Civil Engineering DepartmentConcrete Technology Concrete Technology The word “concrete” originates from the Latin verb “concretus”, which means to grow together. Objectives • To explain the basic concepts of concrete • To explain briefly the properties of freshly mixed concrete • To explain briefly the properties of hardened concrete • To explain briefly mix design of concrete What is Concrete? • Concrete is one of the most commonly used building materials. • In the United States almost twice as much concrete is used as all other building materials combined. • It is a mixture of cement, water, fine aggregates, coarse aggregates and in some cases, admixtures. • Cement and water form a paste that hardens and bonds the aggregates together. • Concrete is a versatile material that can easily be mixed to meet a variety of special needs and formed to virtually any shape. • Concrete is often looked upon as “man made rock”. • Demand for concrete with higher strength and better quality, coupled with larger and faster mixer trucks, led to the emergence of the ready-mix concrete industry in the post-World War II period. Contd….. Cement → Powder Cement + Water →Cement Paste Cement Paste + Fine Aggregate (FA) → Mortar Mortar + Coarse Aggregate (CA) → Concrete Portland cement, water, sand, and coarse aggregate are proportioned and mixed to produce concrete suited to the particular job for which it is intended. When paste and aggregates are mixed together the particles of aggregates get coated with the paste. Because of the chemical reaction of the cement and water the paste hardens and binds the aggregates together to form a rocklike mass called “Concrete” Definition of Cement Cement is a binding material that is used to bind different aggregates (coarse and fine) in the presence of moisture (water) through a chemical process known as hydration. Cement contains limestone, clay , cement rock and iron ore blended and heated to 1200 to 1500 C°. The resulting product "clinker" is then ground to the consistency of powder. Gypsum is added to control setting time. 75mm. Chemical Admixtures •Materials added to alter the properties of concrete including: Air entrainment Set accelerators Set retarders Water reducers • Air entraining admixtures add microscopic air bubbles to the concrete. • Makes up 40%-45% of the mixture.. . comprised of particles greater than 4. enhancing its resistance to freeze/thaw cycles and makes the concrete easier to finish.75mm •Generally accounts for 30%-35% of the mixture.Contd…. Coarse Aggregate •May be either gravel or crushed stone. this component can be natural sand or crushed stone. Fine Aggregate •Normally called sand. and represents particles smaller than 4. •Set retarders have the opposite effect. useful during cold weather pours. Yield It is the volume of fresh concrete produced from known quantities of component materials. slowing the set and enabling delivery to distant sites and finishing during hot weather. . By reducing the amount of water required. They also provide a ball bearing effect. •Set accelerators speed the set-time of the mixture. and produce better cement hydration..Contd…. cement amounts can be reduced because concrete strength is directly related to the water/cement ratio. enabling finishing operations to begin sooner. making the concrete easier to finish. •Water reducers are used to reduce the amount of water required to produce a given slump. Generally expressed in cubic yards or cubic meters. • On-site fabrication • Needs little or no finish or final treatments. longevity. • Can be reused or recycled. and chemical inertness. Concrete can be reused with bituminous asphalt as road base materials. including durability.Advantages of concrete • Concrete has many environmental advantages. natural -mineral pigments and colouring agents can be added at the mixing to provide a rainbow of options. can be recycled and reused by crushing into aggregates for new concrete or as fill material for road beds or site works. • Ability to be cast • Economical • Durable • Fire resistant • Energy efficient. . heat storage capability. Chemically inert concrete doesn't require paint to achieve a given colour. • Low maintenance. Disadvantages of concrete • • • • Low tensile strength Low ductility Volume instability Low strength to weight ratio Progress in Concrete Technology Lightweight Concrete High-Strength Concrete High Workability or Flowing Concrete Shrinkage Compensating Concrete Fiber-Reinforced Concrete Concrete Containing polymers Heavyweight Concrete Mass Concrete Roller-Compacted Concrete . . Paste Requirement • Quality of paste greatly affects the quality of the concrete • Paste should be sufficient enough to completely coat each particle of aggregate and to fill spaces between aggregate particles completely. shape and particle size distribution (gradation). • The size. that will cause deterioration of concrete.Quality of Concrete Aggregate Requirement • Aggregates should not contain deleterious materials such as chloride. sulfate. etc. of the aggregates should be such that the least amount of paste is required to fill the spaces between aggregate particles. • The quality of hardened concrete is determined by the amount of water used in relation to the amount of cement (W/C ratio of the paste). thus increased water-tightness and lower absorption. • Reducing water demand • Increasing workability in case of a very low w/c ratio • Intentionally entrained air in concrete . • Less volume change from wetting and drying • Reduced shrinkage cracking tendencies. • Lower permeability. • Better bond between successive layers and between concrete and reinforcement. • Increased resistance to weathering. Uses of Admixtures to Improve the Quality of Concrete • Adjusting setting time or hardening in abnormal conditions of concreting such as cold and hot.Advantages of reducing the W/C ratio of the paste • Increase compressive strength and flexural strength. . • For stiffer mixtures having low w/c ratio the consolidation should be done by vibration.Mixing Requirements • All the ingredients of concrete should be mixed properly so as to get a homogeneous mixture. • For a highly workable concrete the consolidation should be done by hand rodding. Consolidation Requirements • Consolidation of the freshly placed concrete removes voids in concrete and improves the quality of concrete on account of increased density. • Design. • Size of the batch in relation to the size of the mixer. • The sequence of charging ingredients into the mixer plays an important part in the uniformity of the finished product. configuration. • The elapsed time between batching and mixing. and condition of the mixer drum and blades. a peninsula in the English Channel where it was first produced in the 1800's. and both materials are ground into a fine powder which is portland cement. a number of developments and improvements have been made in the production process and cement properties. gypsum is added. • Three types of portland cement are used for construction purposes Type I Type II Type III . • The production process for portland cement first involves grinding limestone or chalk and alumina and silica from shale or clay. and then burned in large rotary kilns at approximately 1500°C until partially fused into marblesized masses known as clinker. • After the clinker cools. mixed.Portland Cement • Portland cement was named for the Isle of Portland. • The raw materials are proportioned. • Since that time. . making it useful for cold weather jobs. or for suspension bridges. heavy retaining walls. It is very finely ground and sets rapidly. It is more suitable for projects involving large masses of concrete . Type II It releases less heat during hardening. Unless an alternative is specified. Type I is usually used. Type III It produces concrete that gains strength very rapidly.Contd…… Type I cement is the general purpose and most common type. and aggregates. organic matter and excessive chemicals and/or minerals. . • Admixtures are added to the concrete mixture immediately before or during mixing. Admixtures • Admixtures are ingredients other than portland cement. Aggregates • Aggregates occupy 60 to 80 percent of the volume of concrete.Water • Good water is essential for quality concrete. • Sand. • It should be good enough to drink--free of trash. water. gravel and crushed stone are the primary aggregates used. • The strength and other properties of concrete are highly dependent on the amount of water and the water-cement ratio. • All aggregates must be essentially free of silt and/or organic matter. are used to increase the rate of hardening-usually during cold weather. • They are useful for concrete that is placed during hot weather. • Entrained air bubbles: – improve the durability of concrete exposed to moisture and freeze/thaw action.Air Entraining agents • These are the most commonly used admixtures for agricultural concrete. • produce microscopic air bubbles throughout the concrete. Accelerating admixtures • such as calcium chloride. Retarding admixtures • are used to slow the rate of concrete hardening. . – Improve resistance to scaling from deicers and corrosive agents such as manure or silage. 25 is required for complete hydration – Practically. which in turn densifies the hydrated cement paste – This increases strength and reduces permeability • It also makes the concrete more difficult to work • In combination. the useful limit is around 0. . • Theoretically. is the single most important parameter with regards to concrete quality and used to determine the water used in the mix.22 to 0.Water-to-Cement Ratio • The ratio of water-to-cement.33 • Reducing the water for a given amount of cement will move the cement particles closer together. about 0. the w/c and degree of hydration control many of the properties of the hardened concrete . or w/c. compact and finish without harmful segregation. • Strongly associated with the slump test . • A concrete mix satisfying these conditions is said to be workable. place. • It is desirable that freshly mixed concrete be relatively easy to transport. • There is no single test method that can simultaneously measure all the properties involved in workability. • It is determined to a large extent by measuring the “consistency” of the mix.Workability Properties of fresh concrete • Workability is the most important property of freshly mixed concrete. Slump Cone Test • Slump Test is related with the ease with which concrete flows during placement . Measure the slump by determining the vertical difference between the top of the mold and the displaced original center of the top surface of the specimen.10 cm 30 cm 20 cm The slump cone is filled in 3 layers. . Every layer is evenly rodded 25 times. Contd…. . shape and surface texture Quantity and characteristics of chemical admixtures Amount of water Amount of entrained air Fluidity. compactability and finishability These properties are affected by: Design of mix Adjustment to the mix constituents Environmental Conditions: Ambient and concrete temperature Relative humidity and the air speed Degree of agitation and friability of aggregrates Elapsed time since mixing . pumpability. stability.Factors Affecting Workability • • • • • • • Method and duration of transportation Quantity and characteristics of cementing materials Aggregate grading. Consistency • • • Consistency is the fluidity or degree of wetness of concrete. Test methods for measuring consistency are: Flow test → measures the amount of flow Kelly-Ball test → measures the amount of penetration Slump test (Most widely used test!) . It is a major factor in indicating the workability of freshly mixed concrete. It is generally dependent on the shear resistance of the mass. The primary causes of segregation are differences in specific gravity and size of constituents of concrete. – Decrease in the amount of fine particles. – Particle shape and texture. – Water/cement ratio. resulting in a non-uniform mix. Some of the factors affecting segregation: – Larger maximum particle size (25mm) and proportion of the larger particles. – Improper mixing.• Segregation refers to a separation of the components of fresh concrete. Segregation . – High specific gravity of coarse aggregate. improper placing and improper consolidation. • Water rising to the surface carry fine particles of cement which weaken the top portion and form laitance. or paste and reinforcement. These large voids under the particles may lead to weak zones and reduce the bond between paste and agg. Thus the resistance of concrete to freezing-thawing decreases. C3A and alkalies) Adding pozzolans Reducing water content . • A special case of segregation. the top portion becomes weak and porous (high w/c).• Bleeding is the tendency of water to rise to the surface of freshly placed concrete. It is decreased by: Increasing the fineness of cement Increasing the rate of hydration (C3S. • Water may accumulate under the coarse agg. This portion is not resistant to abrasion. Bleeding • Undesirable effects of bleeding are: With the movement of water towards the top. and reinforcement. It is caused by the inability of solid constituents of the mix hold all of the mixing water as they settle down. Mixing of concrete The aim of mixing is to blend all of the ingredients of the concrete to form a uniform mass and to coat the surface of aggregates with cement paste. Ready-Mix concrete: In this type ingredients are introduced into a mixer truck and mixed during transportation to the site. • Wet – Water added before transportation • Dry – Water added at site Mixing at the site • Hand mixed • Mixer mixed Mixing time should be sufficient to produce a uniform concrete. Undermixing → non-homogeneity Overmixing → danger of water loss. The time of mixing depends on the type of mixer and also to some properties of fresh concrete. brekage of aggregate particles . Ready Mix Concrete . Mixing at site . Methods of transporting concrete • • • • • • Wheelbarrows Hoists Trucks Chutes Pumps Pipelines . 5 metre truck will carry 18.e 6 wheeler or 8 wheeler – A cubic metre concrete weighs 2.5 metres capacity • When using trucks we may need to specify – Size of truck i.5t – A 7.Trucks • Trucks range from 1.8 mini trucks to 7.75t of concrete – This will need to be taken account of when driving over structures – Always be aware that after trucks discharge concrete they actually get higher Chutes A convenient method to transport concrete • Items that can be used to make a chute – Roof sheeting – Plywood . Pumps and pipelines • Concrete pumps come in two types. line and boom pumps Concrete pumps • When ordering pumps consideration – A pump’s footprint (a 42m boom pump may need up to 12m in width to operate properly) – Generally boom pumps will take up 2 lanes of road traffic and traffic management plans will need to be put in place – Boom pumps can reach approximately 15 floors after this concrete line pumps can only be used . Placing of Concrete • Placed vertically and near its final position • If it needs to be moved it needs to be done with shovels • Dropping of concrete should be restricted to 1.8m to avoid segregation • Sequence should be planned to avoid cold joints on large slabs Compacting • Compaction is required to achieve – Maximum Strength – Watertight Concrete – Fill in Sharp Corners – Good bond to reinforcement – Good surface appearance . Inadequate Compaction • This has a severe effect on concrete strength . Consolidating concrete Inadequate consolidation can result in: – Honeycomb – Excessive amount of entrapped air voids (bug holes) – Sand streaks – Placement lines (Cold joints) . Vibration of concrete The process of compacting concrete consists essentially of the elimination of entrapped air. The poker is easily removed from point to point. rigid forms. This can be achieved by: – Tamping or rodding the concrete – Use of vibrators Internal vibrator: The poker is immersed into concrete to compact it. External vibrators: External vibrators clamp direct to the formwork requiring strong. Vibrator d 1½ R Internal Vibrator Radius of Action . The actual completion of vibration is judged by the appearance of the concrete surface which must be neither rough nor contain excess cement paste.Internal Vibrators • To aid in the removal of trapped air the vibrator head should be rapidly plunged into the mix and slowly moved up and down. . Adapted from ACI 309 Diameter Recommended Approximate Rate of of head.3-8 50-90 8000-12. beams.500 130-250 2.000 180-360 4. radius of placement.) action.8-4 Plastic and flowing concrete in thin members.000 80-150 0. precast piles. . Also used for lab test specimens. Plastic concrete in thin walls. (mm) (m3/h) (mm) Application 20-40 9000-15. thin slabs. frequency.Contd…. and along construction joints.6-15 Stiff plastic concrete (less than 80-mm slump) in general construction . 30-60 8500-12. columns. (vib./min.. Forms must be strong and tied enough to prevent distortion and leakage of the grout. A considerable amount of work is needed to vibrate forms. • • .External Vibrators • Form vibrators • Vibrating tables (Lab) • Surface vibrators – Vibratory screeds – Plate vibrators – Vibratory roller screeds – Vibratory hand floats or trowels • External vibrators are rigidly clamped to the formwork so that both the form & concrete are subjected to vibration. . Vibrating Table: used for small amounts of concrete (laboratory and some precast elements) .Contd…. Systematic Vibration CORRECT Vertical penetration a few inches into previous lift (which should not yet be rigid) of systematic regular intervals will give adequate consolidation INCORRECT Haphazard random penetration of the vibrator at all angles and spacings without sufficient depth will not assure intimate combination of the two layers . Curing of concrete • Properties of concrete can improve with age as long as conditions are favorable for the continued hydration of cement. • These improvements are rapid at early ages and continues slowly for an indefinite period of time. placed. • A seven-day (or longer) curing time is recommended. • Hydration reactions can take place in only saturated water filled capillaries. • Concrete that has been specified. is often neglected even by professionals. • Curing is usually the last step in a concrete project and. and finished "letterperfect" can still be a failure if improperly or inadequately cured. unfortunately. • Curing is the procedures used for promoting the hydration of cement and consists of a control of temperature and the moisture movement from and into the concrete. mixed. . batched. • The primary objective of curing is to keep concrete saturated or as nearly saturated as possible. – Using wet covers – Sprinkling – Ponding or immersion Keep water on the concrete during the curing period. . Methods which supply additional water to the surface of concrete during early hardening stages.Curing Methods 1. Contd…. – Water proof plastics – Use liquid membrane-forming compounds – Forms left in place Such methods provide some cooling through evaporation. Methods that prevent loss of moisture from concrete by sealing the surface. 2. which is beneficial in hot weather.. . Methods that accelerate strength gain by supplying heat & moisture to the concrete.. 3.Contd…. . – By using live steam (steam curing) – Heating coils. More durability Effect of curing on Strength . Curing Requirements Advantages of curing • • • • • More strength and abrasion resistance More watertigtness Less volumetric changes. to allow the complete hydration of the cement. More resistance to freezing and thawing and deicer salts.• Curing of a placed and finished concrete is done for maintaining a satisfactory moisture and temperature in concrete for some defined period after placing and finishing. more volume stability. insulation – Rely on heat of hydration for larger sections – Heated ingredients concrete hot when placed – High early strength cement . excessive evaporation – Direct sunlight Solutions – Windbreaks – Cooled Concrete Ingredients – Water ponding (cooling due to evaporation) – Reflective coatings/coverings Cold Weather Concrete • Keep concrete temperature above 5 °C to minimize danger of freezing Solutions – Heated enclosures.Hot Weather Concrete • Rapid hydration early setting rapid loss of workability • Extra problems due to – Low humidity – Wind. Uniformity of concrete Concrete uniformity is checked by conducting tests on fresh and hardened concretes. unit weight. non-homogeneous nature – Batch-to-Batch Variations : type of materials used. These variations are grouped as: – Within-Batch Variations : inadequate mixing. changes in moisture content of aggregates . air content tests Strength tests Due to heteregeneous nature of concrete. changes in gradation of aggregates. Slump. there will always be some variations. Because Concrete is used for compressive loads Compressive strength is easily obtained It is a good measure of all the other properties.Response to temperature variations 5.Control of cracking out of these compressive strength is the most important property of concrete. Strength 2. Permeability & durability 3.Shrinkage & creep deformations 4. • • • .Properties of Hardened concrete The principal properties of hardened concrete which are of practical importance can be listed as: 1. Strength Development and Strength Measurement • • • • Aggregates “glued” together by cement paste to form concrete Cement hydration is a chemical reaction which requires water Strength gain reflects degree of hydration Strength gain depends on – Type of cement – Temperature history – temperature and time – Curing – Admixtures Factors Affecting Strength • Effect of materials and mix proportions • Production methods • Testing parameters . The strength of a concrete specimen prepared. cured and tested under specified conditions at a given age depends on: w/c ratio Degree of compaction Strength of concrete . Contd….. . Cylinder: h/D=2 with h=15 To decrease the amount of friction. . Cubic: 15x15x15 cm Cubic specimens are crushed after rotating them 90° to decrease the amount of friction caused by the rough finishing.Compressive strength Compressive Strength is determined by loading properly prepared and cured cubic. cylindrical or prismatic specimens under compression. capping of the rough casting surface is performed. Tensile Strength can be obtained either by direct methods or indirect methods. Direct methods suffer from a number of difficulties related to holding the specimen properly in the testing machine without introducing stress concentration and to the application of load without eccentricity. Tensile Strength Direct Tensile strength Split Tensile Strength Due to applied compression load a fairly uniform tensile stress is induced over nearly 2/3 of the diameter of the cylinder perpendicular to the direction of load application. σst = 2P πDl Contd….. P: applied compressive load D: diameter of specimen l: length of specimen Splitting Tensile Strength • The advantage of the splitting test over the direct tensile test is the same molds are used for compressive & tensile strength determination. • The test is simple to perform and gives uniform results than other tension tests. Flexural Strength The flexural tensile strength at failure or the modulus of rupture is determined by loading a prismatic concrete beam specimen. The results obtained are useful because concrete is subjected to flexural loads more often than it is subjected to tensile loads. Factors depended on the test type: – Size of specimen – Size of specimen in relation with size of agg. Factors independent of test type: – – – – – – Type of cement Type of agg. – Support condition af specimen – Moisture condition of specimen – Type of loading adopted – Rate of loading – Type of test machine 2.Factors Affecting the Strength of Concrete 1. Degree of compaction Mix proportions Type of curing Type of stress situation . In some structural members permeability itself is of importance. The permeability of concrete is controlled by capillary pores. . consequently causing cracks & spalling of concrete cover. The permeability depends mostly on w/c. degree of hydration. dams. water retaining tanks. The penetration of some aggresive solution may result in leaching out of Ca(OH)2 which adversely affects the durability of concrete. age. In R/C ingress of moisture of air into concrete causes corrosion of reinforcement and results in the volume expansion of steel bars.Permeability of concrete Permeability is important because: 1. 3. In general the higher the strength of cement paste. such as. the higher is the durability & the lower is the permeability. 2. The moisture penetration depends on permeability & if concrete becomes saturated it is more liable to frost-action. Contd…… . Failure modes of concrete Normal Abnormal . followed by prompt and effective curing.Durability • If acceptable materials are used. • These properties--and thus the desired concrete quality--can only be fully achieved through proper placement and finishing. if specified. the properties of concrete. is the most desirable. and strength depend on the cement mixture. wear resistance. the effects of service conditions to which it will be subjected. . • A mixture with a sufficiently low ratio of water to cement plus entrained air. Factors Affecting Durability: External → Environmental Internal → Permeability. freeze/thaw resistance. Characteristics of ingredients. • A durable concrete is the one which will withstand in a satisfactory degree. such as durability. Air-Void System. ettringite. monosulfate.• Macrostructure – Aggregates (CA. porosity: gel. capillary pores entrained/ entrapped air voids) – Transition zone (TZ) Structure of “un-damaged” Concrete Macrostructure Microstructure . FA) – Hydrated cement paste (hcp) – Entrapped air voids • Microstructure – Hydrated cement paste (Hydration products: C-S-H. microstructure should be examined) Microstructure Alkali-silica reaction: Reaction product forms at TZ and expands Frost action: Water freezes in capillary pores and expands Sulfate attack: reaction products form in hcp and expand .Structure of “damaged” Concrete Macrostructure Visible cracks in hcp and aggregates due to volume changes (to understand cause of cracks. When water penetrates into concrete. sulfates and carbonates of Na. Ca) Remember C-S-H and CH is produced upon hydration of C3S and C2S These salts are taken outside of concrete by water and leave a salt deposit. K. Leaching & Efflorescence . it dissolves the non-hydraulic CH (and various salts. Use proper cement → reduced C3A and C3S 3. Use low w/c ratio→ reduced permeability & porosity 2. these sulfates do not cause severe deleterious expansion/cracking because both gypsum and ettringite are soluble in solutions containing the Cl ion. Magnesium sulfate may lead to the decomposition of the C-S-H gel. Later. problem with seawater is the frequent wetting/drying and corrosion of reinforcing steel in concrete. gypsum and calcium alumina sulfates together with water react to form “ettringite”. These solutions attack CH to produce gypsum.Sulphate Attack Ground water in clayey soils containing alkali sulfates may affect concrete. To reduce the sulfate attack 1. Use pozzolans → they use up some of the CH to produce C-S-H . Seawater contains some amount of Na and Mg Sulfates. However. Formation of ettringite is hardened cement paste or concrete leads to volume expansion thus cracking. Moreover. However. Thus this volume expansion causes cracks in reinforced concrete. steel is protected by a thin film provided by concrete against corrosion. However. In fact. that shield is broken by CO2 of air or the Cl. Corrosion .ions. Electrochemical reactions in the steel rebars of a reinforced concrete structure results in corrosion products which have larger volumes than original steel. . pop–outs may occur. Important for exterior concrete. To prevent the concrete from this distress airentraining admixtures are used to produce air-entrained concrete.Freezing and Thawing Water when freezes expands in volume. If aggregates or concrete absorbs so much water that when the water freezes and expands the concrete cannot accommodate the build up of internal pressure. This will cause internal hydraulic pressure and cracks the concrete. Method These Methods are based on two basic assumptions Compressive Strength of Concrete is governed by its WaterCement Ratio Workability of Concrete is governed by its Water Content . Coarse Aggregate which would produce concrete possessing specified properties such as workability.S. Cement.Concrete Mix Design Cement Concrete Mix Design means. Water.e.C. determination of the proportion of the concrete ingredients i. strength and durability with maximum overall economy. Fine Aggregate. Methods of Concrete Mix Design I.I. Method British Method A. In-Situ Piling.: RCC-M30-A20 Slump required in mm e.g. Pumped Concrete.I. IS:456-2000) Placing Conditions Blinding Concrete. Trench fill.g.: Moderate Grade of Cement e. Tremie Concrete Degree of Workability Very Low Slump(mm) See 7.: 25 – 75 mm Degree of Site Control e. Floors. Pavements using pavers Mass Concrete. Columns.g.S.: OPC 43 Grade Workability (Clause 7.g. Columns. Method of concrete mix design Data required for concrete mix design Grade of Concrete e. Strip Footings Heavily reinforced sections in Slabs.1 Low 25-75 Medium High 50-100 100-150 . Lightly reinforced sections in Slabs. Walls. Beams. Slip form work. Walls. Shallow Sections.1. Beams.1. Hand placed Pavements.: Good Type of Exposure e.g. Canal lining. 3. Approximate Quantity of Materials required for concrete mix design 1. and periodical checking of workability and strength. Coarse Aggregate : 180 Kg. (20 mm) 180 Kg. Fine Aggregate : 240 Kg. Good Fair Site control having deviation from the above. (10 mm) 69 . Controlled addition of water. IS:456-2000) Site control having proper storage of cement. aggregate grading and moisture content. regular checking of all materials. Cement : 200 Kg. weigh batching of all materials. 2.Degree of Site Control (Table 8. i) Environment Exposure Conditions Concrete surfaces protected against weather or aggressive conditions. Concrete continuously under water. Concrete completely immersed in sea water. v) Extreme . Concrete surfaces sheltered from saturated salt air in coastal area. IS:456-2000) Sl. No. Concrete in contact or buried under non-aggressive soil/ground water. Concrete surfaces sheltered from severe rain or freezing whilst wet. alternate wetting and drying or occasional freezing whilst wet or severe condensation. Concrete exposed to condensation and rain. Surface of members in tidal zone. Concrete exposed to coastal environment. Members in direct contact with liquid/solid aggressive chemicals. corrosive fumes or severe freezing conditions whilst wet. Concrete surfaces exposed to severe rain. except those situated in coastal area. Concrete in contact with or buried under aggressive sub-soil/ground water.Type of Exposure (Table 3. Mild ii) Moderate iii) Severe iv) Very Severe Concrete exposed to sea water spray. 1 2 Particulars of Test Standard consistency (% by weight) Setting Time in minutes a) Initial b) Final Specifications As per IS:8112-1976 30-32 30 Minimum 600 Maximum 23 Minimum 33 Minimum 43 Minimum 2.7 225 Minimum 3 4 5 Compressive Strength in N/sq.Determine the physical properties of concrete ingredients. Cement (OPC 43 Grade) Sl.Steps Involved in concrete mix design Step I:. I.5-2.No.mm at the age of a) 3 days b) 7 days c) 28 days Specific Gravity Fineness in Sq.m/Kg . 20. Fine Aggregate Sieve Analysis Sieve Size 10.75 mm 2.0 mm 4.00mm 20. Specifications for Zone–II (passing) As per IS:383-1970 III.00mm 10.36 mm 1.75mm .18 mm 600 micron 300 micron 150 micron 100 90-100 75-100 55-90 35-59 8-30 0-10 contd….00mm 4.0mm Coarse aggregate Sieve Analysis Sieve Size Specifications As per IS:383-1970 Graded 100 95-100 25-55 0-10 Single Sized 100 85-100 0-20 0-5 40.II. 10.50mm 10.00mm 4.0mm Coarse aggregate Sieve Analysis Sieve Size 12. Specifications As per IS: 383-1970 1 2 3 Crushing Value in % Impact Value in % Los Angeles Abrasion Value in % 30 Maximum For wearing surfaces 45 Maximum For other concrete 30 Maximum For wearing surfaces 45 Maximum For other concrete 30 Maximum For wearing surfaces 50 Maximum For other concrete V.IV.No. Particulars of Test contd….36mm Specifications As per IS:383-1970 Graded – – – – Single Sized 100 85-100 0-20 0-5 . Mechanical properties Sl.75mm 2. M45 M50 Assumed Standard Deviation (N/Sq.mm A Statistic. depending on accepted proportion of low results.5 5.mm Standard Deviation in N/Sq.contd….5 4. M15 M20. IS:456-2000) Grade of Concrete M10. M25 M30.0 .40. Step II:Fck = Where.0 6. 1.mm Characteristic Compressive Strength at 28 days in N/Sq.mm) Good Site Control 3. Fck = fck S t = = = = Compute Target Mean Compressive Strength: fck + t * S Target Mean Compressive Strength at 28 days in N/Sq.0 5.65 for 1 in 20 accepted proportion of low results Assumed Standard Deviation (Table 8. M35 M.0 Fair Site Control 4. 55 4 5 6 7 8 M25 M30 M35 M40 M45 0.9 0.Select the Water-Cement ratio of trial mix from experience S.S: 10262-2009.No.7 0.35 0. Maximum size of Aggregate (mm) Water Content per cubic meter of concrete (Kg) 10 208 20 40 186 165 .45 0.50 0. Step III:.40 0.contd….30 Step IV:.Select the water content per cubic meter of concrete from table 2 of I. 1 2 3 Concrete Grade M10 M15 M20 Minimum expected W/C 0. 75 Zone III 0.48 0.44 0.64 0.46 0. SP:23-1982) Slump (mm) 30-50 80-100 150-180 Maximum Size of Aggregate (mm) 10 205 225 240 20 185 200 210 40 160 175 185 Volume of Coarse Aggregate per Unit Volume of Total Aggregate (Table 3. IS:10262-2009) Maximum Size of Aggregate (mm) 10 20 40 Volume of Coarse Aggregate per Unit Volume of Total Aggregate Zone IV 0.50 0.73 Zone II 0.66 0. Approximate water content (Kg) per cubic meter of concrete (Table 32.60 0.62 0.69 .71 Zone I 0.contd…. Compute the quantity of cement as follows. Step V:. Water Cement = ------------W/C Ratio Step VI:. V = (W+C/Sc+(1/p) * (fa/Sfa)) * (1/1000) {for fine aggregate} and V = (W+C/Sc+(1/(1-p)) * (ca/Sca)) * (1/1000) {for coarse aggregate} Where V = Absolute volume of fresh concrete = 1 m3 W = Mass of Water (Kg) per m3 of concrete C = Mass of Cement (Kg) per m3 of concrete p = Percentage of fine aggregate. . Sfa = Specific gravity of fine aggregate.Then we find the quantities of Fine & Coarse aggregate by absolute volume method.contd…. fa = Mass of fine aggregate ca = Mass of coarse aggregate Sc = Specific gravity of cement. Sca = Specific gravity of coarse aggregate. obtained from the graph.Calculate the mix proportions corresponding to the W/C ratio.40 & 0.Check the cement content & W/C ratio against the limiting values given in Table-5 of I. Step XIII:. Step VIII:. Make corrections to the water content & %FA. Step XI:.Draw a graph between compressive strength Vs C/W Ratio. Step VII:. taking %FA as 34% and 38% respectively. Step IX:.50.Make slump trials to find out the actual weight of water to get required slump. Step XIV:.From the graph. .S: 456-2000 for given type of exposure & type of Concrete.Test the cubes for compressive strength at 28 days.contd….Cast atleast 3 cubes for each trial mix. if required.Compute 2 more trial mixes with W/C ratios as 0. Step XII:. find the W/C ratio for the required target mean compressive strength. Step X:. 45 Minimum Grade of Concrete M15 M20 M20 Reinforced Concrete Minimum Cement Content kg/m3 300 300 320 340 Maximum Free Water Cement Ratio 0.contd….55 0.60 0.50 0. No .60 0.40 M40 . i) ii) iii) iv) Plain Concrete Exposure Mild Moderate Severe Very Severe Minimum Cement Content kg/m3 220 240 250 260 Maximum Free Water Cement Ratio 0.40 M25 360 0.45 0.45 Minimum Grade of Concrete M20 M25 M30 M35 v) Extreme 280 0. Table-5 (IS:456-2000) Minimum Cement content Maximum Water-Cement ratio and Minimum Grade of Concrete for different exposures with normal weight of aggregate of 20mm nominal maximum size.50 0. Sl. and many other factors depend on the relative amounts and properties of the individual components. aggregates. it is a far easier selection to choose to cure a concrete structure or not. and curing techniques under the proper conditions of moisture and temperature are not used. admixtures. • It is not possible for any individual to know even 10% of the total available knowledge about concrete. • It is a mixture of Portland cement. • A perfect mix can result in poor quality concrete if correct placement.• Concrete is a highly versatile construction material. well suited for many agricultural applications. • Strength. However. durability. and in some cases. receptive. • But it is possible to learn how to function as a forward – looking. Conclusion . finishing. water. discriminating and contributing member of the concrete fraternity. • It is a fairly simple exercise to determine the correct selection of curing system needed for a particular application.