Although not specified in this way in ASTM standards, Type III is bought and sold on the basis of its 1-day strength (or even 16-hour strength), which is proportional to the fineness and the C3S. Clearly, the modern 50% boost in early strength given by Type III can't be achieved by tweaking C3S content. Main uses are in pre-cast concrete and in pre-stressed units, where fast mould turn-around is called for. The usage text given fails to address this and appears to describe the situation 50 years ago. In general Type III can not be used in contact with ground waters!!

The whole section really needs a re-write from scratch.LinguisticDemographer 16:55, 27 September 2006 (UTC)

Plastic Cement
I deleted the section on Plastic Cement, because it is not a Portland cement, since it contains components that are prohibited in the Portland specification. It is covered under cement, although the item might need a little expansion.LinguisticDemographer 16:57, 29 September 2006 (UTC)

Setting Mechanism
I have a problem with the existing text which implies that setting is due to calcium aluminate hydration. This really isn't true. C3A causes flash-set if not controlled by sulfate addition. Addition of sulfate causes formation of a very limited initial amount of ettringite, which forms an insoluble crust over the C3A surfaces and prevents further hydration. The normal set occurs as a result of initial hydration of C3S. Pure C3S, in fact, sets in a manner similar to well-controlled Portland cement, after a delay of an hour or two. The ettringite layer passivating the C3A subsequently redissolves quite slowly to form Afm after the C3S-based set is well established. LinguisticDemographer 00:31, 9 October 2006 (UTC)
 * May I suggest that you edit the article along the lines you propose above? Adding references and/or footnotes would be welcome, also. For guidelines, please see WP:RS and WP:FN. In particular, citation of a standard textbook would be very helpful to our readers. Best wishes, Walter Siegmund (talk) 02:44, 9 October 2006 (UTC)

Slag
Reference to slag as a raw material should not be confined to ggbs, since the physical state of the slag is irrelevant when it is used as a raw material. Furthermore, slags other than blastfurnce slag are also in use. . . .LinguisticDemographer 14:55, 25 January 2007 (UTC)

 * Thanks for not reverting without comment. Gracious of you.

 * It's not the physical state that matters, I think but the ubiquity of GGBFS as a pozzolan in the industry. I've never seen reference to ground slag being anything but blast-furnace slag, i.e. FHWA, Portland Cement Association, Slag Cement Association, ASTM C989 and AASHTO M302, or my various concrete materials and design texts. I seriously doubt that the total combined smelting of copper, bauxite, lead, etc. makes up a noticeable fraction of iron, and I'd really be surprised if GGBFS isn't as ubiquitous in the UK and EU as it is in North America.

 * Now bauxite is smelted in significant quantities in Australia, Brazil, Venezuela, and Guyana relative iron ore. Do they use ground bauxite slag in significant quantities that you know of? (Australia seems a very likely candidate.) Can you provide references or standards?

 * Even so, this article should link to GGBFS as that article is much closer to the point; and your latest version says blast furnace slag. The Slag article is off the point of cement admixtures, but is linked to in the first line of the GGBFS article. MARussellPESE 16:45, 25 January 2007 (UTC)

I think there is a misunderstanding here. Various raw matereials (and this entry is in the raw materials section of the Portland cement article) are used in formulating rawmix. The resulting Portland cement clinker may then be ground on its own to make Portland cement, or interground with pozzolans (such as flyash) or materials with incipient hydraulic activity (such as ggbs) to make Blended Cements. Materials used in the rawmix are selected purely for their chemistry, since their physical state is annihilated in the burning process. These materials include raw slag, ggbs (although because of relatively high cost, this is not favored), steel slag (in VAST quantities in the USA), basic oxygen furnace slag, and slags from the non-ferrous industries, which are used not for their own qualities, but because cement manufacturers are paid to dispose of them. Bauxite is also used, but, of course, not as a Blended Cement component. Thus, it may be appropriate to include this reference (and I thought it was already included) in the article on Cement (NOT Portland cement). I agree that there is no good article on blast furnace slag in general, but then, this is Wikipedia. Maybe someone should write one. It doesn't need to be any good! I can't write it myself because I don't know much about the iron industry. But I know an awful lot about cement manufacture. Incidentally, VASTLY more ggbs is used in Europe than in North America. In countries such as Belgium and the Netherlands, PBFC is practically the only cement on the market. . . .LinguisticDemographer 12:39, 26 January 2007 (UTC)

 * I finally get the article's point. While the article is about PC and this section discusses its manufacture (I was reading: "use"), the text in this spot was very unclear. I hope this fixes it. Completely agree with you on the manufacturing and raw materials. Since "slag" really does mean more than GGBFS here, I've changed the list to read "Slag". Hopefully the new reference is of use.

 * My references were totally off-track and belonged in the Concrete article. I fixed that to discuss mineral admixtures and blended cements. I'll update Cement with these, which is where they belong.

 * Cheers, MARussellPESE 18:32, 26 January 2007 (UTC)

Reorganized 11 Feb 2007
I have changed the order of the article to give (I hope) a more logical read. I have also eliminated one or two redundancies (see "Setting mechanism" above), and have added a bunch of text which I think is probably valuable. This also seeds two new articles: rawmill and cement mill. I'm on the lookout for good photos for these. The wiki server was playing up as I pasted this, and there may be a few typos, errors etc. Please fix if you get to it before I do.

LinguisticDemographer 17:56, 11 February 2007 (UTC)

Edits 18 March 2007
I changed a section that seems to be based on a very old text, in order to reflect modern usage. There are many repeated and circular wikilinks: I have taken out some of these. Is there some sort of "bot" that does this automatically? . . .LinguisticDemographer 15:08, 18 March 2007 (UTC)

Portland cement business
The current section 4 needs to be relocated to the "Cement" article. The text refers explicitly to "hydraulic cement", on which the world production is based. A large proportion of this is strictly non-Portland, as is the large majority of the Chinese production. I'll move it if there are no objections. . . .LinguisticDemographer 19:04, 24 April 2007 (UTC)

Bogue's Compounds
Are the cement components namely C3S, C2S, etc. are known as Bogue's Compounds? —Preceding unsigned comment added by Rohit.k88 (talk • contribs) 10:10, 26 May 2007

The notional compounds C3S, C2S, C3A and C4AF are informally referred to as "Bogue compounds", and the process of calculating their amounts is referred to as "Bogue analysis", because this calculation was first proposed by Bogue. The actual minerals present in Portland cement clinker (alite, belite, tricalcium aluminate and calcium aluminoferrite) differ substantially from the notional Bogue compounds in composition, so that the calculated Bogue compound composition is often very different from the true mineral composition. For this reason, and because direct methods of mineralogical analysis are now available, "Bogue analysis" is now gradually going out of favor. . . .LinguisticDemographer 11:02, 27 May 2007 (UTC)

"Rawmix" → 'raw mix' etc.
"Rawmix" does not seem to be the usual term. Relevant sources show that the normal term is 'raw mix'. Likewise for "rawmill"/'raw mill', etc.. Here are a couple of examples: — DIV (128.250.204.118 08:26, 22 June 2007 (UTC))
 * — official industry site calls it "raw mix"
 * — UN document uses "raw mix" almost exclusively throughout, except for a singe instance (which might be a misprint).

I'm not unsympathetic to this edit. Rawmix may be two words in Australia (obviously the industry doesn't have an "official" website), and it's certainly not used at all in Britain. I'm not sure about other parts of the English-speaking world - e.g. India. But in North America, it's usually (not always) written as one word. Also rawmill. I have reverted the edit because it has been done without regard to proper capitalization and updating of links, and generally makes the article look unprofessional. If anyone would like to make this change in a disciplined manner, it's fine by me. . . .LinguisticDemographer 10:18, 23 June 2007 (UTC)

Okay ...I didn't notice I'd messed up any of the capitalisation — sorry if that was the case. I acknowledge that I hadn't simultaneously revised the rawmill article, but the links did still all work (as far as I know) after my edits, so I'm not sure exactly what you're referring to. In any case, the discussion is here, and hopefully someone will spend the time to modify the article according to consensus. As I say, most of the stuff I saw online used separate words for the two terms. By the way, I thought it would be clear I intended the first link to be read as "an official industry site". —DIV (128.250.204.118 10:18, 5 July 2007 (UTC))

Rawmix blending; please define alite and belite here. How about a section in rawmix about deleterious elements, e.g. Mg, F, P, also problems of sulphides in feedstock and alkalis in cement

What do people think of a section on cement aggregate reactions, such as alkali silica, alkali-dolomite reactions, also some info on sulphate attack of cementitious materials? I can do an outline if necessary, but I'm not top of the field in either area at present.

suggested changes
Rawmix blending; please define alite and belite here. How about a section in rawmix about deleterious elements, e.g. Mg, F, P, also problems of sulphides in feedstock and alkalis in cement

What do people think of a section on cement aggregate reactions, such as alkali silica, alkali-dolomite reactions, also some info on sulphate attack of cementitious materials? I can do an outline if necessary, but I'm not top of the field in either area at present.

Premix isn't the same thing as rawmix
When I go to the hardware store to buy cement, I've been told to ask for something called 'premix'. In what way is 'premix' different from 'rawmix'? I'm not an expert on this sort of thing, and I thought I'd go to Wikipedia to get an answer on the matter. 216.99.198.63 (talk) 23:31, 10 August 2008 (UTC)

 * Premix is cement mixed with sand or sand and gravel: it's really mortar or concrete in a "just add water" form – useful if you only need a little. Rawmix is a stage in the manufacture of cement, so it's not at all the same thing – it's like the difference between wheat and cake-mix.  By the way (and I don't in the least mean to sound unfriendly) WP isn't really meant to be a Q&A site – try one like www.answerbank.com.  Richard New Forest (talk) 14:08, 11 August 2008 (UTC)

Original Research
Substantial parts of this article were written by me. I am a well known researcher in this field. I hereby assert that all those parts of the article that were written by me and are not provided with references are the results of my own original research. Wikipedia rules state that information that is the result of original research is prohibited, and where such information is unambiguously present in an article, it is the duty of every editor to remove it forthwith. LinguisticDemographer (talk) 21:56, 15 April 2010 (UTC)

Rawmix or rawmeal (raw meal)?
The article talks about 'rawmix' or 'raw mixture', but not 'raw meal'. In both wet, semi-wet and dry process kiln systems the terms 'rawmix'(raw mix) or 'raw mixture' invariably refer to the heterogeneous mixture of the unground raw materials which are fed to the raw mill. However, the homogenous powdered material which comes out of the raw mill in a dry process kiln (or the dried powdered slurry in a semi-wet process) is generally referred to as 'raw meal'. For clarity, I suggest that this convention also be observed in the article. Ted Krapkat (Cement Australia) 203.161.131.164 (talk) 01:17, 27 July 2010 (UTC)

Safety
In the Safety section, it says:
 * As of 2010, however, the development of formulations of cement that include fast-reacting pozzolans such as silica fume as well as some slow-reacting products such as fly ash have allowed for the production of comparatively low-alkalinity cements (pH<11)[6] that are much less toxic and which have become widely commercially available, largely replacing high-pH formulations in much of the United States. Once any cement hydrates, the hardened mass loses chemical reactivity and can be safely touched without gloves.

Argyriou (talk) 00:54, 6 October 2010 (UTC)
 * Low-alkalinity cements have been available since before 2010. I've changed that.
 * There needs to be a citation for low-alkalinity formulations "largely replacing high-pH formulations in much of the United States."
 * The loss of chemical reactivity occurs after the cement sets, not hydrates. I've fixed that.

Heat During Curing
I understand that the curing process of Portland cement generates heat, and that for very large castings, measures must be taken to prevent heat damage. Perhaps this is worth mentioning in the article. — Preceding unsigned comment added by Mohanchous (talk • contribs) 16:18, 6 March 2011 (UTC)

Flux ?
The article has a link to flux_(metallurgy), which is confusing. I had hoped to correct the link, but the Flux_(disambiguation) page did not enlighten me either. Some more explanation would be useful.Brinerustle (talk) 11:05, 25 April 2011 (UTC)

Unreferenced and original research
There is a problem with this article: certain sections have been marked as "unreferenced" for two years, during which time no attempt has been made to supply references. The author of these sections freely admits that they are Original Research. Original Research is absolutely prohibited in Wikipedia. Accordingly I have deleted them. Do not restore them - you are absolutely forbidden by Wikipedia rules to restore them - unless you also supply valid references from a reliable - i.e. peer reviewed - source. — Preceding unsigned comment added by 193.61.220.13 (talk) 11:55, 24 November 2011 (UTC)

Energy Requirements
"Typical electrical energy consumption is of the order of 90-150 kWh per tonne cement, equivalent to 0.09-0.15 kg CO2 per kg finished cement if the electricity is coal-generated."

This is FLAT wrong and out by an order of 1000!!!!!!!!!!

See, table at page 4 of http://www.wbcsdcement.org/pdf/CSI%20GNR%20Report%20final%2018%206%2009.pdf

Jono2013 (talk) 16:36, 4 April 2013 (UTC)

 * Jono2013, the reference you cite, p 14, declares that about 5000 megajoules of energy are used per tonne of clinker. Does clinker mean cement? There are 3.6 MJ per kilowatt hour, so 5000 MJ is about 1400 KwHr. But why quote KwHr? Energy quoted in MJ makes sense because fossil fuel and combustible waste are used for heating the kiln. When electric power is mentioned, does this mean that cement kilns are electrically heated? DavidJErskine (talk) 06:22, 7 March 2014 (UTC)

EMC Section reads like an advertisement and is not representative of Portland cement.
The linked entry under the EMC section is tagged for deletion, for apparently good reason. This product most definitely doesn't belong on the Portland cement entry page. — Preceding unsigned comment added by 98.26.94.209 (talk) 06:35, 4 May 2013 (UTC)

ASTM and EN standards naming convention
ASTM itself identifies its standards with no space between the letter and numbers (for example, ASTM C150). Even the page ASTM International identifies a page without the superfluous space. I realise that it is fairly common usage to insert a space. But the space contributes nothing to readability or clarity. I think that the nomenclature by which an organisation identifies its own standards should prevail. EN apparently identifies its standards with a space. So EN 197-1 is the canonical form. "EN197" and "EN-197" are not in proper form. Whatever the organisation's preferred form is, that is what we should use. 75.210.43.64 (talk) 03:26, 1 July 2013 (UTC)

Complex Series of Chemical Reactions Still Only Partly Understood
Can it really still be true that the most important property of one of the central and widespread materials of 20th and 21st century civilisation, tightly and widely formulated, and composed only of inorganic molecules, is still, more than 150 years after its formulation, only partly understood?

That's what it used to say in my chemistry books when I was growing up in the 60s. The books were probably repeating what was known in the 30s. That's the 1930s. If this statement is true, what use the scientific century? Atconsul (talk) 10:18, 2 September 2013 (UTC)

Environmental Effects Sections Are Ruining Articles
I understand many people have their own political views and ambitions but they don't belong in these articles since all they do is derail the entire page from the intro. I get it that some people think we all need to hear about carbon this and carbon that but they shouldn't be wrecking these articles by pushing a political agenda. Someone needs to just create large articles about the "Environmental Effects of.." and put a link to it. Making a page called "Environmental Effects of Road Construction" is more appropriate than complaining about how building roads is evil for the environment in every single article related to it.

Another thing too: this bias isn't just honest inquiry either. There's a clear pattern of abuse on these pages where anything that in any way, shape, or form that benefits rural and suburban America is inundated with massive amounts of environmental criticism. I can't even read an article about roads without hearing someone's diatribe about how they think everyone should be forced to live in big cities due to mother nature.

Either make separate pages about the environmental connections to various subjects or, if no one wants to give up their political grandstanding, then just clear out those sections altogether. When I can't even find any information on the comparison between asphalt and regular concrete roads or the history of asphalt usage but I can find detailed criticism of the asphalt/concrete industry, then things need to change.75.167.216.168 (talk) 06:40, 11 May 2015 (UTC)
 * I totally agree. Most of the CO2 produced from rocks is returned back into building materials to form carbonates. The only contribution into atmosphere is by burning hydrocarbons... which may be recaptured and used for other industries. AXO NOV  (talk) ⚑ 20:02, 4 August 2022 (UTC)

completely agree. The intro should focus on all the marvellous accomplishments that were made using portland cement. Fsikkema (talk) 20:17, 1 February 2022 (UTC)
 * Extensive, often repetitive, and weakly sourced commentary about environmental impact, etc often damage articles. Some of that material is valuable, but often it is garbage, hearsay, WP:UNDUE, WP:OR, or just preaching. My guess is that editors who introduce such content are incapable to contribute core information, but they fervently want to contribute somehow. Warnings are easy to post. Its our job as editors to weed out that content when it is inferior (as well as our jobs to enhance such content when appropriate).--Smokefoot (talk) 21:49, 4 August 2022 (UTC)

Dentistry
Do mention some uses in dentistry. Jidanni (talk) 16:33, 20 April 2022 (UTC)

Portland Cement and Capitalization
The term "portland cement" and "portland cement concrete" should not be capitalized. See ASTM pages on portland cement and the textbook "Materials for Civil and Construction Engineers" by Mamlouk for support of non-capitalized usage. Although it was originally based on a proper noun place-name, the meaning of the noun-phrase has not significantly changed since the late 1800s, which I believe is why it eventually became a non-proper noun phrase. I recommend changing the article to reflect the non-capitalized usage.

Link to ASTM: https://www.astm.org/c0150_c0150m-22.html

Dag330 (talk) 20:56, 22 April 2024 (UTC)

 * I don't think this is the way to go for a Wikipedia article - the lowercase form really is a North American-specific usage; internationally, Portland cement almost always takes a capital. ASTM and the Mamlouk textbook are US-focused sources.
 * See for example:
 * - the Global Cement and Concrete Association (the dominant international producer and research entity), https://gccassociation.org/our-story-cement-and-concrete/ - "Today Portland clinker based cement is the most common type of cement in use. Portland cement was first developed in the beginning of the 1800s".
 * - the website of the UK Mineral Products Association (the main trade association in that country) - https://cement.mineralproducts.org/ - "MPA Cement is the trade association representing the six major UK Portland cement manufacturers,..."
 * etc.
 * Could we please change the usage back to the globally accepted form? Johnprovis (talk) 10:08, 25 April 2024 (UTC)

title: Talk:Portland cement


text:
Talk:Bob Bakker

The original referred to Bakker as "oddball" and "eccentric." While these terms aren't offensive, and this image may even be a source of pride for Mr. Bakker, it seemed that the characterizations where inappropriate unless the could be credited.

I knew nothing about him; but the original article was so sparse that I had to do a Google search to at least add some external links (and fix some typos, and add some internal wikipedia links).

The external links were chosen for sites that seemed credible, even reputable, and stable. Anyone with the time and inclination should be able to read all those articles and profiles to expand and refine this entry. A GFDL or PD picture of him would be a nice addition!

I'd be interested in confirmation of whether Bob Bakker was the inspiration for the hero (protagonist) in the books and movie Jurassic Park by Michael Crichton

 * http://www.geocities.com/dannsdinosaurs/fiction.html (books by both of them and others)

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

title: Talk:Bob Bakker


text:
Hadamard matrix

In mathematics, a Hadamard matrix, named after the French mathematician Jacques Hadamard, is a square matrix whose entries are either +1 or −1 and whose rows are mutually orthogonal. In geometric terms, this means that each pair of rows in a Hadamard matrix represents two perpendicular vectors, while in combinatorial terms, it means that each pair of rows has matching entries in exactly half of their columns and mismatched entries in the remaining columns. It is a consequence of this definition that the corresponding properties hold for columns as well as rows.

The n-dimensional parallelotope spanned by the rows of an n × n Hadamard matrix has the maximum possible n-dimensional volume among parallelotopes spanned by vectors whose entries are bounded in absolute value by 1. Equivalently, a Hadamard matrix has maximal determinant among matrices with entries of absolute value less than or equal to 1 and so is an extremal solution of Hadamard's maximal determinant problem.

Certain Hadamard matrices can almost directly be used as an error-correcting code using a Hadamard code (generalized in Reed–Muller codes), and are also used in balanced repeated replication (BRR), used by statisticians to estimate the variance of a parameter estimator.

Properties
Let H be a Hadamard matrix of order n. The transpose of H is closely related to its inverse. In fact:

 * $$H H^\textsf{T} = n I_n$$

where In is the n × n identity matrix and HT is the transpose of H. To see that this is true, notice that the rows of H are all orthogonal vectors over the field of real numbers and each have length $$\sqrt{n}\,.$$ Dividing H through by this length gives an orthogonal matrix whose transpose is thus its inverse. Multiplying by the length again gives the equality above. As a result,

 * $$\operatorname{det}(H) = \pm\, n^{n/2},$$

where det(H) is the determinant of H.

Suppose that M is a complex matrix of order n, whose entries are bounded by |Mij | ≤ 1, for each i, j between 1 and n. Then Hadamard's determinant bound states that

 * $$|\operatorname{det}(M)| \leq n^{n/2}.$$

Equality in this bound is attained for a real matrix M if and only if M is a Hadamard matrix.

The order of a Hadamard matrix must be 1, 2, or a multiple of 4.

The proof of the nonexistence of Hadamard matrices with dimensions other than 1, 2, or a multiple of 4 follows:

If $$n>1$$, then there is at least one scalar product of 2 rows which has to be 0. The scalar product is a sum of n values each of which is either 1 or −1, therefore the sum is odd for odd n, so n must be even.

If $$n = 4 m + 2$$ with $$m \geq 1$$, and there exists an $$n \times n$$ Hadamard matrix $$H = (h_{i,j})_{i,j \in \{0,1,...,n-1\}}$$, then it has the property that for any $$k \neq l$$:
 * $$\sum_{i=0}^{n-1} h_{k,i} h_{l,i} = 0$$

Now we define the matrix $$A = (a_{i,j})_{i,j \in \{0,1,...,n-1\}}$$ by setting $$a_{i,j} = h_{0,j}h_{i,j}$$. Note that $$A$$ has all 1s in row 0. We check that $$A$$ is also a Hadamard matrix:
 * $$\sum_{i=0}^{n-1} a_{k,i} a_{l,i} = \sum_{i=0}^{n-1} h_{0,j} h_{k,i} h_{0,j} h_{l,i} = \sum_{i=0}^{n-1} h_{0,j}^2 h_{k,i} h_{l,i} = \sum_{i=0}^{n-1} h_{k,i} h_{l,i} = 0.$$

Row 1 and row 2, like all other rows except row 0, must have $$n/2$$ entries of 1 and $$n/2$$ entries of −1 each. (*)

Let $$\alpha$$ denote the number of 1s of row 2 beneath 1s in row 1. Let $$\beta$$ denote the number of −1s of row 2 beneath 1s in row 1. Let $$\gamma$$ denote the number of 1s of row 2 beneath −1s in row 1. Let $$\delta$$ denote the number of −1s of row 2 beneath −1s in row 1.

Row 2 has to be orthogonal to row 1, so the number of products of entries of the rows resulting in 1, $$\alpha + \delta$$, has to match those resulting in −1, $$\beta + \gamma$$. Due to (*), we also have $$n/2 = \alpha + \gamma = \beta + \delta$$, from which we can express $$\gamma = n/2 - \alpha$$ and $$\delta = n/2 - \beta$$ and substitute:

 * $$\alpha + \delta = \beta + \gamma$$
 * $$\alpha + \frac{n}{2} - \beta = \beta + \frac{n}{2} - \alpha$$
 * $$\alpha - \beta = \beta - \alpha$$
 * $$\alpha = \beta$$

But we have as the number of 1s in row 1 the odd number $$n/2 = \alpha + \beta$$, contradiction.

Sylvester's construction
Examples of Hadamard matrices were actually first constructed by James Joseph Sylvester in 1867. Let H be a Hadamard matrix of order n. Then the partitioned matrix
 * $$\begin{bmatrix}

H & H\\ H & -H \end{bmatrix}$$

is a Hadamard matrix of order 2n. This observation can be applied repeatedly and leads to the following sequence of matrices, also called Walsh matrices.

 * $$\begin{align}

H_1 &= \begin{bmatrix} 1 \end{bmatrix}, \\ H_2 &= \begin{bmatrix} 1 & 1 \\    1 & -1  \end{bmatrix}, \\ H_4 &= \begin{bmatrix} 1 & 1 &  1 &  1\\    1 & -1 &  1 & -1\\    1 &  1 & -1 & -1\\    1 & -1 & -1 &  1  \end{bmatrix}, \end{align}$$

and

H_{2^k} = \begin{bmatrix} H_{2^{k-1}} & H_{2^{k-1}}\\ H_{2^{k-1}} & -H_{2^{k-1}} \end{bmatrix} = H_2 \otimes H_{2^{k-1}}, $$

for $$ 2 \le k \in N $$, where $$ \otimes $$ denotes the Kronecker product.

In this manner, Sylvester constructed Hadamard matrices of order 2k for every non-negative integer k.

Sylvester's matrices have a number of special properties. They are symmetric and, when k ≥ 1 (2k > 1), have trace zero. The elements in the first column and the first row are all positive. The elements in all the other rows and columns are evenly divided between positive and negative. Sylvester matrices are closely connected with Walsh functions.

Alternative construction
If we map the elements of the Hadamard matrix using the group homomorphism $$ (\{1, -1\}, \times) \mapsto (\{0, 1\}), \oplus\} $$, we can describe an alternative construction of Sylvester's Hadamard matrix. First consider the matrix $$ F_n $$, the $$ n\times 2^n $$ matrix whose columns consist of all n-bit numbers arranged in ascending counting order. We may define $$ F_n $$ recursively by

 * $$\begin{align}

F_1 &= \begin{bmatrix}0 & 1\end{bmatrix} \\ F_n &= \begin{bmatrix} 0_{1\times 2^{n-1}} & 1_{1\times 2^{n-1}} \\ F_{n-1}            & F_{n-1} \end{bmatrix}. \end{align}$$

It can be shown by induction that the image of the Hadamard matrix under the above homomorphism is given by

 * $$H_{2^n} = F_n^\textsf{T} F_n.$$

This construction demonstrates that the rows of the Hadamard matrix $$ H_{2^n} $$ can be viewed as a length $$ 2^n $$ linear error-correcting code of rank n, and minimum distance $$ 2^{n-1} $$ with generating matrix $$ F_n. $$

This code is also referred to as a Walsh code. The Hadamard code, by contrast, is constructed from the Hadamard matrix $$ H_{2^n} $$ by a slightly different procedure.

Hadamard conjecture
The most important open question in the theory of Hadamard matrices is one of existence. Specifically, the Hadamard conjecture proposes that a Hadamard matrix of order 4k exists for every positive integer k. The Hadamard conjecture has also been attributed to Paley, although it was considered implicitly by others prior to Paley's work.

A generalization of Sylvester's construction proves that if $$H_n$$ and $$H_m$$ are Hadamard matrices of orders n and m respectively, then $$H_n \otimes H_m$$ is a Hadamard matrix of order nm. This result is used to produce Hadamard matrices of higher order once those of smaller orders are known.

Sylvester's 1867 construction yields Hadamard matrices of order 1, 2, 4, 8, 16, 32, etc. Hadamard matrices of orders 12 and 20 were subsequently constructed by Hadamard (in 1893). In 1933, Raymond Paley discovered the Paley construction, which produces a Hadamard matrix of order q + 1 when q is any prime power that is congruent to 3 modulo 4 and that produces a Hadamard matrix of order 2(q + 1) when q is a prime power that is congruent to 1 modulo 4. His method uses finite fields.

The smallest order that cannot be constructed by a combination of Sylvester's and Paley's methods is 92. A Hadamard matrix of this order was found using a computer by Baumert, Golomb, and Hall in 1962 at JPL. They used a construction, due to Williamson, that has yielded many additional orders. Many other methods for constructing Hadamard matrices are now known.

In 2005, Hadi Kharaghani and Behruz Tayfeh-Rezaie published their construction of a Hadamard matrix of order 428. As a result, the smallest order for which no Hadamard matrix is presently known is 668.

By 2014, there were 12 multiples of 4 less than 2000 for which no Hadamard matrix of that order was known. They are: 668, 716, 892, 1132, 1244, 1388, 1436, 1676, 1772, 1916, 1948, and 1964.

Equivalence and uniqueness
Two Hadamard matrices are considered equivalent if one can be obtained from the other by negating rows or columns, or by interchanging rows or columns. Up to equivalence, there is a unique Hadamard matrix of orders 1, 2, 4, 8, and 12. There are 5 inequivalent matrices of order 16, 3 of order 20, 60 of order 24, and 487 of order 28. Millions of inequivalent matrices are known for orders 32, 36, and 40. Using a coarser notion of equivalence that also allows transposition, there are 4 inequivalent matrices of order 16, 3 of order 20, 36 of order 24, and 294 of order 28.

Hadamard matrices are also uniquely recoverable, in the following sense: If an Hadamard matrix $$H$$ of order $$n$$ has $$O(n^2/\log n)$$ entries randomly deleted, then with overwhelming likelihood, one can perfectly recover the original matrix $$H$$ from the damaged one. The algorithm of recovery has the same computational cost as matrix inversion.

Special cases
Many special cases of Hadamard matrices have been investigated in the mathematical literature.

Skew Hadamard matrices
A Hadamard matrix H is skew if $$H^\textsf{T} + H = 2I.$$ A skew Hadamard matrix remains a skew Hadamard matrix after multiplication of any row and its corresponding column by −1. This makes it possible, for example, to normalize a skew Hadamard matrix so that all elements in the first row equal 1.

Reid and Brown in 1972 showed that there exists a doubly regular tournament of order n if and only if there exists a skew Hadamard matrix of order n + 1. In a mathematical tournament of order n, each of n players plays one match against each of the other players, each match resulting in a win for one of the players and a loss for the other. A tournament is regular if each player wins the same number of matches. A regular tournament is doubly regular if the number of opponents beaten by both of two distinct players is the same for all pairs of distinct players. Since each of the n(n − 1)/2 matches played results in a win for one of the players, each player wins (n − 1)/2 matches (and loses the same number). Since each of the (n − 1)/2 players defeated by a given player also loses to (n − 3)/2 other players, the number of player pairs (i, j ) such that j loses both to i and to the given player is (n − 1)(n − 3)/4. The same result should be obtained if the pairs are counted differently: the given player and any of the n − 1 other players together defeat the same number of common opponents. This common number of defeated opponents must therefore be (n − 3)/4. A skew Hadamard matrix is obtained by introducing an additional player who defeats all of the original players and then forming a matrix with rows and columns labeled by players according to the rule that row i, column j contains 1 if i = j or i defeats j and −1 if j defeats i. This correspondence in reverse produces a doubly regular tournament from a skew Hadamard matrix, assuming the skew Hadamard matrix is normalized so that all elements of the first row equal 1.

Regular Hadamard matrices
Regular Hadamard matrices are real Hadamard matrices whose row and column sums are all equal. A necessary condition on the existence of a regular n × n Hadamard matrix is that n be a square number. A circulant matrix is manifestly regular, and therefore a circulant Hadamard matrix would have to be of square order. Moreover, if an n × n circulant Hadamard matrix existed with n > 1 then n would necessarily have to be of the form 4u 2 with u odd.

Circulant Hadamard matrices
The circulant Hadamard matrix conjecture, however, asserts that, apart from the known 1 × 1 and 4 × 4 examples, no such matrices exist. This was verified for all but 26 values of u less than 104.

Generalizations
One basic generalization is a weighing matrix. A weighing matrix is a square matrix in which entries may also be zero and which satisfies $$WW^\textsf{T} = wI$$ for some w, its weight. A weighing matrix with its weight equal to its order is a Hadamard matrix.

Another generalization defines a complex Hadamard matrix to be a matrix in which the entries are complex numbers of unit modulus and which satisfies H H* = n In where H* is the conjugate transpose of H. Complex Hadamard matrices arise in the study of operator algebras and the theory of quantum computation. Butson-type Hadamard matrices are complex Hadamard matrices in which the entries are taken to be qth roots of unity. The term complex Hadamard matrix has been used by some authors to refer specifically to the case q = 4.

Practical applications

 * Olivia MFSK – an amateur-radio digital protocol designed to work in difficult (low signal-to-noise ratio plus multipath propagation) conditions on shortwave bands.
 * Balanced repeated replication (BRR) – a technique used by statisticians to estimate the variance of a statistical estimator.
 * Coded aperture spectrometry – an instrument for measuring the spectrum of light. The mask element used in coded aperture spectrometers is often a variant of a Hadamard matrix.
 * Feedback delay networks – Digital reverberation devices which use Hadamard matrices to blend sample values
 * Plackett–Burman design of experiments for investigating the dependence of some measured quantity on a number of independent variables.
 * Robust parameter designs for investigating noise factor impacts on responses
 * Compressed sensing for signal processing and under-determined linear systems (inverse problems)
 * Quantum Hadamard gate for quantum computing and the Hadamard transform for quantum algorithms.

title: Hadamard matrix


text:
Wikipedia talk:Recent additions 4

I quite like this "Did you know ?" thing. But I guess this page is just to archive things from new articles. Perhaps we should have 'Did you know' thing for old articles.

SEE: MediaWiki talk:Dyk for main DYK talk.
This is odd. Thinking that Did You Know was to feature new articles, I see an article mentioned that I know are not new articles -- Deluge, which has been on Wikipedia for quite few months. So I go looking for some sign of who, where & why this article was included, & come to this page. Hmm, nothing here; well, there's a link above to the "main DYK talk", so I follow it, only to come to a list of rules for being included on Did You Know, one of which is "this section is only for items that have been listed on 'NEW PAGES' since the last update of DYK."

So admittedly this article shouldn't have been included, but I'm still in the dark about who, where & why these articles are selected. I guess it's all the work of the Wikipedian branch of the Illuminati, those all-knowing, all-powerful powers behind every throne & every important event. I guess the only way I have to talk to them is to write a message or two into a file on my harddrive, & delete it, & they will then contact me. -- llywrch 01:02, 21 Apr 2004 (UTC)

title: Wikipedia talk:Recent additions 4


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Jannah

In Islam, Jannah (جَنَّةٍ, pl. جَنّٰت jannāt, lit. 'paradise' or 'garden') is the final abode of the righteous. According to one count, the word appears 147 times in the Qur'an. Belief in the afterlife is one of the six articles of faith in Sunni and Twelver Shi'ism and is a place in which "believers" (Mumin) will enjoy pleasure, while the unbelievers (Kafir) will suffer in Jahannam. Both Jannah and Jahannam are believed to have several levels. In the case of Jannah, the higher levels are more desirable, and in the case of Jahannam, the lower levels have a higher level of punishments. — in Jannah the higher the prestige and pleasure, in Jahannam the severity of the suffering. The afterlife experiences are described as physical, psychic and spiritual.

Jannah is described with physical pleasures such as gardens, beautiful houris, wine that has no aftereffects, and "divine pleasure". Their reward of pleasure will vary according to the righteousness of the person. The characteristics of Jannah often have direct parallels with those of Jahannam. The pleasure and delights of Jannah described in the Qu'ran, are matched by the excruciating pain and horror of Jahannam.

Jannah is also referred to as the abode of Adam and Eve before their expulsion. Most Muslims hold that Jannah and Jahannam co-exist with the temporal world, rather than being created after Judgement Day. Humans may not pass the boundaries to the afterlife, but it may interact with the temporal world of humans.

Terminology
Jannah is found frequently in the Qur'an (2:30, 78:12) and often translated as "Heaven" in the sense of an abode in which believers are rewarded in afterlife. Another word, سماء samāʾ (usually pl. samāwāt) is also found frequently in the Quran and translated as "heaven" but in the sense of the sky above or the celestial sphere. (It is often used in the phrase as-samawat wal-ard ٱلسَّمَٰوَٰتِ وَٱلۡأَرۡضِ "the heavens and the earth", an example being Qu'ran 38:10.) The Qu'ran describes both samāʾ and jannah as being above this world.

Jannah is also frequently translated as "paradise", but another term with a more direct connection to that term is also found, Firdaus (Arabic: فردوس), the literal term meaning paradise, which was borrowed from the Persian word Pardis, which is also the source of the English word "paradise". Firdaus is used in Qu'ran 18:107 and 23:11 and also designates the highest level of heaven.

In contrast to Jannah, the words Jahannam, an-Nār, jaheem, saqar, and other terms are used to refer to the concept of hell. There are many Arabic words for both Heaven and Hell that also appear in the Qu'ran and in the Hadith. Most of them have become part of Islamic beliefs.

Jannah is also used as the name of the Garden of Eden in which Adam and Hawa (Eve) dwelt.

Salvation/inhabitants

Scholars do not all agree on who will end up in Jannah, and the criteria for whether or not they will. Issues include whether all Muslims, even those who've committed major sins, will end up in Jannah; whether any non-Muslims will go there or all go to Jahannam.

Inhabitants according to Quran
The Quran specifies the qualities for those allowed to inhabit Jannah (according to Smith and Haddad) as: "those who refrain from doing evil, keep their duty, have faith in God's revelations, do good works, are truthful, penitent, heedful, and contrite of heart, those who feed the needy and orphans and who are prisoners for God's sake." Another source (Sebastian Günther and Todd Lawson) gives as the basic criterion for salvation in the afterlife more detail on articles of faith: the belief in the oneness of God (tawḥīd), angels, revealed books, messengers, as well as repentance to God, and doing good deeds (amal salih). All these qualities are qualified by the doctrine that ultimately salvation can only be attained through God's judgment.

Jinn, angels, and devils
The idea that jinn as well as humans could find salvation was widely accepted, based on the Quran (Q.55:74) where the saved are promised maidens "untouched before by either men or jinn" – suggesting to classical scholars al-Suyūṭī and al-Majlisī that jinn also are provided their own kind of houri maidens in paradise. Like humans, their destiny in the hereafter depends on whether they accept God's guidance. Angels, on the other hand, because they are not subject to desire and so are not subject to temptation, work in paradise serving the "blessed" (humans and jinn) guiding them, officiating marriages, conveying messages, praising them, etc. The devils cannot return to paradise, because Islamic scripture states that their father, the fallen jinn Iblis, was banished, but never suggests that he or his offspring were forgiven or promised to return.

The eschatological destiny of these creatures is summarized in the prophetic tradition: "One kind of beings will dwell in Paradise, and they are the angels; one kind will dwell in Hell, and they are the demons; and another kind will dwell some in Paradise and some in Hell, and those are the jinn and the humans."

Salvation of non-Muslims
Muslim scholars disagree about exact criteria for salvation of Muslim and non-Muslim. Although most agree that Muslims will be finally saved – shahids (martyrs) who die in battle, are expected to enter paradise immediately after death – non-Muslims are another matter.

Muslim scholars arguing in favor of non-Muslims' being able to enter paradise cite the verse:

Those arguing against non-Muslim salvation regard this verse to have applied only until the arrival of Muhammad, after which it was abrogated by another verse:

Historically, the Ash'ari school of theology was known for having an optimistic perspective on salvation for Muslims, but a very pessimistic view of those who heard about Muhammad and his character, yet rejected him. The Maturidi school also generally agreed that even sinners among Muslims would eventually enter paradise, but its unclear whether they thought only Muslim would go to Jannah,  or if non-Muslims who understood and obeyed "God's universal law" would be saved also. The Muʿtazila school held that free will and individual accountability was necessary for Divine justice, thus rejecting the idea of intercession (Shafa'a) by Muhammad on behalf of sinners. Unlike other schools it believed Jannah and Jahannam would be created only after Judgement Day. Like most Sunni, Shia Islam hold that all Muslims will eventually go to Jannah, and like the Ash'ari school, believe heedless and stubborn unbelievers will go to hell, while those ignorant of the truth of Islam but "truthful to their own religion", will not. Modernist scholars Muhammad Abduh and Rashid Rida rejected the notion that the People of the Book are excluded from Jannah, referring to another verse.
 * ˹Divine grace is˺ neither by your wishes nor those of the People of the Book! Whoever commits evil will be rewarded accordingly, and they will find no protector or helper besides Allah. But those who do good—whether male or female—and have faith will enter Paradise and will never be wronged ˹even as much as˺ the speck on a date stone. (Q.4:123–124)

Delights
Inside Jannah, the Quran says the saved "will have whatever they wish for, forever"; (Q.25:16). Other verses give more specific descriptions of the delights of paradise: 'And whoever is in awe of standing before their Lord will have two Gardens ... ˹Both will be˺ with lush branches. ... In each ˹Garden˺ will be two flowing springs. ... In each will be two types of every fruit. ... Those ˹believers˺ will recline on furnishings lined with rich brocade. And the fruit of both Gardens will hang within reach. ... In both ˹Gardens˺ will be maidens of modest gaze, who no human or jinn has ever touched before. ... Those ˹maidens˺ will be ˹as elegant˺ as rubies and coral. ... Is there any reward for goodness except goodness? ... And below these two ˹Gardens˺ will be two others. ... Both will be dark green. ... In each will be two gushing springs. ... In them are fruits, palm trees, and pomegranates. ... In all Gardens will be noble, pleasant mates ...˹They will be˺ maidens [houris] with gorgeous eyes, reserved in pavilions. .... No human or jinn has ever touched these ˹maidens˺ before. ... All ˹believers˺ will be reclining on green cushions and splendid carpets. Then which of your Lord's favours will you both deny? (Q.55:46–76, Mustafa Khattab, the Clear Quran)

Smith and Haddad summarize some of the Quranic pleasures: "Choirs of angels will sing in Arabic (the only language used in paradise), the streets will be as familiar as those of the dwellers' own countries, inhabitants will eat and drink 100 times more than earthly bodies could hold and will enjoy it 100 times more, their rooms will have thick carpets and brocade sofas, on Fridays they will go to a market to receive new clothing to enhance their beauty, they will not suffer bodily ailments or be subject to functions such as sleeping, spitting, or excreting; they will be forever young."

As the gates of Jannah are opened for the arrival of the saved into Jannah they will be greeted (Q.39:73) by angels announcing, "Peace be upon you, because ye have endured with patience; how excellent a reward is paradise!" (Q13:24).

Inside there will be neither too much heat nor bitter cold; there will be fountains (Q.88:10), abundant shade from spreading tree branches green with foliage (Q.53:14–16, also Q.36:56–57). They will be passed a cup (Q.88:10–16) full of wine "wherefrom they will get [no] aching of the head” (hangovers) [Q.56:19], and "which leads to no idle talk or sinfulness" (Q.52:23), and every meat (Q.52:22) and trees from which an unceasing supply of fruits grow (Q.36:56–57),  "that looks similar ˹but tastes different˺"; (Q.2:25) adornment with golden and pearl bracelets (Q.35:33) and green garments of fine silk and brocade (Q.18:31); attended upon by [ghulman] (Q.52:24), servant-boys (eternal youths (56:17, 76:19)) like spotless pearls (Q.52:24).

While the Quran never mentions God being in the Garden, the faithful are promised the opportunity to gaze upon His face, something the inhabitants of the Fire will be deprived of.

Inhabitants will rejoice in the company of any parents, spouses, and children who were admitted to paradise (Q52:21) —conversing and recalling the past.

"One day in paradise is considered equal to a thousand years on earth. Palaces are made from bricks of gold, silver, pearls, among other things. Traditions also note the presence of horses and camels of 'dazzling whiteness', along with other creatures. Large trees whose shades are ever deepening, mountains made of musk, between which rivers flow in valleys of pearl and ruby." While the Quran is full of "graphic" descriptions of the "physical pleasures" for the inhabitants of the Garden, it also states that the "acceptance [riḍwān] from God" felt by the inhabitants "is greater" than the pleasure of the Gardens (Q.9:72), the true beauty of paradise, the greatest of all rewards, surpassing all other joys. On the day on which God brings the elect near to his throne (‘arsh), "some faces shall be shining in contemplating their Lord".
 * Non-physical pleasures

The visit is described as Muhammad leading the men and Fatimah leading the women to approach the Throne, "which is described as a huge esplanade of musk". As "the veil of light before the Throne lifts, God appears with the radiance of the full moon, and His voice can be heard saying, 'Peace be upon you.'"

Hadith include stories of the saved being served an enormous feast where "God Himself is present to offer to His faithful ones delicacies kneaded into a kind of pancake". In another series of narratives, God personally invites the inhabitants of Jannah "to visit with Him every Friday".

 * Houri

"Perhaps no aspect of Islamic eschatology has so captured the imagination" of both "Muslims and non-Muslims" as houri (ḥūr). Men will get untouched Houri in paradise (Q55:56), virgin companions of equal age (56:35–38) and have large, beautiful eyes (37:48). Houri have occasioned "spectacular elaborations" by later Islamic eschatological writers, but also "some derision by insensitive Western observers and critics of Islam".

The Quran also states the saved "will have pure spouses," (without indicating gender) (Q2:25, Q4:57), accompanied by any children that did not go to Jahannam (Q52:21), and attended to by servant-boys with the spotless appearance similar to a protected pearls (Q52:24).

Despite the Quranic description above, Houris have been described as women who will accompany faithful Muslims in Paradise. Muslim scholars differ as to whether they refer to the believing women of this world or a separate creation, with the majority opting for the latter.

Size, geography and structure
The Qur'an describes paradise as a "great kingdom" (Q.76:20) stretching out over and above the entire world, and "lofty" (Q.69:22).

Paradise is "as vast as the heavens and the earth" (Q.3:133). There are four rivers: one each of water, milk, honey, and wine (47:15). (They were later identified as Kawthar, Kafur, Tasnim, and Salsabil.)

Despite the details given in the Quran about Jannah/Garden, "nowhere" is there found "an ordered picture of the structure" of the abode. "For the most part Islamic theology has not concerned itself with questions about the location and structure of the Garden and the Fire on the understanding that only God knows these particulars."

Layers/levels
Many sources agree that paradise has "various degrees and levels". One conservative Salafi source, quotes as evidence a sahih hadith where Muhammad reassures the mother of a martyr, "O Umm Haarithah, there are gardens in Paradise ... and your son has attained the highest Firdaws”, indicating a hierarchy of levels, but does not how many there are. On the basis of "several scriptural suggestions", scholars have created "a very detailed structure" of paradise, but there is more than one, and not all of the traditions on location of paradise and hell "are easily pictured or indeed mutually reconcilable".

For example, Qu'ran 23:17 states "We created above you seven paths [Ṭarā'iq]" from which is drawn a heaven of seven tiers (which is also "a structure familiar to Middle Eastern cosmogony since the early Babylonian days"). Another school of thought insists Jannah actually has "eight layers or realms" as the Quran gives "eight different names ... for the abode of the blessed".

Some descriptions of Jannah/the Garden indicate that the most spacious and highest part of the Garden, Firdaws, which is directly under the Throne and the place from which the four rivers of Paradise flow. Others say the uppermost portion is either the Garden of Eden or 'Iliyi and that is the second level from the top.

Another possibility is that there are four separate realms of the blessed, of which either Firdaws or Eden is the uppermost. This is based on Surah 55, which talks about two Gardens: ("As for him who fears standing before his Lord there are two Gardens [Jannatan]") [S 55:46). All descriptions following this verse are of things in pairs, (i.e. in the Arabic dual form) – two fountains flowing, fruit of every kind in pairs, beside these two other gardens with two springs (Q.55:62,66).

Still others have proposed that the seven levels suggested by the Qur'an are the seven heavens, above which is the Garden or final abode of felicity, while many see paradise as only one entity with many names. (According to one source – a member of the fatwa team at Islamweb.net – only God knows the exact number of the levels of Paradise, but reliable hadith say the number of levels of Jannah may be the same as the number of verses in the Quran, i.e. over 6000 verses.)

One version of the layered Garden conceptualization describes the highest level of heaven (al-firdaws) as being said to be so close that its inhabitants could hear the sound of God's throne above. This exclusive location is where the messengers, prophets, Imams, and martyrs (shahids) dwell. Al-Suyuti and Kitāb aḥwāl al-qiyāma each gives names to the levels that do not always coincide (see table to right).

Gates/doors
Two verses of the Quran (Qu'ran 7:40, 39:73) mention "gates" or "doors" (using the plural form) as the entrance of paradise, but say nothing about their number, names or any other characteristics. As in the case of the levels of Jannah, later sources elaborate, giving names and functions but don't agree on all details (see table to right).
 * "To those who reject Our signs and treat them with arrogance, no opening will there be of the gates of heaven ..." (Qu'ran 7:40)
 * "And those who kept their duty to their Lord (Al-Muttaqoon – the pious) will be led to Paradise in groups till when they reach it, and its gates will be opened" (Qu'ran 39:73)

In traditions, each level of the eight principal gates of Paradise is described as generally being divided into a hundred degrees guarded by angels (in some traditions Ridwan). The highest level is known as firdaws (sometimes called Eden) or Illiyin. Entrants will be greeted by angels with salutations of peace or As-Salamu Alaykum.

Jannah is accessible vertically through its gates (Qu'ran 7:40), by ladders (ma'arij) (Qu'ran 70:3), or sky-ropes (asbab). However, only select beings such as angels and prophets can enter. Iblis (Satan) and devils are kept at bay by angels who throw stars at them, whenever they try to climb back to heaven (Q.37:6–10). Notably and contrary to many Christian ideas on heaven, God (Allah) does not reside in paradise.

Rivers
A few hadith name four rivers in paradise, or coming from paradise, as: Saihan (Syr Darya), Jaihan (Amu Darya), Furat (Euphrates) and Nil (Nile). Salsabil is the name of a spring that is the source of the rivers of Rahma (mercy) and Al-Kawthar (abundance). Sidrat al-Muntaha is a Lote tree that marks the end of the seventh heaven, the boundary where no angel or human can pass. Muhammad is supposed to have taken a pomegranate from jannah, and shared it with Ali, as recorded by Nasir al-Din al-Tusi. However, some scholars, like Ghazali, reject that Muhammad took the fruit, argued he had only a vision instead.

Literal or allegorical
According to scholars Jane I. Smith, Yvonne Y. Haddad, while there are Muslims of a "philosophical or mystical" bent who interpret descriptions of heaven and hell "metaphorically", "the vast majority of believers", understand verses of the Quran on Jannah (and hellfire) "to be real and specific, anticipating them" with joy or terror, although this view "has generally not insisted that the realities of the next world will be identical with those of this world". Besides the material notion of the paradise, descriptions of it are also interpreted as allegories, whose meaning is the state of joy believers will experience in the afterlife. For some theologians, seeing God is not a question of sight, but of awareness of God's presence. Although early Sufis, such as Hallaj, took the descriptions of Paradise literal, later Sufi traditions usually stressed out the allegorical meaning.

Eternal, not temporal
While some Quranic verses suggest hellfire is eternal and some that its punishment will not necessarily be forever for Muslims who committed grave sins, verses on Jannah are less ambiguous. Eternality assured in verses about paradise such as Qu'ran 3:198, 4:57, and 57:12, which say that the righteous will be khālidūn fīhā (eternally in it), and Qu'ran 35:35, which describes the reward of dār al-maqāma [the abode of everlastingness]. Consequently, neither "theologians nor the traditionalists" have had any doubts about the eternal nature of paradise or the residence of the righteous in it.

Other characteristics
To classical scholars on the afterlife al-Suyūṭī and al-Majlisī, one of the characteristics of Jannah (like hellfire) is that events are not "frozen in one eternal moment", but form cycles of "endless repetition" and "unceasing self renewing clockwork". For example, when a fruit is plucked from a tree, a new fruit immediately appears to takes its place; when a hungry inhabitant sees a bird whose meat they would like to eat it falls already roasted into their hands, and after they are done eating, the bird "regains its form shape and flies away"; houri regain their virginity after being deflowered by one of the saved, but they also grow like fruit on trees or plants on the land and "whenever one of them is taken" by one of the saved in paradise one for his pleasure, "a new one springs forth in her place". (So too in hellfire are the skin of the damned replaced each time that they are burned off by the fire to be burned again, and drowning sinners driven back into the sea by giant snakes and scorpions whernever they reach the safety of shore.)

Garden of Eden and Paradise

Muslim scholars differ on whether the Garden of Eden (jannāt ʿadni), in which Adam and Eve (Adam and Hawwa) dwelled before being expelled by God, is the same as the afterlife abode of the righteous believers: paradise. Most scholars in the early centuries of Islamic theology and the centuries onwards thought it was and that indicated that paradise was located on earth. It was argued that when God commanded Adam to "go down" (ihbit) from the garden, that did not indicate a vertical movement (such as "falling" from a heaven above to earth), but instead was used in the same sense as Moses telling Israelites to "go down to Egypt".

However, as paradise came over the centuries to be thought of more and more as "a transcendent, otherworldy realm", the idea of it being located somewhere on earth fell out of favor. The Garden of Eden, on the other hand lacked many transcendent, otherworldy characteristics. Al-Balluti (887–966) reasoned that the Garden of Eden lacked the perfection and eternal character of a final paradise: Adam and Eve lost the primordial paradise, while the paradisiacal afterlife lasts forever; if Adam and Eve were in the otherworldly paradise, the devil (Shaiṭān) could not have entered and deceive them since there is no evil or idle talk in paradise; Adam slept in his garden, but there is no sleep in paradise.

Many adherences of the Muʿtazila, also refused to identify Adam's abode with paradise, because they argued that paradise and hell would not be created until after Day of Judgement, an idea proposed by Dirar b. Amr. Most Muslim scholars, however, assert that paradise and hell have been created already and coexists with the contemporary world, taking evidence from the Quran, Muhammad's heavenly journey, and the life in the graves.

Islamic exegesis regards Adam and Eve's expulsion from paradise not as punishment for disobedience or a result from abused free will on their part, but as part of God's wisdom (ḥikma) and plan for humanity to experience the full range of his attributes, his love, forgiveness, and his creation's power. By experiencing hardship, they better appreciate paradise and its delights. Khwaja Abdullah Ansari (1006–1088) describes Adam and Eve's expulsion as ultimately caused by God, since man has no choice but to comply to God's will. However, that does not mean that complying is not a "sin" and that humans should not blame themselves for it. That is exemplified by Adam and Eve in the Quran (Qu'ran 7:23 "Our Lord! We have wronged ourselves. If You do not forgive us and have mercy on us, we will certainly be losers".)

Comparison with Judaism
Jannah shares the name "Garden of the Righteous" with the Jewish concept of paradise. In addition, paradise in Judaism is described as a garden, much like the Garden of Eden, in which people live and walk and dance, wear garments of light and eat the fruit of the tree of life. Like the feast of Jannah, Jewish eschatology describes the Messiah holding a Seudat nissuin, called the Seudat Chiyat HaMatim, with the righteous of every nation at the end time.

Comparison with Christianity
Jesus in the Gospels uses various images for heaven that are similarly found in Jannah: feast, mansion, throne, and paradise. In Jannah, humans stay as humans, but the Book of Revelation describes that in heaven Christ "will transform our lowly bodies so that they will be like his glorious body" (Philippians 3:21). God (Allah) does not reside in paradise or heaven. However, in Christianity, the new heavens and the new earth will be where God dwells with humans.

title: Jannah


text:
Richard Ellis

Richard Ellis may refer to:

Academics

 * Richard Ellis (astronomer) (born 1950), Caltech professor and former director of Palomar Observatory
 * Richard Ellis (biologist) (1938–2024), American marine biologist, author, and illustrator
 * Richard Ellis (librarian) (1865–1928), Welsh librarian and scholar
 * Richard S. Ellis (1947–2018), American mathematician
 * Richard Ellis (paediatrician) (1902–1966), British paediatrician
 * Richard Keith Ellis (born 1949), British theoretical physicist

Politicians

 * Richard Ellis (Texas politician) (1781–1846), Texas legislator
 * Richard Ellis (MP), in 1417 and 1421, MP for Great Yarmouth
 * Richard Ellis (Massachusetts politician), 17th century representative to the Great and General Court
 * Richard Ellis (Dedham), 19th century representative to the Great and General Court

Other people

 * Richard Ellis (English cricketer) (born 1960), former English cricketer
 * Richard Ellis (New Zealand cricketer) (born 1945), New Zealand cricketer
 * Richard Ellis (journalist), British former editor of the Sunday Telegraph
 * Richard H. Ellis (1919–1989), U.S. Air Force general and former Strategic Air Command commander
 * Richard Ellis (American photographer) (born 1960), news photographer and founder of the photo agency Newsmakers
 * Richard Ellis (Maltese photographer) (1842–1924), British-Maltese photographer
 * Richard Ellis (mayor) (1820–1895), English builder, property developer, alderman, mayor, and public benefactor

Other uses

 * Richard Ellis International Limited, now part of CBRE Group, real estate company

title: Richard Ellis


text:
To Record Only Water for Ten Days

To Record Only Water for Ten Days is the third studio album by American musician John Frusciante, released in 2001 through Warner Music Group. Unlike his previous two solo albums, Niandra LaDes and Usually Just a T Shirt and Smile from the Streets You Hold, the record differs significantly in that Frusciante explores elements of electronica, synthpop and new wave.

Background
Following a month in rehab for his heroin addiction and his rejoining the Red Hot Chili Peppers, Frusciante felt deeply connected to the spiritual plane and was inspired by the many visions he had of spirits; the ideology of recording water for ten days refers to ten separate periods of time in which an album is conceived. In an interview he explained that the title comes from a symbolic picture of his body being a tape recorder that records the water for ten days as a way to take his "chemical makeup" off, in order to make a possible representation of the feelings and places he wanted to represent through music. Frusciante was encouraged to record the album by producer Jimmy Boyle who had helped him overcome his addiction. The lyrics express this theme and deal mostly with philosophical and spiritual matters as well as delving into his usual brand of psychedelia-tinged personalism.

Frusciante's main influences for this album were 1980s synthpop, post-punk and electronica bands that did their own programming, including bands such as Depeche Mode and New Order.

Recording and release
Frusciante recorded the album after kicking his addiction to heroin. As with his first two albums, Niandra Lades and Usually Just a T-Shirt and Smile from the Streets You Hold, Frusciante recorded this album at home. But while he had taken a conspicuously lo-fi approach on the earlier albums, using a 4-track cassette recorder and even a boombox, he produced To Record Only Water for Ten Days in much higher fidelity. Frusciante switched to a Yamaha MD8 – a digital 8-track recorder that used Minidisc technology – to record the raw tracks, which he later transferred to analog tape for further individual track equalization. All guitars were recorded direct-in without amplification.

Contrary to the title of the album, it took longer than ten days to record: according to Frusciante, he spent up to three days on each song.

Frusciante admitted his frustration with digital recording during the making of the album and has since felt inclined towards recording his albums with analog equipment. "When we came to mix that record, I realized how bad it sounded. After that album, I vowed that I wasn't going to record anything on digital anymore."

WMG released the album on February 13, 2001. It charted at #30 on Heatseekers. Vincent Gallo directed a video for every track on the record.

"Murderers" is featured in the "Invisible Boards" segment of the skateboarding home video Yeah Right!. The track "Remain" features on episode 18 of the hit Fox series 24.

In 2017, the Australian label Twelve Suns rereleased the album on vinyl in a limited edition of 1500 copies.

Non-album tracks
Dozens of songs were recorded for the album but left off. The following have been released in some form. Many of these tracks have been released on Frusciante's first internet album, From The Sounds Inside.

Personnel

 * John Frusciante – vocals, electric guitar, acoustic guitar, synthesizer, drum machine, producer
 * Lawrence Azerrad – design, art assistant
 * Jimmy Boyle – mixing and production
 * Vladimir Meller – mastering

title: To Record Only Water for Ten Days


text:
Bryant & Stratton College

Bryant & Stratton College (informally Bryant & Stratton or simply BSC) is a private college with campuses in New York, Ohio, Virginia, and Wisconsin, as well as an online education division. Founded in 1854, the college offers associate degree and bachelor's degree programs. The college is approved by the New York State Board of Regents and accredited by the Middle States Commission on Higher Education.

History
John Collins Bryant, Henry Beadman Bryant, and Henry Dwight Stratton were early graduates of Folsom Business College in Cleveland, Ohio, which they later purchased from the owner of the school, Ezekiel G. Folsom, who founded his school in 1848. Folsom was a former student of Platt Rogers Spencer who developed a standardized style of writing useful in business transactions before the invention of the typewriter.

Platt Spencer also played a role in the formation of Bryant & Stratton College, serving as a partner and teacher at the school which originally focused on bookkeeping and Spencerian penmanship. Bryant & Stratton College was organized in 1854 to provide practical workplace education, and was formerly known as Bryant & Stratton Business Institute.

In addition to purchasing the Cleveland school, Bryant and Stratton established a number of business schools that operated under the name of Bryant & Stratton Chain of Business Schools in most major US cities. By 1864, as many as 50 schools existed and tuition was $40 for an entire program of study. Today, there are schools across four states.

Academics
Bryant & Stratton College offers diplomas, associate degrees, and bachelor's degrees in business, technology, hospitality, human and legal services, healthcare, nursing, education, and design.

Athletics
Bryant & Stratton College offers multiple sports programs including: soccer, football, basketball, baseball, volleyball, and tennis. The school's sports team are the Bobcats.

title: Bryant & Stratton College