MRRS UNIT 3 Special Concretes AND ITS TYPES
- 1. EXCEL ENGINEERING COLLEGE (Autonomous) B.E Civil Engineering Fourth Semester CE8020 Maintenance, Repair and Rehabilitation of Structures Regulations 2017 Question Bank UNIT – III (Special Concretes) PART- A Q.No Questions Marks CO BL 1. What is expansive cement? Expansive cement is special type of cement when mixed with water, which forms a paste that tends to increase in volume to a significantly greater degree than Portland cement paste after setting. The expansion of the cement mortar or concrete is compensated for the shrinkage losses 2 CO3 U 2. What is sulphur infiltrated concrete? Sulphur infiltrated concrete was developed as an economical alternative to polymer impregnated concrete (PIC) to be used for higher strength and durable precast elements. Sulphur is considerably cheaper than polymers and the technique of impregnation is more simple. These factors result in cost benefits. 2 CO3 U 3. Differentiate polymer impregnated concrete and Polymer cement concrete. Polymer-impregnated concrete It can only be produced in a manufacturing facility, which means it is precast concrete. Contractors then use blocks or panels of precast concrete to build structures. Polymer impregnation can't be performed on-site since it would be difficult to remove all of the water inside the concrete. Any water trapped inside the concrete by the polymer would weaken it over time. Polymer cement concrete It differs from standard ready-mix concrete in that workers replace a between 10 and 15 percent of its cement content with an appropriate form of polymer. Latex is one of the most popular polymers used in to create such concrete. Not only does latex help protect the concrete against water intrusion, but it also makes the concrete stronger and more resistant to damage than regular concrete. 2 CO3 R 4. What are the uses of curing compounds? Curing compounds are used to help prevent shrinkage cracking by reducing the evaporation of water from the concrete. A curing compound should be applied as soon as bleed water ceases to collect on the pavement surface. 2 CO3 U 5. What are the uses of sealants? Sealants are materials that prevent fluids and other substances from passing through surfaces and mechanical joints. Sealants also block air leakage, insects, dust, sound, and heat. 2 CO3 R 6. Write the mechanism of accelerators. A cement accelerator is an admixture for the use in concrete, mortar, rendering or screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier. This allows concrete to be placed in winter with reduced risk of frost damage. 2 CO3 R
- 2. 7. With a simple sketch mention the ferrocement jacketing. 2 CO3 R 8. What are the advantages of SIFCON? SIFCON possess excellent durability, energy absorption capacity, impact and abrasion resistance and toughness. Modulus of elasticity (E) values for SIFCON specimens is more compared with plain concrete. SIFCON exhibits high ductility. 2 CO3 U 9. With respect to FRC write about the effect of volume fraction on fresh concrete properties. The strength of the composite largely depends on the quantity of fibers used in it. Fig 1 and 2 show the effect of volume on the toughness and strength. It can see from Fig 1 that the increase in the volume of fibers, increase approximately linearly, the tensile strength and toughness of the composite. Use of higher percentage of fiber is likely to cause segregation and harshness of concrete and mortar. 2 CO3 U 10. What do you mean by critical length of fibre? The value of critical length defines if the fiber is long enough to act as reinforcement or it is only an incorporated load. In other words, whether or not there is stress transfer from matrix to the fiber . 2 CO3 U PART- B Q.No Questions Marks CO BL 1. i) Explain the manufacturing process, properties, types and uses of polymer concrete. ii) What is meant by Vacuum concrete? Explain with its advantages and disadvantages. Ans: i) Manufacturing process of polymer concrete: Polymer cement concrete is made by mixing cement, aggregates, water and monometer. Such plastic mixture is cast in moulds, cured, dried and polymerised. The monomers that are used in PCC are: Polyster–styrene Epoxy – styrene Furans Vinylidene chloride The results obtained by the production of PCC shown relatively modest 8+8 CO3 R
- 3. improvement of strength and durability. In many cases, materials poorer than ordinary concrete are obtained. The organic materials are incompatible with aqueous system and sometimes interfere with the alkaline cement hydration process. Recently the production of the superior polymer cement concrete by the incorporation of furfuryl alcohol and aniline hydrochloride in the wet mix. The materials is to be specially dense and non-shrinking and to have high corrosion resistance, low permeability and high resistance to vibrations and axial extension. Properties of Polymer concrete: The proportions of polymer incorporated also vary considerably and range from under 1% to over 30% of the solid volume of cement. Concrete mixes become more workable and so the water content can be reduced in the addition of polymers. Reduction of the water content increase the crushing strength but the extra voids have the reverse effect. There is significant increase in the flexural strength of the concrete which may be attributed to an improved bond between the aggregates and the matrix. The durability of concrete with polymer admixture depends upon the properties of polymer used and proportion included. At least 5% polymer by weight of cement is required to obtain changes in the properties of the hardened concrete. The polymer concretes have a greater resistance to abrasion than plastic concretes wear rates being reduced by much as 75%. Due to the less wear rates and improved durability, PCC have been used for factory floors. Application For factory floors, particularly where chemicals or oil are liable to be split For repair of old or damaged structure For surfacing steel bridge or ship deck For flooring in a frozen food factory For loading ramps where the abrasive wear of concrete is high For cementing ceramic tiles to concrete ii) Vacuum Concrete: Vacuum concrete is the effective technique used to overcome the requirements of workability and high strength. With this technique both these are possible at the same time. Advantages of Vacuum concrete Due to dewatering through vacuum, both workability and high strength are achieved simultaneously. Reduction in water-cement ratio may increases the compressive strength by 10 to 50% and lowers the permeability. It enhances the wear resistance of concrete surface. The surface obtained after vacuum dewatering is plain and smooth due to reduced shrinkage. The formwork can be removed early and surface can be put to use early. The strength of concrete and its resistance to wear and abrasion increases and total shrinkage is reduced. Vacuum treated concrete provides a good bond with the underlying concrete. Vacuum concrete attains its 28 day compressive strength in 10 days and has a 25% higher crushing strength.
- 4. Disadvantage of vacuum concrete The vacuum treatment is not verry effective for water cement ratio below 0.4. The suction pressure on the concrete is to be maintained about one-third the atmospheric pressure. The vacuum treatment has been found to considerably reduced the time of final finishing of floor and stripping of walls forms. The vibration of concrete before vacuum treatment can assist the process. The application of vibration simultaneously with vacuum treatment after initial vibration is very effective. Continued vibration beyond 90’s may damage the structure of concrete and hence the vibration should be stopped beyond this period and only vacuum needs to be applied for the remaining duration of the treatment. 2. Explain the following i. High performance concrete ii. Fibre reinforced concrete iii. Sulphur infiltrated concrete iv. Self compacting concrete Ans: 1. High performance concrete High performance concrete (HPC) is defined as a concrete meeting special combination of performance and uniformity requirement that cannot always be achieved routinely using conventional constituents and normal mixing, placing and curing practices. Properties: The following are the properties of High performance concrete: Higher resistance towards abrasion Chemical resistance Compaction without segregation Resistance to impact High modulus of elasticity Durability Applications: Many sophisticated structures are now being designed for longer service life, for example 100 to 120 years. When exposed to aggressive fluids and demanding environmental exposure condition, it is essential that the concrete should remain crack – free and impermeable for a long time. Example of HPC mixtures and relevant features of the construction practice are described as follows: Off-shore, oil drilling platforms Long span bridges Bridge-deck, pavements, and parking structures Highway bridges decks 2. Fiber reinforced concrete Fiber reinforced concrete is defined as the concrete made with hydraulic cement containing fine or fine and coarse aggregate and discontinuous discrete fibers. A fiber reinforced concrete requires a considerably greater amount of fine aggregates than that for conventional concrete for convenient handling. 4+4+4 +4 CO3 R
- 5. For FRC to be fully effective, each fiber needs to be fully embedded in the matrix, thus the cement paste requirement is more. The improvement on structural performance depends upon the strength, characteristics, volume, spacing, dispersion and orientation, shape and their aspect ratio of fibers. Types of fiber reinforced concrete Steel fiber reinforced concrete (SFRC) Polypropylene fiber reinforced concrete (PFRC) Glass fiber reinforced concrete (GFRC) ADVANTAGES Mix becomes cohesive and possibilities of segregation reduced. Fibers helps to reduce cracking and permit the use of thin concrete section Strength, ductility, impact resistance, tensile and bending strength improved. DISADVANTAGES Fibers reduces the workability of a mix and may cause the entrainment of air. Steel fibers tend to intermesh and form balls during mixing of concrete. APPLICATIONS Fiber reinforced concrete has been tried on overlays of airfield, road pavements, industrial flooring, bridge deck, canal lining, explosives resistant structure, refractory linings etc. The fiber reinforced concrete can also be used for fabrication of precast products like pipes, boats, beams, staircase steps, wall panels, roof panels, manhole covers etc. 3. Sulphur infiltrated concrete(SIC) Sulphur infiltrated concrete is made in a similar way to polymer impregnated concrete, but the Sulphur is considerably cheaper than monomers and the impregnation technique is simpler, there will be obvious cost benefit. SIC is obtained by infiltering the lean concrete with the molten Sulphur. The water cement ratio of the concrete to be infiltered should be high between 0.7 to 0.8. so that there is no need for external pressure to drive in the Sulphur. The infiltration procedure consists of moist curing of concrete for 24 hours at 23°C followed by drying at about 1210 C for a period of 24 hours. The concrete is immersed in molten sulphur for a period of time which depends upon the type and size of the member. Properties: Filling of capillary voids in the hydrated cement paste and larger voids present at the interface between aggregates and cement paste with infiltered sulphur modifies the physical and mechanical properties of concrete. The final porosity determines the mechanical properties of SIC. The improvement in the properties like compressive strength, split tensile
- 6. strength and elastic modulus. The stress-strain relationship of SIC is linear. The performance of SIC is satisfactory against freezing and thawing, sea- water attack, wetting and drying. The Sulphur infiltrated concrete is more durable than conventional concrete in higher concentration of H2 SO4. Application: The Sulphur infiltrated concrete is best suited for precast unit such as Krebs, sewer pipes, sidewalks and precast units for tunnel fillings. For industrial application of SIC, high impermeability requires for high corrosion resistance. SIC can also be used for the repair of deteriorated structures and bridge decks. 4. Self-compaction concrete Self-compaction concrete is defined as the concrete mixture that can consolidate under its own weight. The highly fluid matter of SCC makes it suitable for the placing in difficult conditions and in sections with congested reinforcement. Advantages: Improved quality of concrete and reduction of onsite repairs. Faster construction times. Lowers overall costs. Easier placing Better surface finishing Thinner concrete section Improved durability, reliability of concrete structures 3. Explain the following i. Self compacting concrete ii. Reactive powder concrete iii. List out the Concrete made with industrial wastes and explain each in detail. Ans: I) Self-compacting concrete Self-compaction concrete is defined as the concrete mixture that can consolidate under its own weight. The highly fluid matter of SCC makes it suitable for the placing in difficult conditions and in sections with congested reinforcement. Advantages: Improved quality of concrete and reduction of onsite repairs. Faster construction times. Lowers overall costs. Easier placing Better surface finishing Thinner concrete section Improved durability, reliability of concrete structures II) Reactive powder concrete Reactive powder concrete is a developing composite material that will allow the concrete industry to optimize the material use, generate economic benefits and build structures that are ecofriendly, strong and durable. Properties The density of fresh RPC and HPC mixture is found to be in the range of 4+4+8 CO3 U
- 7. 2500 to 2650 Kg/m3 . The compressive strength analysis shows that RPC has higher compressive strength than HPC. The maximum compressive strength of RPC obtained is 200 Mpa while the maximum strength obtained for HPC is 75 MPa. The quality of RPC is one among the desired properties of nuclear waste containment materials. Advantages It has the potential to structurally compete with steel RPC can be used to resist all but directly primary tensile stress. Improves seismic performance b reducing inertia load with lighter member. Superior strength combined with the higher shear capacity result in significant dead load reduction. Low and non-interconnected porosity diminishes mass transfer, making penetration of liquid / gas non-existence. Disadvantages More expensive The fine sand used in RPC becomes equivalent to the coarse aggregates of conventional concrete, the Portland cement plays the role of fine aggregates in the silica fumes that of the cement. The mineral component optimization alone results n a substantial increase in cost over and that of conventional concrete about 5 to 10 times higher than HPC. RPC should be used in areas where substantial weight saving can be realized and where some of the remarkable characteristics of the material can be fully utilized. III) List of concrete made with industrial waste: a. Concrete made with cement replacement material from industrial waste: Fly ash concrete Ground granulated blast furnace concrete Rice husk ash concrete Silica fumes concrete Metakaolin concrete Limestone filler Sugarcane – Bagasse ash concrete Sludges concrete b. Concrete made from coarse aggregate replacing material: Crushed concrete Steel slag Ceramic waste concrete Rubber waste Brick bats concrete Fly ash concrete (Note:*Blooms Level (R – Remember, U – Understand, AP – Apply, AZ – Analyze, E – Evaluate, C – Create) PART A- Blooms Level : Remember, Understand, Apply PART B- Blooms Level: Understand, Apply, Analyze, Evaluate(if possible) Marks: 16 Marks, 8+8 Marks, 10+6 Marks) Subject In charge Course Coordinator HOD Dept Academic Coordinator
- 8. (Name & Signature) (Name & Signature)