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है”ह”ह

IS 14591 (1999): Temperature Control of Mass Concrete forDams - Guideline [WRD 9: Dams and Spillways]

.-

Is 14591 : 1999

w@7m’m

tid%pnmbiik mnTl––qf%im–r–

m R%--i-d

Indian Standard

TEMPERATURE CONTROL OF MASSCONCRETE FOR DAMS — GUIDELINES

I

ICS 93.160

0 BIS 1999

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

May I999 Price Group 6

/

il.

Dams (Overflow and Non-ovefflow) and Diversion Works Sectional Committee, RVD 9

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Dams(Ovefflow and Non-overflow) and Diversion Works Sectional Committee had been approved by the RiverValley Division Council.

Mass concrete structures undergo volumetric changes with time after the placement of concrete. A rapid risein the temperature of mass concrete takes place during the phase when the concrete mass is in plastic stageand undergoes hardening. After hardening, the concrete gradually cools due to effect of atmospheric temperature,which tends to subject the concrete to high tensile stresses. Cracking occurs in the concrete when these tensilestresses exceed the tensile strength of the concrete. This cracking is undesirable because it affects the watertightness, durability and appearance of hydraulic structures. The cracking tendency maybe reduced to acceptablelevels through appropriate design, construction and concrete placement procedures.

Temperature control is essential to (a) minimize volumetric changes and control the size and spacing ofundesirable cracks and (b) facilitate completion of the structure during the specified construction period byincreasing lift heights.

For the purpose of deciding whether a particular requirement of this standard is complied with, the finalvalue, observed or calculated expressing the result of a test or analysis, should be rounded off in accordancewith IS 2:1960 ‘Rules for rounding off numerical values (revised)’. The number of significant places retainedin the rounded off value should be the same as that of the specified value in thk standard.

..s-

IS 14591 : 1999

Iluiian Standard

TEMPERATURE CONTROL OF MASSCONCRETE FOR DAMS — GUIDELINES

1 SCOPE

This standard mainly covers precooking methodsadopted for temperature control in respect of massconcrete in dams. It also alludes to postcooling asthe same is also adopted for overall temperature control.

2 NOTATIONS

For the purpose of this standard, the following lettersymbols shall have the meaning indicated against each:

c=

D, =

h: =

K=

P=w=

H=

T=

T,, =

t=

specific heat of concrete (J/kg’’C),

depth of lift (m),

thermal diffusivity of concrete (mZ/hour),

thermal conductivity of concrete (J/m.h “C),

density of concrete (kg/m3),

mass of effective cement content in unitvolume of concrete (kg),

evolution of heat of hydration per unit massof cement (J/kg),

adiabatic temperature rise in concrete (“C) atany time t,

ultimate adiabatic rise of temperature inconcrete (“C), and

time interval between successive lifts (h).

3 TERMINOLOGY

For the purpose this standard, the following definitionsshall apply.

3.1 Adiabatic Temperature

It is the temperature attained by concrete due to heatof hydration without any gain or loss of heat from/to the atmosphere.

3.2 Ambient Temperature

It is the atmospheric temperature at the dam site.

3.3 Coefficient of Thermal Expansion ( ct )

It is the change in linear dimension of a material perunit length per degree of temperature change.

3.4 Density ( p )

It is the mass per unit volume of the material.

3.5 Placement Temperature of Concrete

It is the temperature of the mass concrete at the timeof its placement at site.

3.6 !@ctic Heat ( C )

It is the amount of heat required to raise the temperatureof unit mass of concrete by one degree celsius.

3.7 Stable Temperature of Concrete

It is the temperature which a dam would achieve incourse of time, say 8 to 10 years, or even moredepending upon the reservoir water temperature andthe mean annual ambient temperature.

3.7.1 Stable Temperature at Downstream Face of Dam

Ignoring the effect of daily or seasonal variation ofsurrounding temperature, the stable temperature ofconcrete near the downstream face can be assumedto be equal to the mean annual ambient temperature.This should be slightly modified if the downstreamface of the dam is shadowed by surrounding hills.

3.7.2 Stable Temperature at Upstream Face of Dam

Since the upstream face will remain in contact withreservoir water, its stable temperature will be sameas that of the reservoir water which may be taken asmean annual river water temperature.

3.8 Thermal Conductivity (K)

It is the rate of heat flow per unit area under a unittemperature difference between the two faces ofmaterial of unit length.

3.9 Thermal Diffusivity (h: )

It is the index of the facility with which a materialwill undergo temperature change. It is a constantwhich determines the rate of temperature change ina homogeneous isotropic material when heated orcooled. Diffusivity can be defined as h: = K/pC.

4 TEMPERATURE RISE

4.1 General

Volume change and development of tensile stress ina concrete dam depend upon the temperature rise acrossthe section of the dam. Newly placed concreteundergoes a rise in temperature due to the exothermicreaction of the cementing materials in the concrete.For final temperature control studies, the heatgeneration for particular concrete mix should beobtained by laboratory tests. The adiabatic temperaturerise in the concrete relates to heat of hydration. Theactual temperature ”rise in the concrete will be affecteddue to the flow of heat between the concrete in the

1

.s-

1s 14591 : 1999

body of the dam and that at the exposed faces of thedam. Temperature cracking in the mass concrete isrelated to the dimensions and shape of the concreteblocks, thickness of lifts, time interval between liftsand height differential between the blocks.

4.2 Factors Affecting Temperature Risein Concrete

4.21 Heut of Hydration of Cement

Heat of hydration should be computed by conductinglaboratory tests. Source of cement should be identifiedin advance and only one type of cement from the samesource should be used in a dam. However, in absenceof laboratory test results, heat of hydration for ordinaryPortland cement may be assumed as 335 kJ/kg at 28days.

4.2.2 Specific Heat

Specific heat of normal weight concrete varies onlyslightly with aggregate characteristics, temperature andother parameters, Values from 0.85 to 1.05 kJ/kg.°Care representative over a wide range of conditionsand matgxials. This value maybe adopted in the absenceof laboratory test results.

4.2.3 Thermal Diffusivity

This is an index of the ease, or difficulty, with whichconcrete undergoes temperature change. For normalweight concrete where density and specific heat varywithin narrow range, thermal diffusivity reflects theconductivity value. High diffusivity indicates greaterease in gaining or losing heat.

4.2.4 Thermal Conductivity

Thermal conductivity is a measure of the capabilityof concrete to conduct heat. The thermal conductivityvaries with mineralogical characteristics of aggregate,moisture content, density and temperature of concrete.Values of thermal conductivity should be obtainedby laboratory tests.

In the absence of laboratory tests, the values ofdiffusivity and thermal conductivity of concrete asgiven in Table 1 may be adopted for preliminarystudies.

Table 1 Typical Values of Diffusivityand Thermal Conductivity of

Concrete Made with Different Rocks

Coarse Diffusivity ThermalAggregate Conductivity

mVh J/mhC

Basalt 0.0030 7 534.8 to 7 57’6.66Rhyolite 0.0033 7 367.36 to 7 451.08Grisnitc 0.0040 9 418.50 to 9 878.96Dolomite 0.004 6 11 762.66 to 12 139.40Limestone 0,0047 11 302.20 to 11 637.08(.)uwtzite 0.0054 12 611.72 to 12 767.30

4.2.5 The coefficient of thermal expansion for concreteis essentially constant over the normal temperaturerange, and tends to increase with increasing cementcontent and decrease with age. The main factorsaffecting the value of the coefficient of thermalexpansion of concrete are aggregate type and moisturecontent; other factors such as mix proportion, cementtype and age influence its magnitude to a lesser extent.Typical values of coefficient of thermal expansionof concrete using various aggregates is given inTable 2.

Table 2 Coefficient of Thermal Expansion ofConcrete with Various Aggregates

Coarse Aggregate Coefficient of ThermatExpansion/ “C

Quartzite 1.35 x ICJ5

Sandstone 1.04 x 1CJ5

Basalt 0.83 X ]tT5

Limestone 0.58 X 11T5

Granite 0.81 X 1CJ5

Dolerite 0.77 x 10-5

Gravel 1.22 x 10-5

4.2.6 Adiabatic Temperature Rise in Mass Concrete

Newly placed concrete undergoes a rise in temperaturedue to exothetmic reaction of the cementing materialin the concrete. Hence, for temperature computationsof mass concrete, certain parameters are required tobe known or assumed. One of the important parametersis adiabatic temperature rise in concrete. This is requiredto determine the amount of heat generated for a specificperiod of time and effective cement content. Compoundcompositions and fineness of cement largely influencegeneration of heat.

Adiabatic temperature rise is governed by the law:

T = T, (l-e-m’)where ‘T,’ and ‘m’ are constantsfor a particular concrete.

4.2.6.1 For temperature rise, the specific heat of allthe ingredients of concrete is the governing factor andthe concrete absorbs the heat generated by the cement.

Heat generated by cement= Heat absorbed by concrete

WH = p.C.To

WHor To= —

pc

4.2.6.2 Placement temperature of concrete

This is the temperature of the mass concrete at thetime of its placement. This has to be predeterminedin order to ensure that the maximum permissibletemperature rise is not exceeded.

4

2

This can be computed by the formula:

0.22 (TU,.WC,+TPA.Wr~+TC.W] + (TrWf+Tw.ww-79.6.Wi)T_=

1,

where

TP =

TC, =

T,. =

T, =

Tf =

Tw =

Wca =

w,, =

Wc =

w, =

w, =

Ww =

4.2.7 LOSS

0.22 (Wra+wrm+wc)+ w,+ W*+ w,

placement temperature of concrete in “C,

temperature of coarse aggregate at thetime of mixing in ‘C,

temperature of fine aggregate at the timeof mixing in “C,

temperature of cement at the time ofmixing in “C,

temperature in ‘C of free and absorbedmoisture in aggregate which may beassumed to be same as that of aggregateunless otherwise specified,

temperature of batch mixing water in “C,

dry mass of coarse aggregate in kg,

dry mass of fine aggregate in kg,

mass of cement in kg,

mass of free and absorbed moisture inaggregate in kg,

mass of ice in kg, and

mass of batch mixing water in kg.

of Heat from the Mass Concrete AfterPlacement and Net Temperature Rise

4.2.7.1 The entire quantum of heat generated byhydration of cement does not go into raising thetemperature of concrete. As heat is generated, thereis also a loss to, or gain from, the atmosphere dueto the difference in temperature between concrete andthe atmosphere. For all practical purposes, it issufficient to estimate the loss of heat from the exposedtop surface of the lift. The heat loss from the verticalsides of the lift may be neglected. Also, the heat lossafter successive lifts have been laid over the lift inquestion, is relatively small and can be neglected, thatis, the heat lost from the exposed top surface duringthe interval between two lifts only is considered forestimating total heat loss. The loss of heat is calculatedseparately for the following three idealized conditionsand then the total loss is obtained by summation ofthese losses:

a)

b)

Heat loss (q3) from the exposed surface of alift of depth D initially at temperature O°C,exposed to O“C at its upper surface andgenerating heat according to the lawT = T{, ( 1 - e-’”’), if cast on an inert liftinitially at O“C. A lift is considered to be inertif the generation of heat by chemical actionin the cement has ceased;

Heat loss (q2) from the exposed surface of aninert lift of depth D initially at temperaturee,, (where 9,, = placement temperature –atmospheric temperature), exposed to O°C at

c)

4.2.7.2

IS 14591: 1999

it’s upper surface and cast on an inert lift atO“C; and

Heat loss (g,) from the exposed surface of aninert lift initially at O°C, exposed to O“C atit’s upper surface and cast on an inert liftinitially at temperature (11.

The first idealized condition assumes that theplacement temperature of the concrete and theatmospheric temperature are the same that is O°C andthe lift is cast upon an inert lift initially at O“C. Theloss of heat as it is generated is given by the equation.

93 =qCp DT,

or in terms of temperature equivalent of qf,

T3=q To

where

% = heat lost per unit area of the exposed surfacein Joules, and

q = ratio of heat lost to the total heat generated.

The value of q can be determined from Fi . 1 after

bcalculating the dimensionless quantities D/ 4h~t andmt where t is the time of exposure that is the intervalbetween two lifts.

04

0’6

0.8

lo

I .2

I.&

1.6

1. 8.

2.0-

2. 2

2. 4.

2. 6-

2.8

I.OL I \ 1OI234567O91O!I 12131 L 151617181920

ml

RATIO OF HEAT LOSS TO TOTALHEAT GENERATED IN LIFT OF

~=L . DEPTH Dc PD To HEAT BEING GE NERATEO IN LIFT

AC CO ROING 10 RELbTl ON l= M!. aml)

FIG. 1 PARTOFTOTALHEATLOSTFROMSURFACEOFLIIT

4.2.7.3 Under the second idealized condition, the heatloss due to the difference between the placementtemperature and atmospheric temperature, which wasassumed to be at O°C in the first condition, is calculated.Since the heat loss due to internal heat generation iscalculated under the first condition given in 4.2.7.1(a), the lift is assumed inert, that is no internal heatgeneration is considered in the second condition. Theheat loss from the exposed surface of an inert liftinitially at a temperature qO above atmospherictemperature, cast on an inert lift initially at the sametemperature as that of atmosphere,

,2=24JZHh

is given by:

3

IS 14591 : 1999

or in terms of temperature equivalent of q2

T,= 92P.C.D

where

92 =

e,, =

heat loss per unit surface area of the lift, and

difference between placement temperature andatmospheric temperature and]

t

1=

1-

~-4h:t

&dt

2

d

o

I can be calculated from Fig. 2.

I— DFIG.2PLOTOF -=$ Vs

r 4h; td

4.2.7.4 In the first and second idealized conditions,the lift is assumed to be cast on an inert lift whichis at the same temperature as that of atmosphere.However, as at the end of the exposure period of theprevious lift that is, at the time of placement of thenew lift, some part of the total heat generated in theprevious lift still remain unlost, the temperatureof theprevious lift is increased above atmospherictemperature due to this remaining heat. Therefore,some heat from the previous lift is lost through theexposed surface of the lift in question during theexposure period of this new lift. This heat loss isgiven by the equation:

2K92 I9,= &

or in terms of temperature equivalent of q,

where

q, =

1=

02 =

heat lost per unit area of the exposed surface,

same as given in 4.2.7.3, and

difference of temperature between the. .

temperature of the previous lift and the

atmospheric temperature.

The temperature of the previous lift is calculated bysubtracting the temperature loss during the exposureperiod from the total adiabatic temperature rise. Thus

e, =TP+TO-(T3+T2)

NOTE — Temperatmv. loss T1is neglected in this calculation.

4.2.7.5 The total heat loss (q) is calculated bysummation of q3, q2 and q,. Thus

9=93+92+9,

or temperature equivalent of the heat loss q is

9TL=— =T3+TZ+T1

CpD

4.2.8 Evaluation of Thermal Stress

Magnitude of thermal stress developed due totemperature change using the stress temperature relationmay be computed from the following formula:

f=aEp R(Tp+~, -TL -T,)

where

f=

a=

Ep=

R=

thermal stress resulting due to temperaturegradient in MPa (This thermal stress shouldbe limited to permissible tensile stress whichis about 10 percent of the compressivestrength),

coefficient of thermal expansion on concrete,

sustained modulus of elasticity of concrete inMPa. In absence of laboratory values it canbe taken as approximately 0.5 to 0.6 timesthe instantaneous modulus of elasticity ofconcrete (lower values being applicable whenconcrete is loaded at early ages, that is 2 days,7 days, etc, after casting and higher valuesapplied when concrete is loaded at later ages,that is 90 days, 365 days etc. Intermediatevalues are applicable for intermediate loadingages).

restraint factor. It has value of 1 at the contactof dam and foundation and also at a levelwhere concreting is interrupted for a periodof more than two weeks time. It decreasesrapidly at higher levels. It may be taken as

.

i

._.Q-

IS 14591: 1999

0.5 at a height of about 0.15 B, where B isthe base width of the dam at foundation levelor at the level where R has been taken as 1,

TP= placement temperature of concrete in ‘C,

~, = ultimate adiabatic rise in temperature ofconcrete in “C,

T~ = temperature loss, that is T1 + T2+ T3 in ‘C,and

T, = final stable temperature of dam in “C.

A typical example illustrating the computation fordetermination of thermal properties of mass concreteis given at Annex A.

5 METHODS OF TEMPERATURE CONTROL

5.1 Most commonly used methods are precooking,post cooling and reducing heat of hydration by propermix design. The ideal condition would be simply toplace the concrete at stable temperature of dam andheat of hydration removed, as it is generated, so thattemperature of concrete is not allowed to rise abovestable temperature. However this is not possible toachieve practical y. Therefore, the most practicalmethod is to mecool concrete so as to restrain thenet temperatu~e rise to acceptable levels.

5.2 Precooking

5.2.1 One of the most effective and positivetemperature control measure is precooking whichreduces the placement temperature of concrete(see 4.2.6.2). The method, or combination of methods,used to reduce concrete placement temperatures willvary with the degree of cooling required and theequipment available with the project authority or thecontractor. In this method usually the fine and coarseaggregates and the water are separately cooled to therequisite temperatures.

5.2.1.1 Mixing water may be cooled to varying degrees,usually from O“C to 4“C. Adding crushed ice or iceflakes to the mix is an effective method of coolingbecause it takes advantage of the latent heat of fusionof ice. The addition of large amount of ice flakes,however, may not be possible in cases where bothcoarse aggregate and sand contain appreciable amountof free water, in which case the amount of water tobe added to the mix may be so small that substitutionof part of the water to be added with ice may notbe feasible. From practical considerations, not morethan 70 percent of water should be replaced by crushedice.

Although most rock minerals have comparatively lowheat capacity, since aggregates comprise the greatestproportion of concrete mix, the temperature of theaggregate has the greatest influence on the temperature.of the concrete. Cooling of coarse aggregate to about1.7°C may be accomplished in several ways. Onemethod is to chill the aggregates in large tanks ofrefrigerated water for a given period of time or byspraying cold water. Effective cooling of coarseaggregate is also attained by forcing refrigerated air

through the aggregate while the aggregate is drainingin stock piles, or while it is in a conveyer belt or whileit is passing through the bins of the batching plant.

5.2.1.2 Sand may be cooled by passing it throughvertical tubular heat exchangers. A chilled air blastdirected on the sand as it is transported on conveyerbelts may also be used. Sand may also be cooled bypassing it through screw conveyers, the blades of whichcarry chilled water inside. Immersion of sand in coldwater is not practical because of the difficulty inremoving free water from the sand after cooling. Thisalso leads to bulking of sand.

5.2.1.3 Cementitious materials used in concrete arehydraulic materials, so their quality control requiresthat they be handled and batched dry. If the temperatureof the cement is brought down below the dew pointof the surrounding atmosphere, moisture will condenseand adversely affect the ultimate quality of the cement.Generally, the temperature of bulk cement suppliedis about 37”C; hence it neither cools naturally norlooses a sizable portion of excess heat before it isused. Therefore, cooling of cement is not normallydone.

5.2.1.4 Refrigeration plant capaci~

As the temperatures of aggregates will generally followthe annual cycle of ambient air temperature, therefrigeration plant capacity requirement should bedetermined for a specific segment of time, that is fora week or a month. The refrigeration may be designedto produce a single material, such as ice, or may bedivided into various cooling systems for productionof ice, chilled water and/or cooled air according toheat balance needs. The size of the cooling plantrequired is expressed in tonnes of refrigeration.Refrigeration capacity of plant is worked out in termsof ice equivalent (see Annex B).

5.3 Post Cooling

5.3.1 Post cooling is a means of crack control. Controlof concrete temperature may be effectivelyaccomplished by circulating cold water through thinwalled pipes embedded in concrete. This will reducethe temperature of newly placed concrete by severaldegrees, but the primary purpose of the system is toaccelerate the subsequent heat removal andaccompanying volume decrease, during early ageswhen the elastic modulus is relatively low. Post coolingis also used where longitudinal contraction joints areprovided in order to reduce the temperature of concreteto the desired value prior to grouting of transversecontraction joint. Post cooling will create a flattertemperature gradient between the warm concrete andthe cooler exterior atmosphere which, in turn, helpsin avoiding temperature cracks. Other methods suchas evaporative cooling with a fine water spray, coldwater curing and shading may prove beneficial, butthe results are variable and do not significantly affectthe temperature in the interior of massive placement.

5.3.1.1 The embedded cooling system consist of

5

IS 14591 : 1999

f ,—

aluminium or synthetic plastic pipe or tubing generallyot_25 mm dia and 1.50 mm wall thickness placed ingrid like coils over the top of each concrete lift. Whenthe expected active cooling period exceeds 3 months,steel tubing should be used. The number of coils ina block depends upon the size of the block and thehorizontal spacing of the pipes. For practical reasons,pipe coils are placed and tied to the top of a hardenedconcrete surface and thus vertical spacing of the pipecorresponds to lift thickness. A horizontal spacingsame as the vertical spacing will result in the mostuniform cooling pattern but variations may be allowed.Supply and return headers, with manifolds to permitindividual connections to each coil are normally placedon the downstream face of the dam. In some case,cooling shafts, galleries and embedded header systemmay be used to advantage.

5.3.1.2 Postcooling by running chilled water throughembedded pipes is nowadays recommended only whenlongitudinal joints are provided. Postcooling isgenerally avoided mainly because it is costlier thanprecooking system. Improved techniques for precookingthe dry components would be beneficial when a largereduction in placement temperature is necessary. Withrecent advancement in concrete technology, thequantity of cement used for producing concrete ofrequired strength has been reduced appreciably andthus postcooling may not be considered necessaryin dams.

5.4 Pre-design Measures for AchievingTemperature Control

Cracking tendencies in concrete due to temperaturechanges may be reduced to an acceptable level bysuitable design and construction procedures. Thevolumetric changes are caused by the temperature dropfrom the peak temperature attained by concrete shortlyafter placement to the final stable temperature of thestructure. To bring down net temperature rise toacceptable limits, in order to avoid cracking, the

parameters given in 5.4.1 to 5.4.4 are to bepredetermined or suitably modified for a concrete dam.

5.4.1 The cement content in the concrete plays animportant role in evolution of heat of hydration. Bysuitably modifying the concrete mix design, thequantity of cement per cubic metre of concrete maybe reduced so as to reduce the amount of heat generatedby cement.

5.4.2 The height, of the placement lift is generallygoverned by economic considerations. Shallow liftsnot only slow down the construction but also resultin increased construction joints which entail additionalcosts for cleaning and preparation for placement ofthe next lift. The thickness of lift is also related tothe temperature control measures proposed and theambient temperature at the site. To reduce the nettemperature rise, the lift thickness should be reducedif time is not a constraint.

5.4.3 There is always some time lag betweenplacement of concrete in successive lifts. Dependingupon ambient temperatures, these delays can bebeneficial or harmful. Allowance of sufficient timebetween two construction lifts to allow large dissipationof heat from the surface is an effective and importantfactor to control the rise in the temperature duringconstruction. The minimum elapsed time betweenplacing of successive lifts in any block is usuallyrestricted to 72 hours, but temperature studies shouldbe made to relate heat loss or heat gain to the placementlift heights.

5.4.4 During summer months the ambienttemperature is very high and, as such, heat gain fromthe atmosphere is also high. This may be reducedby continuous curing of the concrete by sprinklersusing river water, after concrete has set. In such acase, ambient temperature for calculation purposesmay be assumed as average of curing water temperatureand actual ambient temperature.

{.,—

TYPICAL ILLUSTRATION FORCONCRETE IN

Data

IS 14591 : 1999 .

ANNEX A

(Clause 4.2.8) JDETERMINATION OF THERMAL PROPERTIES OF MASS

I

~

HEATING ZONE OF A CONCRETE DAM

1

23456789

101112131415161718

192021

22

2324

Mix proportion of concrete by mass(Cement:Fine aggregate: Coarse aggregite)Cement content of concreteTotal coarse aggregate in concreteTotal fine aggregate in concreteTotal water content in concreteDensity of concrete (p)Mean annual air temperatureMean summer temperatureMean winter temperature (November to February)Mean annual river water temperatureSpecific heat of concrete (C)Thermal conductivity of concrete (K)Ultimate adiabatic rise in temperature (To)Factor m for the concreteExposure period of the lift (t)Lift height (D)Desired placement temperature of concreteTemperature of ingredients of concrete atthe time of mixing

a) cementb) coarse aggregatec) fine aggregated) batched mixing water

Ice percent of mixing waterPermissible temperature dropPermissible tensile stress at 10 percentof the compressive strength of concreteCo-efficient of thermal expansionof concrete (et)Sustained modulus of elasticity of concrete (Ep)Restraint factor (R)

COMPUTATIONS

1 : 2.56: 11.54

162 kg/rn~1928 kg/mq416 kg/m’89 kglrd2610 kg/mg27.8°C31.7°C24.4°C26.7°C857.33 J/kg°C2.235 5 J/m.s.°C21.8°C0.025 per h72 h1.50 m15.5°C

37.8°C21.l°C32.2°C26.7°C70 percent11 to 16.7°C

1.5 to 2.0 MPa

4 x 104 per “C2 x 104 MPa1.00

A) Verification of Desired Placement Temperature of Concrete

Placement temperature of concrete is computed by the formula given in 4.2.6.2.

0.22 (TC, WC,+ T,, W~,+ TCWC)+ T~ W~+ TWWW– 79.6WiT, =

0.22 (Wcl + w,, + Wc) + w, + Ww + Wi

0.22 (21.1 X 1928 + 32.2 X 416 + 37.8 X 162) + 32.2 X O + 26.7 X 89 X 0.3 – 70.6 X 89 X 0.7T, =

0.22 (1 928 + 416 + 162) + O + 89 X 0.3 + 89 X 0.7

0.22 (40 680.8 + 13 395.2 + 6 123.6) + O + 712.89-4959.08Tp =

0.22 (2 506) + 89

13243.91 - 4246.19 8997.72T=P

= = 14.05°c551.32 + 89 640.32

7

.“

f ,—

IS 14591 : 1999

The placement temperature at the site of work is expected to be about 15.5°C as desired.

B) Determination of Loss of Heat from the Surface of the Lift

i) The drop in temperature of the concrete due to heat loss q3 is obtained by the following formula:

T, = q T,,

The value of q is obtained from Fig. 1 after calculating mt and D/~

m = 0.025 per hour and t = 72 h

mt = 0.025 x 72 = 1.80

a“’’&=&The diffusivity h: of concrete is calculated by the formula:

Kh; =_=

2.2355

Cp 857.33 X 2610

hi = 9.994 x 10-7 m2/s

1.50

‘enter% == 1.4735

d 44 X 3.598 X 10-3 X 72

Now, corresponding to the values of mt = 1.8 and D/@= 1.47 the value of q as obtained fromFig. 1 is 0.25.

Thus, T, = 0.25 T,

= 0.25 x 21.8

= 5.45 “c

NOTE — In the absence of laboratory dataj the vafue of 7’0may be calculated by the formula given in 4.2.6.1 as illustrated below:

Assuming heat of hydration of cement, H = 343527 J/kg

Effective cement content (W) considering 25 percent pozzokma content of efficiency 0.50

= 162.00 x 0.75 + 162 x 0.25 x 0.50 = 141.75 kg/m3

HWThus, ~, = —

pc

343 527 X 141.75

2610 X 857.33

—— 21.76°C say 21 .8°C

ii) The temperature drop due to heat loss qz is calculated by the formula:

[r12h: 00 tT2= — —– I

DA h:

8

.,—

,

IS 14591: 1999

iii)

---Placement temperature — Atmospheric temperature

15.5-31.67

- 16.2°C

3.598 x 10-~ mzlhr.

1.5 m

72 h.

1.50Hence — = = 1.4735

d4h:t 44 x 3.598 x 10-3 x 72

IFrom Fig. 2, — = 0.011

D/ 2h:

0.011 x 1.5Hence, I = ‘2 X (3.598 X 10-3) = 2“30

T, =2“[3”59::2-16”2)] x [LT22”31=-0w38@916)

c)

I

Here

.

=— 6.09°C

Temperature drop due to heat loss q, is calculated by the formula:

* = 2h;91

~xlD&

0, = (TP + To – T, – TJ – atmospheric temperature

= (15.5 + 21.8-5.45 + 6.09) -31.7

= 6.2°C

2 X (3.598 X 10-3) X 6.24 X 2.30Hence T, =

I.s&

= o.04°c

Therefore, the total temperature drop due to loss of heat from the exposed surface of the lift,

TL=T3+T, +T1

= 5.45-6.09 + O.ti

= -0.6

Evaluation of thermal stresses

Maximum temperature attained by concrete

= TP+ ~, – losses

= 15.5 + 21.8- (-0.6)

= 37.90”C

Final stable temperature of concrete, T, is eqw!d to mean annual air temperature.

Thus T, = 27.8°C

Thermal stresses, F = a E, R (TP + To - T, - T>

= 4 X 10-’ X 2 X 10’ X 1 (15.5 + 21.8 + 0.6- 27.8)

= 0.81 MPa < 1.5 MPa, hence acceptable.

9

*M-

IS 14591 : 1999

ANNEX B

(Clause 5.2. 1.4)

DETERMINATION OF REFRIGERATION PLANT CAPACITY

B-1 The capacity of refrigeration plant can be designed so as to constitute all cooling media into one materialsuch as production of ice or can be divided into different cooling systems such as production of ice, chilledwater and/or chilled air according to requirements of heat balance. Use of ice is one of the basic methodsto lower the concrete placement temperature. Refrigeration capacity of plant is worked out in terms of iceequivalent.

B-2 EXAMPLE

It is proposed to cool coarse aggregate (CA) having temperature of 32.22°C to 26.67°C using river waterat a temperature of 26.67”C, then further cooling to 21.11 ‘C by chilled water having temperature of O“C.

Following data has been used for estimating the refrigeration capacity of the plant:

Specific heat of coarse aggregate = 946.2168 J/kg°CSpecific heat of water = 4 186.8 J/kg°CHeat of fusion of ice = 334609 J/kg°C

Heat required to be extracted from CA to lower the temperature from 26.67°C to 21.11 ‘C.

= Wt of CA x Sp heat of CA x Temperature difference= 1 928 X 946.2168 X (26.67°C - 21.11°C)= 10 143 141 J/rn~.

Heat available from every kilogram of chilled water at O°C to lower the temperature of CA to 21.11 ‘C.

= Sp heat of water x temperature difference= 4 186.8 x (21.11°c - O“c)= 88383.348 J/kg.

Therefore, quantity of chilled water at O“C required for cooling the coarse aggregate up to 21.11 “C.

10 143 141

= 88 383.348

= 114.76 kg/m~

Since it would be necessary to immerse the aggregates in chilled water completely, it is assumed that20 percent extra quantity would be necessary for cooling coarse aggregate up to 21. 11°C.

Quantity of chilled water at O“C required per cubic metre of concrete:

= 1.20 X 114.76= 137.71 kg

Heat required to be extracted from river water at 26.67°C to chill it to O“C, per cubic metre of concrete:

= Weight of chilled water x sp heat of water x temperature difference

= 137.71 X 4 186.8 X (26.67°C – O°C)

— 15 376968 J

Equivalent chilled water quantity per cubic metre of concrete

1.,,

15 376968=

334 609 + (4 186.8 X 21.11)

= 36.35 kg

10

Is 14591 : 1999

Now considering a batching plant capacity of 800 cubic metre of concrete per day,

Ice equivalent of chilled water quantity needed per day

= 800 X 36.35 = 29080 kg

The ice required in place of water is proposed to be about 70 percent; therefore, quantity of ice requiredfor mixing per cubic metre of concrete:

= 89.00 X 0.70

= 62.30 kg

Assuming 25 percent wastage, total quantity of ice required per cubic metre of concrete

= 62.30 X 1.25

= 77.875 kg

Again considering a batching plant capacity of 800 cubic metre of concrete per day.

Ice required per day = 800 x 77.875 = 62300 kg

Total

Total

ice required is

= 29080 + 62300= 91 380 kg

kilo Joule equivalent of 91 380 kg of ice per day

= 91 380 [334.609 + 4.1868 X (26.67)]

= 40780244 kJ/day

The refrigeration capacity of a plant in terms of Tonne Refrigeration (TR), assuming that 1 TR is equivalentto 3.489 kJ/s and the plant works for

40780244TR=

3.89 X 3 600 X 16

= 202.9 TR, say 203 TR

16 hours a day, is g~ven by:

Assuming 35 T R for cooling of the building and surroundings, total capacity of refrigeration plant

= 35 + 203

= 238 TR.

11

Bureau of Indian Stapdards

t%—

[ BIS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to promote

1 “

harmonious development of the activities of’ standardization, marking and quality certification of goods.,:,.,,,,:- and attending to connected matters in the country.

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Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are alsoreviewed periodically; a standard along with amendments is reaffirmed when such review indicates thatno changes are needed; if the review indicates that changes are needed, it is taken up for revision. Usersof Indian Standards should ascertain thot they are in possession of the latest amendments or edition byreferring to the latest issue of ‘BIS Handbook’ and ‘Standards: Monthly

.W”

This Indian Standard has been developed from DOC : No. RVD 9 (4497.

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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