تحقیق و بررسی در مورد سیمان 17 ص

اختصاصی از حامی فایل تحقیق و بررسی در مورد سیمان 17 ص دانلود با لینک مستقیم و پر سرعت .

لینک دانلود و خرید پایین توضیحات

فرمت فایل word  و قابل ویرایش و پرینت

تعداد صفحات: 16

سیمانهای نوع IP , IS,I‌ و P I(PM) II , و III با مواد هوا زا نیز که با علامت A مشخص می شود ، ساخته می شوند.

جدول (2 ـ 8 ) مقادیر متوسط ترکیبات سیمانهای پرتلند

سیمان

ترکیبات سیمان ، درصد

C3S

C2S

C3A

C4AF

CaSO4

CaO آزاد

MgO

پس ماند نامحلول

نوع I

59

15

12

8

9/2

8/0

4/2

2/1

نوع II

46

29

6

12

9/2

6/.

2

1

نوع III

60

12

12

8

9/3

3/1

6/2

9/1

نوع IV

20

46

5

12

9/2

3/0

7/2

1

نوع V

43

36

4

12

7/2

4/0

6/1

1

مقادیر حداکثر و حداقل در جدول فوق بر اساس دستورالعمل ASTM C150-84

شکل (2 ـ 4 ) روند افزایش مقاومت بتن های ساخته شده با 335 کیلوگرم از سیمانهای مختلف در متر مکعب بتن ،

سیمان پرتلند معمولی (تیپ I ) ، سیمان اصلاح شده (نوع II ) ، سیمان زود سخت شونده (نوع III ) ، سیمان با حرارت زایی کم ( نوع IV ) و سیمان ضد سولفات (نوع V )

تقسیم بندی سیمانها به تیپ های مختلف به این معنی نیست که سیمان های قرار گرفته در یک نوع خاص با یکدیگر متفاوت نیستند. بعلاوه خواص بعضی سیمانها به گونه أی است که می توان آنها را در چند نوع طبقه بندی نمود. یک نوع سیمان ممکن است خاصیت خواسته شده أی را برآورد نماید ، لیکن از نقطه نظرهای دیگر مسائلی را ایجاد کند. به این دلیل باید تعادلی بین خواص درخواستی بوجود آورده و بعلاوه ملاحظات اقتصادی را نیز منظور داشت.

سیمان نوع 2 مثالی است از سیمانی که این تعادل در آن رعایت شده است . امروزه روش ساخت سیمان پیشرفت زیادی نموده است و سعی می شود با توسعه بیشتر آن سیمانهای مختلف با خواص خواسته شده و مطابق با استاندارد تهیه شود .

سیمان پرتلند معمولی (نوع 1)

این نوع سیمان معمولترین سیمانی است که در همة موارد به غیر از مواردی که بتن در معرض سولفات موجود در خاک یا آب قرار می گیرد ، بکار می رود . استاندارد B S12 : 1978 ضریب اشباع آهک را برای این نوع سیمان بین 66/0 و 02/1 محدود می کند . این ضریب بر اساس فرمول زیر که عبارات داخل پرانتزها درصد وزنی اکسیدهای تشکیل دهنده سیمان هستند ، قابل محاسبه می باشد .

آهک آزاد اضافی سلامت سیمان را به مخاطره می اندازد ، لذا باید محدود گردد . اگرچه در استاندارد ASTM C150-84 محدودیت خاصی برای آهک توصیه نشده است و لیکن مقدار آهک آزاد معمولاً کمتر از 5/0 درصد می باشد .

سایر مشخصات استاندارد در زیر خلاصه می شود .

BS 12:1978

ASTM C 150-84

مقدار اکسید منیزیم

% 4 >

% 6 >

پس ماند نامحلول

% 5/1 >

%75/0 >

افت سرخ شدن

% 2 >

% 3 >

مقدار گچ ( بصورت So3 ) وقتی که درصد C3A :

% 5 >

% 5/2

-

% 5 >

% 3

-

% 8 >

-

% 3

% 8 >

-

% 5/3

طی سالها تولید سیمان نوع 1 ، تغییراتی در مشخصات آن پدید آمده است . در مقایسه با 40 سال قبل سیمانهای جدید C3S و ریزی بالاتری را دارا می باشند . استاندارد B S 12:1978 حداقل سطح مخصوص 225 m2/kg را مشخص می کند . در نتیجه مقاومت فشاری 28 روزه سیمانهای جدید بیشتر بوده ولی افزایش مقاومت دراز مدت آنها کمتر است . نتیجة عملی این تغییرات این است که باید انتظار مقاومت بیشتر با زمان را در سیمانهای جدید تا حدی تقلیل داد . این نکته مهمی است که باید در نظر داشت بخصوص که امروزه مقاومت 28 روزه معمولاً اساس سنجش قرار می گیرد .

سیمان پرتلند نوع 1 معمولترین سیمانی است که دارای مرغوبیت بالایی است و امروزه در مقیاس وسیعی در جهان مصرف قرار دارد .

سیمان پرتلند زود سخت شونده ( نوع 3 )

همانطوریکه از نام سیمان پیداست مقاومت این سیمان به سرعت افزایش می یابد . (جدول 2-8 را ببینید) این خاصیت به علت درصد بالای C3S در این سیمان ( تقریباً 70 درصد ) و ریزی بالا ( حداقل 225 m2/kg ) می باشد . البته در سالهای اخیر وجه تمایز این سیمان با سیمان نوع 1 در ریزی بالای این سیمان است و اختلاف مابین ترکیبات شیمیایی آنها ناچیز است .

استفاده اساسی از این سیمان موقعی است که قالبها باید برای بتن ریزی مجدد سریعاً بازشوند و یا زمانی که برای پیشرفت سریعتر کار ساختمان به مقاومت زودرس نیاز می باشد . این سیمان به علت ایجاد حرارت خیلی بالا نبایستی در بتن ریزی های حجیم و یا در قطعات بزرگ بتنی بکار رود . اما از طرف دیگر در بتن ریزی در هوای سرد بعلت حرارت بالا این سیمان می تواند از یخ زدگی سریع جلوگیری نماید . زمان گیرش سیمانهای نوع 1 و نوع 3 تقریباً یکسان است . قیمت تمام شده سیمان نوع 3 کمی بیش از سیمان پرتلند نوع 1 می باشد .

سیمان پرتلند زود سخت شوندة مخصوص

این سیمان که مقاومت بالایی در زمانی کوتاه ایجاد می کند ، برای کارهای خاص و بر اساس سفارش مخصوص ساخته می شود . مقاومت زودرس بالا توسط ریزی ( 700 تا 900 متر مربع بر کیلوگرم ) و گچ بالاتر تامین می گردد . استفاده خاص این سیمان در قطعات پیش تنیده و در تعمیرات فوری بتن های خراب می باشد .

در پاره ای از کشورها سیمانی با گیرش تنظیم شده از مخلوطی از سیمان پرتلند ، فلوئور و آلومینات کلسیم با یک کند گیر کننده مناسب (معمولاً اسید سیتریک ) ساخته می شود. زمان گیرش (1 تا 20 دقیقه ) توسط مواد خام تشکیل دهنده و آسیاب و پختن آنها کنترل می گردد. در حال که مقاومت زود رس اولیه با مقدار فلوئور و آلومینات کلسیم کنترل می گردد. این سیمان قابل منبسط شدن می باشد ولی ارزش آن موقعی است که مقاومت بالایی در زمانی کوتاه مورد نیاز می باشد.

شکل (2 ـ 5 ) ـ افزایش حرارت هیدراتاسیون سیمانهای پرتلند نگهداری شده در C ْ21 (نسبت آب به سیمان 4/0 می باشد).

سیمان

سیمان پرتلند با حرارت زایی کم (نوع 4 )

این سیمان که نخستین بار جهت مصرف در سدهای وزنی عظیم ساخته شد ، در واکنش با آب حرارت کمی تولید می کند. هر دو استاندارد ASTM C150 – 84 و BS1370:1979 حرارت هیدراتاسیون را به j/g 250 ( cal/g 60 ) پس از 7 روز و به j/g 290 ( cal/g 70 ) بعد از 28 روز محدود می کنند.

بر اساس استاندارد BS1370 محدودیت ضریب اشباع آهک بین 66/0 تا 08/1 بوده و به علت درصد کمتر ترکیبات C3S و C3A در این سیمان ، آهک افزایش مقاومت این سیمان کندتر ازسیمان پرتلند معمولی است لیکن مقاومت نهائی بی اثر باقی می ماند. میزان ریزی این سیمان نبایستی از m 2/kg 320 کمتر باشد تا بدینوسیله افزایش مقاومت لازم تأمین گردد.

تحقیق و بررسی در مورد ورزس و بیماریهای مفصلی

اختصاصی از حامی فایل تحقیق و بررسی در مورد ورزس و بیماریهای مفصلی دانلود با لینک مستقیم و پر سرعت .

لینک دانلود و خرید پایین توضیحات

فرمت فایل word  و قابل ویرایش و پرینت

تعداد صفحات: 2

What is pelvic arthropathy?The joints of the pelvis can cause pain during pregnancy. The diagnosis is not hard to make when you are aware of the existence of this condition and its symptoms. Pelvic arthropathy causes such pain that movement is limited and the ability to walk is impaired.

A woman with pelvic arthropathy will feel pain mostly around her pubic area spreading out to the groin and the front and back of the thighs.

Some kinds of movement, such as lying on her back and trying to turn onto her side, worsens the pain. When she walks, her steps will get shorter until she is almost waddling. Walking up and down stairs is especially difficult.

Some degree of pelvic joint pain affects most women in the later stages of pregnancy but the discomfort for a small group of women is often underestimated. For these women, pelvic arthropathy might develop early in pregnancy and last well after delivery.

What causes pelvic arthropathy?The pelvis is made up of several bones that are jointed in a way that usually does not allow any movement. Under the influence of hormones produced in pregnancy, the cartilage of the joints becomes softer and allows the bones to move. It is this movement and displacement of the bones that causes the pain. In addition, the weight of the growing uterus and baby causes a shift in the pregnant woman's centre of gravity. This often causes lower backache.

What can be done about pelvic arthropathy?If a woman experiences the kinds of pain described above, she should consult her doctor or midwife. Pain relief is often appropriate but the best source of advice and support will be from a specially trained physiotherapist (obstetric physiotherapist).

The physiotherapist will explain the condition and offer advice about certain exercises and postures that should be adopted and others that should be avoided.

Occasionally, a support garment such as a corset can be helpful and walking sticks are sometimes necessary. You may be advised regarding the most appropriate position in which to give birth.

What happens after the birth?If pelvic arthropathy is diagnosed and treated correctly the chances of a successful delivery and an easier time afterwards are increased. The discomfort does not disappear immediately after delivery but a gradual improvement over the first few weeks can be expected.

It is impossible to predict whether a woman will be troubled to the same degree in any future pregnancies or not

Sport & Physical Activity

Portsmouth boasts a wide range of sporting activities from Aikido to Yachting. There are many providers, including voluntary sports clubs, private fitness centres and public sector facilities.

Portsmouth City Council aims to encourage participation in sports and physical activity by:

Promoting Sport in Education

Developing the quality of sport in and out of the curriculum, providing sport facilities on schools sites and promoting sport and physical activity as part of a healthy lifestyle.

Developing Community through Sport

Using sport to promote community involvement and regeneration, offer lifelong learning via coach education programmes and to raise the profile of the City.

Promoting Sport in the Community

Providing an accessible, affordable and inclusive network of community sports facilities, developing grass roots sport and volunteering opportunities and supporting talented sports people.

Please scroll down the page for opportunities in Portsmouth.

For information on facilities or venues, please click on Facilities & Venues link

دانلود تحقیق کامل درباره ورزس و بیماریهای مفصلی

اختصاصی از حامی فایل دانلود تحقیق کامل درباره ورزس و بیماریهای مفصلی دانلود با لینک مستقیم و پر سرعت .

لینک دانلود و خرید پایین توضیحات

فرمت فایل word  و قابل ویرایش و پرینت

تعداد صفحات: 2

What is pelvic arthropathy?The joints of the pelvis can cause pain during pregnancy. The diagnosis is not hard to make when you are aware of the existence of this condition and its symptoms. Pelvic arthropathy causes such pain that movement is limited and the ability to walk is impaired.

A woman with pelvic arthropathy will feel pain mostly around her pubic area spreading out to the groin and the front and back of the thighs.

Some kinds of movement, such as lying on her back and trying to turn onto her side, worsens the pain. When she walks, her steps will get shorter until she is almost waddling. Walking up and down stairs is especially difficult.

Some degree of pelvic joint pain affects most women in the later stages of pregnancy but the discomfort for a small group of women is often underestimated. For these women, pelvic arthropathy might develop early in pregnancy and last well after delivery.

What causes pelvic arthropathy?The pelvis is made up of several bones that are jointed in a way that usually does not allow any movement. Under the influence of hormones produced in pregnancy, the cartilage of the joints becomes softer and allows the bones to move. It is this movement and displacement of the bones that causes the pain. In addition, the weight of the growing uterus and baby causes a shift in the pregnant woman's centre of gravity. This often causes lower backache.

What can be done about pelvic arthropathy?If a woman experiences the kinds of pain described above, she should consult her doctor or midwife. Pain relief is often appropriate but the best source of advice and support will be from a specially trained physiotherapist (obstetric physiotherapist).

The physiotherapist will explain the condition and offer advice about certain exercises and postures that should be adopted and others that should be avoided.

Occasionally, a support garment such as a corset can be helpful and walking sticks are sometimes necessary. You may be advised regarding the most appropriate position in which to give birth.

What happens after the birth?If pelvic arthropathy is diagnosed and treated correctly the chances of a successful delivery and an easier time afterwards are increased. The discomfort does not disappear immediately after delivery but a gradual improvement over the first few weeks can be expected.

It is impossible to predict whether a woman will be troubled to the same degree in any future pregnancies or not

Sport & Physical Activity

Portsmouth boasts a wide range of sporting activities from Aikido to Yachting. There are many providers, including voluntary sports clubs, private fitness centres and public sector facilities.

Portsmouth City Council aims to encourage participation in sports and physical activity by:

Promoting Sport in Education

Developing the quality of sport in and out of the curriculum, providing sport facilities on schools sites and promoting sport and physical activity as part of a healthy lifestyle.

Developing Community through Sport

Using sport to promote community involvement and regeneration, offer lifelong learning via coach education programmes and to raise the profile of the City.

Promoting Sport in the Community

Providing an accessible, affordable and inclusive network of community sports facilities, developing grass roots sport and volunteering opportunities and supporting talented sports people.

Please scroll down the page for opportunities in Portsmouth.

For information on facilities or venues, please click on Facilities & Venues link

دانلودتحقیق درمورد بیماری قلبی 3

اختصاصی از حامی فایل دانلودتحقیق درمورد بیماری قلبی 3 دانلود با لینک مستقیم و پر سرعت .

لینک دانلود و خرید پایین توضیحات

فرمت فایل word  و قابل ویرایش و پرینت

تعداد صفحات: 5

A heart attack is when low blood flow causes the heart to starve for oxygen. Heart muscle dies or becomes permanently damaged. Your doctor calls this a myocardial infarction

Causes

Most heart attacks are caused by a blood clot that blocks one of the coronary arteries. The coronary arteries bring blood and oxygen to the heart. If the blood flow is blocked, the heart starves for oxygen and heart cells die.

A clot most often forms in a coronary artery that has become narrow because of the build-up of a substance called plaque along the artery walls. (See: atherosclerosis) Sometimes, the plaque cracks and triggers a blood clot to form.

Occasionally, sudden overwhelming stress can trigger a heart attack.

It is difficult to estimate exactly how common heart attacks are because as many as 200,000 to 300,000 people in the United States die each year before medical help is sought. It is estimated that approximately 1 million patients visit the hospital each year with a heart attack. About 1 out of every 5 deaths are due to a heart attack.

Risk factors for heart attack and coronary artery disease include:

Bad genes (hereditary factors)

Being male

Diabetes

Getting older

High blood pressure

Smoking

Too much fat in your diet

Unhealthy cholesterol levels, especially high LDL ("bad") cholesterol and low HDL ("good") cholesterol

Higher-than-normal levels of homocysteine, C-reactive protein, and fibrinogen may also increase your risk for a heart attack. Homocysteine is an amino acid. C-reactive protein and fibrinogen are linked to inflammation. Fibrinogen is also involved in blood clotting

Angina is the primary symptom of coronary artery disease and, in severe cases, of a heart attack. It is typically experienced as chest pain and occurs when the heart muscle does not get as much blood (hence as much oxygen) as it needs for a given level of work (ischemia). Angina is usually referred to as one of two states:

Stable Angina (which is predictable)

Unstable Angina (which is less predictable and a sign of a more serious situation)

Click the icon to see an image about angina.

The intensity of the pain does not always relate to the severity of the medical problem. Some people may feel a crushing pain from mild ischemia, while others might experience only mild discomfort from severe ischemia.

Angina itself is not a disease. Much evidence indicates that onset of angina less than 48 hours before a heart attack may be protective, possibly by conditioning the heart to resist the damage resulting from the attack. Angina may be experienced in different ways and can be mild, moderate, or severe.

Stable Angina and Chest Pain

Stable Angina. Stable angina is predictable chest pain. Although less serious than unstable angina, it can be extremely painful or uncomfortable. It is usually relieved by rest and responds well to medical treatment (typically nitroglycerin). Any event that increases oxygen demand can cause an angina attack. Some typical triggers include:

Exercise

Cold weather

Emotional tension

Large meals

Angina attacks can occur at any time during the day, but most occur between 6 a.m. and noon.

Specific symptoms that are more likely to indicate angina include:

Angina pain or discomfort is typically described by patients as fullness or tingling, squeezing, pressure, heavy, suffocating, or griplike. It is rarely described as stabbing or burning. Changing one's position or breathing in and out does not affect the pain.

A typical angina attack lasts minutes. If it is more fleeting or lasts for hours, it is probably not angina.

Pain is usually in the chest under the breast bone. It often radiates to the neck, jaw, or left shoulder and arm. Less commonly, patients report symptoms that radiate to the right arm or back, or even to the upper abdomen.

Stable angina is usually relieved by rest or by taking nitroglycerine under the tongue.

Other symptoms that may indicate angina or accompany the pain or pressure in the chest include:

Shortness of breath

Nausea, vomiting, and cold sweats

A feeling of indigestion or heartburn

Unexplained fatigue after activity (more common in women)

Dizziness or lightheadedness

Palpitations

Unstable Angina and Symptoms of Possible Heart Attack

Unstable angina is a much more serious situation and is often an intermediate stage between stable angina and a heart attack, in which an artery leading to the heart (a coronary artery) becomes completely blocked. A patient is usually diagnosed with unstable angina under one or more of the following conditions:

Pain awakens a patient or occurs during rest.

A patient who has never experienced angina has severe or moderate pain during mild exertion (walking two level blocks or climbing one flight of stairs).

Stable angina has progressed in severity and frequency within a 2-month period, and medications are less effective in relieving its pain.

Fainting episode.

Unstable angina is now usually discussed as part of a condition called acute coronary syndrome (ACS). ACS also includes people with a condition called NSTEMI (non ST-segment elevation myocardial infarction) -- also referred to as non-Q wave heart attack. With NSTEMI, blood tests suggest a developing heart attack. These conditions are less severe than heart attacks but may develop into full-blown attacks without aggressive treatment. <!--[For more information, see In-Depth Report #12: Heart attack and acute coronary syndrome.]-->

Doctors use a number of factors to help predict which patients with unstable angina or acute coronary syndrome are most at risk for developing a heart attack.

First, patients are categorized by whether they have a history of heart disease or risk factors for heart disease (such as diabetes, high blood pressure, and peripheral artery disease) or other complicating conditions (such as lung disease and heart failure). The doctor also evaluates the severity of the angina. Other factors that pose a high risk for ACS include:

Age 65 years or older

Evidence of severe heart tissue injury

A history of severe chronic angina

Abnormal lung sounds called rales (a bubbling or crackling sound) on examination

ST-segment deviation on the electrocardiogram

Either very slow or very fast heat beats

Very low blood pressure

Heart Attack. A full-blown heart attack occurs with severe damage to the heart, which blocks oxygen.

People with known heart disease and any unusual chest pain or other symptoms described above that do not clear up with medications should call 911. The degree of pain and the specific symptoms before a heart attack vary greatly among individuals. Symptoms can be abrupt, gradual, or intermittent. Some studies suggest that nearly half of patients with heart attack do not have chest pain as the primary symptom. Patients most likely to have atypical symptoms are women and the very elderly (although they can certainly have classic heart attack symptoms as well).

Symptoms That Are Less Likely to Indicate Angina or a Heart Attack. The following symptoms are less likely to be due to coronary artery disease:

Sharp pain brought on by breathing in and or when coughing

Pain that is mainly or only in the middle or lower abdomen

Pain that can be pinpointed with the top of one finger

Pain that can be reproduced by moving or pressing on the chest wall or arms

Pain that is constant and lasts for hours (although no one should wait hours if they suspect they are having a heart attack)

Pain that is very brief and lasts for a few seconds

Pain that spreads to the legs

However, the presence of these symptoms does not always rule out a serious heart event.

Other Types of Angina

Prinzmetal's Angina. A third type of angina, called variant or Prinzmetal's angina, is caused by a spasm of a coronary artery. It almost always occurs when the patient is at rest. About two-thirds of people with it have severe atherosclerosis in at least one major blood vessel. Irregular heartbeats are common, but the pain is generally relieved immediately with standard treatment.

Silent Ischemia. Some people with severe coronary artery disease do not have angina pain. This condition is known as silent ischemia, which some experts attribute to the brain abnormally processing of heart pain. This is a dangerous condition because patients have no warning signs of heart disease. Some studies suggest that people with silent ischemia experience higher complication and mortality rates than those with angina pain.

Syndrome X. Syndrome X is a condition that occurs when patients have atypical angina chest pain. Their electrocardiograms are abnormal during a stress test, but they have no signs of blocked arteries. It is more likely to occur in women. Although it is unclear what causes this condition, imaging tests suggest that Syndrome X may also be caused by ischemia, as is angina.

Other Causes of Chest Pain or Discomfort

Chest pain is a very common symptom in the emergency room, but heart problems account for only 10 - 33% of all episodes.