UNIT I CONSTITUENT MATERIALS
•Cement
•Different types
•Chemical composition and Properties
•Tests on cement-IS Specifications
•Aggregates
•Classification
•Mechanical properties and tests as per BISGrading requirements
•Water
•Quality of water for use in concrete.
UNIT II CHEMICAL AND MINERAL ADMIXTURES
•Accelerators
•Retarders
•Plasticisers
•Super plasticizers
•Water proofers
•Mineral Admixtures like
•Fly Ash
•Silica Fume
•Ground Granulated Blast Furnace Slag and
•Metakaoline
•Their effects on concrete properties
UNIT III PROPORTIONING OF CONCRETEMIX
•Principles of Mix Proportioning
•Properties of concrete related to Mix Design
•Physical properties of materials required for MixDesign
•Design Mix and Nominal Mix
•BIS Method of Mix Design
•Mix Design Examples
UNIT IV FRESH AND HARDENEDPROPERTIES OF CONCRETE
•Workability
•Tests for workability of concrete
•Slump Test and Compacting factor Test
•Segregation and Bleeding
•Determination of Compressive and Flexural strength as perBIS
•Properties of Hardened concrete
•Determination of Compressive and Flexural strength
•Stress-strain curve for concrete
•Determination of Young’s Modulus.
UNIT V SPECIAL CONCRETES
•Light weight concretes
•High strength concrete
•Fibre reinforced concrete
•Ferrocement
•Ready mix concrete
•SIFCON
•Shotcrete
•Polymer concrete
•High performance concrete
•Geopolymer Concrete
TEXTBOOKS:
1.Gupta.B.L., Amit Gupta, "ConcreteTechnology", Jain Book Agency, 2010.
2.Shetty,M.S, "Concrete Technology", S.Chandand Company Ltd, New Delhi, 2003
REFERENCES:
1.Santhakumar,A.R; "Concrete Technology" ,Oxford University Press, New Delhi, 2007
2.Neville, A.M; "Properties of Concrete", PitmanPublishing Limited, London,1995
3.Gambir, M.L; "Concrete Technology", 3rd Edition,Tata McGraw Hill Publishing Co Ltd, New Delhi,2007
4.IS10262-1982 Recommended Guidelines forConcrete Mix Design, Bureau of IndianStandards, New Delhi, 1998
Cement is a well-known building material andhas occupied an indispensable place inconstruction works.
A cement is a binder, a substance that sets andhardens and can bind other materials together.
There are variety of cements available in themarket and each type is used under certainconditions due to its special properties.
A mixture of cement and sand when mixed withwater to form a paste is known as cementmortar whereas the composite product obtainedby mixing cement, water and an inert matrix ofsand and gravel or crushed stone is calledcement concrete.
The cement commonly used is Portlandcement and the fine and coarse aggregatesused are those that are usually obtainable,from nearby sand, gravel or rock deposits.
In order to obtain a strong, durable andeconomical concrete mix, it is necessary tounderstand the characteristics andbehaviour of the ingredients.
Portland cement is defined as hydrauliccement, i.e. a cement that not only hardensby reacting with water but also forms a water-resistant product.
The ingredients of concrete can be classifiedinto two groups, namely active and inactive.
The active group consists of cement andwater, whereas the inactive group comprisesfine and coarse aggregates.
The inactive group is also sometimes calledthe inert matrix.
Although all materials that go into a concretemixture is essential, cement is by far the mostimportant constituent because it is usually thedelicate link in the chain.
The function of cement is, first to bind the sandand coarse aggregates together and second tofill the voids in between sand and coarseaggregate particles to form a compact mass.
Although cement constitutes only about 10percent of the volume of the concrete mix, it isthe active portion of the binding medium and theonly scientifically controlled ingredient ofconcrete.
Joseph Aspdin patented a similar material,which he called Portland cement, becausethe render made from it was in color similarto the prestigious Portland stone.
The raw materials used for the manufacture ofcement consist mainly of lime, silica, aluminaand iron oxide.
These oxides interact with one another in thekiln at high temperature to form more complexcompounds.
The relative proportions of these oxidecompositions are responsible for influencingthe various properties of cement, in addition torate of cooling and fineness of grinding.
The table below shows the approximateoxide composition limits of ordinary PortlandCement.
Oxide
Percent content
CaO
60-67
SiO2
17-25
Al2O3
3.0-8.0
Fe2O3
0.5-6.0
MgO
0.1-4.0
Alkalies (k2O, Na2O)
0.4-1.3
SO3
1.3-3.0
Functions of cement ingredients
Lime:
Controls strength and soundness. Its deficiencyreduces
strength and setting time.
Silica:
Gives strength due to the formation of dicalcium and
tricalcium silicates. Excess of it causes slow setting.
Alumina:
Responsible for quick setting. It acts as a flux and
lowers the clinkering temperature. If in excess it
lowers the strength.
Calcium Sulphate: Present in the form of gypsumand its function is to increase the initial setting timeof cement.
Iron Oxide: Imparts color and help in fusion of
different ingredients of cement.
Magnesia: Imparts color and hardness. If in excess
causes cracks and makes cement unsound.
Sulphur: A small amount is used in making sound
cement. If in excess causes cement to become
unsound.
Alkalies: If excess in cement, causes alkali- aggregate
reaction (aggregates having silica react with the alkali
hydroxides in concrete, causing expansion and
cracking ) , efflorescence and discoloration when used
in concrete.
The oxides present in the raw materialswhen subjected to high clinkeringtemperature combine with each other to formcomplex compounds.
The identification of the major compounds islargely based on R.H. Bogue’s work andhence it is called “Bogue’s Compounds”.
The table below lists the major compounds.
Name of the Compound
Formula
Abbreviated Formula
Tricalcium silicate
3 CaO.SiO2
C3S
Dicalcium silicate
2CaO.SiO2
C2S
Tricalcium Aluminate
3CaO.Al2O3
C3A
Tetracalciumaluminoferrite
4CaO.Al2O3.Fe2O3
C4AF
It is to be noted that for simplicty sake abbreviated notations areused.
C stands for CaO, S for SiO2, A for Al2O3, F for Fe2O3 and H for H2O
In addition to the four major compounds, thereare many minor compounds formed in thekiln.
The influence of these minor compounds onthe properties of cement or hydratedcompounds is not significant.
Two of the minor oxides namely K2O andNa2O referred to as alkalis in cement are ofsome importance.
Tricalcium silicate and dicalcium silicateare the most important compoundsresponsible for strength.
Together they constitute 70 to 80 percent ofcement.
Anhydrous cement does not bind fine andcoarse aggregate.
It acquires adhesive property only when mixedwith water.
The chemical reactions that take placebetween cement and water is referred ashydration of cement.
The chemistry of concrete is essentially thechemistry of the reaction between cement andwater.
On account of hydration certain products areformed.
These products are important because theyhave cementing or adhesive value.
The quality, quantity, continuity, stability andthe rate of formation of the hydrationproducts are important.
Anhydrous cement compounds when mixedwith water, react with each other to formhydrated compounds of very low solubility.
The hydration of cement can be visualised in twoways.
The first is “through solution” mechanism.
In this the cement compounds dissolve toproduce a supersaturated solution from whichdifferent hydrated products get precipitated.
The second possibility is that water attackscement compounds in the solid state convertingthe compounds into hydrated products startingfrom the surface and proceeding to the interior ofthe compounds with time.
It is probable that both “through solution” and“solid state” types of mechanism may occurduring the course of reactions betweencement and water.
The former mechanism may predominate inthe early stages of hydration in view of largequantities of water being available, and thelatter mechanism may operate during the laterstages of hydration.
The reaction of cement with water isexothermic.
The reaction liberates a considerable quantityof heat.
This liberation of heat is called heat ofhydration.
On mixing cement with water, a rapid heatevolution, lasting a few minutes, occurs.
The heat evolution is probably due to the reactionof solution of aluminates and sulphates(ascending peak A).
This initial heat evolution ceases quickly when thesolubility of aluminate is depressed bygypsum(descending peak A).
Next heat evolution is on account of formation ofettringite and also may be due to the reaction ofC3S (ascending peak B)
The chemical reaction of C3S with water can beexpressed as
C3S + water C-S-H + C-H +Heat
Where C-S-H is calcium silicate hydrate and C-H iscalcium hydrate.
C-S-H calcium silicate hydrate constitutes 50-60% ofthe solids in the paste.
It forms a continuous binding matrix.
It is amorphous and fibrous and hence has a largesurface area.
It is an important factor for the strength developmentof cement paste.
C-H calcium hydrate makes up about 20% ofthe solids in the paste.
It exists in the form of thick, crystallinehexagonal plates and is embedded in theC-S-H matrix.
Its growth fills the pore spaces.
It does not significantly contribute to strength.
Its leaching causes white patches andefflorescence.
The hydration of C2S is similar to the hydrationof C3S.
The same products are generated.
However, C2S reacts slowly and hencegenerates less heat.
It contributes to strength development at latterstages.
This hydration reaction produces a substancecalled ettringite as follows:
C3A + gypsum + water ettringite +heat
C3A+ettringite+water monosulphoaluminate
If the amount of gypsum is too little, C3A willreact fast and can cause a ‘flash set’.
On the other hand, too much gypsum will delaysetting and cause undue expansion.
As shown in the figure, ettringite is a crystalline andneedle like substance.
It constitutes about 10–20% of the solidcontent.
It is a long, slender and prismatic crystal and isstable only in the presence of gypsum.
It plays a minor role in strength developmentbut contributes considerably to durability.
Monosulphoaluminate is a stable hydrationproduct.
It is fairly crystalline.
The figure shows thin irregular plates clusteredlike a flower.
Hence it fills the pores and can reform ettringitein the presence of sulphate ions.
The hydration of C4AF is similar to that of C3A,the same products are formed.
However, C4AF reacts slowly and hencegenerates less heat and combines well withgypsum.
In summary, the hydration of cement occurs atthe surface of the grain.
All the compounds react simultaneously;a compound reaction takes place.
The smaller grains hydrate first and the largergrains become smaller while they hydrate.
Some very large grains never hydratecompletely.
The hydration rate has the following hierarchy:
C3A, C3S, C4AF and C2S
Ettringite is formed first, followed by C-H andC-S-H.
There is no change in the total volume of thecement paste as a result of hydration.
After hydration, the paste composition consists ofboth the solid and water phases.
Thus hydration is a chemical reaction.
The Bogue compounds react to form C-S-H, C-H,ettringite, monosulphoaluminate and heat.
Ordinary Portland Cement
Ordinary Portland Cement 33 Grade –IS 269:1989
Ordinary Portland Cement 43 Grade –IS 8112: 1989
Ordinary Portland Cement 53 Grade –IS 12269:1987
Rapid hardening cement – IS 8041: 1990
Extra Rapid Hardening Cement
Sulphate Resisting Cement – IS 12330:1998
Portland Slag Cement – IS 455: 1989
Quick Setting Cement
Super Sulphated Cement - IS 6909 :1990
Low Heat Cement – IS 12600: 1989
Portland Pozzolana Cement –
IS 1489(Part I) 1991 (Flyash based)
IS 1489(PartII) 1991 (Calcined based)
Air Entraining Cement
Coloured Cement : White Cement –
IS 8042:1989
Hydrophobic Cement – IS 8043 : 1991
Masonry Cement – IS 3466: 1988
Expansive Cement
Oil Well Cement – IS 8229:1986
Rediset Cement
Concrete Sleeper grade Cement –
IRS-T 40: 1985
High Alumina Cement – IS 6452:1989
Very High Strength Cement
Prior to 1987, there was only one grade ofOPC which was governed by IS 269-1976.
After 1987 higher grade cements wereintroduced in India.
The OPC was classified into three grades,namely 33 grade, 43 grade and 53 gradedepending upon the strength of the cement at28 days when tested as per IS 4031-1988.
It has been possible to upgrade the qualitiesof cement by using
high quality limestone
Modern equipments
Closer on line control of constituents
Maintaining better particle sizedistribution
Finer grading
Better packing
This is similar to OPC.
As the name indicates it develops strengthrapidly and as such it may be more appropriateto call it as high early strength cement.
Rapid hardening cement develops strength atthe age of three days, the same strength asthat is expected of ordinary portland cement atseven days.
The rapid rate of development of strength isattributed to
the higher fineness of grinding (specificsurface not less than 3250 sq.cm pergram)
higher C3S
lower C2S content
A higher fineness of cement particles exposegreater surface area for action of water and alsohigher proportion of C3S results in quickerhydration.
Consequently, rapid hardening cement givesout much greater heat of hydration during theearly period.
Therefore, rapid hardening cement should notbe used in mass concrete construction.
The use of rapid hardening cement isrecommended in the following situations:
In pre-fabricated concrete constructionwhere formwork is required to be removedearly for re-use elsewhere.
Road repair works
In cold weather concrete where the rapidrate of development of strength reduces thevulnerability of concrete to the frostdamage.
It is obtained by inter grinding calciumchloride with rapid hardening PortlandCement.
The normal addition of calcium chlorideshould not exceed 2 percent by weightof the rapid hardening cement.
It is necessary that the concrete made byusing extra rapid hardening cement shouldbe transported, placed and compacted andfinished within about 20 minutes.
It is also necessary that this cement shouldnot be stored for more than a month.
This cement accelerates the setting andhardening process.
A large quantity of heat is evolved in a veryshort time after placing.
The acceleration of setting, hardening andevolution of this large quantity of heat in theearly period of hydration makes the cementvery suitable for concreting in cold weather.
The strength is about 25 percent higher thanthat of rapid hardening cement at one or twodays and 10–20 percent higher at 7 days.
The gain of strength will disappear with age andat 90 days the strength of extra rapid hardeningcement or the OPC may be nearly the same.
There is some evidence that there is smallamount of initial corrosion of reinforcementwhen extra rapid hardening cement is used, butin general, this effect does not appear to beprogressive and as such no harm in using thiscement in reinforced work.
However, its use in prestress concreteconstruction is prohibited.
Ordinary Portland cement is susceptible to theattack of sulphates, in particular to the action ofmagnesium sulphate.
Sulphates react both with the free calciumhydroxide in set-cement to form calciumsulphate and with hydrate of calcium aluminateto form calcium sulphoaluminate, the volume ofwhich is approximately 227% of the volume ofthe original aluminates.
Their expansion within the frame work ofhardened cement paste results in cracks andsubsequent disruption.
Solid sulphate do not attack the cementcompound.
Sulphates in solution permeate intohardened concrete and attack calciumhydroxide, hydrated calcium aluminate andeven hydrated silicates.
This is known as sulphate attack.
Sulphate attack is greatly accelerated ifaccompanied by alternate wetting and dryingwhich normally takes place in marinestructures in the zone of tidal variations.
To remedy the sulphate attack, the use ofcement with low C3A content is found to beeffective.
Such cement with low C3A andcomparatively low C4AF content is knownas Sulphate Resisting Cement.
In other words, this cement has a highsilicate content.
The specification generally limits the C3Acontent to 5 percent.
In many of its physical properties, sulphateresisting cement is similar to OPC.
The use of sulphate resisting cement is recommendedunder the following conditions:
Concrete to be used in marine condition
Concrete to be used in foundation andbasement, where soil is infested with sulphates
Concrete used for fabrication of pipes whichare likely to be buried in marshy region orsulphate bearing soils.
Concrete to be used in the construction ofsewage treatment works.
Portland slag cement is obtained by mixingportland cement clinker, gypsum andgranulated blast furnace slag (a waste productfrom blast furnaces) in suitable proportions andgrinding the mixture to get a thorough andintimate mixture between the constituents.
Portland blast furnace cement is similar to OPCwith respect to fineness, setting time, soundnessand strength.
It is generally recognized that the rate ofhardening of Portland blast furnace slagcement in mortar or concrete is somewhatslower than that of OPC during the first 28days, but thereafter increases, so that at 12months the strength becomes close to oreven exceeds those of Portland cement.
The heat of hydration of Portland blastfurnace cement is lower than that of OPC.
So this cement can be used in massconcrete structures with advantage.
However, in cold weather the low heat ofhydration of Portland blast furnace cementcoupled with moderately low rate of strengthdevelopment, can lead to frost damage.
Extensive research shows that the presence ofGGBS leads to the enhancement of theintrinsic properties of the concrete both in freshand hardened states.
The major advantages currently recognisedare:
Reduced rate of hydration
Refinement of pore structure
Reduced permeability
Increased resistance to chemical attack.
This cement as the name indicates sets veryearly.
The early setting property is brought out byreducing the gypsum content at the time ofclinker grinding.
This cement is to be mixed, placed andcompacted very early.
It is used mostly in under waterconstruction where pumping is involved.
Use of quick setting cement in suchconditions reduces the pumping time andmakes it more economical.
It is also used in grouting operations.
It is manufactured by grinding together amixture of 80–85 percent granulated slag,10–15 percent hard burnt gypsum andabout 5 percent Portland cement clinker.
The product is ground finer than that of OPC.
Specific surface must not be less than 4000cm2per gm.
It has a low heat of hydration of about 40–45 calories/gm at 7 days and 45–50 at 28days.
It has high sulphate resistance.
Because of this property, it is used infoundation and marine constructions.
It is used in fabrication of reinforcedconcrete pipes which are likely to be buriedin sulphate bearing soils.
A low heat evolution is achieved byreducing the contents of C3S and C3Awhich are the compounds evolving themaximum heat of hydration andincreasing C2S.
A reduction of temperature will retard thechemical action of hardening and so furtherrestrict the rate of evolution of heat.
The rate of evolution of heat will,therefore, be less and evolution of heatwill extend over a longer period.
Therefore, the feature of low heatcement is a slow rate of gain ofstrength.
But the ultimate strength is same asthat of OPC.
It is manufactured by the intergrinding of OPCclinker with 10 to 25 % of pozzolanic material.
A pozzolanic material is essentially a siliceousor aluminous material which while in itselfpossessing no cementitious properties, whichwill, in finely divided form and in the presenceof water, react with calcium hydroxide,liberated in the hydration process, at ordinarytemperature, to form compounds possessingcementitious properties.
The pozzolanic materials generally used formanufacture of PPC are calcined clay orFlyash.
Calcium silicates produce considerablequantities of calcium hydroxide, which is byand large a useless material from the point ofview of strength or durability.
If such useless mass could be converted intoa useful cementitious product, it considerablyimproves quality of concrete.
The use of fly ash performs such a role.
The pozzolanic action is shown below.
Calcium hydroxide+Pozzolana+ water C-S-H (gel)
PPC can be used in all situations whereOPC is used except where high earlystrength is of special requirement.
As PPC needs enough moisture forsustained pozzolanic activity, a little longercuring is desirable.
Use of PPC would be particularly suitable forthe following situations:
For hydraulic structures
For mass concrete structures like dam,bridge piers and thick foundation
For marine structures
For sewers and sewage disposal worksetc.
This cement is made by mixing a smallamount of an air-entraining agent withOPC clinker at the time of grinding.
The following types of air-entrainingagents could be used:
Alkali salts of wood resins
Synthetic detergents of the alkyl-arylsulphonate type
Calcium lignosulphate derived from thesulphite process in paper making
Calcium salts of glues and otherproteins obtained in the treatment ofanimal hides.
For manufacturing various coloured cementseither white cement or grey Portland cement isused as a base.
The use of white cement as a base is costly.
With the use of grey cement only red or browncement can be produced.
It consists of Portland cement with 5–10percent of pigment.
The raw materials used for manufacture ofwhite cement are high purity limestone(96% CaCO3 and less than 0.07% ironoxide).
The other raw materials are china clay withiron content of about 0.72 to 0.8%, silicasand, flourspar as flux and selenite asretarder.
Sea shells and coral can also be used asraw materials for production of white cement.
It is obtained by grinding OPC clinker withwater repellant film-forming substance suchas oleic acid and stearic acid.
The water–repellant film formed around eachgrain of cement, reduces the rate of deteriorationof the cement during long storage, transport, orunder unfavourable conditions.
The film is broken out when the cement andaggregate are mixed together at the mixerexposing the cement particles for normalhydration.
The film forming water-repellant materialwill entrain certain amount of air in the bodyof the concrete which incidentally willimprove the workability of concrete.
The properties are same as the OPCexcept that it entrains a small quantity of airbubbles.
Ordinary cement mortar, though good whencompared to lime mortar with respect to strengthand setting properties, is inferior to lime mortarwith respect to workability, water-retentivity,shrinkage property and extensibility.
Masonry cement is a type of cement which isparticularly made with such combination ofmaterials, which when used for making mortar,incorporates all the good properties of limemortar and discards all the not so idealproperties of cement mortar.
This kind of cement is mostly used, as thename indicates, for masonry construction.
It contains certain amount of air-entrainingagent and mineral admixtures to improvethe plasticity and water retentivity.
Concrete made with OPC shrinks whilesetting due to loss of free water.
This is known as drying shrinkage.
Cement used for grouting anchor bolts orgrouting machine foundations or the cementused in grouting the prestress concrete ducts,if shrinks, the purpose for which the grout isused will be to some extent defeated.
The type of cement which suffers no overallchange in volume on drying is known asexpansive cement.
Cement of this type has been developed byusing an expanding agent and a stabilizervery carefully.
About 8–20 parts of the sulphoaluminateclinker are mixed with 100 parts of thePortland cement and 15 parts of thestabilizer.
It is manufactured as per specification laiddown by ministry of railways under IRS – T40:1985.
It is a very finely ground cement with highC3S content designed to develop high earlystrength required for manufacture of concretesleeper for Indian Railways.
This cement can be used for prestressedconcrete elements, high rise buildings andhigh strength concrete.
The desired properties of oil-well cement canbe obtained in two ways:
By adjusting the compoundcomposition of cement or
By adding retarders to OPC
The retarders are starches or celluloseproducts or acids.
These retarding agents prevent quick settingand retains the slurry in mobile condition tofacilitate penetration to all fissures andcavities.
Sometimes workability agents are also addedto this cement to increase the mobility.
A new product was needed for use in theprecast concrete industry, for rapid repairs ofconcrete roads and pavements and slip-forming.
Associated Cement Company of India havedeveloped this cement.
Properties of Rediset Cement
The cement allows a handling time of justabout 8 to 10 minutes.
The strength pattern is similar to that of OPC.
It releases a lot of heat which is advantageousin winter concreting but excess heat liberationis detrimental to mass concrete.
The rate of shrinkage is fast but the totalshrinkage is similar to OPC.
The sulphate resistance is poor.
Rediset can be used for
Very high early (3 to 4 hours)strengthconcrete and mortar.
Patch repairs and emergency repairs
Quick release of forms in the precastconcrete products industry.
Slip-formed concrete construction
Construction between tides.
High alumina cement is obtained by fusingor sintering a mixture, in suitableproportions, of alumina and calcareousmaterials and grinding the resultant productto a fine powder.
The raw materials used for the manufactureof high alumina cement are limestone andbauxite.
An important use of high alumina cement isfor making refractory concrete to withstandhigh temperatures in conjunction withaggregate having heat resisting properties.
RC is used for foundations of furnaces,boiler settings.
It is also used in fire pits, construction ofelectric furnaces, kilns etc.
Macro-defect-free cements(MDF)
MDF refers to the absence of relatively large voidsor defects which are usually present in conventionalmixed cement pastes because of entrapped air andinadequate dispersion.
In this process, 4–7% of one or several water solublepolymers (such as hydroxypropylmethylecellulose, polyacrylamide of hydrolysedpolyvinylacetate) is added as rheological aid topermit cement to be mixed with very small amount ofwater.
Densely packed system (DSP)
Normal Portland cement and ultra-finesilica fume are mixed.
The size of cement particles may vary from0.5 to 100 and that of silica fume varies from0.005 to 0.5.
Silica fume is generally added from 5 to 25%.
A compressive strength of 270MPa have beenachieved with silica fume substituted paste.
Pressure densification and warm pressing
A new approach has been developed forachieving very high strength by a methodcalled “warm pressing” (applying heat andpressure simultaneously) to cement paste.
Compressive strength as much as 650MPaand tensile strength upto 68MPa have beenobtained by warm pressing Portland andcalcium aluminate cements.
High early strength cement
Lithium salts have been effectively used asaccelerators in high alumina cement.
This has resulted in very high early strength incement and a marginal reduction in laterstrength.
Strength as high as 4MPa has been obtainedwithin 1 hour and 27MPa has been obtainedwithin 3 hours time and 49MPa in one day.
Pyrament cement
Some cement industries in USA have developed asuper high early strength and durable cementcalled by trade name “pyrament cement”.
This product is a blended hydraulic cement.
In this cement no chlorides are added during themanufacturing process.
It produces a high and very early strength ofconcrete and mortar which can be used for repairof Air Field Run-ways.
Magnesium Phosphate Cement (MPC)
It has been developed by Central RoadResearch Institute, New Delhi.
This is an important development foremergency repair of airfields, launching pads,road pavements suffering damage due toenemy bombing and missile attack.
MPC has been found to possess uniquehydraulic properties, controlled rapid set andearly strength development.
MPC is prepacked mixture of dead burntmagnesite with fine aggregate mixed withphosphate.
It sets rapidly yields durable high strengthcement mortar.
Testing of cement can be brought undertwo categories:
Field testing
Laboratory Testing
It is sufficient to subject the cement to fieldtests when it is used for minor works.
The following are the Field tests:
Open the bag and take a good look at thecement. There should not be any visiblelumps. The colour of the cement shouldnormally be greenish grey.
Thrust your hand into the cement bag. Itmust give you a cool feeling. There shouldnot be any lump inside.
Take a pinch of cement and feel betweenthe fingers. It should give a smooth and nota gritty feeling.
Take a handful of cement and throw it on abucket full of water, the particles shouldfloat for some time before they sink.
Take about 100 grams of cement and asmall quantity of water and make a stiffpaste.
From the stiff paste, pat a cake with sharpedges.
Put it on a glass plate and slowly take itunder water in a bucket.
See that the shape of the cake is notdisturbed while taking it down to thebottom of the bucket.
After 24 hours the cake should retain itsoriginal shape and at the same time itshould also set and attain some strength.
The following tests are conducted in thelaboratory:
Fineness test
Soundness test
Setting time test
Strength test
Heat of hydration test
Chemical composition test
The fineness of cement has an importantbearing on
the rate of hydration
Rate of gain of strength
Rate of evolution of heat
Finer cement offers a greater surface areafor hydration and hence faster thedevelopment of strength.
Maximum number of particles in a sample ofcement should have a size less than about100 microns.
The smallest particle may have a size ofabout 1.5 microns.
Fineness of cement is tested in two ways:
By sieving – IS 4031(Part I) : 1996
By determination of specific surface(total surface area of all the particles in onegram of cement) by air-permeabilityapparatus. Expressed as cm2/gm orm2/gm. Generally Blaine Air Permeabilityapparatus is used - IS 4031(Part 2) : 1999
DETERMINATION OF FINENESS
BY DRY SIEVING
To determine fineness of cement and particlesize of cement.
Sample size – 100gms; sieving period – 15minutes.
The standard sieve size used is 90 .
The % residual (retained) of cement on 90 sieve shall not exceed 10%.
Sieve used for determining Fineness of Cement
DETERMINATION OF FINENESS BY BLAINE AIRPERMEABILITY METHOD
Specific surface test(Blaine Test)(Air Permeability Test)
To determine fineness of cement (particle size ofcement) (5 to 30 ).
The fineness of cement is expressed in specificsurface of cement i.e. cm2/gm or mm2/gm.
It is determined by Air Permeability test or Lea-nursetest.
The specific surface of cement shall not be less than2250 cm2/gm or 225000 mm2/gm, for OPC.
For rapid hardening cement (RHC), it shall not be lessthan 3250 cm2/gm.
Consistency Test (Vicat Apparatus Test)
IS : 4 0 3 1 ( Part 4 ) - 1 9 8 8
To determine standard quantity of water toproduce standard cement paste.
The Vicat apparatus is used where thepenetration of plunger in standard cement pastekept in Vicat mould shall be in a range of 33 to35 mm from the top of the mould (5 to 7 mmfrom the bottom).
DETERMINATION OF INITIAL AND FINALSETTING TIMES
Initial setting time test (Vicat Apparatus)
IS : 4031 (Part 5) – 1988 (Reaffirmed 2000)
To determine the time required by cementpaste to loss its plasticity.
The Vicat apparatus is used to determineinitial setting time of cement where thepenetration of the needle in the cementpaste kept in Vicat mould (40 mm height)shall be in a range of 33 to 35 mm from thetop.
It shall not be less than 30minutes(≥30min)for normal cement, 60 minutes for low heatcement and 5 minutes for rapid hardeningcement.
Final setting time of cement (Vicat Apparatus)
The time required by cement paste to gain the propershape and becoming hard considering from the instantof adding water is called final setting time.
i.e., the time elapsing from the instant of adding waterto the cement and the instant when paste becomeshard(solid) is known as final setting time which isdetermined by Vicat apparatus where the enlargeneedle should not penetrate the specimen of cement.
Final setting time shall not exceed 10hrs for normalcement, 30 minutes for rapid hardening cement.
DETERMINATION OF SOUNDNESS
Lechatelier Test IS 4031 (Part 3 ) – 1988
To determine the soundness or unsoundnessof cement due to presence of free lime only.
The expansion of cement paste specimen inLechatelier mould shall not exceed 10mm.
Autoclave test
To determine soundness or unsoundness ofcement due to presence of magnesia.
Due to presence of steam around thespecimen expands caused by magnesia.
It shall not exceed 0.8% for soundness ofcement.
Autoclave for determining soundness
Compressive Strength Test
IS : 4031(Part 6):1988
To determine compressive strength of cementwhere the specimen is made up of 1:3(cement : sand) proportion i.e. 185 gmcement and 555gm sand or 200gm cementand 600gm sand.
The specimen is tested under compressionmachine at an age of 1 day, 3, 7 and 28days.
The compressive strength of rapid hardeningcement at 1 day curing shall not be less than16 MPa and at an age of 3 days it shall notbe less than 27.5 MPa.
Briquette Test
To determine strength of cement or concretewhere the specimen is made in dumbbellshape (Zig Zag).
The tensile force is applied in the lab on thespecimen till the specimen fails in tension.
The tensile strength shall be of 10% ofcompressive strength.
DETERMINATION OF HEAT OF HYDRATION
Test for Heat of Hydration IS : 4031 ( Part 9 )– 1988.
To determine the heat of hydration, especiallyfor low heat cement.
A calorimeter is used in the lab.
The heat of hydration of low heat cement shallnot exceed 75 cal/gm at 28 days.
Hydration Test Apparatus
Chemical Composition Test
Ratio of percentage of lime to percentage ofsilica, alumina and iron oxide, when calculatedby the formulae
Not greater than 1.02 and not less than 0.66.
The above is called lime saturation factor percent.
The aggregate is a relatively inert materialand it imparts volume stability.
The aggregate provide about 75% of thebody of the concrete and hence its influenceis extremely important.
An aggregate should be of proper shape andsize, clean, hard and well graded.
It must possess chemical stability and it mustexhibit abrasion resistance.
Functions of Aggregate
It provides bulk to the concrete
It increases the density of the concrete mix.
It imparts volume stability.
It imparts durability to the concrete.
It is an inert material and is cheaper thancement.
The functions of Fine aggregate are
To assist in producing workability anduniformity in the mix.
To assist the cement paste to hold thecoarse aggregate particles in suspension.
To promote plasticity in the mixture andprevent possible segregation of paste andcoarse aggregate.
The natural source of aggregate is obtainedfrom Igneous rocks (Granite, Basalt).
They are normally hard, tough and dense.
But the metamorphic rock (marble) is notsuitable for aggregates.
The most widely used artificial aggregates are(i) clean broken bricks (ii) blast furnace slag.
The crushing strength of brick shall not be lessthan 30 to 35 MPa.
Classification of Aggregate Based on Size
Fine Aggregate
It is the aggregate, most of which passes througha 4.75mm IS sieve.
The lowest size of sand is about 0.07 mm.
The fine aggregate may be natural sand, crushedstone sand or crushed gravel sand.
According to IS 383-1970, there are 4 gradingzones of the fine sand, grade 1, grade 2, grade3and grade 4.
Coarse Aggregate
The aggregates, most of which are retainedon 4.75mm IS sieve are termed as coarseaggregates.
The coarse aggregates may be
Crushed stone
Uncrushed gravel
Partially crushed stone or gravel.
Sometimes combined aggregates areavailable in nature consisting of differentfractions of fine and coarse aggregates,which are known as all in aggregate.
The all in aggregates are not generally usedfor making high quality concrete.
Classification of Aggregates according toShape
Rounded Aggregate
The aggregate with rounded particles (river orsea shore gravel) has minimum voids rangingfrom 32 to 33%.
It gives minimum ratio of surface area to thevolume, thus requiring minimum cement pasteto make good concrete.
The only disadvantage is that theinterlocking between its particles is less, andhence the development of the bond is poor,making it unsuitable for high strengthconcrete and pavement.
Irregular aggregates
The aggregate having partly round particles(pit sand and gravel) has higher percentage ofvoids ranging from 35 to 38 %.
It requires more paste for a given workability.
The interlocking between particles, thoughbetter than that obtained with the roundedaggregate, is inadequate for high strengthconcrete.
Angular aggregates
The aggregate with sharp angular and roughparticles (crushed rock) has a maximumpercentage of voids ranging from 38 to 40%.
The interlocking between particles is good,providing a good bond.
The aggregate requires more paste to makeworkable concrete of high strength.
The angular aggregate is suitable for highstrength concrete and pavements subjected totension.
Flaky and elongated aggregates
An aggregate is termed flaky when its leastdimension (thickness) is less than three-fifth ofits mean dimension.
The particle is said to be elongated when itsgreatest dimension (length) is more than nine-fifth (1.8 times) of its mean dimension.
Classification based on Unit Weight
Normal Weight Aggregate
The commonly used aggregates i.e. sand,gravel, crushed rocks such as granite, basalt,sandstone (sedimentary) and limestone whichhave specific gravities between 2.5 and 2.7produce concrete with unit weight ranging from23 to 26 kN/m3 and crushing strength at 28days between 15 to 40 MPa are termedNormal weight aggregate.
Heavy Weight Aggregate (High Densityaggregate)
Heavy weight aggregates are
Baryte(Gs = 4 to 4.6)
Ferrophosphorus (Gs = 5.8 to 6.8)
Haematite (Gs = 4.9 to 5.3)
Magnetite (Gs= 4.2 to 5.2)
Scrap Iron and Iron Shots (Gs = 6.2 to 7.8)
Heavy weight cocnrete is produced fromheavy weight aggregate, which is moreeffective as a radiation shield.
The unit weight of concrete varies from 30 to57 kN /m3.
Light weight Aggregate
The light weight aggregates have unit weightupto 12 kN/m3.
These aggregates are obtained from pumice,volcanic cinder, Diatomite, blast furnace slag,fly ash etc,.
The weight of concrete (structure) is reducedto a great extent and it provides betterthermal insulation and improved fireresistance.
Fineness Modulus
The fineness modulus is a numerical index offineness, giving some idea of the mean sizeof the particles present in the entire body ofthe aggregate.
The fineness modulus is the sum of thecumulative percentages retained on thesieves divided by 100.
According to IS 2386-1963, the sieves thatare to be used for the sieve analysis of theaggregate for concrete are 80mm, 40mm,20mm, 10mm, 4.75mm, 2.36mm, 1.18mm,600, 300 and 150
The fineness modulus can be regarded as aweighted average size of a sieve on whichmaterial is retained.
For example, a fineness modulus of 6 can beinterpreted to mean that the sixth sieve, i.e.4.75 mm is the average size.
The value of fineness modulus is higher forcoarser aggregate.
The fineness modulus for fine sand variesbetween 2 and 3.5, for coarse aggregate itvaries between 5.5 and 8, for all in aggregateit varies from 3.5 to 6.5.
Any sand having FM more than 3.2 will not besuitable for making satisfactory concrete.
The object (purpose) of finding FM is to gradethe given aggregates for the most economicalmix for the required strength and workabilitywith minimum quantity of cement.
If the test aggregates gives higher FM, themix will be harsh and if on the other handgives a lower FM, it produces anuneconomical mix.
Gradation
Gradation refers to the particle size distributionof aggregates.
The gradation of coarse aggregate plays animportant role in workability and pasterequirements.
The gradation of fine aggregate affects theworkability and finishability of concrete.
Types of gradation
Uniform grading
All particles are of same size.
It produces a large volume of voids irrespectiveof particle size.
Hence the paste requirement for this concreteis high.
Continuous grading
Incorporates a combination of particles ofmany sizes.
Hence, it minimises the volume of voids butincreases the particle surface area.
This is the preferred gradation.
Gap gradation
This involves grading in which one or moresizes are omitted. This type of concrete isgenerally for architectural or aestheticpurposes.
Water