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Supplemetary Cementitious Material - cementitious...

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CHAPTER 2 SUPPLEMETARY CEMENTITOUS MATERIAL 2.1 Pozzolana A Pozzolana is essentially a siliceous material, which itself posses no cementitious properties. But in its finely divided form and in the presence of water, react with calcium hydroxide at ordinary temperature to form compounds of cementitious properties. Some of the important pozzolanas that are commonly used in concrete these days are Fly ash, Silica fume, Blast furnace slag, Microsilica 600 etc. 2.2 Mechanism of Pozzolanic Reaction In hardened concrete, calcium hydroxide (CH) is weaker than calcium silicate hydrates (CSH), and the presence of CH contributes to many durability problems. Pozzolanic, which are defined as siliceous or calcareous and aluminous materials, which in the presence of moisture, chemically react with CH at ordinary temperatures to form compounds or
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Unformatted text preview: cementitious properties. This secondary reaction as a result of pozzolanic reaction increases the volume of CSH at the expense of CH. Also CSH formed is denser than that formed due to the hydration of ordinary Portland cements. This means that pozzolanic materials can exhibit secondary reaction on hydration resulting in concrete having higher strength, greatly reduced permeability, potentially greater durability, and better appearance in many environments than plain Portland cement concrete. The presence of CH can also cause efflorescence and this is reduced in concrete containing pozzolanic materials. The pozzolanic reaction is rather slow and requires the presence of moisture in concrete, which includes both mixing, and to a lesser extent curing water. 2.3 Different types of Pozzolonas 2.3.1 Fly ash General...
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