Exages And Disadvantages And Disadvantages Of Self-Compacting Concrete

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1.3 Advantages and Disadvantages of Self-Compacting Concrete
Some advantages of SCC over normal concrete are:

• High performance and more calculable quality
• Compact and even surface texture
• Reduces noise pollution at construction sites
• Reduction on site manpower for all operations
• Improved durability and high strength
• Shorter construction periods
• Faster construction since no mechanical vibrators are used
• Safer and cleaner working environment
• More scope to build different structural and architectural shapes
Some disadvantages of Self-Compacting Concrete are:
• SCC is more prone to settlement cracking
• It results in rapid drying and requires increased curing to avoid increased plastic shrinkage cracking
• Increased formwork
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These are:
• Powder type SCC: This mix achieves the fluidity requirements through the reduction of the coarse aggregate volume and the use of High Range Water Reducers (HRWR). The stability comes from a low water to cement ratio with high sand to paste ratio i.e. larger amounts of fine aggregates are necessary to resist segregation in the mix.
• VMA type SCC or Stabilizers: VMAs are the viscosity modifying agents. To evolve a VMA-type SCC mix, a higher target water to cement ratio of the 0.45 has been used. The higher water content in this mix requires a smaller amount of HRWR than that in other SCC mixes. To ensure adequate segregation resistance of this mix, a relatively large amount of VMA is required. The higher amount of VMA meant that segregation could be controlled with fewer fine aggregates and a higher coarse aggregate content than in the previous SCC mixes.
• Combination type SCC: This mix is obtained by adding a low amount of stabilizer or the powder type SCC to neutralize the moisture fluctuations. The target water-to-cement ratio is 0.4. Because of the increased amount of water in this mix, a lower amount of HRWR is used than in the powder-type SCC mix. Compared to powder-type mix, the combined mix design shall have a larger coarse aggregate content and a reduced amount of fine
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On combustion of coal, the combustible matter burns and incombustible material such as rock debris results in coal ash. The rock debris varies from one source to another therefore causes variation in the properties of coal ash as well. Coal ash that has been extracted from the boiler flue gases is called fly ash and the coarser part that is collected at bottom of the furnace is called coal bottom ash. The construction industry has enormous potential for coal bottom ash as construction material. Coal bottom ash is a well-graded material and its particle size distribution is similar to that of the river sand. Bottom ash is composed of silica, alumina and iron with smaller amount of calcium, magnesium, sulfates, and other compounds. Its particles intend to have interlocking characteristics. Coal bottom ash is light in weight and more brittle as compared to natural river sand. Coal bottom ash with low specific gravity has a porous surface texture and readily degrades under loading or compaction. Coal bottom ash derived from high sulfur coal and low rank coal is not very porous in texture and is quite dense. The properties of coal bottom ash depend upon the degree of pulverization of coal, firing temperature in the furnace and type of furnace. The use of water reducing admixtures, improves the abrasion resistance of bottom ash concrete significantly in comparison to that of bottom ash

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