Concrete: Royal University of Bhutan PDF

ROYAL UNIVERSITY OF BHUTAN 1 COLLEGE OF SCIENCE AND TECHNOLOGY 1 1 PHUNTSHOLING: BHUTAN CONCRETE 9/30/2024 Ingredients of Concrete 9/30/2024 2 Aggregate Aggregates are the materials basically used as filler with bindin...

ROYAL UNIVERSITY OF BHUTAN 1 COLLEGE OF SCIENCE AND TECHNOLOGY 1 1 PHUNTSHOLING: BHUTAN CONCRETE 9/30/2024 Ingredients of Concrete 9/30/2024 2 Aggregate Aggregates are the materials basically used as filler with binding material in the production of mortar and concrete. Aggregates form the body of the concrete. They occupy 70-80 per cent of the volume and have considerable influence on the properties of the concrete. Assumed to be inert material until 1940. Reduce shrinkage and increases the bulk density of concrete. 9/30/2024 3 Classification of Course Aggregates 1.On the Basis of Geological Origin There are natural aggregates and artificial aggregates. Natural aggregates: These are obtained by crushing from quarries of igneous, sedimentary or metamorphic rocks. e.g. Gravels and sand Artificial aggregates: These are obtained artificially. e.g. Broken bricks, blast furnace slag and synthetic aggregates 2.On the Basis of Size 10 mm 20mm 30mm and so on…….. 9/30/2024 4 Classification of Course Aggregates 3.On the Basis of Shape Aggregates are classified as rounded, irregular, angular, and flaky. Rounded aggregate: These are generally obtained from river or sea shore and produce minimum voids (about 32 per cent) in the concrete. Irregular aggregate: They have voids about 36 per cent and require more cement paste as compared to rounded aggregate. Angular aggregate: They have sharp, angular and rough particles having maximum voids (about 40 per cent). Flaky aggregate: Aggregates are called flaky when thickness is small relative to width. The least lateral dimension of flaky aggregate (thickness) should be less than 0.6 times the mean dimension. For example, the mean sieve size for an aggregate piece passing through 50 mm and retained on 40 mm sieve is (50 + 40)/2 =45.0 mm. Elongated 9/30/2024 5 Classification of Course Aggregates 9/30/2024 6 Classification of Course Aggregates 4.Based on Unit Weight Aggregates are classified as normal-weight, heavy-weight and light-weight aggregate depending on weight and specific gravity as given in Table 9/30/2024 7 Classification of fine Aggregates Based on Source Natural sand Crushed stone sand Crushed gravel sand Based on mineralogical composition Quartz Felspar Carbonaceous varieties Based on size Coarse (Fineness modulus 2.9-3.2) Medium(Fineness modulus 2.6-2.9) Fine(Fineness modulus 2.2-2.6) 9/30/2024 8 Classification of fine Aggregates Based on particle size distribution 9/30/2024 9 Characteristics of Aggregates Strength: (implies to CA) Stiffness:(implies to both CA and FA) Bond Strength: (implies to CA) Shape and Texture:(implies to CA) Specific Gravity(𝐺𝑠 ):(implies to both CA and FA) Bulk Density:(implies to both CA and FA) Voids: (implies to CA) Porosity:(implies to CA) Moisture Content: (implies to both CA and FA) Bulking (implies to FA) Fineness Modulus: (implies to both CA and FA) Soundness:(implies to both CA and FA) 9/30/2024 10 Testing of Aggregates Specific gravity:(implies to both CA and FA) Water absorption:(implies to both CA and FA) Bulk density and void:(implies to both CA and FA) Crushing value:(implies to CA) Impact value:(implies to CA) Abrasion test:(implies to CA) Ten percent fines test:(implies to CA) Fineness Modulus:(implies to both CA and FA) 9/30/2024 11 WATER 1.Initiates Hydration 2.Conssitency/Workability 3.Washing Aggregates 4.curing Quality of mixing water Portable water Excessive impurities may affect setting time , strength ,durability and may cause efflorescence, surface discoloration, and corrosion of steel. 9/30/2024 12 Water for washing aggregate When aggregate is washed with water, they get coated with layers of silt, salt and organic matter which will reduce the bond between aggregate and cement and ultimately affect the strength Curing water Water which is suitable for making concrete can be used for curing. 9/30/2024 13 Water-cement ratio It plays a vital role in concrete workability. If aggregate is too dry, they will absorb (steal) water from the mix. If aggregate is too wet, the excess moisture must be subtracted from the intended mix water quantity. The strength of concrete is greatly influenced by the water-cement ratio. READ Abram’s law. 9/30/2024 14 Admixture For concrete (IS: 9103-1999) Admixtures are the materials other than the three basic ingredients of cement concrete— cement, aggregate and water—added to the concrete mix before or during mixing to improve certain of its properties like: Rate of hydration Workability Dispersion and air entrainment General Function: accelerate the initial set of concrete, i.e., to speed up the rate of development of strength at early ages, retard the initial set, increase the strength of concrete reduce heat of evolution, increase durability of concrete—resistance to freezing and thawing control expansion caused by aggregate-alkali reaction decrease capillary flow of water and to make it impermeable reduce segregation in grouts strengthen the bond between old and new concrete surfaces and that between steel reinforcement and concrete increase resistance to chemical attack produces non-skid concrete surfaces. 9/30/2024 15 Classification of Admixtures: Admixtures may be classified as accelerators, retarders, water proofers, workability agents, surface active agents, puzzolanas, etc. Accelerator. Retarder. Water proofer. Finely divided workability agent. Bleeding agent. Coloring agent. Air entraining agent. Plasticizer. Puzzolanas. Bonding Admixture. Grouting Admixture. Expansion producing admixture Fungicides algaecides 9/30/2024 16 Accelerator: Normally reduce the setting time, Accelerate the rate of hydration of cement and consequently the rate of gain of strength. Reduce segregation and increase density and compressive strength. Reduce water requirement, bleeding, shrinkage and time required for initial set. 9/30/2024 17 Retarder: Normally increase the setting time and thus delay the setting of cement Since these reduce the rate of hydration, more water is available and better is the workability Retarders increase the compressive strength under freezing and thawing Reduces bleeding and segregation where poor sand grading are unavoidable 9/30/2024 18 Finely divided workability agent: Increase the workability by increasing the amount of paste in concrete and hence the cohesiveness. However, if used in excess, the quantity of water has to be increased which causes cracking and loss of strength. Few examples of workability agents are Lime, bentonite, kaolin, chalk, diatomaceous earth. Bleeding agent: To avoid bleeding of concrete. To check bleeding, paraffin wax at about. 0.2– 0.75 per cent by mass of cement used. 9/30/2024 19 Coloring agent: Used in concrete work are mainly; Raw umber (brown), Ferrous oxide (black), Red oxide (red), Chromium oxide (green). 9/30/2024 20 Air entraining agent: The air intentionally introduced in the cement during its manufacture or during making concrete is known as entrained air. It is different from entrapped air where the continuous channels are formed, thus increasing the permeability. Advantages: Reduce bleeding and segregation because of : Attachment of air bubbles with cement particle and linking them. Increase in inter particle attraction caused by adsorption. Bubbles acting as extra fine filler and increase total surface area of constituents relative to water volume. Water flow between cement particle is restricted Resistance of concrete to weathering. The air entrainment may be done by surface active agents, chemicals, or by cement dispersing agents. 9/30/2024 21 Plasticizer: Are organic or a combination of organic and inorganic substances, which allow a water reduction for a given workability, or give higher workability at the same water content. 9/30/2024 22 Super plasticizer: They are hydrodynamic lubricants which impart high workability by reducing friction between the grains or by reducing the amount of water to be added. They are improved version of plasticizers interact both physically and chemically with cement particles. The mechanism of action of super plasticizers is same as that of plasticizer. 9/30/2024 23 Bonding admixtures They are usually water emulsions of organic materials including rubber, polyvinyl chloride, polyvinyl acetate, acrylics, styrene butadiene copolymers, and other polymers. They are added to Portland cement mixtures to increase the bond strength between old and new concrete. Bonding agents are often used in restoration and repair work. 9/30/2024 24 Grouting admixtures Portland cement grouts are used for a variety of purposes: to stabilize foundations, set machine bases, fill cracks and joints in concrete work, cement oil wells, fill cores of masonry walls, grout pre stressing tendons and anchor bolts, and fill the voids in preplaced aggregate concrete. To alter the properties of grout for specific applications, various air-entraining admixtures, accelerators, retarders, and non-shrink admixtures are often used 9/30/2024 25 Puzzolanas : These are siliceous materials which are themselves inactive but react, in the presence of water, with lime to form compounds having cementitious properties. The examples of puzzolana are lime, fly ash, burnt clay and blast furnace slag. Uses: Puzzolanas react with free lime in cement and improve the durability of concrete, Reduce the rate of hardening of concrete, which is the principal objection to its use. 9/30/2024 26  Expansion producing admixture Fungicides algaecides 9/30/2024 27  CONCRETE:IS456:2000(CODE OF PRACTICE FOR PLAIN AND REINFORCE CONCRETE) 9/30/2024 28  CONCRETE:A homogenous mixture of binding material(cement or lime), coarse & fine aggregate and water which yields a hard mass due to chemical reaction between the water and cement. The coarser aggregate acts as a filler. The fine aggregate fills up the voids between the paste and the coarse aggregate. The cement in conjunction with water acts as a binder. The mobility of the mixture is aided by the cement paste, nowadays, increasingly by the use of admixtures. Freshly mix concrete before setting is known as wet or green concrete whereas after setting or hardening its known as set or hardened concrete. Most of the ancient structures have been constructed with lime concrete. Concrete is better due to its mouldibility, early hardening and early high compressive strength, properties of concrete can be altered using suitable admixture, pumpability and durability. 9/30/2024 29 Classification of concrete 1. Based on cementing materials Lime concrete Gypsum concrete Cement concrete 2. Based on the GRADE of concrete:Depending upon the strength (N/mm2) of concrete cubes (150 mm side) at 28 days concrete is classified as shown in table. 9/30/2024 30 Classification of concrete 9/30/2024 31 Classification of concrete 9/30/2024 32 Classification of concrete 9/30/2024 33 3. Based on bulk density : Super heavy= over 2500 kg/m3 Dense = 1800-2500 kg/m3 Light weight = 500-1800 kg/m3 Extra light weight = below 500 kg/m3 4. Based on place of casting Cast in-situ and precast 9/30/2024 34 Production of concrete The stages of concrete production are: Batching or measurement of materials Mixing Transporting Placing Compacting Curing Finishing 9/30/2024 35 Batching or measurement For good quality concrete a proper and accurate quantity of all the ingredients should be used. The aggregates, cement and water should be measured with an accuracy of ± 3 per cent of batch quantity and the admixtures by 5 per cent of the batch quantity. Two types of batching 1. Volume batching The amount of each solid ingredient is measured by loose volume using standard box known as gauge box (Fig. 10.1). The volume of a bag of cement (50 kg) is 0.035 m. The volume of one gauge box is made equal to 0.035m3. 9/30/2024 36 Batching or measurement 2. Weigh Batching Different types of weigh batchers are used. 9/30/2024 37 Mixing Objective: homogeneity and uniformity Two types 1. Hand mixing Used for small jobs. Done on imperious floor. All ingredients added in layer and mixed. 9/30/2024 38 2. Machine Mixing Used for quality works Two types of mixing: batch and continuous Various types of mixing plant are used Vertical batching mixing 9/30/2024 39 Pan type or stirring mixer 9/30/2024 40 Drum mixer: tilting, non tilting, reversing 9/30/2024 41 Transit mixer with dumpers 9/30/2024 42 Transportation Concrete should be transported to the place of deposition at the earliest without the loss of homogeneity obtained at the time of mixing should be ensured that segregation does not take place during transportation and placement. transporting concrete depend upon the size and importance of the job, the distance of the deposition place from the mixing place, and the nature of the terrain Various methods of transportation are adopted. 9/30/2024 43 Mortar Pan This is the most common method of transporting concrete. This is labor intensive method This method may lead to evaporation of water from concrete In this method of transporting Concrete does not lead to segregation. 9/30/2024 44 Wheel barrows are used for transporting concrete to be placed at ground level. These are used for concreting rigid payments. segregation may take place. These are most useful for small jobs, small hauls, and over muddy ground. The average capacity of a wheel barrow is 35 liters (80 kg). 9/30/2024 45 CHUTES Chutes are used to transport concrete below the ground levels. These are made with metal sheets with a slope more than 1V: 2.5H to ensure that unloaded concrete slides easily without segregation. 9/30/2024 46 Transit mixer with DUMPERs Dumpers, lorries or, trucks are used economically for hauls up to 5 km. capacity of 2 to 3 cu m. For long hauls agitators are used to prevent segregation. The concrete should be covered with tarpaulins to prevent evaporation of water from concrete. 9/30/2024 47 Bucket and ropeway These are used when concreting is to be done in a valley or for construction work of piers, dams etc. The bucket is brought close to the mix site, filled and moved over ropeway to the site of deposition. 9/30/2024 48 Belt Conveyor The use of belt conveyors for transporting concrete is very little. The two main objections are segregation and drying, and stiffening of concrete. Concrete segregates due to steep slopes, changes of directions, and the points where belt passes over rollers. The drawback is that the concrete will have to be remixed at the place of deposition which is not recommended. 9/30/2024 49 Skip and Hoist This is the most useful and advantageous method of transporting concrete for multi storey buildings. The mixer feeds the skip which moves up over rails up to the level of deposition. If height of travel is too much, the concrete may require a turning over before deposition in to the place. 9/30/2024 50 Pumping Pumping of concrete is done for multi storey buildings, tunnels, and bridges. The concrete is fed from the hopper into the pump cylinder largely by gravity, assisted by the vacuum created on the suction stroke of the piston and forced into the pipe line on the pressure stroke. 9/30/2024 51 SACK 9/30/2024 52 Placing To achieve quality concrete it should be placed with utmost care securing the homogeneity achieved during mixing and the avoidance of segregation in transporting. Placing of various situations are: Foundation Beams, columns and slabs Mass concreting Concreting highways and runways Concreting underwater 9/30/2024 53 Compaction Compaction of the concrete is the process to get rid of the entrapped air and voids, elimination of segregation occurred and to form a homogeneous dense mass. It has been found that 5 per cent voids in hardened concrete reduce the strength by over 30 per cent and 10 per cent voids reduce the strength by over 50 per cent. Therefore, the density and consequently the strength and durability of concrete largely depend upon the degree of compaction. 9/30/2024 54 Types of compaction 1. Hand compaction This method of compaction is used for small and unimportant jobs. However, this method is extremely useful for thin elements such as slabs, and for members with congested reinforcements. Hand compaction is achieved by rodding ramming, or tamping. Rodding is done with the help of 16 mm diameter, 2 m long steel rod to pack the concrete between the reinforcement, sharp corners and edges. 9/30/2024 55 2. Compaction by vibration This is the most common and widely used method of compacting concrete for any structural element. The vibrations imparted to the fresh concrete reduce the internal friction between the particles of concrete by setting the particles in motion and thus produce a dense and compact mass 3. Compaction by spinning 4. Compaction by jolting 5. Compaction by rolling 9/30/2024 56 Curing As such sufficient water should be made available to concrete to allow it to gain full strength. The process of keeping concrete damp for this purpose is known as curing. Curing must be done for at least three weeks and in no case for less than ten days. 9/30/2024 57 Types of curing 1. Water curing is done by covering the concrete surface with gunny bags and then sprinkling water over them regularly or with water proof paper. Sealing compounds such as rubber latex emulsion, resins, varnish and wax may also be used as an alternative to bitumen Layer. 9/30/2024 58 2. Steam curing The temperature can be raised by placing the concrete in steam, hot water or by passing an electric current through the concrete. In the hydration process of cement at higher temperatures, the released calcium hydroxide reacts with finely divided silica, present in the coarse and fine aggregates and forms a strong and fairly insoluble compound which results in higher strengths. 9/30/2024 59 3. Curing by Infra Red Radiation: A much more rapid gain of strength can be obtained with the help of infra red radiation than even with steam curing. The normal operative temperature is 90°C. 9/30/2024 60 4. Electrical Curing: Concrete products can be cured by passing alternating current of low voltage and high amperage through electrodes in the form of plates covering the entire area of two opposite faces of concrete. Evaporation is prevented by using an impermeable rubber membrane on the top surface of the concrete. By electrical curing, concrete can attain the normal 28-day strength in a period of 3 days. The technique is expensive. 9/30/2024 61 5. Chemical Curing Chemical membranes can be sprayed on to cure concrete. Liquid membrane forming curing compounds such as sodium silicate (water glass) solution retard or prevent evaporation of moisture from concrete. 9/30/2024 62 Finishing Concrete takes up the shape of the form which are not always favorable as required. proper care are taken in placing formwork. Road surface should have sufficient roughness to resist skidding: surface are scratch and broomed to maintain roughness External walls should be smooth: surface should be scratch and plaster is applied. 9/30/2024 63  Workability Property of concrete which determines the amount of useful internal work necessary to produce full compaction OR it is the easiness with which concrete can be compacted 100%. Factors affecting workability: Water content Mix proportion Aggregate size Shape of aggregate Surface texture grading of aggregate admixture 9/30/2024 64  Strength of concrete (explained in class) 9/30/2024 65 Non destructive test machines (Demonstration in lab) 9/30/2024 66 Defects Cracks Crazing Sulphate deterioration Efflorescence Segregation Bleeding laitance 9/30/2024 67 Important terminology Poison ratio-ratio of lateral strain to longitudinal strain. Creep-The continued deformation with time under applied load is known as creep Shrinkage-contraction of concrete in the absence of load is known as shrinkage. 9/30/2024 68 QUALITY CONTROL OF CONCRETE Definition The term quality control of concrete refers to the supervision adopted on the site to ensure that the quality and quantity of cement, fine aggregate, course aggregate and water is consistent and that the correct proportions of these materials are used in concrete mix. Statically, there will always be some variation between the strength of concrete made at site. However of good supervision is exercised, then these variation will be small. Hence, a measure of the quality control can be made from the variation of 28-days cube strength test of different batches cast at site and cured under standard conditions. Choice of material, design and workmanship indicates the degree of quality 9/30/2024 69 Aim of monitoring the quality of work To get expected end result Reduction of scrap and rework Economy in use of materials Quality caution at all levels To check the variation during construction To prevent poor quality of end product 9/30/2024 70 QUALITY CONTROL Use approved drawings for construction Read blue prints and specifications Check the equipment for testing and ensure its calibration when ever necessary Material Testing as per contract requirement and in approved laboratories. Quality improvement Acceptance decision Visit site and ensure activity at the site are as approved method statement. Monitor operations to ensure that they meet the standards. Rework and process adjustment Compilation of test results for future reference. 9/30/2024 71  Fine aggregate test Test on cement Specific gravity Consistency test Bulking of sand TESTS Initial and final Sieve analysis setting time Silt content Soundness test Fineness test Coarse aggregate test Soil test specific gravity and moisture content test Non destructive water absorption Compaction test Test(NDT) Los Angeles Atterberg limit test abrasion test Rebound hammer Impact test ultrasonic Pulse Velocity Flakiness and equipment (UPV) elongation test Profometer Soundness test Sieve analysis 9/30/2024 72  CONCRETE MIX DESIGN PROCEDURE IS 10262-1982 9/30/2024 73