Concrete Making Materials, Chemical and Mineral Admixtures, Concreting Methods and Mix Design, Fresh and Hardened Properties of Concrete, Special Concrete

Concrete Making Materials, Chemical and Mineral Admixtures, Concreting Methods and Mix Design, Fresh and Hardened Properties of Concrete, Special Concrete

1. CONCRETE TECHNOLOGY

2. UNIT II CHEMICAL AND MINERAL ADMIXTURES Accelerators – used to fast rate of setting of concrete Retarders - used to slow the rate of setting of concrete Plasticizers - to produce or promote plasticity Super plasticizers - high range water reducers Water proofers - prevent permeation by water Mineral admixtures like Fly ash Silica fume Ground granulated blast furnace slag and Metakaoline

3. Accelerators – speed up the initial set of concrete. Retarders – delay the setting time of concrete mix. Plasticizers and Super-plasticizers - water reducers. Air entraining admixtures Water proofers Pigments Corrosion - inhibiters Chemicals Anti-fungal admixtures

4. ADMIXTURES Admixtures are ingredients other than cement, fine aggregate and coarse aggregate to improve the quality of concrete. The addition of an admixture may improve the concrete with respect to its strength, hardness, workability, water resisting power etc.

5. Needs of Admixtures To modify properties of fresh and hardened concrete. To ensure the quality of concrete during the mixing, transporting, placing, and curing. To overcome certain unexpected emergencies during concrete operations by using admixtures and etc… 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

6. Types of Admixture Concrete admixtures are generally divided into 2 types 1. Chemical admixture 2. Mineral admixture Chemical Admixtures Chemicals mixed with concrete ingredients and spread throughout the body of concrete to favorably modify the molding and setting properties of concrete mix known as chemical admixtures . Chemicals added to the concrete immediately or during mixing to modify its properties in the fresh hardened state.

7. Accelerators – speed up the initial set of concrete. Retarders – delay the setting time of concrete mix. Plasticizers and Super-plasticizers - water reducers. Air entraining admixtures Water proofers Pigments Corrosion - inhibiters Chemicals Anti-fungal admixtures Types of Chemical Admixtures

8. CHEMICAL ADMIXTURES The following are some of the chemical admixtures: 1. Plasticizers 2. Super plasticizers 3. Accelerators 4. Retarders 5. Water proofers MINERAL ADMIXTURES some of the mineral admixtures are given below: Fly Ash Silica Fume Ground Granulated Blast furnace Slag (GGBS) Metakaolin

9. Plasticizers are used during the process of making fresh concrete. They are used to increase the workability of concrete without adding any extra water. Water reducing admixtures require less water to make a concrete of equal slump, or increase the slump of concrete at the same water content. They can have the side effect of changing initial setting time. Water reducers are mostly used for hot weather concrete placing and to aid pumping. A water reducer plasticizers, however, is a hygroscopic powder , which can entrain air into the concrete mix that its effects on water surface tension, thereby also obtaining some of the benefits of air-entrainment . PLASTICIZERS ( WATER REDUCER)

10. Concrete should possess good workability. It requires different degree of workability in different situations like Tremie concreting Hot weather concreting Pumping of concrete Deep beams Beam and Column joints Ready mixed concrete industries Thin walled structures, etc..,

11. ( i ). Conventional Method For High Workability The following are the methods for increasing workability by conventional method: Improving the gradation Using higher percentage of fine aggregate Increasing the content of cement Using extra amount of water (ii). Effects or Use of Extra Water In Concrete Excess of water in concrete leads to the effects given below: Harmful to concrete strength and durability Improve the consistency but not the workability of concrete No improvement in homogeneity and cohesiveness of the mix, reducing the tendency for segregation and bleeding.

12. (iii). Effects of Use of Plasticizer In Concrete Effects due to the use of plasticizers in concrete are: mass concrete. Reduces water/cement ratio for the given workability, which in turn increasing the strength. The reduction in water/cement ratio improves the durability of concrete. Sometimes reduce it used to reduce cement content and heat of hydration in mass concrete. It is used in the amount of 0.1% to 0.4% to the weight of cement. At these stage, with constant workability the reduction in mixing water are in the order of 5% to 15%. This naturally increases the strength. The increase in workability at the same water/cement ratio may be from 30 mm to 150 mm slump, depending on the dosage, initial slump of concrete cement content and type.

13. Super plasticizers (High Range Water Reducers-HRWR) are chemical admixtures used where well-dispersed particle suspension is required. Super plasticizers are also known as plasticizers, include water-reducing admixtures. Comparing to the commonly referred as water reducer or mid-range water reducers, super plasticizers are called as High Range Water Reducers . High range water reducers are admixtures that allow large water reduction or greater flow ability without substantially slowing set time or increasing air entrainment . Each type has defined ranges for the required quantities of concrete mix ingredients, along with the corresponding effects. They can maintain a specific consistency and workability at a greatly reduction in the amount of water. SUPER PLASTICIZERS

14. Dosages needed vary by the particular concrete mix and type of super plasticizer used. They can also produce a high strength concrete. As with most types of admixtures, super plasticizers can affect other concrete properties as well. The specific effects should be found from the manufacturer or concrete supplier. These are used as dispersants to avoid particle segregation (gravel, coarse and fine sands) and to improve the flow characteristics such as in concrete applications. Use of super plasticizers has made it possible to use water/cement ratio as low as 0.25 or even lower and yet to make concrete to obtain strength of the order 120 N/mm2 or more.

15. Following are the effects of superplasticizer in fresh concrete: The dramatic improvement in workability is not showing up when super plasticizers are added to zero slump concrete at nominal stages. A mix with an initial slump of about 2 to 3 cm can only be fluidized by super plasticizers at dosages. A high dosage is required to fluidize no slump concrete. An improvement in slump value can stained to the extent of 25 cm or more depending upon the initial slump of the mix, the dosage and cement content. It is noticed that slump increases with increases in dosage but after certain limitation of dosage there is no increase in slump. As a fact, that the over dosage may harm the concrete. (1). Use of Superplasticizer in Fresh Concrete

16. Following are the effects of superplasticizer in hardened concrete: Super plasticizers does not participate in any chemical reactions with cement or blending material used in concrete. The actions of superplasticizers are only physical in fluidizing the mix made even with low water content. D The superplasticizers fluidizing action last only as the mix is in plastic condition. D If the effect of absorbed layer is lost, the hydration process continues normally . The use of right quality of super plasticizers when used in usual small dose of about 3% by weight of cement, there is no bad effect on the properties of hardened concrete. Super plasticizers improves the workability, compactability and reduction in water/cement ratio, and thereby increase the strength of concrete, this gives overall improvement in the properties of hardened concrete. The use of super plasticizer improves the properties of hardened concrete and it became as an unavoidable material in the high performance concrete. (2). Use of Superplasticizer in Hardened Concrete

17. ACCELERATORS Accelerating admixtures are added to concrete to increase the rate of early strength development in concrete to 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.

18. 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)

19. Advantages / Effects of accelerator on concrete properties Reduced bleeding, Earlier finishing Improved protection against early exposure to freezing and thawing, Earlier use of structure Reduction of protection time to achieve a given quality, Early removal of form, and early load application. Increases the rate of gain of strength. Enables earlier release from precast moulds thus speeding production. Reduces segregation and increase density and compressive strength. Cures concrete faster and therefore uniform curing in winter and summer can be achieved. Early use of concrete floors by accelerating the setting of concrete. Reduces water requirements, bleeding, shrinkage and time required for initial set.

20. Retarders , as the name implies that the delay in setting time of cement. The rate of chemical reaction gets decreased and setting time increases. Calcium sulphate in the form of gypsum is generally added during the manufacture of cement to retard the setting. But the amount of gypsum, if added beyond a limited quantity produces unsoundness and other undesirable effects . Calcium sulphate in the form of plaster of Paris can also be used. At normal temperatures, 0.2% addition of sugar can extend the final setting time to about 72 hours or more. Skimmed milk powder has a retarding effect due to its sugar content. RETARDERS

21. By the use of 0.1% of sodium hexametaphosphate , the initial and final setting times of 12 hours and 13 hours respectively can be obtained. Retarding admixtures slow down the hydration of cement, lengthening the set time. Retarders are beneficially used in hot weather conditions in order to overcome the accelerating effects of higher temperatures and large masses of concrete on concrete setting time. Most of the retarders also act as water reducers, they are frequently called water reducing retarders.

22. RETARDING MATERIALS Some of the materials which are effectively used to retard the rate of hydration are : Ammonium chloride Ferrous and ferric chlorides Calcium borates and ( sodium bicarbonate) Annie acid, gallic acid, humic acid and sulphonic acid in sodium hydroxide solutions Various forms of starch Salts of carboxy methyl cellulose and oxidized cellulose Calcium or sodium salt of lignin sulphuric acid

23. A waterproof concrete has to fulfill two separate and distinct functions are To be impervious to the water under pressure To resist the absorption of water A concrete having proper mix design, low water cement ratio and good sound aggregate is impervious and needs no additives. However, resistance of concrete to absorption of water can be improved with the use of additives. Alkaline silicates (silicate of soda), aluminium , zinc sulphates and calcium chlorides are the chief pore filling materials. These are all chemically active and hence may accelerate the setting time of the concrete thus making it more impervious at an early age . Materials for the water repellent class are soda and potash soap are used. Sometimes lime, alkaline silicates or calcium are also used . Chemically inactive materials are calcium soaps, resin, vegetable oils, fats. waxes, coal residues and bitumen are also act as pore block agents. WATER PROOFERS

24. MINERAL ADMIXTURES SILICA FUME Silica fume, also referred to as micro silica or condensed silica fume is another material that is used as an artificial pozzolanic admixture. Silica fume is very fine pozzolanic material composed of ultrafine, amorphous glassy sphere (average diameter. 0.10 to 0.15 mm) of silicon dioxide (Si02) produced during the manufacture of silicon or ferro -silicon by electric arc furnaces at temperature of over 2000°C. The micro silica is formed when SiO gas produced in the furnace mixes with oxygen, oxidizes to Si02 condensing into the pure spherical particles of micro silica that form the major part of the smoke or fume from the furnace.

25. SILICA FUME These fumes are collected and bagged called silica fume. It is further processed to remove impurities and to control particle size. Condensed silica fume is essentially silicon dioxide (more than 90%) in non crystalline form. Since it is an airborne material like fly ash, it has spherical shape. It is extremely fine with particle size less than 1 micron and with an average diameter of about 0.1 micron, about 100 times smaller than average cement particles. MINERAL ADMIXTURES

26. FORMS OF SILICA FUME Various forms of silica fume are listed below: Undensified forms with bulk density of 200-300 kg/m3 Densified forms with bulk density of 500-600 kg/m3 Micro- pelletised forms with bulk density of 600-800 kg/m3 Slurry forms with density 1400 kg/m3 and surface area 15-20 m2/g CHARACTERISTICS OF SILICA FUME The following are the characteristics of silica fume: They are spherical shaped Mean particle size between 0.1 and 0.2 micron Specific surface area is about 15,000 m2/kg It has about 90% Si02 content.

27. 3. EFFECTS OF USE OF SILICA FUME IN FRESH CONCRETE Following are the effects of silica fume in fresh concrete: The addition of micro silica will lead to. lower slump but more cohesive mix. The micro silica makes the fresh concrete sticky in nature and hard to handle. Concrete with micro silica has large reduction in bleeding, could be handled and transported without segregation. Concrete containing micro silica is vulnerable to plastic shrinkage cracking. Micro silica concrete produces more heat of hydration at the initial stage of hydration. Finally, the total generation of heat will be less. 4. EFFECTS OF USE OF SILICA FUME IN HARDENED CONCRETE Concrete containing micro silica showed outstanding characteristics in the development of strength. It has been found out that modulus of elasticity of micro silica concrete is less than that of concrete without micro silica it will be at the same level of compressive strength.

28. Ground Granulated Blast-furnace Slag (GGBS) is a non-metallic product consisting essentially of silicates and aluminates of calcium. The molten slag is cooled rapidly by quenching in water to form a glassy sand like granulated material . The granulated material when further reduced to less than 45 micron will have specific surface of about 400 to 600 m2/kg (Blaine). In India, we produce about 7.8 million tons of blast furnace slag, where they are granulated by quenching the molten slag by high power water jet, making glassy slag granules of 0.4 mm size. The blast furnace slag is mainly used in India for manufacturing slag cement. There are two methods for making Blast Furnace Slag Cement. In the first method, blast furnace slag is inter ground with cement clinker along with gypsum. 4- In the second method, blast furnace slag is separately ground and then mixed with the cement. GROUND GRANULATED BLAST FURNACE SLAG (GGBS)

29. EFFECTS OF USE OF GGBS IN FRESH CONCRETE Following are the effects of GGBS in fresh concrete: Replacing cement with GGBS will reduce the unit water content necessary to obtain the same slump. This redtuction of unit water content will be more pronounced with increase in slag content and also on the fineness of slag. In addition, water used for mixing is not immediately lost, as the surface hydration of slag is slightly slower than that of cement. Reduction of bleeding is not significant with slag of 4000 cm2/g fineness. But significant beneficial effect is observed with slag fineness of 6000 cm2/g and above. 2. EFFECTS OF USE OF GGBS IN HARDENED CONCRETE Following are the effects of GGBS in hardened concrete: Reduction in heat of hydration Reduced permeability to the external agencies Higher ultimate strength Resistance to chemical attack is higher Resistance to corrosion of steel reinforcement Saving of cement in concrete mix Improved workability of site mix

30. Considerable research has been done on natural pozzolans , namely on thermally activated ordinary clay and kaohnitic clay. These unpurified materials have ollen been called as metakaolin . Even though it showed certain amount of pozzolanic properties, they are not highly reactive . Highly reactive metakaolin is made by water processing to remove unreactive impurities to make 100% reactive pozzolan . Such a product, white or cream in color , purified, thermally activated is called High Reactive Metakaolin (HRM ). High reactive metakaolin shows high pozzolanic reactivity and reduction in Ca(OH)2 even as early as one day. METAKAOLIN

31. The cement paste undergoes distinct densification and improvement offered by the densification includes an increase in strength and decrease in permeability. The high reactive metakaolin is having the potential to compete with silica fume. High reactive metakaolin called by trade name Metacem is being manufactured and marketed in India by speciality Minerals Division, Head office at South Baroda. Another Company, named as zigma intemational manufacturing and supplying metakaolin by trade name Pozzofliz is by. They claim that the use of pozzafilz 5-10% replacing the cement brings about many useful properties to concrete and which is a substitute for silica fume. Metakaolin is not a by-product as other pozzolanic materials, it is a specially manufactured material with definite properties. It has been used in many other major projects like a"' Sri Ram Mills Construction at Mumbai clr Burge Khalifa in Dubai co' Kobra Tower

32. FLY ASH Fly ash or pulverized fuel ash (PEA) is the residue from the combustion of pulverized coal collected by mechanical of electrostatic separators from the fuel gases of power plants. Its composition depends on Type of fuel burnt Load on the boiler Type of separator, etc. Fly ash obtained from electrostatic precipitators may have a specific surface of about 3500 to 5000 cm2/g, which is finer than Portland cement. Fly ash obtained from cyclone separators is comparatively coarser and also contains a large amount of unburnt fuel. Fly ash consists generally of spherical particles, some of which may be like glass and hollow and of irregularly shaped particles of unburnt fuel and carbon . The color may be light grey, dark grey or brown The Principal constituents are Silicon Dioxide — Si02 (30 to 60%) CI Aluminium Oxide — AI203 (15 to 30%) Calcium Oxide — Ca0,(1 to 7%) Cr Carbon iii the form of unburnt fuel (% may be as high as 30%) cr Small quantities of Magnesium Oxide (Mg0), Sulphur Trioxide (SO3 )

33. CLASSIFICATION OF FLY ASH ASTM broadly classify fly ash into two classes: ❖ Class F Fly ash normally produced by burning anthracite or bituminous coal, usually has less than 5% CaO . Class F fly ash has pozzolanic properties only. ❖ Class C Fly ash normally produced by burning lignite or sub-bituminous coal. Some class C fly ash may have Ca0 content in excess of 10%. In addition to pozzolanic properties, class C fly ash also possesses cementitious properties.

34. CHARACTERISTICS OF FLY ASH The following are the characteristics of fly ash Fly ash should have very low carbon content, fineness should be as high as possible and its silica content should be very finely divided as high as possible Fly ash be used in concrete either as an addition or in part replacement of the cement but in the fbrmer case its use is not so economical. Fly ash is considered as pozzolanic as its silica contents combine slowly over a very long period with the lime liberated during the hydration of cement. A fine grinding of silica in ball mill increases the reactivity. Curing at high pressure and temperature of about 38°C in an autoclave promotes the reaction between the lime of cement and silica in fly ash.

35. USES OF FLY ASH Some of the uses of fly ash are: The use of fly ash particularly as an admixture rather than as a replacement of the cement reduces segregation and bleeding. When fly ash is used as a replacement for up to 30% of cement, the compressive strength of concrete is reduced at 7 and 28 days, may be about equal at 3 months and is increased thereafter. The substitution of fly ash for sand, keeping the cement content constant has a beneficial effect on strength ever, at early ages but particularly at the later ages. If fly ash is substituted for cement the modulus of elasticity is lower at early ages and higher at latei ages. The use of fly ash has no appreciable effect on the drying shrinkage of concrete . EFFECTS OF USE OF FLY ASH IN FRESH AND HARDENED CONCRETE Following are the effects of fly ash in fresh and hardened concrete: When fly ash is mixed with cement, the silica of pozzolana combines with the free lime released during the hydration of cement. The optimum amount of fly ash ( pozzolana ) us a replacement for cement may normally range between 10 to 33% but is usually nearer the lower limit may be as low as 4 to 6% for natural pomlanas .

36. The use of pozzolana along with air-entraining agent requires less amount of water and leads to an increase in strength, especially when it is very finely ground. At early ages there is a decrease in the compressive strength which disappears at ages of 3 months and more. The addition of pozzolanas increases the strength appreciably up to a certain percentage but if it is used or regarded as replacing cement there is a reduction of strength at early ages and increase of strength at later ages for substitutions up to 15 to 30% depending on the type of pozzolana . Due to replacement of cement by pozzolanas there is a small increase in the tensile strength at later ages .

37. As per the Indian Standards, the pozzolana cement has to satisfy the requirements of IS: 1489-1967. The pozzolana is used in construction work to replace a part of the cement, in large dams, where the reduction in the rate of hydration is of greater importance and slower gain in strength is not of much hindrance. Pozzolana cement is generally used in the construction of retaining walls, wharf walls, culverts and drains, etc. The use of fly ash as a replacement of sand in a lean-mix increases the workability and it has no appreciable effect on the drying shrinkage of concrete. It reduces the permeability of concrete, improves the resistance to sulphate waters and does not have much effect on the freezing and tha resistance of concrete.