MODULE 4 Special Concrete (1).ppt
- 3. Light Weight Concrete - LWC • It is a type of concrete which – includes an expanding agent – increases volume of mixture – Gives additional qualities such as nailability and lessened the dead weight. • It is lighter than conventional concrete • Has a dry density of 300 kg/m3-1840 kg/m3; 87 to 23% lighter.
- 4. Light Weight Concrete • LWC is produced by using LWA. • LWC weigh 300 kg/m3-1840 kg/m3, depending on type of LWA used or method of production. • Lightness depends on inorganic aggregates which are light in weight.
- 5. Light Weight Concrete • LWC has been used in USA for more than 50 years. • Its strength is roughly proportional to its weight. • Its resistance to weathering is same as that of ordinary concrete.
- 6. Light Weight Concrete - Advantage • Reduction in dead loads • Decreased foundation sizes because of decreased loads • Savings in transporting & handling precast units on site. • Reduction in formwork and supports.
- 7. Light Weight Concrete - Advantage • Savings in structural steel supports – light weight • Improved fire resistance. • Better insulation against heat and sound.
- 8. Light Weight Concrete - Disadvantages • greater COST (30-50%) • Need for more care in placing • Greater POROSITY • More drying shrinkage
- 9. Light Weight Concrete - Use • Construction of under-beds for floors and roof slabs, where huge savings are made by decreasing dead load. • Insulated sections of floors and walls
- 11. High Density Concrete • HD or HW concrete: density > 2600kg/m3 or range between 30KN/m3- 64KN/m3. • HDC is made from natural heavyweight aggregates such as magnetite which give densities of 3900kg/m3.
- 12. High Density Concrete • Made using iron or lead as a replacement for a portion of the aggregate. • These give even greater densities of – 5900kg/m3 for iron or – 8900kg/m3 for lead.
- 13. High Density Concrete • It is designed in same way as NWC, but additional self weight is taken into account. • Transported and Placed in the same way as NWC, but additional density means that smaller volumes can be transported & placed. • Unit weight of HDC is > 25% higher than that of NWC (24KN/m3).
- 14. High Density Concrete • Construction of – Nuclear radiation shield walls: selection of concrete for radiation shielding is based on space requirements, & on type & intensity of radiation. – Ballast blocks – Counterweights – Sea walls
- 15. High Density Concrete • Except for density, physical properties of HDC are SIMILAR to Normal weight concrete. • Desirable Properties of HDC: high modulus of rigidity, low thermal expansion, low elastic & creep deformations • HDC containing higher cement show HIGH creep & shrinkage. • HDC having - Cement-CA ratio as 1:5 – 1:9; w/c ratio as 0.5 to 0.65 produce dense & crack-free concrete.
- 16. High Density Concrete • Care must be taken to avoid overloading the mixer especially • Batch size should be reduced to 50% of mixer capacity. • Formwork: stronger to withstand higher load.
- 17. High Density Concrete • To prevent segregation of heavier aggregates from the rest of the aggregates, better workability help in reducing the segregation. • Pre-placed aggregate method of concreting is used for placing HDC in confined areas to minimize segregation of scrap steel.
- 18. Vacuum Concrete
- 19. Vacuum Concrete • Excessive w/c ratio is detrimental for concrete. • Restrict w/c ratio in order to achieve higher strength. • Chemical reaction of cement with water requires a w/c ratio of < 0.38, whereas the adopted w/c ratio is generally much more than that mainly because of the requirement of workability. • Workability is also important for concrete, so that it can be placed in the formwork easily without honeycombing.
- 20. Vacuum Concrete • After the requirement of workability is over, this excess water will eventually evaporate leaving capillary pores in the concrete. • These pores result into high permeability & less strength in concrete. • Therefore, workability and high strength don’t go together as their requirements are contradictory to each other.
- 21. Vacuum Concrete • Vacuum concreting is the effective technique used to overcome this contradiction of opposite requirements of workability & high strength. • With this technique both these are possible at the same time.
- 22. Vacuum Concrete • In this technique, excess water after placement and compaction of concrete is sucked out with the help of vacuum pumps. • This technique is effectively used in industrial floors, parking lots and deck slabs of bridges etc. • Magnitude of applied vacuum is 0.08 MPa & water content is reduced by 20-25%. • Reduction is effective up to a depth of 100-150mm only.
- 23. Advantages of vacuum concreting • Due to dewatering through vacuum, both workability and high strength are achieved simultaneously. • Reduction in w/c ratio increase the compressive strength by 10-50% & lowers the permeability. • It enhances the wear resistance of concrete surface.
- 24. Advantages of vacuum concreting • Surface obtained after vacuum dewatering is plain and smooth due to reduced shrinkage. • Formwork can be removed early and surface can be put to use early.
- 25. SHOTCRETE
- 26. Shotcrete • Shotcrete is concrete (or mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique. • Shotcrete is usually an all-inclusive term that can be used for both wet-mix & dry-mix versions. • The term "shotcrete" refers to wet-mix and "gunite" refers to dry-mix. • Shotcrete undergoes placement and compaction at the same time due to the force with which it is projected from the nozzle.
- 27. Shotcrete • It can be impacted onto any type or shape of surface, including vertical or overhead areas. • Shortcreting has proved to be the best method for construction of curved surfaces. • Domes are now much easier to construct with the advent of shotcrete technology. • Tunnel linings are also becoming easy with this technology.
- 28. Shotcrete • Usually patented polypropylene fibers are included in the shotcrete which increases the cohesive nature of shotcrete through mechanically binding the Cementitious materials together. • This mechanism reduces the rebound waste that occurs through the shotcreting process and these fibers also resist plastic shrinkage and cracking through their ability to enhance the early stage tensile strength of concrete.
- 29. Shotcrete • Shotcrete also gives better surface finishes and reduces surface tearing on non-linear sections. • Cementitious material containing the polypropylene fibers resist cycles of freezing and thawing and also reduces the chances of water and chemical penetrations.
- 30. SHOTCRETE VERSUS CONVENTIONAL CONCRETE • Unlike conventional concrete, which is first placed and then compacted in the second operation, shotcrete undergoes placement & compacted at the same time due to force with which it is projected from the nozzle. • Shotcrete is MORE dense, homogeneous, strong, and waterproof.
- 31. SHOTCRETE VERSUS CONVENTIONAL CONCRETE • Shotcrete needs less repair & suffers little deteriorations. • Shotcrete is not placed or contained by forms. • It can be impacted onto any type or shape of surface, including vertical or overhead areas. • It forms an excellent bond and can be given a variety of surface finishes.
- 32. Functions of Shotcrete • Seal Surface, curved or folded sections, canal, reservoir & tunnel lining • Preserve Ground Strength • Support of Individual Blocks • Form a Structural Arch • Bridges / Dams • Sewer – Sanitary – Storm (Culverts / Basins) – Headwalls / Wing Walls • Piers / Docks • Ditches • Retaining Walls – Waterproofing • Slope Stabilization
- 33. Shotcrete
- 34. Types of Shotcrete • Dry Mix Process • Wet Mix Process
- 35. Dry Mix Process • Mixture of cement & damp sand is conveyed through a delivery hose pipe to a mechanical feeder or gun. • Mixture is carried by compressed air through the delivery hose to a special nozzle. • Nozzle is fitted with a perforated through which water is introduced under pressure & intimately mixed with other ingredients.
- 36. Dry Mix Process • Mortar is jetted from the nozzle at high velocity on to the surface to be shotcreted. • Amount of water should be so adjusted that wastage of material by rebounding is minimum. • w/c ratio: 0.33-0.5. Lower w/c ratio leads to – higher strength, less creep & drying shrinkage & higher durability. • Preferred for LWC.
- 37. Wet Mix Process • In this process, all ingredients (cement, sand, small- sized CA & water) are mixed before entering the chamber of delivery equipment. • RMC is conveyed by compressed air at a pressure to a nozzle. • Additional air is injected at the nozzle to increase the velocity & improve the gunning pattern. • w/c ratio is very accurately controlled. • Does not cause dust problem
- 38. Wet Mix Process • Rebounding of jetted concrete depends on – w/c ratio: decreases with higher w/c ratio – Nature & position of surface treated: higher rebounding for vertical & overhead surfaces • Hz Slab: 5-15% rebound; Sloping & VR Surface: 15-30% rebound; Overhead surface: 20-50% • Higher durability is achieved by using air-entraining agents. • Larger capacity available in wet mix results in higher rates of placing of concrete.
- 39. Advantage of Shotcrete • Formwork is used only on 1 side of the work • Suitable for thin section & for sites where accessibility is difficult • Bonds perfectly well with the existing old concrete masonry, exposed rocks, etc. • Very effective in repair of structures.
- 40. Disadvantage of Shotcrete • Dusting problem from sand & cement (dry mix) • High cost • Wastage due to rebound
- 42. Fibre Reinforced Concrete • Presence of micro-cracks at mortar-aggregate interface is responsible for the inherent weakness of plain concrete. • This weakness can be removed by inclusion of fibres in the mix which transfer loads at the internal micro-cracks.
- 43. Discreet Fibre Reinforced Concrete • In this system, concrete is reinforced by random dispersal of short, discontinuous & discreet fine fibres of specific geometry. • Fibres interlock & entangle around aggregate particles which leads to – Reduced workability – More cohesive mix – Mix less prone to segregation – Restrain shrinkage
- 44. Discreet Fibre Reinforced Concrete • Fibres are produced from – Steel, Glass & Organic polymers. • Naturally occurring asbestos fibres & vegetable fibres (jute) are also used for reinforcement.
- 45. Discreet Fibre Reinforced Concrete • Fibres are classified into 2 categories: – Hard Intrusion: have higher elastic modulus; Steel, Carbon & Glass; it improves Flexural & Impact resistances. – Soft Intrusion: have lower elastic modulus; Polypropylene & Vegetable Fibres; it improves Impact resistance of concrete but do not contribute much to flexural strength.
- 46. Fibre Reinforced Concrete • Major factors affecting characteristics of FRC – w/c ratio – % of fibres – Diameter & Length of fibres • Location & extent of cracking depends on – Orientation of fibres – Number of fibres
- 47. Fibre Reinforced Concrete - Disadvantage • Reinforcement bars in RCC are continuous & carefully placed in the structure to have optimize performance; • Fibres are discontinuous & randomly distributed throughout the concrete which leads to its inferior performance. • Fibres are more expensive than reinforcement bars.
- 48. Fibre Reinforced Concrete - Advantage • Fibre act as Crack arrestor restricting the development of cracks & thus transforming a brittle matrix (portland cement with its low tensile & impact resistances) into a strong composite with – superior crack resistance – Improved ductility – Distinctive post-cracking behaviour before failure
- 49. Preplaced or Slurry Infiltrated Fibre Concrete (SIFCON)
- 50. Preplaced or Slurry Infiltrated Fibre Concrete (SIFCON) • For achieving high fibre volume, dry fibres are pre- placed in the formwork & cement slurry is made to infiltrate the bed of fibres. This composite is called SIFCON. • Another form SIFCON has recently been developed is known as SIMCON (Slurry Infiltrated MAT Concrete).
- 51. Preplaced or Slurry Infiltrated Fibre Concrete (SIFCON) • SIMCON is a new generation of high performance fibre reinforced concrete (HPFRC), made by infiltrating sheet of stainless steel fibres with a specially designed cement-based slurry. • Fibre mats are shaped & wrapped around existing columns & beams; & injected with concrete slurry to strengthen them.
- 52. Advantage of SIMCON • Add tensile strength & ductility to concrete • Smaller fibre volume fraction is required to achieve substantial increase in mechanical properties • At failure, mass of fibres & concrete crumbles into small harmless flakes which pose little danger • Steel fibre mats provides inherent strength & utilize fibres with much higher aspect ratio (length/dia) • SIMCON is easier to handle & construct than with SIFCON • It exhibit better mechanical properties with lower fibre volume fraction.
- 53. Steel-fibre Reinforced Concrete • Round steel fibres: cutting round wires into short lengths (dia 0.25-0.75mm); 0.3-0.5 mm - India. • Rectangular steel fibres are produced by cutting the sheets about 0.25mm thick. • For improving the bond between fibre & matrix, fibres are – Indented, Crimped, Machined & Hook- ended. • Aspect ratio (length/dia) of fibres: 30-250.
- 54. Properties of Steel-fibre Reinforced Concrete • Slump test & Compacting Factor is a poor indicator of workability for steel-fibre concretes. • This is because internal structure & flow characteristics are different due to presence of fibre; which form a stable system due to interlocking of fibres thus resisting the flow of fresh concrete.
- 55. Properties of Steel-fibre Reinforced Concrete • Vee-bee test which incorporates the effects of vibration give a realistic assessment of workability of fibre concretes. • Workability decreases with an increase in fibre concentration & aspect ratio. • There is a critical fibre content for each aspect ratio beyond which response to vibration decreases rapidly.
- 56. Application of Steel-fibre Reinforced Concrete • Highway & Airfield Pavements: higher flexural strength results in reduction in thickness; resistance to impact & repeated loading is increased; smooth riding surface without irregular depressions. • Hydraulic Structures: resistance to cavitations & erosion damage by high velocity flow • Fibre Shotcrete: used in rock slope stabilization, tunnel lining & bridge repair
- 57. Application of Steel-fibre Reinforced Concrete • Refractory Concrete: more durable when exposed to high thermal stress, thermal cycling, thermal shock. • Precast Applications: include manhole covers, concrete pipes, machine bases & frames. • Structural Applications: increased impact resistance, inhibit crack growth & crack widening, more ductile & shear strength.
- 58. Polypropylene Fibre-Reinforced Concrete • Polypropylene fibres are used in small volume fractions between 0.5-1% in concrete to improve impact strength of hardened concrete. • Low modulus of elasticity. • These fibres being hydrophobic can be easily mixed as they do not need lengthy contact during mixing & only need to evenly dispersed in the mix.
- 59. Polypropylene Fibre-Reinforced Concrete • Hence these are added shortly before the end of mixing normal constituents. • Inclusion of these fibres reduces workability. • Highly air-entrained concretes can be stabilized by fibres. • They deteriorate under attack from ultraviolet radiation.
- 61. POLYMER CONCRETE COMPOSITE • PCC are obtained by combined processing of polymeric materials with some or all ingredients of cement concrete composite. • Depending upon the process by which the polymeric materials are incorporated, polymer concrete are classified as: – Polymer-impregnated Concrete (PIC) – Resin or Polymer concrete – Polymer Modified Concrete
- 62. Polymer-impregnated Concrete (PIC) • In PIC, low viscosity liquid monomers or pre- polymers are partially or completely impregnated into the pore systems of hardened cement composite & are then polymerised. • It improves the durability & chemical resistance. • Modest improvement in structural properties.
- 63. Polymer-impregnated Concrete (PIC) • Total or in-depth impregnation improves structural properties considerably. • It is used as surface impregnation of bridge decks to make them impervious to intrusion of moisture, chemicals & chloride ions. • It is used repairing cavitations & erosion in dams.
- 64. Resin or Polymer concrete • It is composite wherein the polymer replaces the cement-water matrix in cement concrete. • It is manufactured in a manner similar to cement concrete. • Monomers or pre-polymers are added to the graded aggregates & mixture is thoroughly mixed by hand or machine; which is then cast in moulds of wood, steel or aluminium to the required shape or form.
- 65. Resin or Polymer concrete • Mould releasing agents can be added for easy demoulding. • This is then polymerized either at room temperature or at an elevated temperature. • The polymer phase binds the aggregate to give strong composite. • PC pipes are used for transporting a variety of chemicals, for carrying effluents & wastewater, etc.
- 66. Polymer Modified Concrete • It is a composite obtained by incorporating a polymeric material into concrete during mixing stage. • But this polymer should not interfere with the hydration process. • The composite is then cast into required shape & cured in conventional manner.
- 67. Polymer Modified Concrete • Hydrated cement & polymer film formed due to curing of polymeric material constitute an inter-penetrating matrix that binds the aggregate. • PMC is also called as Polymer Cement Concrete (PCC)
- 68. FERROCEMENT
- 69. Ferrocement • In ancient India, construction was done using mud walls with woven bamboo mats. • In present form, in a thin reinforced concrete construction, cement mortar matrix is reinforced with many layers of continuous & small diameter wire meshes over the entire surface. • In Ferrocement, mortar provides the mass & wire mesh imparts tensile strength & ductility to the material. • Ferrocement provide very high tensile strength-weight ratio & superior cracking performance.
- 70. Ferrocement • FC improves following properties –High resistance against cracking –Toughness –Fatigue resistance –Impermeability
- 71. Advantages of Ferro-Cement • FC structures are thin & light. • A 30% reduction in self-weight of structure, 15% reduction in steel consumption & 10% in roof cost can be achieved. • FC is suitable for manufacturing precast units which can be easily transported.
- 72. Advantages of Ferro-Cement • Construction technique is simple & hence does not require highly skilled labour. • Partial or complete elimination of formwork is possible. • FC construction can be easily repaired in case of local damage due to abnormal loads.
- 73. Properties of Ferro-cement • Its strength per unit mass is high • It has the capacity to resist shock load. • It can be given attractive finish like that of teak and rose wood. • FC elements can be constructed without using formwork. • It is impervious.
- 74. Uses of Ferro-cement • It can be used for making: – Partition walls – Window frames, chajjas and drops – Shelf of cupboards – Door and window shutters – Domestic water tanks – Precast roof elements – Reapers and rafters required for supporting roof tiles. – Pipes – Silos – Furnitures – Manhole covers – Boats.
- 75. Applications of Ferrocement • FC behaves as Steel Plates due to very high % of well distributed & continuously running steel reinforcement. • FC can be easily moulded to any desired shape, lightness, firmness & toughness of steel plates. • Due to very high tensile strength-weight ratio & superior cracking behaviour, FC is an attractive material for light & water-tight structure & other portable structures such as mobile homes.
- 76. Ferrocement In Building Industry • FC planks, panels can be used for construction of beams, columns, floor, roofs, walls, chajjas and lintels. • It can be used in combination with PCC or RCC. • FC being a thin material single piece panel of size up to 4.5m x 4.5m or more can be manufactured as floors & walls. Large span beams, roofs can also be constructed. • FC being crack resistant and anti-corrosive material lasts much more than R.C.C.
- 77. Ferrocement In Building Industry • Dead load of FC building is reduced by at least 50%. Consequently the foundation cost gets reduced. • FC membrane lining is used for water proofing of terraces, basements, tanks. • FC water proofing is the only treatment where reinforcement is used in the form of wire mesh layers . • Therefore FC water proofing treatment should generally last longer than conventional.
- 78. Ferrocement In Building Industry • FC is a good material for elevation treatment. Since it is constructed in thin sections, it contributes negligible dead weight, and at the same time it is crack resistant, water proof and strong. • FC is a very good fire resistant material having capacity to resist fire up to 750°C for long period of 48 hours & even more. FC can be modified to resist even high temperatures, 1200°C to 1500°C. • FC building are better pollution and fire resistant as compared to RCC. Therefore, FC building are preferable to RCC for functional VIP and strategic buildings.
- 80. High Performance Concrete • Definition by American Concrete Institute (ACI) • HPC was defined as ‘concrete, which meets special performance & uniformity requirements that cannot be achieved routinely by using only conventional materials & normal mixing, placing & curing practices.’
- 81. High Performance Concrete • REQUIREMENTS may involve – enhancement of placement & compaction without segregation – long-term mechanical properties – Early age strength – volume stability or increased service-life in severe environments.
- 82. High Performance Concrete • A HPC element is that which is designed to – give optimized performance characteristics for a given set of load, usage and exposure conditions, consistent with requirement of cost, service life and durability.
- 83. High Performance Concrete • HPC has – Very low porosity through a tight & refined pore structure of cement paste. – Very low permeability of the concrete – High resistance to chemical attack. – Low heat of hydration – High early strength and continued strength development – High workability and control of slump – Low w/c ratio, Low bleeding and plastic shrinkage
- 84. Salient Features of HPC • Compressive strength > 80 Mpa, even upto 800 Mpa • w/c ratio: 0.25-0.35 ,therefore very little free water • Reduced flocculation of cement grains • Wide range of grain sizes • Densified cement paste • No bleeding - homogeneous mix • Less capillary - porosity • Discontinuous pores • Stronger transition zone at interface between cement paste & aggregate • Low free lime content
- 85. Salient Features of HPC • Powerful confinement of aggregates • Little micro-cracking until about 65-70% of fck • Smooth fracture surface • High degree of impermeability to prevent ingress of water/moisture/CO2 /SO4 /air /oxygen /chloride • High resistance to sulphate attack, abrasion, erosion, & cavitation • Absence of micro-cracking, High level of corrosion resistance, High electrical & chemical resistivity
- 86. Advantages of Using HPC • Reduction in member size, resulting in increase in plinth area/useable area & direct savings in the concrete volume. • Reduction in the self-weight and super- imposed DL with the accompanying saving due to smaller foundations.
- 87. Advantages of Using HPC • Reduction in form-work area and cost with the accompanying reduction in shoring & stripping time due to high early-age gain in strength. • Construction of High–rise buildings with the accompanying savings in real-estate costs in congested areas.
- 88. Advantages of Using HPC • Longer spans & fewer beams for same magnitude of loading. • Reduction in the number of supports and the supporting foundations due to the increase in spans. • Reduction in thickness of floor slabs and supporting beam sections-which are a major component of the weight and cost of the majority of structures.
- 89. Advantages of Using HPC • Superior long-term service performance under static, dynamic and fatigue loading. • Low creep and shrinkage. • Greater stiffness as a result of a higher modulus, Ec • Higher resistance to freezing & thawing; chemical attack • Improved long-term durability & crack propagation. • Reduced maintenance & repairs. • Smaller depreciation as a fixed cost.
- 90. Application of High Performance Concrete • Major applications of HPC have been in the areas of –Pavements –Long-span bridges –High-rise buildings.
- 91. Application of High Performance Concrete • Pavements – early strength gain of HPC – its reduced permeability – increased wear or abrasion resistance – improved freeze-thaw durability.
- 92. Application of High Performance Concrete • While the conventional normal strength concrete continue to be used in most cases of pavement construction, different types of HPC are being considered for pavement repairs for early opening to traffic, bridge deck overlays, & special applications in rehabilitation of structures & other developments.
- 93. Application of High Performance Concrete • Bridges – Use of HPC would result in smaller loss pre- stress & consequently larger permissible stress and smaller cross-section being achieved, i.e. it would enable the standard pre-stressed concrete girders to span longer distances or to carry heavier loads.
- 94. Application of High Performance Concrete • Bridges – Enhanced durability allow extended service life of the structure. – Precast girders: due to reduced weight transportation & handling will be economical. – Concrete structures are preferable for railway bridges to eliminate noise & vibration problems and minimize the maintenance cost.
- 95. Application of High Performance Concrete • High-rise Buildings – The reasons for using the high strength concrete in high-rise buildings are to REDUCE • Dead load, • Deflection • Vibration & noise • Maintenance cost.
- 96. Ingredients of HPC • Cement – Physical & chemical characteristics of cement play a vital role in developing strength & controlling rheology of fresh concrete. – Fineness affects water requirements for consistency.
- 97. Ingredients of HPC • Cement – When looking for cement to be used in HPC, one should choose cement containing as little C3A as possible because lower amount of C3A, the easier to control the rheology & lesser the problems of cement-super plasticizer compatibility. – Finally from strength point of view, cement should be finely ground & contain a fair amount of C3S.
- 98. Ingredients of HPC • Fine aggregate – Both river sand & crushed stones may be used. – Coarser sand may be preferred as finer sand increases water demand of concrete – Sand particles should also pack to give MIN void ratio as test results show that higher void content leads to requirement of more mixing water.
- 99. Ingredients of HPC • Coarse aggregate – By usage of mineral admixtures, the cement concrete becomes more homogeneous and there is marked enhancement in strength properties as well as durability characteristics of concrete. – Strength of HPC is controlled by strength of CA.
- 100. Ingredients of HPC • Water – It is an important ingredient of concrete as it actively participates in the chemical reactions with cement. – The strength of cement concrete comes mainly from the binding action of the hydrated cement gel. – The requirement of water should be reduced to that required for chemical reaction of unhydrated cement as the excess water would end up in only formation of undesirable voids in the hardened cement paste in concrete. – From HPC mix design considerations, it is important to have the compatibility between the given cement & chemical/ mineral admixtures along with the water used for mixing.
- 101. Ingredients of HPC • Chemical Admixtures – These are essential ingredients in the concrete mix, as they increase efficiency of cement paste by improving workability of mix & there by resulting in considerable decrease of water requirement. – Different types of chemical admixtures are • Plasticizers • Super plasticizers • Retarders • Air entraining agents
- 102. Ingredients of HPC • Chemical Admixtures – Placticizers & super-placticizers help to disperse cement particles in the mix & promote mobility of concrete mix. – Retarders help in reduction of initial rate of hydration of cement, so that fresh concrete retains its workability for a longer time. – Air entraining agents artificially introduce air bubbles that increase workability of the mix & enhance resistance to deterioration due to freezing & thawing actions.
- 103. Ingredients of HPC • Mineral admixtures – The major difference between CCC & HPC is the use of mineral admixtures in HPC. – Some of the mineral admixtures are • Fly ash • Silica fumes • Carbon black powder • Anhydrous gypsum based mineral additives
- 104. Ingredients of HPC • Mineral admixtures – MA like fly ash & silica fume act as puzzolonic materials & fine fillers, thereby the microstructure of hardened cement matrix becomes denser & stronger. – Use of silica fume fills the space between cement particles & between aggregate & cement particles. – Note: addition of silica fume to the concrete mix does not impart any strength to it, but acts as a rapid catalyst to gain the early age strength.
- 106. Self Compacting Concrete • Concrete that is able to – flow & consolidate under its own weight, – completely fill the formwork of any shape, even in presence of dense reinforcement, while – maintaining homogeneity & – without the need for any additional compaction.
- 107. Self Compacting Concrete • Origin – Introduced to the concrete industry, in Japan, primarily, through the work of Prof. Okamura in the late 1980’s. – Motivation behind this was gradual reduction of skilled labor, which led to reduction in quality of construction work, affecting adversely, the durability of concrete due to poor compaction.
- 108. Self Compacting Concrete • SCC has more powder content & less CA. • Fillers used can be – flyash, ground GBFS, condensed silica fume, rice husk ash, lime powder, chalk powder & quarry dust • SCC incorporates – high range water reducers (HRWR, Super plasticizers) & – viscosity modifying agent in small amount.
- 110. Potential Benefits of SCC • Contractor – Reduced labor requirement & cost – Reduced plant requirement – Reduced remedial work – Reduced noise, improved site health & safety – No vibrating equipment required, Reduces placing costs
- 111. Potential Benefits of SCC • Designer / client – Used in more complex design & heavy reinforcement – Improved aesthetics & durability – Quicker construction time – Less variation in the production of concrete & more homogeneous concrete – Better surface finish
- 112. SCC Potentials beyond conventional concrete • Improved efficiency • Use with close meshed reinforcement • For complex geometric shapes • For slender components • Generally where compaction is difficult • Fast installation rates • Noise reduction • Reduced damage to health
- 113. Fresh SCC Properties • Filling ability: “The ability of SCC to flow into & fill completely all spaces within the formwork, under its own weight.”
- 114. Fresh SCC Properties • Passing ability: “The ability of SCC to flow through tight openings such as spaces between steel reinforcing bars without segregation or blocking.”
- 115. Fresh SCC Properties • Segregation resistance: “The ability of SCC to remain homogeneous in composition during transport and placing.”
- 116. Test Methods for Determining Fresh SCC Properties • FILLING ABILITY – Slump flow & T50CM slump flow – V- Funnel • PASSING ABILITY – L-Box – U-box – J-ring – Fill Box • SEGREGATION RESISTANCE – V-Funnel at T5 Minutes – GTM Screen stability test
- 117. Test Methods for Determining Fresh SCC Properties • Slump flow (spread) – Secondary measurement of T50 cm can be made – Represents time taken in seconds to reach horizontal diameter of 50 cm. – Recommended limits are 2-5 sec
- 118. Test Methods for Determining Fresh SCC Properties • V-Funnel Test – To assess the FLOWABILITY of fresh concrete – Time taken for concrete to flow through the narrow end is measured – Measures VISCOSITY of concrete – Recommended value for V-funnel flow < 12sec
- 119. Test Methods for Determining Fresh SCC Properties • L-Box Test – PASSING ABILITY of fresh concrete. – T20 cm & T40 cm marks of horizontal section of L – box are the indications of ease of flow of concrete. – Recommended values of flow time are: T20 cm = 1 ± 0.5 sec & T40 cm = 2 ± 0.5 sec – Height of the concrete at the end of horizontal section is expressed as a % of that of remaining in the vertical section (H2/H1).
- 120. Test Methods for Determining Fresh SCC Properties • L-Box Test – Recommended value for blocking ratio: H2/H1 ≥ 0.80.
- 121. Test Methods for Determining Fresh SCC Properties • U-Box Test (Box-shaped) – Measures the FILLING ABILITY of concrete. – Difference in height of two sections is measured. – Recommended value: difference in height of the limbs < 30 mm
- 122. Test Methods for Determining Fresh SCC Properties • J-Ring Test – Measures PASSING ABILITY of concrete, Simple test – Can be used in conjunction with Slump flow test, combination can test filling ability & passing ability – Difference in height, in between the concrete inside & that just outside the J-ring is measured
- 123. Test Methods for Determining Fresh SCC Properties • J-Ring Test – Difference in height of MAX of 10 mm is considered appropriate – Bars can be of different diameters and also varied spacing: Preferably three times the MAX aggregate size – Used in conjunction with slump flow test
- 124. Test Methods for Determining Fresh SCC Properties • V5min flow time – This is secondary parameter of the V-funnel test – Measures time of flow of concrete after time gap of 5min – Indicates the tendency for segregation – Recommended value is: < +3 sec of time at zero hours
- 125. Test Methods for Determining Fresh SCC Properties • Acceptance of SCC – Combinations may be: • Slump flow, V-funnel and U-box tests (Japan) • Slump flow and L-Box (Sweden) • J-ring and U-box • Slump flow, U-Box/L-Box, V-funnel (at 5min.)
- 127. Types of Crack/Failure • Structural causes of distress of concrete – Externally applied & environmental loads exceeding the design stipulations – Accidents & Subsidence – Poor construction practices – Error in design & detailing
- 128. Types of Crack/Failure • Structural causes of distress of concrete –Construction Overloads –Drying Shrinkage –Thermal stress –Weathering –Chemical reactions –Corrosion of Reinforcement
- 129. Types of Crack/Failure • Plastic concrete suffer damage due to – Plastic Shrinkage – Settlement Cracking • Honeycombing, bolt-holes can be avoided by providing a watertight & rigid framework. • Blowholes develop during concreting operations due to improper design of formwork
- 130. Types of Crack/Failure • Blowholes are formed on the surface of concrete by trapped air & water bubbles against the face of formwork. • These can be REDUCED if the form face is slightly absorbent & adequate compaction is provided. • Large blowholes must be filled with 1:1 or 1:2 cement-sand mortar.
- 131. Types of Crack/Failure • Honeycombing consists of groups of interconnected deep voids due to inadequate compaction or loss of grout through joints in formwork or between formwork & previously cast-concrete. • Unsound material is chipped out to solid concrete • After surface has been prepared, a bonding coat should be applied to all exposed surfaces, & new concrete is placed against the prepared surface.
- 132. Types of Crack/Failure • Cracks in horizontal surface as concrete stiffens due to plastic shrinkage (rapid drying of surface) • Cracks formed above ties, reinforcement, etc., due to plastic settlement or concrete continues to settle after starting to stiffen • Cracks in thick sections, as concrete cools due to restrained thermal contraction.
- 133. Types of Crack/Failure • Voids in concrete due to honeycombing or inadequate compaction. • Colour variation due to variations in mix proportions, curing conditions, materials, characteristics of form face, vibration. Leakage of water from formwork.
- 134. Types of Crack/Failure • Powdery formed surface due to surface retardation, caused by sugars in certain timbers. • Rust-strains due to pyrites in aggregates ; rubbish in formwork. • Plucked surface due to insufficient release agent; careless removal of formwork. • Lack of cover of reinforcement due to movement of reinforcement during placing of concrete; badly fixed reinforcement.
- 135. Diagnosis of Distress in Concrete • Following information helps in diagnosing the cracks: – Whether the crack is new or old – Type of crack: active or dormant – Whether it appears on opposite face of member also – Pattern of cracks
- 136. Diagnosis of Distress in Concrete • Following information helps in diagnosing the cracks: – Soil condition, type of foundation used, sign of movement of ground – Observations on similar structures in same locality – Study of specifications, method of construction used & test results at site – Views of the designer, builder, occupants of the buildings – Weather during which the structure has been constructed
- 137. Crack Control or Repair • It involves 3 processes: – Preparation of surface – Selection of Materials – Application of materials
- 138. Crack Control or Repair • Preparation of surface – Cracked & deteriorated areas are cut or chipped out of the solid concrete. – All the loose material should be cleaned & surface is washed off before actual patching is started.
- 139. Crack Control or Repair • Preparation of surface – Care should be taken to remove excess water from the cavity. – To obtain a good bond, the surface of concrete should be coated with a thin layer of cement grout before placing the patching material.
- 140. Crack Control or Repair • Selection of Materials – Mechanical properties of repair material should be similar to those of structure to be repaired – For conventional repairs, cement-based material – mortar or concrete are used depending on the extent of repair.
- 141. Crack Control or Repair • Application of materials – Methods used for filling the material are • Drypacking • Concrete replacement • Mortar replacement • Grouting • Large volume prepacking of concrete • Shotcrete or guniting
- 142. Repair by Jacketing
- 143. Repair by Jacketing • Process of fastening a durable material over the existing concrete & filling the gap with a grout that improves the performance by strengthening. • Jacketing restores or increases the section of an existing member by encasement in a new concrete. • It is applicable for protecting the member against further deterioration.
- 144. Repair by Jacketing • This method is useful the compression members like columns & piles.
- 145. Repair by Jacketing • REINFORCED CONCRETE JACKET – Size of jacket & number & diameter of steel bars used in jacketing process depend on the structural analysis that was made to the column. – In some cases, before this technique is carried out, we need to reduce or even eliminate temporarily the loads applied to the column; this is done by the following steps: • Putting mechanical jacks between floors. • Putting additional props between floors.
- 147. THANK YOU !!!