chapter 2 blended concrete - Utilization of Industrial...

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Utilization of Industrial Wastes in the Production of Blended Concrete BLENDED CONCRETE Introduction Cement mixtures containing ordinary portland cement (OPC) and at least one supplementary cementitious material are called blended cements. Class C fly ash is often used as a supplementary cementitious material to improve concrete workability and reduce cost, as well as for other technical reasons. Blended cements blended or integrated at cement plants are generally more uniform and produce better results than blended concrete mixtures combined at the concrete mixer. The use of blended cements in concrete reduces mixing water and bleeding improves finishability and workability enhances sulfate resistances inhibits the alkali-aggregate and lessens heat evolution during hydration thus moderating the chances for thermal cracking on cooling. e.g.: Pozzolona Cement, Rapid Hardening Cement etc. Concrete can be produced with blended cement containing fly ash plus other materials (most commonly Blast Furnace Slag and Silica Fume) added at the batch plant. These are considered ternary and tertiary blends. The addition of fly ash, slag and other industrial byproducts to cements can improve concrete workability, durability, and long-term strength, but a gap in knowledge about the variation in performance of concrete containing supplementary cementitious material’s (SCM’s) from various sources has limited its use by the PCC paving industry. The usage of blended cements is growing rapidly in construction industry due to the consideration of cost saving and environmental protection. The use of fly ash, a siliceous material derived from thermal plants, as a partial replacement of ordinary portland cement has found very suitable in developing the durable concrete. Durability of concrete is its resistance to deteriorating agencies to which the concrete may be exposed during its service life. When one deals with the durability aspects of concrete, the chemical attack, which results in loss of weight, cracking of concrete and the consequent deterioration of concrete, becomes an important part of investigation. Ordinary Portland cement concrete usually does not have good resistance to acid attack. The addition of fly ash improves the microstructural properties of concrete like porosity, permeability and sorptivity. The reduction of porosity and permeability implies the improvement in chemical attack and corrosion resistance. Apart from the merits, the greatest drawback of fly ash addition in concrete is the reduction of initial age strength development rate and increasing
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This note was uploaded on 07/17/2011 for the course CIVIL 8 taught by Professor K.b.prakash during the Spring '11 term at Indian Institute of Technology, Chennai.

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chapter 2 blended concrete - Utilization of Industrial...

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