Irregularity Analysis

8/6/2019 Irregularity Analysis

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Acknowledgement

In the name of Allah, the most beneficent and merciful who gave me

strength and knowledge to complete this research. This research is a

part of our Thesis. I would like to express my gratitude to our Professor

Mr. A.R Toor; who gave me this opportunity to fulfill this research. I

would also like to thank all the company financial advisors and marketing

planners who helped me in my research session. They gave me many

helpful comments which helped me a lot in preparing my research.


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What is Cement?

"Cement" is a material with adhesive and cohesive properties that makes itcapable of bonding mineral fragment into a compact and rigid mass. The wordcement seems to have been derived from the middle age English cyment, and

Latin caementum. The latter word "caementum" meant rough quarried stoneor chips of marble from which a kind of mortar was made more than 2000 years

ago in Italy. During the Middle Ages term "cement" or "sement" generally was

made for a mortar. Common lime, hydraulic lime, gypsum plaster, pozzolana,natural and Portland cement are few of the material, which are used for

cementing purposes. These cementing materials may be classified into twogroups:

Non-Hydraulic:Non-hydraulic cement does not have the ability to set and harden under waterbut requires carbon dioxide from air to harden e.g. non-hydraulic lime and plaster

of Paris. Their cementing prosperity arises from the re absorption of gases thatwere expelled during their processing. Their products of hydration are not

resistant to water.

Hydraulic:

Hydraulic cement is defined as cement having the ability to set and developstrength in air or under water and which are insoluble in water after they have

set. Such cement harden even in the absence of air and form a solid product

which is stable in water and can be safely used in all structures in contact withwater. Hydraulic cement includes hydraulic limes, Portland cement (both basic

and blended), oil-well cement, white cement, colored cement, high alumna

cement, expensive cement regulated and hydrophobic cement etc.

Quarrying and crushing

The primary raw material for cement manufacture is calcium carbonate orlimestone. This is obtained from the quarry where, after the removal of

overburden, the rock is blasted, loaded into trucks and transported to thecrusher. A multistage crushing process reduces the rock to stone less than 25

mm in diameter. Most modern cement factories are located close to a source of

limestone as about 1.5 tons of limestone is needed to produce one ton of cement.

Blending and storageThe crushed rock is stored in stockpiles where, by a carefully controlled processof stacking and reclaiming across the stockpile, blending takes place and auniform quality of raw material is achieved. Systematic sampling and laboratory

testing monitor this process. The other raw materials, normally shale, iron oreand sand, are also stored in stockpiles.


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Raw milling and homogenization

Carefully measured quantities of the various raw materials are fed, via raw mill

feed silos, to mills where steel balls grind the material to a fine powder called rawmeal. Homogenizing silos are used to store the meal where it is mixed thoroughly

to ensure that the kiln feed is uniform, a prerequisite for the efficient functioning

of the kiln and for good quality clinker.

BurningThe most critical step in the manufacturing process takes place in the huge rotary

kilns. Raw meal is fed into one end of the kiln, either directly or via a preheatedsystem, and pulverized coal is burnt at the other end. The raw meal slowlycascades down the inclined kiln towards the heat and reaches a temperature of

about 1450 C in the burning zone where a process called clinkering occurs. The

nodules of clinker drop into coolers and are taken away by conveyors to theclinker storage silos. The gas leaving the kiln is cleaned by electrostatic

precipitators prior to discharge into the atmosphere.

Cement millingThe cement mills use steel balls of various sizes to grind the clinker, along with a

small quantity of gypsum to a fine powder, which is then called cement. Without


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gypsum, cement would flash set when water is added and gypsum is thereforerequired to control setting times. The finished cement is stored in silos wherefurther blending ensures consistency.

Quality assurance

Extensive sampling and testing during the manufacturing process ensures theconsistency and quality of the end product. Testing takes place at the stages ofthe manufacturing process indicated by the symbol.

Cement dispatchCement is dispatched either in bulk or packed in 50 kg bags and distributed from

the factory in rail trucks or road vehicles. The 50kg bags are either packeddirectly onto trucks or can be palletized. The pallets can be covered by a layer of

plastic to offer further protection from the elements.


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Types Of Cement:

The types of special cement now being produced can be roughly classified in the

following six categories according to the special purpose for which these havebeen designed. These are:

1. Rapid hardening cement.2. Cement resistant to chemical attack of certain soil and aggregates.3. Low heat of hydration cement.4. Better protecting cement for steel reinforcement.5. Better workability and whether resisting cement.6. Decorative cement and other special cement.

Rapid Hardening Cement:

Under this category following two cement have the desired properties of fast

development of strength viz. the Portland Rapid Hardening Cement and High

Aluminum Cement. Their specific characteristics are as follows:

Rapid Hardening Cement (Type III of A.S.T.M):

This cement has high early strength; it's equal to or better than 3 Days strength

of OPC. This is achieved by having high contents of tricalcium silicates in its

composition. It is mostly used in intended to release the framework within 24

hours or so for subsequent use in the mass production of RCC elements.

The respective 1,2,3,7 and 28 days strengths (in equivalent P.S.I figures) of this

cement under British specifications, German standard, and A.S.T.M. Japanese and

Pakistan standards for mortar cubes are as follows:

B.S.German

StandardAstm Japanese Pakistan

1 day strength - - 1800 923 -

2 days strength - 4350 - - -

3 days strength 4200 - 3500 1846 4205

7 days strength - - - 3266 5220

28 days

strength

6670 7975 - 4686 6670

The difference in strengths given above is basically due to difference in allstandards the 3 days strength is nearly 1-1/2 to 2 times of O.P.C. The

disadvantages of this cement beside its higher cost are its high heat of hydration,

which renders it unsuitable for mass concreting projects.

High Aluminum Structural Cement:


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This cement is used where very rapid setting and very high early strength are

required. This cement has strength at one day nearly equal to 28 days strength of

O.P.C. Its setting is so fast that it must be put in place within a few minutes of its

mixing. It is generally used in plugging leakage in dams etc. or putting in pile

foundations where limited time is available for setting of cement before the

seepage water build up occurs. In Pakistan it has been used in some specific

locations in terbela dam. Abroad it has been used in buildings where it was found

essential to remove the framework after one or two days.

This cement besides its high cost has the disadvantages of the high heat of

hydration and retrogression in strength in time. There have been some s tructural

failures due to miscalculation of its final strength after some years of use

especially in humid and hot atmosphere. This cement has however excellent heat

registering qualities and is therefore extensively used in Kilns, boilers and

Furnace linengings. Cement resistant to chemical attack especially of Sulphate

and Organic acids or Soil and active Silica of aggregate. In this category the

following cement can be included:

2-A Highly Sulphate Resistant Cement

2-B Moderately Sulphate Resisting Cement

2-C Portland Blast France Slag Cement.

2-D pozzolana Cement

2-E Low Alkali Cement

2-A Highly Sulphate Resisting Cement H.F.R.C

The most important and the most widely used chemical resistant cement is

H.S.R.C cement High concentration of Sulphate salts is present in seawater and in

the soil near seashores. These salts are sometimes present in soil and in the

submit water even thousands of miles away from the sea. Even Terbela Dam site

was found not free from Sulphate and H.S.R.C had to be used in foundations at

the site. The Sulphate salt severally attack concrete can start within months. This

cement has lower 3 days strength than OPC and also its capacity to protect

reinforcement steel in structures exposed to atmosphere action is lower than OPC

and hence not recommended for usual R.C.C. work in super structures.

2-B Moderately Sulphate Resisting Cement (M.S.R.C.)

This cement has been developed as a compromise Cement having the good

properties of Sulphate resistance to some extent and of good alkalinity like that

of OPC which useful for reinforcement protection and also of early strength

development better than Highly Sulphate Resisting Cement. No standard exists

for this cement in the B.S and P.S. specifications but under ASTM it is designed a s


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Type II. The three days minimum strength of OPC, H.S.R.C &H.S.R.C is 1800,

1200 and 1500 PSI respectively under ASTM.

This cement though better than H.S.R.C in many respects is not as resistant to

Sulphate as H.S.R.C and should not be used in foundations near the seashore.

Incidentally the O. P. cement produced in most of the Cement Factories around

Karachi are confirming to the ASTM specifications for this type II and hence more

resistant to mild Sulphate attack than the cement produced in the factories in

other parts of country.

2-C Portland Blast Furnace Slag Cement:

This cement has well to moderate resistance to Sulphate attack from soil. This

cement has some other very desirable qualities of stability details of which follow

below under item 3C.

2-D Pozzolana Cement:

This cement has well to moderate resistance to Sulphate attack from seawater or

soil containing Sulphate.

2-E Low Alkali Cement:

This is a variety of ordinary Portland cement in which the total alkali contents of

cement has been controlled to remain below 0.6%. With this reduced percentage

of alkali contents the danger of alakie of cement attacking the active silicacontents of aggregate is eliminated. Generally we do not have active aggregate of

this type in Pakistan but on each large scale-concreting project, test of alkali

aggregate reaction must be performed to ensure safety of the project. Certainvarieties of Chert-stone found in Pakistan contain active Silica and would require

low alkali for making concrete.

Low Heat of Hydration Cement :

Normal and Rapid Hardening Cement generate lot of heat during the setting and

hardening process so much so that the structure under concreting can crack. This

can occur especially while poring large messes of concrete in confine spaces like

those of Dam and Bridge pier foundations. In order to avoid this problem cement

of low Heat of hydration have been developed some of which are as listed below:

3-A Low Hear ofHydration Cement (type IV of A.S.T.M.)

3-B Portland blast Furnace Slag Cement

3-C Pozzolana Cement

3-D Super Sulphate Cement3-A Low Hear of Hydration Cement (type IV of A.S.T.M.):

This is cement specially meant for the concreting of structures where large

masses of concrete have to be poured at one time. Generally it is specified that

heat of hydration on 7 days will not exceed 250Kg. This is achieved by making

this cement with larger percentage of di-calcium silicates in its contents than

normally presents in OPC. In A.S.T.M this cement is designated as type IV and


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under BS as LHP. Under German standards its type is LAHORE with symbol as

N.W. while the Japanese equivalent is type L.H.P with symbol as M.H.C. The

disadvantage of this cement is its slow development of strength and is therefore

not used at sited where rapid hardening or other specific qualities are required.

3-B Slag Cement:

This is another variety of low heat cement. Grinding 35% to 65 % of granulatedblast furnace slag with ordinary Portland cement clinker produces it. The higher

the slag contents, the lower are the 3 and 7 days strengths but better are the

resistance to chemical attack. Under German standards as much as 90% slag canbe used with type HOZ cement and under Japanese standard up to 70% in the

type BSCC. This cement is slower hardening compared to OPC- its strength

compared to OPC in ASTM being as follows:

OPC B.F SLAG CEMENT

3 days strength 1,800 760

7 days strength 2,800 1,400

28 days strength 4,000 3,000

This cement besides being a low heat cement has also the advantage of being

medley Sulphate resistant although it cannot replace the highly Sulphate

resistance cement for marine piles and foundations. This cement has excellent

resistance to weak organic acids present in the soil and has also the very

desirable quality of protecting reinforcement steel better than any other cement.

3-C Pozzolana:

Grinding various proportions of natural pozzolana, tars or volcanic ash with

ordinary Portland clinker makes this cement. It is very good cement in the sensethat it has good workability properties in addition to having low heat and

moderate Sulphate resisting properties. It has been used extensively in the 37KMlong causeway connecting Dhahran with Bahrain in the gulf. So far in Pakistan we

have not been able to locate useful pozzolana deposits, but there is indication

that there may be good deposits of this material in the overburden of coaldeposits of Sindh.

3-D Super Sulphate Cement:

This is another variety of low heat cement. Its standards exist under B.S but not

under A.S.T.M. it is made by grinding about 70-80% B. F. Slag with about 10%

gypsum and 1-2 % Portland clinker or lime. This cement is also middy resistant

to Sulphate attack. It is very finely ground cement and its early strength at 3 day

is comparable to OPC although under the BS its 7 days strength is required to be

comparable to at least the 3 days strength of OPC. This cement is also good

masonry cement due to its good workability but it can be used in RCC and other

construction work in the same manner as OPC is used with excellent results.

Cement For Better Protection of Reinforcement against Corrosion:


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The basic steps for the prevention of resulting of steel in concrete is to use such

cement aggregate and mixing water as are basically free from chlorides,

maximum contents of chlorides in concrete being limited to 0.02 % by weight.

The following properties in cement are essential for greater protection of steel:

1. Cement to be with minimum percentage of Chlorides says not exceeding 0.01

percent.2. Portland Cement preferably having about 6 to 8 per cent Tricalcium Aluminates.

3. Cement made with slag as additive.

If the Tricalcium Aluminates is less than 5 per cent as per ASTM the cement will

not have the capacity to neutralize the stray Chloride entering into concrete and

thus fail toward off the effects of Chlorides? The properties of slag cement with

about 35 percent slag and 60 per cent Portland Clinker is superior to other

cement in this respect.

Cement for Better Workability and Wealth E.W. Resistance These are cement, which are render the corresponding concrete more workablethan other normal cement. This quality is necessary where high compatibility and

better weather resistance is demanded. Because of greater workability the

concrete made from this cement can achieve much higher strength due to lower

water cement ratios achievable compared with other cement.

This property is given to the cement by addition of the entraining agents like lime

or other plasticizers so that the remix and to place in position. Some of the

cement belongs to this category are:

Air Entraining Cement:

Under ASTM four different types of cement have been classified as air-entraining

version for normal Rapid-hardening and Sulphate Resisting Cement and each

concrete thus made is more workable and attains higher weather resisting

property compared to their non-air entrained versions.

Blended Hydraulic and Masonry Cement and Grouts: This cement is basically made for plastering and grouting. Standards have been

laid down for this cement both in the British and ASTM specifications. In fact

under ASTM there are at least 10 versions of Masonry cement. Some of the

standards are for OPC based cement with or without air entraining agents while

others are for Sulphate resistance and low heat versions. This masonry cement is

made by addition of plasticizing materials like lime, ground silica, slag or

Pozzolana and air-entraining agents etc. Portland Cement clinkers during

grinding.

Decorative Cement Oil Well and other Special Purpose Cement:


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This cement is basically of properties similar to O.P.C except that it is made from

such raw materials, which contain the least amounts of coloring pigments like

traces of iron, manganese and chrome. Basically this cement has higher

Tricalcium Aluminates in its contents than OPC and therefore subjects to sharp

attack by Sulphate from any source.

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Irregularity Analysis

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