Construction Materials CSE 20308 Module I 2024 PDF

CSE 20308 Construction Materials  Course Layout Concrete (8 weeks) Module I. Introduction and Basic Concepts Definition Advantages of concrete as a construction material Comparison between structural concrete and steel Types of structural concrete (Plain concrete, Rein...

CSE 20308 Construction Materials  Course Layout Concrete (8 weeks) Module I. Introduction and Basic Concepts Definition Advantages of concrete as a construction material Comparison between structural concrete and steel Types of structural concrete (Plain concrete, Reinforced concrete, Prestressed concrete) Constituent materials of concrete – a brief introduction (cement, aggregates, water and admixtures) Production of concrete – a brief review Module II. Cement Chemical composition of cement Manufacture of Portland cement Module II. Cement (contd.) Hydration of cement Types of Portland cement Tests to evaluate physical and mechanical properties of cement Module III. Aggregates General classification of aggregates Physical and mechanical properties of aggregates Size and grading of aggregates Grading requirements Maximum aggregate size Module IV. Concrete Admixtures Benefits of admixtures Types of admixtures (Water-reducers, Accelerators, Retarders) Mineral admixtures (Silica fume, Fly ash, Blast furnace slag) Performance and properties of blended concretes Module V. Concrete Mix Design Process of mix selection Factors affecting the mix proportions - Durability - Strength - Cost Mix design methods - Absolute volume approach - British method (DOE) - ASTM method Module VI. Properties of Fresh Concrete Workability of concrete Factors affecting workability Measurement of workability Module VI. Properties of Fresh Concrete (contd.) Problems in fresh concrete (Segregation, Bleeding) Placing and compaction of concrete Module VII. Properties of Hardened Concrete Factors affecting the strength of concrete - Water-cement ratio - Aggregate-cement ratio - Strength and maximum size of aggregates - Compaction, mixing temperature and curing method - Effect of age Tensile strength of concrete Relation between tensile and compressive strength of concrete Bond strength of concrete Module VIII. Durability of Concrete Permeability of concrete Sulphate attack Attack by sea water Acid attack Alkali-aggregate reaction Corrosion of reinforcement Text Book A.M. Neville and J.J. Brooks. 2010. “Concrete Technology”. Longman and Hall, London. Reference Books A.M. Neville. 1995. “Properties of Concrete”. Longman and Hall, London. J.F. Young; S. Mindless; R.J. Gray; and A. Bentur. 1998. “The Science and Technology of Civil Engineering Materials”. Prentice-Hall International Inc., New York. Module I. Introduction and Basic Concepts A very old and mordern material  Israel Limestone Quick lime concrete floor 7000 BC Not hydraulic cement Calcium carbonate Water soluble Egypt Not hydraulic cement Water soluble Quicklime; Gypsum (Plaster of paris), and sand mortar 2690 BC  Best source at time: Roman Pozzuli, Italy à Pozzolan Quicklime + Volcano Ash + Heat = Roman cement Hydraulic cement/non-water soluble world’s largest unreinforced concrete dome Pantheon, Italy 128 AD Roman Concrete derived from Latin word “concretus” Hardened or Compounded Right material Engineering 72 AD Artistic design After the Fall of Rome, neither concrete nor cement advanced much, until… Portrait of John Smeaton Brought back the Roman knowledge on hydraulic cement (1750) first use of modern concrete in engineering- Eddystone Lighthouse  Isle of Portland Joseph Asphin (UK) patented Portland cement in 1824 Portland named after famous Portland stone quarry luxury symbol  1871 PA, U.S. In 1845, Isaac Johnson baked a mixture of lime and clay mixture at a temperature of 1400°–1500°C – as is still done today – to produce the first modern Portland Cement.  Concrete Concrete is a stone-like composite material prepared by careful proportioning of cement, aggregates and water mixed in a suitable manner to give the required physical and mechanical properties. Cement Paste Water Mortar Concrete Sand Aggregate Stone Advantages of Concrete as a Construction Material Cheapest and most readily available constituent materials. Easiness to give any structural shape and size. Easy and cheap maintenance. Excellent resistance to water which makes it suitable for the construction of water retaining structures like dams, aqueducts, pipe lines etc. Excellent fire resistance properties. Less requirement of skilled labor. Energy saving and environment friendly. Constituent Materials of Concrete Conventional Concrete Cement Paste Water Mortar Concrete Sand Aggregate Stone Compressive Strength = 25 - 40 MPa Suitable for Ordinary Construction Low to Moderate Durability 1MPa = 1,000,000 N/m2 = 101,971kg/m2 = 102 ton/ m2 × 50  Moder n Concrete Cement Water Concrete Additives Sand Stone Compressive Strength = 60 - 150 MPa Very high Durability  How Cement is Made https://www.youtube.com/watch? v=BTCubpLQTZc  Cement A powdered mixture of calcareous (lime) and argillaceous (clay) minerals, burned at a clinckering temperature and finely grinded upon cooling. Cement by itself is not a binder, but develops the binding property as a result of hydration (i.e., from chemical reaction between cement minerals and water). A cement is called hydraulic when the hydration products are stable in a aqueous environment. The most commonly used hydraulic cement for making concrete is Portland cement, which essentially consists of hydraulic calcium silicates. Gypsum is usually added in cement as a retarder to increase the setting time for cement by delaying the hydration process. Aggregates Aggregate is an inert, inexpensive material dispersed throughout the cement paste so as to produce a large volume of concrete. Aggregates occupies approximately three-quarters of the volume of concrete. The physical, thermal and sometimes, chemical properties of aggregates influence the performance of concrete by improving its volume stability and durability over the cement paste. Classification of Aggregates Coarse Aggregates All those particles which are larger than 4.75 mm (retained on No. 4 sieve). The size usually varies between 4.75-50 mm. They form around 55%-70% of the total aggregate mass. Fine Aggregates Particles smaller than 4.75 mm (passed through No. 4 sieve). Their size usually varies between 4.75 mm - 75µm (No. 200 sieve). They form around 30%-45% of the total aggregate mass. Fine Coarse Admixtures Admixtures are mineral or organic substances which are added to change or improve all/some of the properties of concrete in fresh or hardened state. They are usually added during concrete mixing and can be distinguished from additives which are added at the cement manufacturing stage. Types of Admixtures Accelerators Set-retarders Water-reducers or Superplasticizers Mineral Admixtures or Pozzolans Accelerators They are added to accelerate the hardening or the development of early strength of concrete. Accelerators are commonly used in emergency repairs or in under-water concrete works. Set-retarders These are admixtures which delay the setting of concrete. Retarders are useful when concreting in hot weather, when the normal setting time is shortened by the higher temperature, and in preventing the formation of cold joints between successive lifts. Superplasticizers Suplerplasticizers are admixtures which are added to the concrete to increase its flowability often called workability. These are used for three purposes: To achieve a higher strength by decreasing the water- cement ratio at the same workability as an admixture free mix. To achieve the same workability by decreasing the cement content so as to reduce the heat of hydration in mass concrete which may produce serious cracking. To increase the workability so as to ease placing in inaccessible locations. Mineral Admixtures/Pozzolans Mineral Admixtures often called Pozzolans are siliceous materials (SiO2: 55-90%) of very fine particle size that are capable of entering into chemical reaction with lime at normal temperature forming cementitious products similar to the ones produced from Portland cement hydration thereby increasing the strength of concrete. Pozzolans can be used as an addition or replacement of cement and sometimes also called as Supplementary Cementing Materials. e.g. condensed silica fume, pulverized fly ash, granulated blast furnace slag etc.  Advantages of Adding Mineral Admixtures Produce high to ultra strength concrete Increase abrasion and erosion resistance of concrete Increase cement paste - aggregate bond Ensure superior chemical durability Reduce segregation and bleeding Reduce thermal cracking and plastic shrinkage Provide better resistance to freeze-thaw cycle Water The quality of mixing water is very important as impurities in it may interfere with the setting of the cement, may adversely affect the strength of the concrete or cause staining of its surface, and may also lead to corrosion of the reinforcement. The water fit for drinking is considered to be suitable for concrete making and curing. In mixing water, the amount of dissolved solids should not be more than 2000 ppm (preferably less than 1000 ppm) and it should not have any color or odor. Sea water or any other water containing large amount of chlorides or other alkalis should be avoided.  Water-To-Cement (W/C) Water to cementitous material (w/c) Cementitous materials: cement, fly ash, slag, silica fume, etc. Ratio by weight W/C = (Water)/(Cementitious materials) Production of Concrete Weighing of Materials Removal of Formworks Dry Mixing Curing Wet Mixing Finishing Placing in Formworks Compaction  Types of Concrete Production l On-site mixing Used at small construction sites l Ready-mixed concrete Used in large construction projects In-situ Concrete Production Disadvantages l -Search of suitable materials. l -High risk due to shortage of materials. l -Storage problems. l -Inadequate quality control. l - More labor requirement. l - Increase in dust pollution. l - Careful planning and scheduling. Ready Mixed Concrete Production Advantages l - Close quality control of batching which reduces the variability of the desired properties of the hardened concrete. l - Use on public sites or in highway construction where there is a little space for a mixing plant and aggregate stockpiles. l - Use of mixer trucks to ensure care in transportation, thus preventing segregation and maintain workability. l - Convenient and saving of time. Ready Mixed Concrete Production Disadvantages l - Entry and parking problems at congested sites. l - Non-availability in small amounts. l - Advance order is required. l - Requirement of tower crane or pumps to place concrete. l - Non-availability in emergencies. l - More chances of wastage. Properties of Good Concrete - Consistency in the Fresh State: The mix should be fluid enough to be transported and compacted easily to the desired degree. - Cohesiveness: The mix should not segregate/bleed while being transporting, placing or compacting in the form work. - Uniformity in Strength: The concrete should posses uniform strength. A non-uniform strength is a sign of the presence of honey-combs or flocs in concrete structure resulting from less compaction or segregation. - Absence of Cracks: The pre-mature cracks may be produced in concrete due to excessive heat of hydration, thermal and drying shrinkage and affects the strength and durability remarkably. Advantages of Concrete over Steel Structures NERGY-SAVING NGINEERING PROPERTIES CONOMICAL COLOGICAL A ‘4-E’ Criteria in the Selection of Construction Materials Advantages of Concrete over Steel Structures Engineering Properties Maintenance ð No corrosion. ð No surface treatment in normal environment. Fire Resistance Resistance to Cyclic Loading ð The fatigue strength of steel structures is greatly influenced by local stress fields in welded joints, corrosion pittings and sudden changes in geometry while concrete structures have no such problems.  Advantages of Concrete over Steel Structures Vibration Damping ð Better damping resistance due to greater self weight. Resistance to Cryogenic Temperatures ð Concrete structures continuously show ductile behavior even at very low temperatures like -160oC (for the storage of liquefied natural gas - LNG) while the steel structures show extremely brittle behavior. Ease of Production ð Constituent materials easily available. No need of any complex plant. Advantages of Concrete over Steel Structures Economic Considerations Constituent materials are cheap and easily available. Less requirement of skilled labor and machinery. Energy Considerations Amount of Energy (Kw h/ton) 10000 Production of 1 ton of 8000 concrete saves 82% 6000 energy as compared 4000 2000 to similar capacity 0 steel structure. Steel Brick Concrete Advantages of Concrete over Steel Structures Ecological Considerations No heat radiation produced by sun reflection. No toxic fumes as emitted by paints and surface coatings in steel structures.  Response of Concrete and Steel under Loading Brittle Ductile a. Normal Density Concrete b. Structural Steel APPENDIX Types of Concrete Based upon Weight Normal Weight Concrete ð Density = 2400 kg/m3 ð Prepared by natural sand and gravel or crushed-rock aggregates. Light Weight Concrete ð Density < 1800 kg/m3 ð Prepared by natural or pyro-processed aggregates having lower bulk density. Heavy Weight Concrete ð Density > 3200 kg/m3 ð Prepared from heavy density aggregates and used for radiation shielding. Types of Concrete Based upon Strength Normal Strength Concrete ð Compressive Strength = 20 - 40 MPa ð Used in all sorts of ordinary construction works. Low Strength Concrete ð Compressive Strength < 20 MPa ð Used for non-structural applications such as base concrete for footings. High Strength Concrete ð Compressive Strength > 40 MPa ð Used in lower columns of high rise buildings, bridge decks and piers, off-shore structures, cross-harbor tunnels etc. Types of Concrete Based upon Structural Action Plain Cement Concrete (P.C.C.) ð Essentially consists of cement, aggregates, water and admixtures. ð Used for non-structural applications like base for foundations and pavements, shotcreting etc. P.C.C An ordinary column footing A typical pavement section Types of Concrete Based upon Structural Action Reinforced Cement Concrete (R.C.C.) ð A concrete usually containing steel bars and is designed on the assumption that the two materials act together in resisting forces. ð Used in all structural applications like beams, columns, etc. R.C.C steel steel An ordinary column footing A typical R.C.C. beam Types of Concrete Based upon Structural Action Prestressed Concrete (P.C.) ð A concrete in which by tensioning steel tendons, prestress of such magnitude and distribution is introduced that the tensile stresses resulting from the service loads are counteracted to a desired degree. ð Used for girders of long span bridges, large roof slab where large deflections are a problem. Steel tendon P.C. Fabrication of Prestressed Concrete Pre-tensioning In this method, the prestressing strands are tensioned between massive abutments in a casting yard prior to placing the concrete in the beam forms. The beam is poured around the tension strands, and after the concrete has attained sufficient strength, the jacking pressure is released. This transfers the prestressing force to the concrete by bond and friction along the strands. Fabrication of Prestressed Concrete Post-tensioning In post-tensioning, the pre-stressing is done after the casting the beam. During the casting, a hollow conduit is placed at the specific position to contain pre-stressing strands. Once the beam has acquired sufficient strength, the pre-stressing tendon is passed through the conduit. Usually, one end of the pre-stressing tendon is anchored, and all the force is applied at the other end. After attainment of the desired amount of pre-stress force, the tendon is wedged against the concrete and the jacking equipment is removed.