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CiIvil Engineering RCC design for diploma nd B Tech
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ICS 91.100.
0 BIS 2000
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG NEW DELHI 110002
July 2000 (^) Price Rs 260.
This Indian Standard (Fourth Revision) was adopted by the Bureau of Indian Standards, after the draft finalixed by the Cement and Concrete Sectional Committee had been approved by the Civil Engineering Division Council.
This standard was first published in 1953 under the title ‘Code of practice for plain and reinforced concrete for general building construction’ and subsequently revised in 1957. The code was further revised in 1964 and published under modified title ‘Code of practice for plain and reinforced concrete’, thus enlarging the scope of use of this code to structures other than general building construction also. The third revision was published in 1978, and it included limit state approach to design. This is the fourth revision of the standard. This revision was taken up with a view to keeping abreast with the rapid development in the field of concrete technology and to bring in further modifications/improvements in the light of experience gained while using the earlier version of the standard. This revision incorporates a number of important changes. The major thrust in the revision is on the following lines: a) In recent years, durability of concrete structures have become the cause of concern to all concrete technologists. This has led to the need to codify the durability requirements world over. In this revision of the code, in order to introduce in-built protection from factors affecting a structure, earlier clause on durability has been elaborated and a detailed clause covering different aspects of design of durable structure has been incorporated. b) Sampling and acceptance criteria for concrete have been revised. With tbis revision acceptance criteria has been simplified in line with the provisions given in BS 5328 (Part 4):1990 ‘Concrete: Part 4 Specification for the procedures to be used in sampling, testing and assessing compliance of concrete’.
Some of the significant changes incorporated in Section 2 are as follows:
0
j)
k)
All the three grades of ordinary Portland cement, namely 33 grade, 43 grade and 53 grade and sulphate resisting Portland cement have been included in the list of types of cement used (in addition to other types of cement). The permissible limits for solids in water have been modified keeping in view the durability requirements. The clause on admixtures has been modified in view of the availability of new types of admixtures including superplasticixers. In Table 2 ‘Grades of Concrete’, grades higher than M 40 have been included. It has been recommended that minimum grade of concrete shall be not less than M 20 in reinforced concrete work (see also 6.1.3). The formula for estimation of modulus of elasticity of concrete has been revised. In the absenceof proper correlation between compacting factor, vee-bee time and slump, workability has now been specified only in terms of slump in line with the provisions in BS 5328 (Parts 1 to 4). Durability clause has been enlarged to include detailed guidance concerning the factors affecting durability. The table on ‘Environmental Exposure Conditions’ has been modified to include ‘very severe’ and ‘extreme’ exposure conditions. This clause also covers requirements for shape and size of member, depth of concrete cover, concrete quality, requirement against exposure to aggressive chemical and sulphate attack, minimum cement requirement and maximum water cement ratio, limits of chloride content, alkali silica reaction, and importance of compaction, finishing and curing. A clause on ‘Quality Assurance Measures’ has been incorporated to give due emphasis to good practices of concreting. Proper limits have been introduced on the accuracy of measuring equipments to ensure accurate batching of concrete.
DIN 1045 July 1988 Structural use of concrete, design and construction, Deutsches Institut fur Normung E.V. CEB-FIP Model code 1990, Comite Euro - International Du Belon
The composition of the technical committee responsible for the formulation of this standard is given in Annex H. For the purpose of deciding whether a particular requirement of this standard is complied with, the final value, observed or calculated, expressing the result of a test or analysis shall be rounded off in accordance with IS 2 : 1960 ‘Rules for rounding off numerical values (revised)‘. The number of significant places retained in the rounded off value should be the same as that of~the specified value in this standard.
As in the Original Standard, this Page is Intentionally Left Blank
13.4 Construction Joints and Cold Joints 13.5 Curing 13.6 Supervision
14 CONCRERNG UNDERSPECIALCONDITIONS
14.1 Work in Extreme Weather Conditions 14.2 Under-Water Concreting 15 SAMPLINGAND STRENGTHOF DESIGNEDCONCRETEMrx 15.1 General 15.2 Frequency of Sampling 15.3 Test Specimen 15.4 Test Results of Sample 16 ACCEPTANCECRITERIA 17 INSPECI-IONANDTEFXJNGOFSTRWTURE
18.1 Aim of Design 18.2 Methods of Design 18.3 Durability, Workmanship and Materials 18.4 Design Process I 9 LOADSANDFORCES 19.1’ General 19.2 Dead Loads 19.3 Imposed Loads, Wind Loads and Snow Loads 19;4 Earthquake Forces 19.5 Shrinkage, Creep and Temperature Effects 19.6 Other Forces and Effects 19.7 Combination of Loads 19.8 Dead Load Counteracting Other Loads and Forces 19.9 Design Load 20 STABILITYOFTHE STRUCTURE 20.1 Overturning 20.2 Sliding 20.3 Probable Variation in Dead Load 20.4 Moment Connection 20.5 Lateral Sway 2 1 FIRERESISTANCE 22 ANALYSIS 22.1 General 22.2 Effective Span 22.3 Stiffness
PAGE
22.4 Structural Frames 22.5 Moment and Shear Coefficients for Continuous Beams 22.6 Critical Sections for Moment and Shear 22.7 Redistribution of Moments . 23 BEAMS
23.0 Effective Depth 23.1 T-Beams and L-Beams 23.2 Control of Deflection 23.3 Slenderness Limits for Beams to Ensure Lateral Stability 24 SOLIDSLABS 24.1 General 24.2 Slabs Continuous Over Supports 24.3 Slabs Monolithic with Supports 24.4 Slabs Spanning in Two Directions~at Right Angles 24.5 Loads on Supporting Beams 25 COMPRESSIONMEZMBERS 25.1 Definitions 25.2 Effective Length of Compression Members 25.3 Slenderness Limits for Columns 25.4 Minimum Eccentricity 26 REQUIREMENTSGOVERNING REINFORCEMENT AND DETAILING 26.1 General 26.2 Development of Stress in Reinforcement 26.3 Spacing of Reinforcement 26.4 Nominal Cover to Reinforcement 26.5 Requirements of Reinforcement for Structural Members 27 EXPANSIONJOMTS
SECTION 4 SPECIAL DESIGN REQUIREMENTS FOR STRUCTURAL MEMBERS AND SYSTEMS
28 CONCRETECORBELS 28.1 General 28.2 Design 29 DEEP BEAMS 29.1 General 29.2 Lever Arm 29.3 Reinforcement 30 RIBBED, HOLLOWBLOCKORVOIDEDSLAB 30.1 General 30.2 Analysis of Structure 30.3 Shear 30.4 Deflection
35 35 36 36 36 36 36 37 39 39 39 39 39 41 41 41 41 42 42 42 42 42 42 45 46 46 50
51 51 51 51 51 51 51 52 52 52 52 52
PAGE
38.1 Assumptions
39 LIMIT STATEOFCOLLAPSE: COMPRESSION
39.1 Assumptions 39.2 Minimum Eccentricity 39.3 Short Axially Loaded Members in Compression 39.4 Compression Members with Helical Reinforcement 39.5 Members Subjected to Combined Axial Load and Uniaxial Bending 39.6 Members Subjected to Combined Axial Load and Biaxial Bending 39.7 Slender Compression Members 40 LLWT STATE OF-COLLAPSE: SW 40.1 Nominal Shear Stress 40.2 Design Shear Strength of Concrete 40.3 Minimum Shear Reinforcement 40.4 Design of Shear Reinforcement 40.5 Enhanced Shear Strength of Sections Close to Supports 41 LJMIT STATE OFCOLLAPSE: TORSION 41.1 General 4 1.2 Critical Section 4 1.3 Shear and Torsion 4 1.4 Reinforcement in Members Subjected to Torsion 42 LIMITSTATKOFSERVICEABILITY:DEKIZC~ION 42.1 Flexural Members 43 LIMIT STATE OF SERVICEABILITY:CRACKING
4NNEXA ANNEXB B-l
Flexural Members Compression Members LIST OF REFERRED INDIAN STANDARDS STRUCTURAL DESIGN (WORKING STRESS METHOD) GENERAL B-l.1 General Design Requirements B- 1.2 Redistribution of Moments B-l.3 Assumptions for Design of Members PEaMIsstBLESTrtEssEs B-2.1 Permissible Stresses in Concrete B-2.2 Permissible Stresses in Steel Reinforcement B-2.3 Increase in Permissible Stresses I’iuu@ssm~~Lam IN COMPRESSION MEMBEW B-3.1 Pedestals and Short Columns with Lateral ‘Des B-3.2 Short Columns with Helical Reinforcement B-3.3 Long Columns B-3.4 Composite Columns
IS 456 : 2ooo
B-4 MYERS SUBJECTEDTO COMBINEDAxw. LOADAND BENDING B-4. B-4. B- B-5 SHEAR B-5. B-5. B-5. B-5. B-5.
Design Based on Untracked Section Design Based on Cracked Section Members Subjected to Combined Direct Load and Flexure
Nominal Shear Stress Design Shear Strength of Concrete Minimum Shear Reinforcement Design of Shear Reinforcement Enhanced Shear Strength of Sections Close to Supports B -6 TORSION B-6.1 General B-6.2 Critical Section B-6.3 Shear and Torsion B-6.4 Reinforcement in Members Subjected to Torsion ANNEX C CALCULATION OF DEFLECTION C-l TOTALDEFLECTION C-2 SHORT-TERMDEFLECTION C-3 DEFLECI-IONDUETOSHRINKAGE C-4 DE-ON DUETOCREEP ANNEX D SLABS SPANNING IN TWO DIRECTIONS D-l RESTRAINEDSLAIIS D-2 SIMPLYSIJIWRTEDSLABS ANNEX E EFFECTIVE LENGTH OF COLUMNS ANNEX F CALCULATION OF CRACK WIDTH ANNEX G MOMENTS OF RESISTANCE FOR RECTANGULAR AND T-SECTIONS G- 1 RECTANGULARSECIIONS G- 1.1 Sections without Compression Reinforcement G- 1.2 Sections with Compression Reinforcement G-2 FLANGEDSECTION ANNEX H COMMITTEE COMPOSITION
90 90 92 95 96 96 % 96 96 98
Yc, -^ Calculated^ maximum^ bearing pressure of soil
r - Radius
s - Spacing of stirrups or standard deviation T - Torsional moment
t - Wall thickness
V - Shear force W - Total load WL - Wind load W - Distributed load per unit area
Wd -^ Distributed^ dead load per unit area WI -^ Distributed^ imposed^ load per unit area X - Depth of neutral axis
z - Modulus of section
Z -^ Lever^ arm
OZ,B - Angle or ratio
r, -^ Partial^ safety^ factor for load
snl -^ Percentage^ reduction^ in moment E (^) UC - Creep strain of concrete (Tchc - Permissible stress in concrete in bending compression OLX -^ Permissible^ stress in concrete^ in direct compression <T mc -
% -
Permissible stress in metal in direct compression Permissible stress in steel in compression Permissible stress in steel in tension Permissible tensile stress in shear reinforcement Design bond stress Shear stress in concrete Maximum shear stress in concrete with shear reinforcement Nominal shear stress Diameter of bar
5.1 Cement
The cement used shall be any of the following and the type selected should be appropriate for the intended use:
a)
b)
c)
d)
e) f)
g)
h) j)
k)
33 Grade ordinary Portland cement conforming to IS 269 43 Grade ordinary Portland cement conforming to IS 8 112 53 Grade ordinary Portland cement conforming to IS 12269 Rapid hardening Portland cement conforming to IS 8~ Portland slag cement conforming to IS 455 Portland pozzolana cement (fly ash based) conforming to IS 1489 (Part 1) Portland pozzolana cement (calcined clay based) conforming to IS 1489 (Part 2) Hydrophobic cement conforming to IS 8043 Low heat Portland cement conforming to IS 12600 Sulphate resisting Portland cement conforming to IS 12330 Other combinations of Portland cement with mineral admixtures (see 5.2) of quality conforming with relevant Indian Standards laid down may also be used in the manufacture of concrete provided that there are satisfactory data on their suitability, such as performance test on concrete containing them. 5.1.1 Low heat Portland cement conforming to IS 12600 shall be used with adequate precautions with regard to removal of formwork, etc. 5.1.2 High alumina cement conforming to IS 6452 or supersulphated cement conforming to IS 6909 may be used only under special circumstances with the prior approval of the engineer-in-charge. Specialist literature may be consulted for guidance regarding the use of these types of cements. 5.1.3 The attention of the engineers-in-charge and users of cement is drawn to the fact that quality of various cements mentioned in 5.1 is to be determined on the basis of its conformity to the performance characteristics given in the respective Indian Standard Specification for thatcement. Any trade-mark or any trade name indicating any special features not covered in the standard or any qualification or other special performance characteristics sometimes claimed/ indicated on the bags or containers or in advertisements alongside the ‘Statutory Quality Marking’ or otherwise
have no relation whatsoever with the characteristics guaranteed by the Quality Marking as relevant to that cement. Consumers are, therefore, advised to go by the characteristics as given in the corresponding Indian Standard Specification or seek specialist advise to avoid any problem in concrete making and construction.
5.2 Mineral Admiitures 5.2.1 Poz.zolanas Pozzolanic materials conforming to relevant Indian Standards may be used with the permission of the engineer-in-charge, provided uniform blending with cement is ensured. 5.2.1.1 Fly ash (pulverizedfuel ash) FIy ash conforming to Grade 1 of IS 3812 may be use?, as part replacement of ordinary Portland cement provided uniform blending with cement is ensured. 5.2.1.2 Silicafume Silica fume conforming to a standard approved by the deciding authority may be used as part replacement of cement provided uniform blending with the cement is ensured. NOTE-The silica fume (very fine non-crystalline silicon dioxide)is a by-productof the manufactmeof silicon, kmxilicon or the like, from quartzand carbon in electric arc furnace. It is usuallyusedinpropoltion of 5’m lOpercentofthecementconbcnt of a mix. 5.2.1.3 Rice husk ash Rice husk ash giving required performance and uniformity characteristics -may be used with the approval of the deciding authority. NOTE--Rice husk ash is produced by burning rice husk and contain large propotion of silica. To achieve amorphousstate, rice husk may be burntat controlledtemperatum.It is necessary to evaluatethe productfrom a ptuticularsource for performnnce and uniformitysince it can range from being as dekterious as silt when incorporatedin concmte. Waterdemnnd and drying &i&age should be studied before using ria husk. 5.2.u iuetakaoline Metakaoline having fineness between 700 to 900 m?/kg may be used as ~pozzolanic material in concrete. NOTE-Metaknoline is obtained by calcination of pun or r&ledkaolinticclnyatatempexatumbetweea6soVand8xPc followed by grind& to achieve a A of 700 to 900 n?/kg. The resultingmaterialhas high pozzolanicity. 5.2.2 Ground Granulated Blast Furnace Slag Ground granulated blast furnace slag obtained by grinding granulated blast furnace slag conforming to IS 12089 may be used as part replacement of ordinary
‘lhble 1 Permissible Limit for !Wids (claust? 5.4)
lS456:
SI (^) -apu Permb?dbleLImlt, No. Max
ii) Inorganic IS 3025 (yalt 18) (^) 3ooomo/L iii) Sulphaki (us SOJ IS302s(Part24) (^) amo/l iv) Chlorides (as Cl) IS 3025 (part 32) (^) 2ooompll for fxmaetc not Containing embcd~sti mdsoomg/l for leInfolced collcntc worlr v) Suspfmdedmatter^ IS 3025 (Palt^ 17)^ 2(xJom%l
5.4.4 Water found satisfactory for mixing is also 5.6.1 All reinforcement shall be free from loose mill suitable for curing concrete. However, water used for scales, loose rust and coats of paints, oil, mud or any curing should not produce any objectionable stain or other substances which may destroy or reduce bond. unsightly deposit on the concrete surface. The presence Sand blasting or other treatment is recommended to of tannic acid or iron compounds is objectionable. clean reinforcement.
5.5 Admixtures 5.5.1 Admixture, if used shall comply with IS 9103. Previous experience with and data on such materials should be considered in relation to the likely standa& of supervisionand workmanshipto the work being specified, 55.2 Admixtures should not impair durability of concrete nor combine with the constituent to form harmful compounds nor increase the risk of corrosion of reinforcement.
5.6.2 Special precautions like coating of reinforcement may be required for reinforced concrete elements in exceptional cases and for~rehabilitation of structutes. Specialist literature may be referred to in such cases. 5.6.3 The modulus of elasticity of steel shall be taken as 200 kN/mm*. The characteristic yield strength of different steel shall be assumed as the minimum yield stress/O.2percent proof stress specified in the relevant Indian Standard.
55.3 The workability, compressive strength and the slump loss of concrete with and without the use of admixtures shall be established during the trial mixes before use of admixtures.
5.7 Storage of Materials Storage of materials shall be as described in IS 4082.
6 CONCRETE
5.5.4 The relative density of liquid admixtures shall be checked for each drum containing admixtures and compared with the specified value before acceptance. 5.5.5 The chloride content of admixtures shall be independently tested for each batch before acceptance.
6.1 Grades The concrete shall be in grades designated as per Table 2. 6.1.1 The characteristic strength is defined as the strength of material below which not more than 5 percent of the test results are expectedto fall. 5.5.6 If two or more admixtures are used simultaneously in the same concrete mix, data should be obtained to assess their interaction and to ensure their compatibility.
5.6 -Reinforcement The reinforcement shall be any of the following:
6.1.2 The minimum grade of concrete for plain and reinforced concrete shall be as per Table 5. 61.3 Concrete of grades lower than those given in Table-5 may be used for plain concrete constructions, lean concrete, simple foundations, foundation for masonry walls and other simple or temporary reinforced concrete construction. Mild steel and medium tensile steel bars conforming to IS 432 (Part 1). High strength deformed steel barsconforming to IS 1786.
6.2 Properties of Concrete 63.1 Increase of Strength with Age
Hard-drawn steel wire fabric conforming to IS 1566. Structural steel conforming to Grade A of IS 2062.
There is normally a gain of strength beyond 28 days. The quantum of increase depends upon the grade and type of cement, curing and environmental conditions, etc. The design should be based on 28 days charac- teristic strength of concrete unless there is a evidence to
Table 2 Grades cif Concrete (Clau.re6.1,9.2.2, 15.1.1 and36.1)
Group Grade Designation SpecifiedCharacte~tk Compressive Streng$b of 150 mm Cube at 28 Days in N/mmz (1) (2) (3) Ordinary M 10 10 Concrete M 15 15 M 20 20 Standard M 25 25 Concrete M 30 30 M 35 35 M40 40 M 45 45 M JO 50 M 55 55 High M60 60 Strength M65 65 Concrete M70 70 M75 75 M 80 (^80) NOTES 1 In the designationof concrete mix M mfm to the mix and the number to the specified compressive strengthof 150 mm size cube at 28 days, expressed in N/mn?. 2 For concreteof compressivestrengthgreata thanM 55, design parametersgiven in the stand& may not be applicable and the values may be obtoined from specialized literatures and experimentalresults.
justify a higher strength for a particular structure due to age. 6.2.1.1 For concrete of grade M 30 and above, the rate of increase of compressive strength with age shall be based on actual investigations. 6.2.1.2 Where members are subjected to lower direct load during construction, they should be checked for stresses resulting from combination of direct load and bending during construction. 6.2.2 Tensile Strength of Concrete The flexural and splitting tensile strengths shall be obtained as described in IS 516 and IS 5816 respectively. When the designer wishes to use an estimate of the tensile strength from the compressive strength, the following formula may be used: Flexural strength, f, = 0.7.& N/mm wheref& is the characteristic cube compressive strength of concrete in N/mmz. 6.2.3 Elastic Deformation The modulus of elasticity is primarily influenced by the elastic properties of the aggregate and to a lesser extent by the conditions of curing qd age of the concrete, the mix proportions and the type of cement. The modulus of elasticity is normally related to the compressive strength of concrete. 6.2.3.1 The modulus of elasticity of concrete can be assumed as follows:
where E, is the short term static modulus of elasticity in N/mm*. Actual measured values may differ by f 20 percent from the values dbtained from the above expression. 6.2.4 Shrinkage The total shrinkage of concrete depends upon the constituents of concrete, size of the member and environmental conditions. For a given humidity and temperature, the total shrinkage of concrete is most influenced by the total amount of water present in the concrete at the time of mixing and, to a lesser extent, by the cement content. 6.2.4.1 In the absence of test data, the approximate value of the total shrinkage strain for design may be taken as 0.000 3 (for more information, see-IS 1343). 6.2.5 Cmep of Concrete Creep of concrete depends,in addition to the factors listed in 6.2.4, on the stress in the concrete, age at loading and the duration of loading. As long as the stress in concrete does not exceed one-third of its characteristic compressive strength, creep may be assumed to be proportional to the stress. 6.25.11n the absence of experimental data and detailed information on the effect of the variables, the ultimate creep strain may be estimated from the following values of creep coefficient (that is, ultimate creep strain/ elastic strain at the age of loading); for long span structure, it is advisable to determine actual creep strain, likely to take place:
Age at Loading Creep Coeficient 7 days 2. 28 days 1. 1 year 1.
NOTE-The ultimatecreepstrain,estimatedas described above does not include the elastic strain. 6.2.6 Thermal Expansion The coefficient df thermal expansion depends on nature of cement, the aggregate, the cement content, the relative humidity and the size of sections-The value of coefficient of thermal expansion for concrete with different aggregates may be taken as below:
npe of Aggregate
Quartzite Sandstone Granite Basalt Limestone
Coeficient of Thermal Expansion for CommtePC 1.2 to 1.3 x 10-S 0.9 to 1.2 x 1cP 0.7 to 0.95 x 10-J O.%to 0.95 x lo 0.6 t@.9 x 10s
8.2 Requirements for Durability
8.2.1 Shape and Size of Member
The shape or design details of exposed structures should be such as to promote good drainage of water and to avoid standing pools and rundown of water. Care should also be taken to minimize any cracks that may collect or transmit water. Adequate curing is essential to avoid the harmful effects of early loss of moisture (see 13S).Member profiles and their intersections with other members shall be designed and detailed in a way to ensure easy flow of concrete and proper compaction during concreting. Concrete is more vulnerable to deterioration due to chemical or climatic attack when it is in thin sections, in sections under hydrostatic pressure from one side only, in partially immersed sections and at corners and edges of elements. The life of the strycture can be lengthened by providing extra cover to steel, by chamfering the corners or by using circular cross- sections or by using surface coatings which prevent or reduce the ingress of water, carbon dioxide or aggressive chemicals. 8.2.2 Exposure Conditions 8.2.2.1 General environment The general environment tc, which the concrete will be exposed during its working life is classified into five levels of severity, that is, mild, moderate, severe, very severe and extreme as described in Table 3. Table 3 Environmental Exposure Conditions (Chwes 8.2.2.1 and 35.3.2)
Sl No. Environment (1) (2) i) Mild
ii) (^) Moderate
iii) (^) Severe
iv) Very severe
-4 Extreme
Nominal Maximum Size Entrained Air Aggregate Percentage WW 20 5fl 40 4fl
Since air entrainment reduces the strength, suitable adjustments may be made in the mix design for achieving required strength. 8.2.2.4 Exposure to sulphate attack Table 4 gives recommendations for the type of cement, maximum free water/cement ratio and minimum cement content, which are required at different sulphate concentrations in near-neutral ground water having pHof6to9.
Exposure Conditions (3) Concrete surfaces protected against weatheror aggressiveconditions,except those situatedin coastal area. Concretesurfaces shelteredfrom severe rain or freezing whilst wet Concreteexposedto condensationandrain Concretecontinuously underwater Concretein contact or buriedundernon- aggressive soil/groundwater Concrete surfaces sheltered from saturatedsalt air in coastal area Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation.
For the very high sulphate concentrations in Class 5 conditions, some form of lining such as polyethylene or polychloroprene sheet; or surface coating based on asphalt, chlorinated rubber, epoxy; or polyurethane materials should also be used to prevent access by the sulphate solution.
8.2.3 Requirement of Concrete Cover 8.2.3.1 The protection of the steel in concrete against corrosion depends upon an adequate thickness of good quality concrete. 8.2.3.2 The nominal cover to the reinforcement shall be provided as per 26.4.
Concletecompletelyimmrsedinseawnter Concreteexposed to coastalenvironment Concrete surfaces exposed to sea water spray,corrosivefumes or severe freezing conditions whilst wet Concrete in contact with or buried underaggressive sub-soil/groundwater Surfaceof membersin tidal zone Members in direct contact with liquid/ solid aggressive chemicals
8.2.2.2 Abrasive Specialist literatures may be referred to for durability requirementsof concrete surfaces exposed to abrasive action,for example, in case of machinery and metal tyres. 8.2.2.3 Freezing and thawing Where freezing and thawing actions under wet conditions exist, enhanced durability can be obtained by the use of suitable air entraining admixtures. When concrete lower than grade M 50 is used under these conditions, the mean total air content by volume of the fresh concrete at the time df delivery into the construction should be:
0.2.4 Concrete Mix Proportions 8.2.4.1 General The free water-cement ratio is an important factor in governing the durability of concrete and should always be the lowest value. Appropriate values for minimum cement content and the maximum free water-cement ratio are given in Table 5 for different exposure conditions. The minimum cement content and maximum water-cement ratio apply to 20 mm nominal maximum size aggregate. For other sizes of aggregate they should be changed as given in Table 6.
8.2.4.2 Maximum cement content (^) been given in design to the increased risk of cracking
Cement content not including fly ash and ground due to drying shrinkage in.thin sections, or to early granulated blast furnace slag in excess of 450 kg/x$ thermal cracking and to the increased risk of damage should not be used unless special consideration has due to alkali silica reactions.
Table 4 Requirements for Concrete Exposed to Sulphate Attack (Clauses 8.2.2.4 and 9.1.2)
SI No.
ChSS Concentration of^ Sulphates, Expressed a~ SO, r. In Soil Total SO, SO,in In Ground 2:l water: Water Soil Extract
(1) (2) (3) 0 1 TraCeS (< 0.2)
ii) 2 0.2 to 0.
iii) 3 0.5 to 1.
&d @ (4) (5) Less than LesSthan 1.0 0.
1.oto 0.3 to 1.9 1.
1.9 to 3.
iv) 4 1.0to 3.1 to 2.0 5.
v) 5 More than^ More than 2.0 5.
NOTES
1.2 to 2.
2.5 to
Made with 20 mm Nominal Maximum Size Aggregates Complying with IS 383 r. Minimum Maximum Cement Face Water- Content Cement ~kg/m’ Ratio
(6) Ordinary Portland cement or Portland slag cement or Portland pozzolana cement ’ Ordinary Portland cement or Portland slag cement or Portland pozzolana cement Supersulphated cement or sulphate resisting Portland cement Supersulphated cement or sulphate resisting Portland cement Portland pozzolana cement or Podand slag cement Supersulphated or sulphate resisting Portland cement More than
Sulphate resisting Portland cement or superrulphated cement with protective coatings
(7) (^) (8) 280 0.
330
310
330
350
370
400
1 Cement content given in this table is irrespective of grades of cement. 2 Use of supersulphated cement is generally restricted where the prevailing temperature is above 40 “c. 3 Supersulphated cement gives~an acceptable life provided that the concrete is dense and prepared with a water-cement mtio of 0.4 or less, in mineral acids, down to pH 3.5. 4 The cement contents given in co1 6 of this table are the minimum recommended. For SO, contents near tbe upper limit of any class, cement contents above these minimum are advised. 5 For severe conditions, such as thin sections under hydrostatic pressure on one side only and sections partly immersed, considerations should be given to a further reduction of water-cement ratio. 6 Portland slag cement conforming to IS 455 with slag content more than 50 percent exhibits better sulphate resisting properties. 7 Where chloride is encountered along with sulphates in soil or ground water, ordinary Portland cement with C,A content from 5 to 8 percent shall be desirable to be used in concrete, instead of sulphate resisting cement. Alternatively, Portland slag cement conforming to IS 455 having more than 50 percent slag or a blend of ordinary Portland cement and slag may be used provided sufficient information is available on performance of such blended cements in these conditions.
