Chapter 1 Cement Civil Engineering Material

hapter 1: Cement C hapter 1st Ed, Civil Engineering Materials

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hapter 1 C hapter 1 CEMENT Types of Cement 1.1. 1.1. Chem Chemic ical al Comp Compos osit itio ion n 1.2. Testing of Cement 1.3. Manufacturing of Cement 1.4. 1.4. Meth Method od of Cem Cemen entt Storin Storing g

Ceme Cement nt is a manu manufa fact ctur ured ed cons constr truc ucti tion on mate materi rial al and and wide widely ly used used for for structural constructions such as buildings, bridges, tunnels, dams, factories, pave paveme ment nt and and etc. etc. It is an inst instan antt glue glue and and capa capabl ble e to bond bond mine minera rall fragments into compact whole. There are variety type of cements can be found found in the mare maret. t. !ach !ach type type is manufa manufactu ctured red under under certai certain n conditi condition on depending on its special properties. "owever today, #ortland cement is the most commonly used as mortar and and concrete in concrete in structural construction. Mortar: % mi(ture of cement, fine aggregates aggregates or sand sand and water to form a paste Concrete: % mi(ture of cement, sand, sand, coarse aggregates aggregates and water under certain ratio

#ortland cement was patented by $oseph %spdin in 1&'4 and was named after the limestone cliffs on the Isle of #ortland in !ngland. Types of Cement Cement Cement is manufactured manufactured with two basic raw ingredient ingredients s called called calcareous and and an argillaceous argillaceous material. The cement in maing of concrete has the prop prope erty rty of setting setting an and hardening unde underr wate waterr by virtu virtue e of chem chemic ical al reaction with it and this type of cement is called hydraulic cement. 1.1

Calcareous: The calcareous material is a calcium o(ide, such as limestone, chal, or oyster shells. Argillaceous: %rgillaceous %rgillaceous is a combination of silica and alumina that can be found from clay, shale, and blast furnace slag.

Prepared by: Ahmad Fahmy Kamarudin, January 2010

C hapter 1: Cement 1st Ed, Civil Engineering Materials

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"etting Time Setting refers to the stiffening of the cement paste or the change from a plastic state to a solid state. The setting time refers to changes of the cement paste from fluid to rigid. Setting is usually described in two levels namely, initial setting and final setting. #nitial "etting Initial setting is defined as the beginning of the noticeable stiffening in the cement paste and its corresponding to the rapid rise temperature. This normally taes about 42 3 12 minutes. $inal "etting Time This refers to completion of setting which correspond to the pea temperature in the cement paste. The stiffening of cement paste increase as the volume of the gel increases and the stage at which this is completed, the final hardening process begins. It normally taes between + to 15 hours for this to happen. !ardening This is referred to the gained of the strength of the cement paste. %ctually during the setting time, the cement gained very little strength.

)ifferent concrete applications re*uire cements with different properties. Some applications re*uire rapid strength gain to e(pedite the construction and other applications re*uire low heat hydration to control volume change and associated shrinage cracing. "ence, each type of cement is manufactured by altering the ratios of four basic compounds namely Tricalcium Silicate, )icalcium Silicate, Tricalcium %luminate and Tetracalcium %luminoferitte to fit the applications. Table 1.1:

Main compound of Portland cement

Name of Compound

Usual Abbreviation

eaction

Tricalcium Silicate )icalcium Silicate Tricalcium %luminate Tetracalcium %luminoferitte

C+S C'S C+ % C4 %

-uic Slow ery *uic /ot very important

Cements can be classified into two categories namely hydraulic cement and high alumina cement. 1.1.1 !ydraulic Cement "ydraulic cement is consists of silicates and aluminates of lime. This type of cement can be classified as0



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a. Natural Cement /atural cements are powders obtained from certain natural rocs 6clayey lime stone type7 which are *uarried, crushed and processes. !nough heat is re*uired to dry off carbonic acid gasses. 8esides, it is brown in colour and sets slowly or *uicly when mi(ed with water, depending on the amount of clay in the limestone. The strength is low and not used for concrete wor. b. Aluminous Cement The chief ingredients of aluminous cement are calcareous and aluminious materials 6limestone or chal and bau(ite7. These are heated to a temperature of 1455oC and the whole mass is grinded to powder form. c. Portland Cement The hardening of #ortland cement is a chemical process during which heat is evolved. Modified forms of #ortland based on different ratio of four main compositions are made, to suit the varying demands of different inds of structural application. Table 1.%:

Classification of Portland cements

Name

Application

/ormal

9eneral concrete wor when the special properties of other types are not needed. Suitable for floors, reinforced concrete structures, pavements, etc.

Moderate Sulfate :esistance

#rotection against moderate sulfate e(posure, 5.1; 5.'< weight water soluble sulfate in soil or 125; 1255ppm sulfate in water 6sea water7. Can be specified with moderate heat of hydration, maing it suitable for large piers, heavy abutments, and retaining walls. The moderate heat of hydration is also beneficial when placing concrete in warm weather.

"igh !arly of "ydration

=sed for fast;tract construction when forms need to be removed as soon as possible or structure need to be put in service as soon of possible. In cold weather, reduces time re*uired for controlled curing.

>ow "eat of "ydration

=sed when mass of structure, such as large dams, re*uires careful control of heat of hydration.

"igh Sulfate :esistance

#rotection from severe sulfate e(posure, 5.';'.5< weight water soluble sulfate in soils or 1255;15,&55 ppm sulfate in water



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@hat is cement hydration

"ydration is chemical reaction between cement particles and water. The features of this reaction are the change in matter, the change in energy level, and the rate of reaction. !(ampleA Tricalcium silicate + Water hydroxide

 Calcium

silicate hydrates (C-S-H) + Calcium

C;S;" maes the hydrated cement paste strong and calcium hydro(ide is susceptible to attac by sulfate and acidic water

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'rdinary Portland Cement ( 'PC ) *" 1% : 1+,1& ?#C has a medium rate of hardening and is suitable for most type of wor. It is the one most commonly used for structural purposes when the special properties specified for other four types of cement are not re*uired.

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apid !ardening Portland Cement ( !PC )*" 1% : 1+,1& :"#C hardens rather more rapidly than ?#C. It is similar in chemical composition to ?#C but the proportions of the various compounds may be slightly different, and it is finely ground. )ue to its finer grinding, it will increase the rate of hydration at early ages, and this leads to the increased rate of early hardening as implied by the name. This early strength is achieved by increasing C'S and C+ % content of the cement and finer grinding. Since it has high heat evaluation, :"#C should not be used in large masses. @ith 12< of C+ %, it has lower sulfate resistance. The may be limited to obtain moderate sulfate resistance or to 2< when high sulfate resistance is re*uired. :apid;hardening #ortland cement should not be regarded as *uic;setting cement. The setting time specified in 8S 1'A1B1 for :"#C is similar as specified for ?#C



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-hite and Coloured Portland Cement )*" 1% : 1+,1& 9enerally used for decorative wor. It is made by using China clay in place of ordinary clay to e(clude impurities, especially iron o(ide and limestone. Coloured cements are made by mi(ing pigments with #ortland cement

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o/ !eat Portland Cement ( !PC )*" 10,: 1+,2& >"#C hardens and evolves heat more slowly than ?#C. It has slightly different chemical composition. It is obtained by increasing the proportion of C'S and reducing C+S and C+ %. It thus hydrates more slowly and evolves heat less rapidly than ?#C. The strength of >"#C is slow developed but the ultimate strength is same. "owever, the initial setting time is greater than ?#C. Trace "etting Time for 'PC5 !PC and !PC

"etting Time

?#C :"#C

#nitial "etting Time5 minutes )min& +5 +5

>"#C

D5

Cement Type

v&

$inal "etting Time5 minutes )ma6& D55 D55 D55

Portland *lustfurnace Cement 3 P*C )*" 124: 1+,0& #8C is made by grinding a mi(ture of ?#C cliner with selected granulated blast furnace slag. The proportion of slag is limited by the 8ritish Standard to not more than D2< of the finished cement. The properties of blast furnace cement are very similar to those of ?#C but it hydrates slower than those of #ortland cement so this cement evolves less heat and hardens more slowly than ?#C. The resistance to sulfate is often considered to be intermediate between that of sulfate;resisting #ortland cement.



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"ulfate3esisting Portland Cement ( "PC )*" 2%,: 1+,%& S:#C is specified where there is e(tensive e(posure to sulfate. Typical applications include hydraulic structure e(posed to water with high alali content and structures subEected to seawater e(posure. The surface resistance to S:#C is achieved by reducing the C+ % content to a minimum since that compound is most susceptible to sulfate attac. It usually has a higher content of C4 %. Concrete made with this cement is more resistant to attac by sulfate compounds which may be found dissolved in ground water and which are present in sea water. S:#C tends to be darer in colour than ?#C.

vii&

!igh "trength Portland Cement ( !"PC "S#C is produced from the same material as the case of ?#C. The higher strength achieved by increasing C+S content and also by finer grinding of cliner. The initial and final setting times are the same as that of ?#C. %t higher water cement ratios, the "S#C has about &5< higher strength and at lower cement ratio 45< higher strength than ?#C.

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Masonry Cement )*" 7%%2: 1+,4& or hand wor such as rendering and briclaying, mortar composed only of #ortland cement and sand are not ideal. Such mortars harden too *uicly, are too strong, and lac the plasticity and water retention desirable in a masonry mortar. It has been customary to overcome this difficulty by mi(ing lime with the cement mi(tures. Masonry cement, under various brand names consists of #ortland cement with a fine inert admi(ture and plasticiFing agent.

Table 1.0: Minimum compressive strength of concrete cube specified by *" 277 for Portland cement Compressive "trength )N8mm%& Type of Portland Cement

1.1.2

?#C :"#C

0 days 1+ 1&

, days ; ;

%9 days 'B ++

#8C

&

14

''

>"#C

2

;

1B

S:#C

15

;

'

!igh Alumina Cement



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"igh alumina cement is *uite different both in composition and properties from #ortland cement. It is comparatively slow;setting but rapid hardening, thus, produces very high early strength. %s a considerable amount of heat is generated during the setting and hardening process, it should not be used in rich mi(es or large masses. It is essential that the concrete be ept continuously wet for at least '4 hours from the time it begins to harden. %bout &5
1.%

%lumina 6%l'?+7 erric ?(ide 6e'?+7

+B< 15<

>ime 6Ca?7

+&<

errous ?(ide 6e?7

4<

Silica 6Si?'7

D<

Chemical Composition



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Several types of cements can be obtained by changing the percentages of chemical composition. Table 1.2 shows the chemical composition limit of #ortland cementA Table 1.7: Chemical composition limit of Portland cement Name of a/ Material

Chemical Composition

Percentage imit

>ime Silica %lumina Iron ?(ide Magnesium %lalis 6Soda and orG potash7 Sulphur Trio(ide

Ca? Si?' %l'?+ e'?+ Mg? /a'?,H'? S?+

D5 3 D 1 3 '2 +3& 5.2 3 D 5.1 3 4 5.' 3 1.+ 1;+

The interaction of #ortland cement raw materials are interacted in iln by forming comple( chemical compounds. Calcination in the iln restructures the molecular composition by producing four main chemical compounds. Table 1.4: Main compounds of Portland cement Name of Compound Tricalcium Silicate )icalcium Silicate Tricalcium %luminate Tetracalcium %luminoferitte

Chemical $ormula

Usual ange by -eight )&

+Ca?.Si?' 'Ca?.Si?' +Ca?.%l'?+ 4Ca?.%l'?+.e'?+

42 3 D5 12 3 +5 D 3 1' D;&

The minor compounds such as magnesium o(ide, titanium o(ide, manganese o(ide, sodium o(ide, and potassium o(ide are represented a few percentages by weight of cement. 1.0

Testing of Cement

1.0.1 "etting ;icat "et Time Apparatus Setting time can be determined with the icat apparatus. The icat test re*uires sample of cement using the amount of water re*uired for normal consistency according to a specified procedure.

Procedure:



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The 1 mm 65.54in7 diameter needle is allowed to penetrate the paste for +5 seconds and the amount of penetration is measured. The penetration process is repeated every 12 minutes until a penetration of '2 mm 61in7 or less is obtained. 8y interpolation, the time when a penetration of '2 mm occurs is determined and recorded as the initial set time. The final set time is when the needle does not penetrate visibly into the paste.

$igure 1.1: ;icat set time apparatus
$igure 1.%:
"oundness



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Soundness of the cement paste refers to its ability to retain its volume after setting. !(pansion after setting, caused by delayed or slow hydration or reactions, could result if the cement is unsound. The autoclave e(pansion test is used to chec the soundness of the cement paste. In this test, cement paste bars are subEected to heat and high pressure, and the amound of e(pandsion is measure. %STM C125 limits autoclave e(pansion to 5.&<.

$igure 1.0: Cement autoclave e6pansion Compressive "trength Compressive strength of mortar is measured by preparing 25mm 6'in.7 cubes and subEecting them to compression according to %STM C15B. The mortar is prepared with cement, water and standard sand 6%STM C&7. Minimum compressive strength values are specified by %STM C125 for different cement types at different ages. The compressive strength of mortar cubes is proportional to compressive strength of cylinders. "owever, the compressive strength of the concrete cannot be predicted accurately from mortar cube strength, since the concrete strength is affected by aggregate characteristics, the concrete mi(ing and the construction procedures. 1.2 Manufacturing of Cement #roduction of #ortland cement deals with two basic raw ingredients namely calcareous and argillaceous. These materials are crushed and stored in the silos. The raw materials, in the desired proportions, are passed through grinding mill, using either wet or dry process. The ground material is stored until it can be sent to the iln.



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Modern dry process cement plants use a heat recovery cycle to preheat the ground material, or feed stoc, with the e(haust gas from the iln. Some plants use a flash furnace to further heat and feed stoc. 8oth the preheater and flash furnace improves the energy efficiency of cement productions. In the iln, the raw materials are melted at temperatures 1455oC to 1D25oC, changing the materials into cement cliner. The cliner is cooled and stored. The small amount of gypsum is added to regulate the setting time of the cement in the concrete. The finished product may be stored and transported in either bul or sacs. The cement can be stored for long periods of time, provided it is ept dry.

$igure 1.2: Portland cement manufacturing processes



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Tutorial 1

=1: @hat is the best storing system for cement. !(plain =%: "ow to speed up the strength development of concrete. !(plain. =0: @hat are the effects of non;potable water on concrete *uality !(plain.


Chapter 1 Cement Civil Engineering Material

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