UNIT II ADMIXTURES AND MIX DESIGN

UNIT II ADMIXTURES AND MIX DESIGN
SNS COLLEGE OF TECHNOLOGY (An Autonomous Institution) Coimbatore- 35 CONCRETE TECHNOLOGY UNIT II ADMIXTURES AND MIX DESIGN P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I
What are Admixtures? Admixtures are the material, other than Cement Water Aggregates which are used as an ingredient of concrete and is added to batch immediately before or during mixing. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Why admixtures? The major reasons for using admixtures are: To reduce the cost of concrete construction. To achieve certain properties in concrete more effectively than by other means. To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in ad-verse weather conditions. To overcome certain emergencies during concreting operations. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Types of admixture for concrete
Chemical Admixtures Mineral Admixtures Types of admixture for concrete P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Important Chemical Admixtures
Plasticizers Super plasticizers Retarders and Retarding Plasticizers Accelerators and Accelerating Plasticizers Damp-proofing and Waterproofing Admixtures P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Plasticizers (water reducers)
Amount used Results - effects At constant workability – The reduction in mixing water is expected to be of the order of 5% to 15%. Naturally increases the strength. At constant w/c ratio – Increased workability. Slump of 30mm to 150 mm. Plasticizers are used in the amount of 0.1% to 0.4% by weight of cement. Limitations A good plasticizer is one which does not cause air-entrainment in concrete more than 1 or 2%. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Plasticizers (water reducers)
Used at Where high degree of workability is required Thin walls of water retaining structures with high percentage of steel reinforcement Deep beams, column and beam junctions Tremie concreting Pumping of concrete Hot weather concreting Concrete to be conveyed for considerable distance and in ready mixed concrete industries. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

COMMONLY USED PLASTICIZERS
P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

SuperPlasticizers (High range water reducers)
Superplasticizers constitute a relatively new category and improved version of plasticizer, the use of which was developed in Japan and Germany during 1960 and 1970 respectively. They are chemically different from normal plasticisers. Classification of Superplasticizers: Sulphonated malanie-formaldehyde condensates (SMF) Sulphonated naphthalene-formaldehyde condensates (SNF) Modified lignosulphonates (MLS) Other types P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Amount used Results - benefits Permits reduction of water content about 30% without reducing the workability It is possible to use w/c ratio as low as 0.25 or even lower and yet to make flowing concrete to obtain strength of order Mpa or more. Based on various types of superplasticizers different amount is used. Lignosulphonates – not more than 0.25% Carboxylic acids – 0.1% Sulphonated malanie-formaldehyde condensates (SMF) – 0.5 to 3% Sulphonated naphthalene- formaldehyde condensates (SNF) – 0.5 to 3% P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Used at Superplasticizer is practiced for Production of flowing, self levelling, self compacting concrete Production of high strength and high performance concrete. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Retarders A retarder is an admixture that slows down the chemical process of hydration so that concrete remains plastic and workable for a longer time than concrete without the retarder. Retarders are used to overcome the accelerating effect of high temperature on setting properties of concrete in hot weather concreting. Very useful when concrete has to be place in very difficult conditions and delay may occur in transporting and placing. .Gypsum and Calcium Sulphate are well known retarders. Other examples are: starches, cellulose products, sugars, acids or salts of acids P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Retarders Limitations Used at Casting and consolidating large number of pours without the formation of cold joints. Grouting oil wells, where temperature is about 200 °C, at a depth of 6000 meters. amount. Access Retarders should be used in proper amount will cause indefinite setting time. At normal temperatures addition of sugar 0.05 to 0.10 percent have little effect on the rate of hydration, but if the quantity is increased to 0.2 percent, hydration can be retarded to such an extent that final set may not take place for 72 hours or more. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

COMMONLY USED RETARDERS

Accelerators Accelerating admixtures are added to concrete to increase the rate of early strength development Why accelerators? Permit earlier removal of formwork Reduce the required period of curing Advance the time that a structure can be placed in service Partially compensate for the retarding effect of low temperature during cold weather concreting In the emergency repair work. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Accelerators Commonly used materials as an accelerator: Calcium chloride (Not used now) Some of the soluble carbonates Silicates fluosilicates (Expensive) Some of the organic compounds such as triethenolamine (Expensive) P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Accelerators Benefits of Accelerators Accelerators are so powerful that it is possible to make the cement set into stone hard in a matter of five minutes are less. With the availability of such powerful accelerator, the under water concreting has become easy. Similarly, the repair work that would be carried out to the waterfront structures in the region of tidal variations has become easy. The use of such powerful accelerators have facilitated, the basement waterproofing operations. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

COMMONLY USED ACCELERATORS

AIR-ENTRAINING ADMIXTURES:  Concrete is made by using air entrained cement or addition of air-entraining agent.  Produce large quantity of air bubbles and modify the concrete properties regarding workability, segregation, bleeding & finishing quality of concrete.  Gains Resistance to frost action & permeability Natural Wood resins, animal and vegetable fats, Water soluble soaps of resin acids etc., P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Commonly used air entraining admixtures

DAMP-PROOFING ADMIXTURES: Advantages in reducing the permeability.  These admixtures are available in powder or liquid form.  It has the property of pore filling inside the concrete  Silicates of soda,Aluminium & zinc sulphates, Aluminum & calcium chlorides are most common damp-proofing admixtures. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Damp-proofing & Waterproofing Admixture
Results - effects Amount used Chemically active pore fillers accelerates the setting of concrete and thus render the concrete more impervious at early age. Chemically inactive pore fillers improve the workability and to facilitate the reduction of water for given workability and to make dense concrete which is basically impervious. Water repelling materials like soda, potash soaps, calcium soaps, waxes, fats, vegetable oils repel water and make the concrete impervious Depends upon various damp-proofing and water proofing admixtures. Limitations Use of admixture should in no case be considered as a substitute for bad materials, bad design or workmanship. In no case can an admixture be expected to compensate for cracks or large voids in concrete causing permeability. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Commonly used air entraining damp-proof admixtures

CONSTRUCTION CHEMICALS
Chemicals which are used to enhance the performance. Some common construction chemicals are, Concrete curing compounds. Polymer bonding agents. Water proofing chemicals. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

CONCRETE CURING COMPOUNDS: In order to prevent the loss of water from the surface these curing compounds are used. Synthetic resin,wax,chlorinated rubber are used as curing compounds Resin and wax based compounds effectively seal the concrete from the surface evaporation. Chlorinated rubber curing compounds forms a thin film on the surface of the concrete which protects drying and at the same time they fill the pores on the surface of the concrete. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

POLYMER BONDING AGENTS: By providing a bond coat between old concrete and new concrete. Mixing of bonding agents with new concrete helps to provide a better bond. Also increase the workability and reduce the shrinkage. Roof bond ERB , Nit bond PVA are most common type of bonding agents used for Concrete repair work such as ceiling of concrete roof, hydraulic structures, prefabricated members, pipes etc., P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Mineral additives Pozzolanic materials are: Siliceous or siliceous-aluminous materials, Little or no cementitious value, In finely divided form and in the presence of moisture, Chemically react with calcium hydroxide liberated on hydration, at ordinary temperature, to form compounds, possessing cementitious properties. They are also known as POZZOLANIC materials. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Why Mineral additives? Improves many qualities of concrete, such as: Lower the heat of hydration and thermal shrinkage; Increase the water tightness; Reduce the alkali-aggregate reaction; Improve resistance to attack by sulphate soils and sea water; Lower susceptibility to dissolution and leaching; Improve workability; Lower costs. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Types of mineral additives
Natural Pozzolans Artificial Pozzolans Clay and Shales Opalinc Cherts Diatomaceous Earth Volcanic Tuffs and Pumicites. Fly ash Blast Furnace Slag Silica Fume Rice Husk ash Metakaoline Surkhi P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Fly ash Fly ash is finely divided residue resulting from the combustion of powdered coal and transported by the flue gases and collected by; Electrostatic Precipitator Fly ash is the most widely used pozzolanic material all over the world. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Fly ash Amount used Up to 35% by mass of cement & minimum shall not be less than 15%. Results - effects Reduction of water demand for desired slump. With the reduction of unit water content, bleeding and drying shrinkage will also be reduced. fly ash is not highly reactive, the heat of hydration can be reduced through replacement of part of the cement with fly ash. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Fly ash Effects of Fly Ash on Hardened Concrete High volume Fly Ash has been used in the Barker Hall Project, University of California at Berkeley for the construction of shear walls. contributes to the strength of concrete due to its pozzolanic reactivity. continued pozzolanic reactivity concrete develops greater strength at later age not at initial stage. contributes to making the texture of concrete dense, resulting in decrease of water permeability and gas permeability. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Fly ash Used at Many high-rise buildings Industrial structures Water front structures Concrete roads Roller compacted concrete dams. In India, fly ash was used for the first time in the construction of Rihand Irrigation Project, Uttar Pradesh in 1962, replacing cement up to about 15 per cent P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Silica fume It is a product resulting from reduction of high purity quartz with coal in an electric arc furnace in the manufacture of silicon or ferrosilicon alloy. Micro silica is initially produced as an ultrafine undensified powder At least 85% SiO2 content Mean particle size between 0.1 and 0.2 micron Minimum specific surface area is 15,000 m2/kg Spherical particle shape P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Silica fume Effect on fresh concrete The increase in water demand of concrete containing microsilica will be about 1% for every 1% of cement substituted. lead to lower slump but more cohesive mix. make the fresh concrete sticky in nature and hard to handle. large reduction in bleeding and concrete with microsilica could be handled and transported without segregation. to plastic shrinkage cracking and, therefore, sheet or mat curing should be considered. produces more heat of hydration at the initial stage of hydration. the total generation of heat will be less than that of reference concrete. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Silica fume Effect on hardened concrete Used for Conserve cement Produce ultra high strength concrete of the order of 70 to 120 Mpa. Increase early strength of fly concrete. Control alkali-aggregate reaction. Reduce sulfate attack & chloride associated corrosion. Modulus of elasticity of microsilica concrete is less. Improvement in durability of concrete. Resistance against frost damage. Addition of silica fume in small quantities actually increases the expansion. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Rice husk ash Rice husk ash is obtained by Burning rice husk in a controlled manner without causing environmental pollution. Material of future as mineral additives. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Rice husk ash Amount used Contains 10% by weight of cement. It greatly enhances the workability and impermeability of concrete. Amorphous silica (90% SiO2) in very high proportion when burnt in controlled manner. 5% carbon. 2% K2O. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Rice husk Ash Effects Reduces susceptible to acid attack and improves resistance to chloride penetration. Reduces large pores and porosity resulting very low permeability. Reduces the free lime present in the cement paste. Decreases the permeability of the system. Improves overall resistance to CO2 attack. Enhances resistance to corrosion of steel in concrete. Reducing micro cracking and improving freeze-thaw resistance. Improves capillary suction and accelerated chloride diffusivity. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Blast furnace slag Blast-furnace slag is a nonmetallic product consisting essentially of silicates and aluminates of calcium and other bases. The molten slag is rapidly chilled by quenching in water to form a glassy sand like granulated material. The granulated material when further ground to less than 45 micron will have specific surface of about 400 to 600 m2/ kg (Blaine). P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Blast furnace slag Effects on fresh concrete Effects on hardened concrete Reduces the unit water content necessary to obtain the same slump. Water used for mixing is not immediately lost, as the surface hydration of slag is slightly slower than that of cement. Reduction of bleeding. Reduced heat of hydration Refinement of pore structures Reduced permeabilities to the external agencies Increased resistance to chemical attack. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Reduction in unit water contain

Metakaolin Highly reactive metakaolin is made by water processing to remove unreactive impurities to make100% reactive pozzolan. Such a product, white or cream in colour, purified, thermally activated is called High Reactive Metakaolin (HRM). P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Metakaolin Effects of Metakaolin Use of Metakaolin High reactive metakaolin shows high pozzolanic reactivity and reduction in Ca(OH)2 even as early as one day. The cement paste undergoes distinct densification. Densification includes an increase in strength and decrease in permeability. The high reactive metakaolin is having the potential to compete with silica fume. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Mix Design Mix design is defined as the process of selecting suitable ingredients of concrete and determine their relative proportions with the object of producing concrete of certain minimum strength and durability economically as possible. as P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 2

Objectives of Mix Design
To achieve the designed/ desired workability in the plastic stage To achieve the desired minimum strength in the hardened stage To achieve the desired durability in the given envir. onment conditions To produce concrete as economically as possible P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Basic Considerations The following point must be considered while designing concrete mixes Cost Specification Workability Strength and Durability P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Basic Considerations Cost The cost of concrete is made up of Material Cost Equipment Cost Labour Cost The variation in the cost of materials arises from the fact that cement is several times costlier than aggregates. So it is natural in mix design to aim at as lean a mix as possible. Therefore, all possible steps should be taken to reduce the cement content of a concrete mixtures without sacrificing the desirable properties of concrete such as strength and durability. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Basic Considerations Specifications The following point may be kept in mind while designing concrete mixes Minimum Compressive Strength required Minimum water/ cement ratio Maximum cement content to avoid shrinkage cracks Maximum aggregate / cement ratio Maximum density of concrete in case of gravity dams P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Basic Considerations Workability The consistency of concrete should no more than that necessary for placing, compacting and finishing. For concrete mixes required high consistency at the time of placing, the use of water-reducing and set-retarding admixtures should be used rather than the addition of more water Wherever possible, the cohesiveness and finishibility of concrete should be improved by increasing sand/ aggregate ratio than by increasing the proportion of the fine particles in the sand. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Workability P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Strength and Durability
require lower w/c ratio. Water demand can by lowered by throughout control of the aggregate grading and by using water reducing admixtures. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Characteristics compressive strength of 150 mm cube at 28 days, N/mm2
Grade of Concrete The concrete shall be in grades designated Group Grade designation Characteristics compressive strength of 150 mm cube at 28 days, N/mm2 Ordinary Concrete M10 M15 M20 10 15 20 Standard Concrete M25 M30 M35 M40 M45 M50 M55 25 30 35 40 45 50 55 High Strength Concrete M60 M65 M70 M75 M80 60 65 70 75 80 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

What is M 20 ? M refers to Mix 20 refers to characteristic compressive strength of 150 mm cube at 28 days in N/mm2 The minimum Grade of Plain Concrete (PCC) shall be 15 N/mm2 The minimum grade of reinforced Concrete ( RCC) shall be 20 N/mm2 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Nominal Concrete Mixes and Design mix concrete
Nominal Mix Concrete The wide use of concrete as construction materials has led to the use of mixes of fixed proportion, which ensures adequate strength. These mixes are called nominal mixes. They offer simplicity and Under normal circumstances, has margin of strength above that specified. Nominal mix concrete may be used for concrete of grades M5, M 7.5, M10, M15 and M20. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Proportions of Ingredients in Nominal Mixes
The proportions of materials for nominal mix shall be in accordance Grade Proportions C: FA: CA M5 1: 5:10 M 7.5 1:4:8 M 10 1:3:6 M 15 1:2:4 M 20 1:1.5:3 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Design Mix Concrete The concrete mix produced under quality control keeping in view the strength, durability, and workability is called the design Mix. Others factors like compaction equipment's available, curing method adopted, type of cement, quality of fine and coarse aggregate etc. have to be kept in mind before arriving at the mix proportion. The design mix or controlled mix is being used more and more in variety of important structures, because of better strength, reduced variability, leaner mixed with consequent economy, as well as greater assurance of the resultant quality. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Factors Influencing Choice of Mix Design
According to IS 456:2000 and IS 1343:1980 the important influencing the design of concrete mix are Grade of Concrete Type of Cement Maximum nominal Size of Aggregate Grading of Combined aggregate Maximum Water/ Cement Ratio Workability Durability Quality Control. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Grade of Concrete The grade M 20 denotes characteristic compressive strength fck of 20 N/mm2. Depending upon the degree of control available at site, the concrete mix is to be designed for a target mean compressive strength (fck) applying suitable standard deviation. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Type of Cement The rate of development of strength of concrete is influenced by the type of cement. The higher the strength of cement used in concrete, lesser will be the cement content. The use of 43 grade and 53 grade of cement, gives saving in cement consumption as much as 15 % and 25 % respectively, as compared to 33 grade of cement. For concrete of grade M25 it is advisable to use 43 and 53 grade of cement. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Types of Cement P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Maximum Nominal Size of Aggregates The maximum size of C.A is determined by sieve analysis. The maximum nominal size of C.A. should not be more than one-forth of minimum thickness of the member. For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of the aggregate should usually be restricted to sum less than the minimum clear distance between the main bars or 5 mm less the minimum cover to the reinforcement, whoever is smaller. The workability of concrete increases with an increase in the maximum size of aggregate. But the smaller size of aggregates provide larger surface area for bonding with the mortar matrix which gives higher strength. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Grading of Combined Aggregates The relative proportions of the fine and coarse aggregate in a concrete mix is one of the important factors affecting the strength of concrete. For dense concrete, it is essential that the fine and coarse aggregate be well graded. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Maximum Water/ Cement Ratio Abram’s water/Cement ratio states that for any given condition of test, the strength of a workability concrete mix is dependent only on water/cement ratio. The lower the water/Cement ratio, the greater is the compressive strength Workability Workability of fresh concrete determines the case with which a concrete mixture can be mixed, transported, placed, compacted and finished without harmful segregation and bleeding. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Durability Durability require low water/Cement ratio. Water demand can be lowered by through control of the aggregate grading and by using water reducing admixtures P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Methods of Proportioning 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Indian Standards Recommended method IS American Concrete Institute Method of Mix DOE method Mix design for pumpable concrete Indian Road Congress , IRC 44 method Road note no.4 (Grading curve method) Design (ACI 211) Mix design based on flexural Arbitrary proportion Fineness modulus methods Maximum density method Surface area method strength P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 5

American Concrete Institute Method of Mix Design (ACI)
Data to be collected: Fineness modulus of fine aggregates Sp gravity of coarse & fine aggregates a) b) c) Absorption characteristics fine aggregates Sp gravity of cement of coarse & d) P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 6

STEPS IN ACI METHOD 1. From minimum strength specified, estimate average design strength using standard deviation method Find w/c ratio from table 2. Find water cement ratio for durability from table 3. adopt lower value. Decide maximum size of aggregate (generally 20 mm for RCC) Decide workability in terms of slump for the type of job in hand. Table 4. Total water in kg/m3 is read from table 5 entering the table with selected slump & selected maximum size of aggregate. Cement content is computed by dividing total water content by w/c ratio. 2. 3. 4. 5. 6. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 7

7. From table 4 the bulk volume of dry rodded coarse aggregate / unit volume of concrete is selected, for particular maximum size of coarse aggregate & fineness modulus of fine aggregate. The weight of CA /M3 of concrete is calculated by multiplying the bulk volume with bulk density. The solid volume of coarse aggregate in one M3 of concrete is calculated by knowing the sp. Gravity of CA Solid volume of cement, water & volume of air is calculated in one m3 of concrete Solid volume of sand is calculated by substracting soild volume of cement, CA,water, & air from total volume of concrete. Weight of fine aggregate is calculated by multiplying the solid volume of fine aggregate by sp gr of FA. 8. 9. 10. 11. 12. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 8

(1) Dry Bulk Volume of coarse aggregate/ unit volume of concrete as per ACI Maximum size of aggregate Bulk volume of dry rodded CA /unit volume of concrete for fineness modulus of sand of FM OO 10 0.5 0.48 0.46 0.44 12.5, 0.59 0.57 0.55 0.53 20 (25,40,50,70) 0.66 0.64 0.62 0.60 150 .87 0.85 0.83 0.81 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 9

(2) Relation between water/cement ratio & average compressive strength of concrete, as per ACI Average compressive strength at 28 days Effective water/cement ratio (by mass) MPa Non air entrained concrete Air entrained concrete 45 0.38 - 40 0.43 - 35 (30,25,20) 0.48 0.4 15 0.8 0.71 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 10

(3) Requirements of ACI for w/c ratio conditions & strength for special exposure Exposure condition Maximum w/c ratio, normal density aggregate concrete Minimum design strength, low density aggregate concrete MPa Concrete intended to be watertight (a) Exposed to fresh water (b) Exposed to sea water 0.5 0.45 25 30 Concrete exposed to freezing in a moist condition 0.45 30 For corrosion protection of reinforced concrete exposed to de icing salts, sea water 0.4 33 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 11

(4) Recommended value of slump for various types of construction as per ACI Type of construction Range of slump (mm) Reinforces foundation walls & footings 20-80 Plain footings,substructure wall 20-80 Beams & reinforced walls 20-100 Building columns 20-100 Pavements & slabs 20-80 Mass concrete 20-80 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 12

(5) Approximate requirements for mixing water & air content for
different workabilities & nominal maximum size of aggregates as per ACI Non air entrained concrete Workability or air content (Slump) Water content, kg/m3 of concrete for indicted maximum aggregate size 10 mm mm mm mm ( 25, 40,50,70) mm 205 200 185 125 mm 225 215 200 140 mm 240 230 210 - Approx entrapped air (%) 3 2.5 2 0.2 13 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

(6) First estimate of density of fresh concrete as per ACI Maximum size of aggregate (mm) First estimate of density of fresh concrete Non air entrained kg/m3 Air entrained kg/m3 10 2285 2190 12.5 (20,25,40,50) 2315 2235 20 2355 2280 150 2505 2435 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 14

(7) Required increase in strength (mean strength) for specified design strength when no tests records are available as per ACI 318-89 Specified design strength (MPa) Required increase in strength (MPa) Less than 21 7 21-35 8.5 35 or more 10 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I 15

IS METHOD P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Cement Concrete Mix Design means, determination of the proportion of the concrete ingredients i.e. Cement, Water, Fine Aggregate,Coarse Aggregate which would produce concrete possessing specified properties such as workability, strength and durability with maximum overall economy. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Methods of Concrete Mix Design
I.S. Method British Method A.C.I. Method etc. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

These Methods are based on two basic assumptions Compressive Strength of Concrete is governed by its Water-Cement Ratio Workability of Concrete is governed by its Water Content P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Data required for concrete mix design Grade of Concrete Eg: RCC-M30-A20 Slump required in mm Eg: 25 – 75 mm Degree of Site Control Eg: Good Type of Exposure Eg: Moderate Grade of Cement Eg: OPC 43 Grade P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Workability (Clause 7.1, IS: ) Placing Conditions Degree of Workability Slump (mm) 1 2 3 Blinding Concrete; Shallow Sections; Pavements using pavers Very Low See 7.1.1 Mass Concrete; Lightly reinforced sections in Slabs, Beams, Walls, Columns; Floors; Hand placed Pavements; Canal lining; Strip Footings Low 25-75 Heavily reinforced sections in Slabs, Beams, Walls, Columns; Slip form work; Pumped Concrete. Medium 50-100 Trench fill; In-Situ Piling; Tremie Concrete High P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Degree of Site Control (Table 8, IS: ) Good Site control having proper storage of cement; weigh batching of all materials; Controlled addition of water, regular checking of all materials, aggregate grading and moisture content; And periodical checking of workability and strength. Fair Site control having deviation from the above. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Type of Exposure (Table 3, IS:456-2000)
Sl. No. Environment Exposure Conditions 1 2 3 i) Mild Concrete surfaces protected against weather or aggressive conditions, except those situated in coastal area. ii) Moderate Concrete surfaces sheltered from severe rain or freezing whilst wet. Concrete exposed to condensation and rain. Concrete continuously under water. Concrete in contact or buried under non-aggressive soil/ground water. Concrete surfaces sheltered from saturated salt air in coastal area. iii) Severe Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation. Concrete completely immersed in sea water. Concrete exposed to coastal environment. iv) Very Severe Concrete exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet. Concrete in contact with or buried under aggressive sub-soil/ground water. v) Extreme Surface of members in tidal zone. Members in direct contact with liquid/solid aggressive chemicals. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Approximate Quantity of Materials required for concrete mix design Cement : 200 Kg. Fine Aggregate : 240 Kg. Coarse Aggregate : 180 Kg. (20 mm) 180 Kg. (10 mm) P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

STEPS INVOLVED IN CONCRETE MIX DESIGN
Step I:- Determine the physical properties of concrete ingredients. I. CEMENT (OPC 43 Grade) Sl. No. Particulars of Test Result Specifications As per IS: 1 Standard consistency (% by weight) 25.6 2 Setting Time in minutes a) Initial b) Final 95 210 30 Minimum 600 Maximum 3 Compressive Strength in N/sq.mm at the age of a) 3 days b) 7 days c) 28 days 24 35 46 23 Minimum 33 Minimum 43 Minimum 4 Specific Gravity 3.00 5 Fineness in Sq.m/Kg 337 225 Minimum P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Specifications for Zone–II
FINE AGGREGATE 1. Sieve Analysis Sieve Size % Passing Specifications for Zone–II As per IS: 10.0 mm 100 4.75 mm 90-100 2.36 mm 98 75-100 1.18 mm 65 55-90 600 micron 42 35-59 300 micron 8 8-30 150 micron 0-10 2. Specific Gravity : 2.60 3. Unit Weight in Kg/Cu.m a) Loose : 1460 b) Rodded : 1580 4. Materials Finer than 75 micron : Max (% by weight) P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

III. 20.0mm COARSE AGGREGATE 1. Sieve Analysis Sieve Size % Passing Specifications As per IS: Graded Single Sized 40.00mm 100 20.00mm 90 95-100 85-100 10.00mm 3 25-55 0-20 4.75mm 0-10 0-5 2. Specific Gravity : 2.65 3. Unit Weight in Kg/Cu.m a) Loose : 1467 b) Rodded : 1633 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

IV. MECHANICAL PROPERTIES Sl. No. Particulars of Test Result Specifications As per IS: 1 Crushing Value in % 28 30 Maximum For wearing surfaces 45 Maximum For other concrete 2 Impact Value in % 24 3 Los Angeles Abrasion Value in % 30 50 Maximum P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

V. 10.0mm COARSE AGGREGATE 1. Sieve Analysis Sieve Size % Passing Specifications As per IS: Graded Single Sized 12.50mm 100 – 10.00mm 85 85-100 4.75mm 19 0-20 2.36mm 0-5 2. Unit Weight in Kg/Cu.m a) Loose : 1427 b) Rodded : 1587 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

VI. BLENDING OF COARSE AGGREGATE: Sieve size (mm) IS: Specifications (Graded) % Passing 20 mm 10 mm 60%+40% 50%+50% 40 100 20 95-100 90 94 95 10 25-55 3 85 44 4.75 0-10 19 7 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step II:- Compute Target Mean Compressive Strength: Fck = fck + t * S Fck = Target Mean Compressive Strength at 28 days in N/Sq.mm fck = Characteristic Compressive Strength at 28 days in S = Standard Deviation in N/Sq.mm t = A Statistic, depending on accepeted proportion of low results. = for 1 in 20 accepted proportion of low results P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Accepted proportion of low results t 1 in 5, 20% 0.84 1 in 10, 10%
Values of t Accepted proportion of low results t 1 in 5, % 0.84 1 in 10, 10% 1.28 1 in 15, % 1.50 1 in 20, 5% 1.65 1in 40, % 1.86 1 in 100, 1% 2.33 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Assumed Standard Deviation (Table 8, IS:456-2000) Grade of Concrete
(N/Sq.mm) Good Site Control Fair Site Control M10, M15 3.5 4.5 M20, M25 4.0 5.0 M30, M35 M,40,M45 M50 6.0 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step III:- Select the Water-Cement ratio of trial mix from experience S. No. Concrete Grade Minimum expected W/C 1 M10 0.9 2 M15 0.7 3 M20 0.55 4 M25 0.50 5 M30 0.45 6 M35 0.40 7 M40 0.35 8 M45 0.30 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Maximum size of Aggregate Water Content per cubic metre of concrete
Step IV:- Select the water content per cubic metre of concrete from table2 of I.S: Maximum size of Aggregate (mm) Water Content per cubic metre of concrete (Kg) 10 208 20 186 40 165 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

per cubic metre of concrete (Table 32, SP:23-1982) Slump (mm)
Approximate water content (Kg) per cubic metre of concrete (Table 32, SP: ) Slump (mm) Maximum Size of Aggregate 10 20 40 30-50 205 185 160 80-100 225 200 175 240 210 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Unit Volume of Total Aggregate (Table 3, IS:10262-2009)
Volume of Coarse Aggregate per Unit Volume of Total Aggregate (Table 3, IS: ) Maximum Size of Aggregate (mm) Volume of Coarse Aggregate per Unit Volume of Total Aggregate Zone IV Zone III Zone II Zone I 10 0.50 0.48 0.46 0.44 20 0.66 0.64 0.62 0.60 40 0.75 0.73 0.71 0.69 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step V:- Compute the quantity of cement as follows. Water Cement = W/C Ratio = 185 / 0.45 = 411 Kg. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step VI:- Then we find the quantities of Fine & Coarse aggregate by absolute volume method. V = (W+C/Sc+(1/p) * (fa/Sfa)) * (1/1000) (Eq.1) and V = (W+C/Sc+(1/(1-p)) * (ca/Sca)) * (1/1000) (Eq.2) 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. fa = Mass of fine aggregate ca = Mass of coarse aggregate Sc = Specific gravity of cement. Sfa = Specific gravity of fine aggregate. Sca = Specific gravity of coarse aggregate. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Substituting the values in Eq(1), we get 1000 = /3.0 + (1/0.36) * fa /2.6) = fa/0.936 = fa/0.936 fa = (1000 – 322) * 0.936 = 678 * 0.936 = 635 Kg. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Substituting the values in Eq(2), we get 1000 = /3.0 + (1/0.64) * ca /2.65) = ca/1.696 = ca/1.696 ca = (1000 – 322) * 1.696 = 678 * 1.696 = 1150 Kg. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

So the mix proportion works out to be W : C : fa : ca = 185 : 411 : 635 : 1150 = : 1 : 1.55 : 2.80 This mix will be considered as Trial Mix No.2 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step VII:- Make slump trials to find out the actual weight of water to get required slump. Make corrections to the water content & %FA, if required. Step VIII:- Compute 2 more trial mixes with W/C ratios as 0.40 & 0.50, taking %FA as 34% and 38% respectively. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Trial Mix No. 1:- Cement = 185 / 0.4 = Kg. Substituting the values in Eq(1), we get 1000 = /3.0 + (1/0.34) * fa /2.6) fa = 584 Kg. Substituting the values in Eq(2), we get 1000 = /3.0 + (1/0.66) * ca /2.65) ca = 1156 Kg. So the mix proportion works out to be W : C : fa : ca = 185 : : 584 : 1156 = 0.4 : 1 : 1.26 : 2.50 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Trial Mix No. 3:- Cement = 185 / 0.5 = 370 Kg. Substituting the values in Eq(1), we get 1000 = /3.0 + (1/0.38) * fa /2.6) fa = 683 Kg. Substituting the values in Eq(2), we get 1000 = /3.0 + (1/0.62) * ca /2.65) ca = 1136 Kg. So the mix proportion works out to be W : C : fa : ca = 185 : 370 : 683 : 1136 = 0.5 : 1 : 1.85 : 3.07 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step IX:- Cast atleast 3 cubes for each trial mix. Step X:- Test the cubes for compressive strength at 28 days. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

28 Days Compressive Strengths of Trial Mixes W/C Ratio C/W Ratio Compressive Strength (Kg/Cm2) 0.40 2.50 457 0.45 2.22 420 0.50 2.00 360 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step XI:- Draw a graph between compressive strength Vs C/W Ratio. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step XII:- From the graph, find the W/C ratio for the required target mean compressive strength. Step XIII:- Calculate the mix proportions corresponding to the W/C ratio, obtained from the graph. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Final Mix:- From the graph, for a target strength of 390 Kg/Cm2, W/C ratio = 0.47 Cement = 185 / 0.47 = 394 Kg. Substituting the values in Eq(1), we get 1000 = /3.0 + (1/0.38) * fa /2.6) fa = 675 Kg. Substituting the values in Eq(2), we get 1000 = /3.0 + (1/0.62) * ca /2.65) ca = 1123 Kg. So the mix proportion works out to be W : C : fa : ca = 185 : 394 : 675 : 1123 = : 1 : 1.71 : 2.85 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step XIV:- Check the cement content & W/C ratio against the limiting values given in Table-5 of I.S: for given type of exposure & type of Concrete. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Table-5 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. Sl. No. Exposure Plain Concrete Reinforced Concrete Minimum Cement Content kg/m3 Maximum Free Water Cement Ratio Minimum Grade of Concrete i) Mild 220 0.60 - 300 0.55 M20 ii) Moderate 240 M15 0.50 M25 iii) Severe 250 320 0.45 M30 iv) Very Severe 260 340 M35 v) Extreme 280 0.40 360 M40 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

From the table 5 of IS: 456–2000, the minimum Cement content & W/C ratio, For moderate, for RCC are 300Kgs. & 0.5 The Cement content = 394Kgs. > 300Kgs. Hence Ok The W/C Ratio = 0.47 < 0.5 Hence Ok P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Concrete Mix RCC M30 with 20.0mm M.S.A.
TEST REPORT Concrete Mix RCC M30 with 20.0mm M.S.A. Sl. No. Particulars Result 1 Characteristic Compressive strength in N/Sq.mm 30 2 Maximum size of Aggregate in mm 20.0 3 Type of Exposure Moderate 4 Type of Site control Good 5 Target Average Compressive Strength in N/Sq.mm 38.2 6 Workability in terms of Slump in mm 25-75 7 Mode of Compaction Vibration 8 Mix Partiuclars: a. Water-Cement Ratio b. Materials per cubic metre of concrete in Kg. i) Water ii) Cement (OPC 43 Grade) iii) Fine Aggregate iv) Coarse Aggregate c. Mix Portion by weight 0.47 185 394 675 1123 1:1.71:2.85 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Sieve Analysis of Fine Aggregate
Weight of sample = 500g (approx) Observations: Sieve size Weight retained(g) Cumulative weight retained (g) % Cumulative weight retained (g) % Passing IS: Specifications Zone =II Trail 1 Trail2 Total 10 mm 100 4.75 mm 2 4 90-100 2.36 mm 6 7 13 17 98 75-100 1.18 mm 166 165 331 348 35 65 55-90 600 micron 118 117 235 583 58 42 35-59 300 micron 175 160 335 918 92 8 8-30 150 micron 36 78 996 0-10 150 micron pass - P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Zones of Fine Aggregate Sieve Size IS : 383 – 1970 % Passing for Zone I Zone II Zone III Zone IV 10.00 mm 100 4.75 mm 90-100 95-100 2.36 mm 60-95 75-100 85-100 1.18 mm 30-70 55-90 600 micron 15-34 35-59 60-79 80-100 300 micron 5-20 8-30 12-40 15-50 150 micron 0-10 0-15 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Sieve Analysis of Coarse Aggregate
2 20 mm aggregate : a. Minimum weight of sample = 25 Kg b. Observations : Sieve size Weight retained (Kg) Cumulative weight retained (Kg) % Cumulative weight retained (Kg) % Passing IS: Specifications Graded Single sized 40 0.0 100 20 4.7 10 90 95-100 85-100 41.5 46.2 97 3 25-55 0-20 4.75 1.6 47.8 0-10 0-5 4.75 P - P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Sieve Analysis of Coarse Aggregate
10 mm aggregate : a. Minimum weight of sample = 12 Kg b. Observations : Sieve size Weight retained (Kg) Cumulative weight retained (Kg) % Cumulative weight retained (Kg) % Passing IS: Specifications Single Sized 12.5 0.0 100 10 5.4 15 85 85-100 4.75 24.3 29.7 81 19 0-20 2.36 6.9 36.6 0-5 2.36 P - P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Target mean compressive strength
Avg = 30 Avg = 35 27,30,30,32,35, 27,33,34,29,28, 30,28,31,32,26, 34,33,25,27,29 28, 32,35,38,40, 34,35,35,36,39, 33,32,32,34,37, 32,35,38,39,36 Total = 600 Total = 700 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

The value of ‘S’ depends on Degree of Site control and grade of concrete as given in I.S: 456–2000 (Table.8) Sl. No. Concrete Grade Good Fair S 1.65XS Fck N/mm2 Kg/cm2 1 M10 3.5 58 15.8 161 4.5 7.4 17.4 178 2 M15 20.8 212 22.4 229 3 M20 4.0 6.6 26.6 271 5.0 8.3 28.3 288 4 M25 31.6 322 33.3 339 5 M30 38.3 390 6.0 9.9 39.9 407 6 M35 43.3 441 44.9 458 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Step IV:-Fixation of Water Cement ratios for trial mixes. Sl. No. Required Grades Trial W/C 1 M20, M15, M10 0.55, 0.6, 0.9 2 M25, M20, M15 0.5, 0.6, 0.7 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Final Mix for RCC-M25:- From the graph, for a target strength of 322 Kg/Cm2, W/C ratio = 0.57 which is > 0.5, So, limit W/C ratio to 0.5 only. Cement = 185 / 0.5 = 370 Kg. Substituting the values in Eq(1), we get 1000 = /3.0 + (1/0.38) * fa /2.6) fa = 683 Kg. Substituting the values in Eq(2), we get 1000 = /3.0 + (1/0.62) * ca /2.65) ca = 1136 Kg. So the mix proportion works out to be W : C : fa : ca = 185 : 370 : 683 : 1136 = : 1 : 1.85 : 3.07 P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Specific Gravity of Cement [ IS : 4031 – 1988]: Specific gravity of cement (Sc) (W2 - W1) = x 0.79 (W4 - W1) - (W3 - W2) Where, W1 = Weight of specific gravity bottle in g W2 = Weight of specific gravity bottle with about half filled cement in g W3 = Weight of specific gravity bottle with about half filled cement & rest is filled with kerosene in g. W4 = Weight of specific gravity bottle completely filled with kerosene in g 0.79 = Specific Gravity of Kerosene. P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

Specific Gravity of Fine Aggregate & Coarse Aggregate [ IS : 2386 (Part.3) ]: D Specific gravity (Gs) = C – ( A – B) Where, A = Weight of Pycnometer vessel containing sample & filled with distilled water in g B = Weight of Pycnometer completely filled with distilled water only in g C = Weight of saturated surface dry sample in g D = Weight of oven dried sample in g P.THARANI CE314/CONCRETE TECHNOLOGY/ UNIT I

UNIT II ADMIXTURES AND MIX DESIGN

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