INITIAL AND FINAL SETTING TIME OF CEMENT TEST (IS: 4031-(PART-5)-1988)

INITIAL AND FINAL SETTING TIME  CEMENT TEST

The initial setting time may be defined as the time taken by the paste to stiffen or solidify to such an extent that the Vicat’s needle is not permitted to move down through the paste to within 5 to 7 mm measured from the bottom of the mould. 

The final setting time is the time after which the paste becomes so hard that the angular attachment to the needle, under standard weight, fails to leave any mark on the hardened concrete.

Factors Affecting Initial And Final Setting Time Of Cement :

The factors influencing the setting properties of cement are : 

• Its composition, The effect of gypsum is to increase the setting time of freshly ground cement. 

• The percentage of retardant. 

• Degree of calcination. 

• Fineness of grinding.

• Aeration subsequent to grinding clinker. 

• Percentage of water used to make cement paste. 

• The temperature of the mixing water. 

• Cement and the atmosphere where the cement paste is placed.

OBJECTIVE 

To determine the initial and final setting time of cement paste of normal consistency.

APPARATUS

• Vicat’s Apparatus :

SAMPLE/SPECIMEN 

300 gm of cement is taken and then mix it with the required water percentage mentioned  in the consistency test of cement.

PROCEDURE FOR INITIAL SETTING TIME

• The prepared cement paste is filled in the vicat mould.
• The square needle of cross-section 1 mm x 1 mm is attached to the movable rod of the Vicat apparatus.

• Then the needle is allowed to quickly release to penetrate in the cement paste. during initial stage, the needle penetrates completely. It is then taken out and dropped at a fresh place. The test procedure is repeated at regular intervals till the needle does not penetrate completely. The needle should penetrate upto about 5 mm measured from bottom.

• The initial setting time is found out by taking  the interval between the addition of water to cement and the stage when needle stops to penetrate completely. The time should be less than 30 minutes for ordinary cement.

PROCEDURE FOR FINAL SETTING TIME :

• 300 gm of cement is taken and then mix it with the required water percentage mentioned  in the consistency test of cement.

• The prepared cement paste is then fill in the vicat mould.

• Instead of square needle, annular collar is used. The annular collar is attached to the movable rod of vicat apparatus.

• The annular rod is gently released. The time at which the annular rod makes an impression on test block and the collar fails to do so is noted.

• The final setting time is found out by taking the difference between the time at which water is added to cement and time as recorded in.

• The final setting time for ordinary cement should be 10 hours.

Initial And Final Setting Time Of Various Types Of Cement :

• Ordinary Portland Cement : The initial setting time of OPC should not be less than 30 minutes and the final setting time of this type of cement should not be greater than 10 hours or 600 minutes.

• Rapid Hardening Cement : for this type of cement, initial and final setting time is same as OPC cement.

• Portland Pozzolana Cement :  For this type of cement, initial and final setting time is same as OPC cement.

• Low Heat Portland Cement : For this type of cement, initial and final setting time is not less than 30 min and not greater than 600 minutes.

• Portland Blast Furnace Slag Cement : For this type of cement, initial and final setting time is same as OPC cement.

FINENESS TEST OF CEMENT (IS:4031-1996)

Test for fineness of cement is carried out for proper grinding of cement and to measure the mean size of the grains in it. 

METHOD OF TESTING FINENESS OF CEMENT  : 

Sieve Analysis Method

Weighing a 100 g of cement with accuracy of 0.1 g as a sample and if any air-set lumps present in the sample are broken with finger. The sample is placed on a 90 micron sieve and continuously sieved for 15 minutes. 

The residue should not exceed the following limits :

• For Ordinary Portland Cement : The residue present in OPC cement should not exceed 10% by the dry weight of cement. The specific surface of this type of cement should not be less than 225 m2/kg.
• For Rapid Hardening Cement : The residue present in this rapid hardening cement should not exceed 5% by the dry weight of cement. The specific surface of this type of cement should not be less than 325 m2/kg.
• For Portland Puzzolana Cement : The residue present in PPC cement should not exceed 5% by the dry weight of cement. The specific surface of this type of cement should not be less than 300 m2/kg.

Test Procedure

Objective

To determine the fineness of cement by dry sieve method.

Apparatus

• Standard BIS Sieve No. 9 : With capacity of retaining particle size over 90 micron.

• Weighing Balance : Measures 10 g of cement with accuracy 0.01 mg.
• Glass rod, Stoppered Jar Pen, Lid other apparatus used.

Sample/Specimen

100 g of cement sample is taken and broken air-set lumps in the sample with fingers.

Procedure 

• Weigh approximately 10 g of cement to the nearest 0.01 g and place it on the sieve.
• Agitate the sieve by swirling, planetary and linear movements, until no more fine material passes through it.
• Weigh the residue and express its mass as a percentage R1,of the quantity first placed on the sieve to the nearest 0.1 percent
• Gently brush all the fine material off the base of the sieve.
• Repeat the whole procedure using a fresh 10g sample to obtain R2. Then calculate R as the mean of R1 and R2 as a percentage, expressed to the nearest 0.1 percent. When the results differ by more than 1 percent absolute, carry out a third sieving and calculate the mean of the three values.

Result

Read and report the value of R, to the nearest of 0.1 percent, as the residue on the 90 micron sieve.

OTHER METHODS

Air Permeability Method

In air permeability test, The fineness of cement is represented or calculated by specific surface, i.e. total surface area in cm2 per gram or m2 per kilogram of cement and is measured by permeability apparatus. 

This permeability apparatus essentially consists of :

• Permeability Test Cell : Place where cement is stored and air pressure is applied. 
• Flowmeter : Flowmeter help to determine the quantity of air passing per second through its capillary tube per unit difference of pressure.
• Manometer : Manometer help to measure the air pressure.

To determine the fineness, a cement sample of 2 cm height is placed on a perforated plate and air pressure is applied. The manometer is connected to the top of the permeability cell and the air is turned on. The lower end of the permeability cell is then slowly connected to the other end of the manometer. The rate of flow is so adjusted that the flowmeter shows a pressure difference (h2) of 30-50 cm. The reading (h1) in the manometer is recorded. The process is repeated till the ratio h1/h2 is constant.

The specific surface should not be less then following limits :

• For Ordinary Portland Cement : The specific surface of this type of cement should not be less than 225 m2/kg.
• For Rapid Hardening Cement : The specific surface of this type of cement should not be less than 325 m2/kg.
• For Portland Puzzolana Cement : The specific surface of this type of cement should not be less than 300 m2/kg.

The Sedimentation Method

The turbidometer is a apparatus used  to estimate the surface area of one gram of cement. The cement is  uniformly in a rectangular glass tank filled with kerosene. Then, parallel light rays are passed through the solution which strike the sensitivity plate of a photoelectric cell. The turbidity of the solution at a given instant is measured by taking readings of the current generated by the cell. By recording the readings at regular intervals while the particles are falling in the solution, it is possible to secure information regarding the grading in surface area and in size of particle. Readings are expressed in cm2/g.

HOW TO PERFORM CONSISTENCY TEST OF CEMENT ?

Consistency test is used to estimate the quantity of mixing water to form a paste of normal consistency. The normal consistency defined as that percentage water requirement of the cement paste, the viscosity of which will be such that the Vicat’s plunger penetrates up to a point 5 to 7 mm from the bottom of the Vicat’s mould.

FACTOR AFFECTING FINENESS OF CEMENT 

1. The chemical composition and the degree of calcination influence the hardness of the clinker and consequently the fineness to which the cement is ground. 

2. Clinker, high in iron or silica, is apt to be hard and difficult to grind. The same is true with a hard burned clinker. 

3. Fineness is also influenced by the time of grinding and the character of the pulverizing machinery. It has been found that cement becomes finer with age provided it does not absorb too much moisture. This is probably due to the decrepitation of the coarser grains resulting from the hydration of the embedded lime particles.

TEST IMPORTANCE

Finer the cement, more is the strength since surface area for hydration will be large. With increase in fineness, the early development of strength is enhanced but the ultimate strength is not affected. An increase in the fineness of the cement increases the cohesiveness of the concrete mix and thus reduces the amount of water which separates to the top of a lift (bleeding), particularly while compacting with vibrators. However, if the cement is ground beyond a certain limit, its cementative properties are affected due to the prehydration by atmospheric moisture. Finer cement reacts more strongly in alkali reactive aggregate. Also, the water requirement and workability will be more leading to higher drying shrinkage and cracking.

TEST PROCEDURE

Objective

To determine the water requirement of the cement paste with normal consistency.

Apparatus

• Vicat’s Apparatus

Sample/Specimen

To makes a viscous paste as a sample, 300 g of cement is mixed with 25 per cent water.

Procedure

• The paste is filled in the mould of Vicat’s apparatus and the surface of the filled paste is smoothened and leveled.

• A square needle 10 mm x 10 mm attached to the plunger is then lowered gently over the cement paste surface and is released quickly. The plunger pierces the cement paste. 
• The reading on the attached scale is recorded. 

• When the reading is 5-7 mm from the bottom of the mould, the amount of water added is considered to be the correct percentage of water for normal consistency.

Result

The normal consistency of cement paste is achieved as a result.

MANUFACTURING OF ORDINARY PORTLAND CEMENT

RAW MATERIALS

• Calcareous (material having content of lime)
• Argillaceous (material having content of silica and alumina)
• Gypsum

Composition Of Raw Materials :

Lime (CaO)	60 to 67%
Silica (SiO2)	17 to 25%
Alumina (Al2O3)	3 to 8%
Iron oxide (Fe2O3)	0.5 to 6%
Magnesia (MgO)	0.1 to 4%
Sulphur trioxide (SO3)	1 to 3%
Soda and/or Potash (Na2O+K2O)	0.5 to 1.3%

MANUFACTURING PROCESSES OF CEMENT (OPC)

Cement is manufactured by the following two processes :

• Dry Process 

• Wet Process

These two processes differ in operation but fundamentals of both these processes are same.

• Crushing and grinding
• Mixing the material in proportion
• Heating the prepared mixture in rotary kiln
• Grinding the heated product known as clinker
• Mixing and grinding of cement clinker with gypsum

DRY PROCESS

The dry process is adopted when the raw materials are quite hard. The process is slow and the product is costly. 

Steps involve in manufacturing of portland cement by dry method :

            

• Limestone and clay are ground to fine powder separately and are mixed. Water is added to make a thick paste. 

• The cakes of this paste, which contain about 14 per cent of moisture, are dried and are charged into rotary kiln. 

                              Rotary Kiln

• The product obtained after calcination in rotary kiln is called clinker. The clinker is obtained as a result of incipient fusion and sintering at a temperature of about 1400°- 1500°C. 
• Because ferric oxide has lower melting point than the other oxides, it acts as a flux. Aeration of cement clinker, which is commonly practised to slake free lime, also causes an absorption of some moisture and carbon dioxide. Absorption of moisture tends to decrease the setting whereas that of carbon dioxide accelerates setting. 
• The clinker is cooled rapidly to preserve the meta stable compounds and their solid solutions dispersion of one solid in another which are made as the clinker is heated. Clinker is then cooled and ground in tube mills.
• where 2-3% of gypsum is added. Generally, cement is stored in bags of 50 kg. The purpose of adding gypsum is to coat the cement particles by interfering with the process of hydration of the cement particles. This retards the setting of cement.

WET PROCESS

The operations in the wet process of cement manufacture are mixing, burning and grinding. 

Step involve in the manufacturing of portland cement by wet process are :

• The crushed raw materials are fed into ball mill and a little water is added. On operating the ball mill, the steel balls in it pulverize the raw materials which form a slurry with water. 

• This slurry is passed to storage tanks where the proportioning of the compounds is adjusted to ensure desired chemical composition. The corrected slurry having about 40 per cent moisture content, is then fed into rotary kiln where it loses moisture and forms into lumps. 

• These are finally burned at 1500-1600°C. The lumps change to clinker at this temperature. Clinker is cooled and then ground in tube mills. While grinding the clinker, about 3 per cent gypsum is added. The cement is then stored in storage tanks from where it is supplied.

SPLITTING TENSILE STRENGTH TEST OF CONCRETE (IS: 516)

SPLITTING TENSILE STRENGTH TEST OF CONCRETE

Tests shall be made at recognized ages of the test specimens, the most usual being 7 and 28 days. Where it may be necessary to obtain the early strengths, tests may be made at the ages of 24 hours ± ½ hour and 72 hours ± 2 hours. The ages shall be calculated from the time of the addition of water to the dry ingredients.Number of Specimens – At least three specimens, preferably from different batches, shall be made for testing at each selected age.

Objective

To determine the tensile strength of concrete

Apparatus

Testing Machine – The testing machine may be of any reliable type, of sufficient capacity for the tests and capable of applying the load at the rate specified in 5.5. The permissible error shall be not greater than ± 2 percent of the maximum load.Cylinders –The cylindrical mould shall be of 150 mm diameter and 300 mm height conforming to IS: 10086-1982 Weights and weighing devices, tool and containers for mixing, tamper(square in cross section) etc.                                                                                                                                                                                              

Sampling Of Material

Samples of aggregates for each batch of concrete shall be of the desired grading and shall be in an air-dried condition. The cement samples, on arrival at the laboratory, shall be thoroughly mixed dry either by hand or in a suitable mixer in such a manner as to ensure the greatest possible blending and uniformity in the material.

Proportioning

The proportions of the materials, including water, in concrete mixes used for determining the suitability of the materials available, shall be similar in all respects to those to be employed in the work.

Weighing

The quantities of cement, each size of aggregate, and water for each batch shall be determined by weight, to an accuracy of 0.1 percent of the total weight of the batch.

Mixing Concrete 

The concrete shall be mixed by hand, or preferably, in a laboratory batch mixer, in such a manner as to avoid loss of water or other materials. Each batch of concrete shall be of such a size as to leave about 10 percent excess after moulding the desired number of test specimens.

Moulding

The cylindrical mould shall be of 150 mm diameter and 300 mm height conforming to IS: 10086-1982.

Compacting Of Concrete

Temping Bar : The tamping bar is a steel bar of 16 mm diameter , 60 cm long and bullet pointed at the lower end.

Hand Compaction

When compacting by hand, the standard tamping bar is used and the stroke of the bar should be distributed in a uniform manner. The number of strokes for each layer should not less than 30. The stroke should penetrate in to the underlying layer and the bottom layer should be rodded throughout its depth. After top layer has been compacted,the surface of the concrete should be finished level with the top of the mould,using a trowel and covered with a glass or metal plate to prevent evaporation.

Curing Of Specimen

The test specimen should be stored in a place at a temperature of 27° +/- 2°C for 24 +/-  0.5 hrs. from the time addition of water to the dry ingredients. After this period the specimen should be marked and removed from the woulds and immediately submerged in clean fresh water or saturated lime solution and kept there until taken out just prior to the test. The water or solution in witch the specimen s are kept should be renewed every seven days and should be maintained at a temperature of 27° +/- 2°c.Concrete cylinder 15 cm diameter &3 0cm long.

NOTE

Cast 6 cylinders (3 for split test &3 for compression test ).

Procedure

• Take the wet specimen from water after 7 days of curing
• Wipe out water from the surface of specimen
• Draw diametrical lines on the two ends of the specimen to ensure that they are on the same axial place.
• Note the weight and dimension of the specimen.
• Set the compression testing machine for the required range.
• Keep are plywood strip on the lower plate and place the specimen.
• Align the specimen so that the lines marked on the ends are vertical and centered over the bottom plate.
• Place the other plywood strip above the specimen.
• Bring down the upper plate to touch the plywood strip.
• Apply the load continuously without shock at a rate of approximately 14-21kg/cm2/minute (Which corresponds to a total load of 9900kg/minute to 14850kg/minute)
• Note down the breaking load(P)

Calculation

As per IS: 456, 

Split tensile strength of concrete.= 0.7Fck

The splitting tensile strength is calculated using the formula :

Tsp = 2P/ pi DL

Where 

P = applied load

D = diameter of the specimen

L = length of the specimen

Therefore,

P = Tsp x pi DL/2

Expected load = P x f.sRange to be selected is…………..

Split Tensile Strength

T = 2P/ pi DL 

Result

Splitting tensile strength of given concrete =……………….N/mm²

HOW TO PERFORM THE VOLUMETRIC SHRINKAGE TEST OF TIMBER (IS : 1708 ( Part 3) – 1986) ?

VOLUMETRIC SHRINKAGE TEST OF TIMBER

This test is performed to determine the amount of volumetric  shrinkage happen in timber when it moves from wet to dry condition. Volumetric shrinkage tells how much a wood species will shrink, but it doesn’t indicate the direction of the shrinkage. The two primary planes or surfaces of wood where shrinkage takes place are across the radial plane, and across the tangential plane, corresponding to radial shrinkage, and tangential shrinkage; these two values, when combined, should roughly add up to the volumetric shrinkage.

OBJECTIVE

To determine the volumetric shrinkage of timber.

APPARATUS :

• Weighing Balance : 0-10 kg.

• Oven : maintain a temperature of  105- 110°C

PREPARATION OF SAMPLE :

The specimens of timber are prepared with  5 × 5  × 15  cm or 2 × 2  × 6  cm sizes.

PROCEDURE :

• The specimen is weighed initially (usually green) and the volume determined.

• A suitable vessel, half filled with water, is kept on the pan of a weighing balance and weighed.

• The specimen is then completely dipped in water by means of a needle and  weighed again. The difference of the two readings is volume of the specimen.

• The specimen is taken out of the water, wiped with dry cloth, end-coated by immersion in hot paraffin, allowed to air-season under room conditions and weighed periodically until moisture content of about 12 per cent is reached. The volume is determined again.

• The specimen is then kept in an oven at 103° 2°C until an approximately constant weight is reached.

•  After oven-drying, the specimen is again weighed and, while still warm, is immersed in hot paraffin wax bath,care being taken to remove it quickly to ensure only a thin coating.

• The volume of the paraffin-coated specimen is determined by immersion as before.

CALCULATION :

Volumetric shrinkage form initial condition to required dry condition =

Moisture Content =

Oven Dry Specific Gravity =

where 

W1 and V1 = Initial weight and initial volume

Wr and Vr = Weight and volume at the initial required dry condition at r per cent moisture content.

W0 and V0 = Final weight and final volume 

WHAT IS MEANT BY HYDRATION OF CEMENT ?

HYDRATION OF CEMENT

The chemical reaction between cement and water is known as hydration of cement. The reaction takes place between the active components of cement and water. 

Active components are :

Tetracalcium Aluminate (C4AF)

Tricalcium Aluminate (C3A)

Tricalcium Silicate (C3S)

Dicalcium Silicate C2S)

Gypsum (CSH2)

The factors responsible for the physical properties of concrete are the extent of hydration of cement and the resultant microstructure of the hydrated cement. When the cement comes in contact with water, the hydration products start depositing on the outer periphery of the nucleus of hydrated cement. This reaction proceeds slowly for 2-5 hours and is called induction or dormant period. As the hydration proceeds, the deposit of hydration products on the original cement grain makes the diffusion of water to unhydrated nucleus more and more difficult, consequently reducing the rate of hydration with time.  At any stage of hydration, the cement paste consists of gel (a fine-grained product of hydration having large surface area collectively), the unreacted cement, calcium hydroxide, water and some minor compounds.

The crystals of the various resulting compounds gradually fill the space originally occupied by water, resulting in the stiffening of the mass and subsequent development of the strength.

The hardened cement paste :

Hardened cement paste consists of the following:

Ettringite                                     - 15 to 20% 

Calcium silicate hydrates, CSH     - 50 to 60% 

Calcium hydroxide (lime)             - 20 to 25% 

Voids     - 5 to 6% (in the form of capillary voids and entrapped and entrained air)

RATE OF HYDRATION

The reaction of compound C3A with water is very fast and is responsible for flash setting of cement (stiffening without strength development) and thus it will prevent the hydration of C3S and C2S. However, calcium sulphate (CaSO4) present in the clinker dissolves immediately in water and forms insolubleB calcium sulphoaluminate. It deposits on the surface of C3A forming a colloidal membrane and consequently retards the hydration of C3A. The amount of CaSO4 is adjusted to leave a little excess of C3A to hydrate directly. This membrane in the process breaks because of the pressure of the compounds formed during hydration and then again C3A becomes active in the reaction.  

              Contribution of cement compounds to strength of cement with increasing age.

The hardening of C3S can be said to be catalyzed by C3A and C3S becomes solely responsible for gain of strength up to 28 days by growth and interlocking of C-S-H gel. The increase in strength at later age is due to hydration of C2S.

                                            Rate of hydration of pure cement compound

COMPOSITION OF ORDINARY PORTLAND CEMENT (IS: 269)

COMPOSITION OF ORDINARY PORTLAND CEMENT

This is the cement used for normal concrete construction. It has adhesive and cohesive properties so as to render and to form good bond with other material. It solidifies when mixed with water. It is the most active binding medium and is perhaps the most scientifically controlled component in concrete. Cement is obtained by burning a mixture of the following materials in a define proportion :

• Siliceous materials

• Argilleceus materials 

• Calcareous materials

The temperature of which the mixture must be burnt is about 1400°C. The clinker so is cooled and powdered to the required fineness. The product so obtained is called cement.

COMPOSITION

Lime (CaO)	60 to 67%
Silica (SiO2)	17 to 25%
Alumina (Al2O3)	3 to 8%
Iron oxide (Fe2O3)	0.5 to 6%
Magnesia (MgO)	0.1 to 4%
Sulphur trioxide (SO3)	1 to 3%
Soda and/or Potash (Na2O+K2O)	0.5 to 1.3%

The above constituent mixing together to form raw material undergo a chemical reaction during burning and fusion, the compounds formed in the burning process have the properties of setting and hardening in the presence of water. They are known as Bogue compounds which are given below :

Compound	Abbreviated designation
Tricalcium silicate (3CaO.SiO2)	C3S
Dicalcium silicate (2CaO.SiO2)	C2S
Tricalcium aluminate (3CaO.Al2O3)	C3A
Tetracalcium aluminoferrite (4CaO.Al2O3.Fe2O3)	C4AF

The properties of Portland cement varies markedly with the proportions of the above four compounds, reflecting substantial difference between their individual behaviour.

FUNCTION OF FOLLOWING COMPOUNDS

Tricalcium Silicate

• Tricalcium silicate is supposed to be the best cementing material and is well burnt cement. It is about 25-50% (normally about 40 per cent) of cement. 

• It renders the clinker easier to grind, increases resistance to freezing and thawing, hydrates rapidly generating high heat and develops an early hardness and strength. 

• However, raising of C3S content beyond the specified limits increases the heat of hydration and solubility of cement in water. 

• The hydrolysis of C3S is mainly responsible for 7 day strength and hardness. 

• The heat of hydration is 500 J/g.

Dicalcium Silicate

• Dicalcium silicate is about 25-40% (normally about 32 per cent) of cement. It hydrates and hardens slowly and takes long time to add to the strength (after a year or more). 

• It imparts resistance to chemical attack. 

• Raising of C2S content renders clinker harder to grind, reduces early strength, decreases resistance to freezing and thawing at early ages and decreases heat of hydration. 

•  The heat of hydration is 260 J/g. 

Tricalcium Aluminate 

• Tricalcium aluminate is about 5-11% (normally about 10.5 per cent) of cement. 

• It rapidly reacts with water and is responsible for flash set of finely grounded clinker. The rapidity of action is regulated by the addition of 2-3% of gypsum at the time of grinding cement. 

• Tricalcium aluminate is responsible for the initial set, high heat of hydration and has greater tendency to volume changes causing cracking. 

• Raising the C3A content reduces the setting time, weakens resistance to sulphate attack and lowers the ultimate strength, heat of hydration and contraction during air hardening. 

• The heat of hydration of 865 J/g.

Tetracalcium Alumino Ferrite

• Tetacalcium allumino ferrite is about 8–14% (normally about 9 per cent) of cement. 

• It is responsible for flash set but generates less heat. 

• It has poorest cementing value. 

• Raising the C4AF content reduces the strength slightly. 

• The heat of hydration is 420 J/g.