Cement, Energy and Environment

• Physical actions and • Chemical action on concrete. Quality of ingredients of Concrete having much influence on strength and durability. Now a days blended cement or concrete with mineral admixtures are preferred choice of construction and structural engineers. Blended cement has not only quality edge over OPC as far as high performance or durable concrete are concerned but has environmental benefit as well. It is well known facts that in manufacturing of 1 MT of cement nearly I MT of CO2 is emitted to environment. By choosing PPC or PSC in construction we are not only using our lime stone (Natural resources) religiously but utilizing waste of thermal plant & steel plant(Fly ash & slag ) and converting it in to wealth. Out of above durability factors when we talk about the service environment the most common and serious cause of it is PERMEABILITY. Permeability of concrete plays an important role in durability because it controls the rate of entry of moisture that may contain aggressive chemicals and the movement of water during heating or freezing. Higher the permeability lesser will be the durability. It can be seen in below figure that one of the most common and serious cause of deterioration of concrete is corrosion of reinforcement and Permeability is an important cause of it among others. Basic Mechanism of corrosion of reinforcement Different areas of the same steel bar become anode and cathode. The electrical connection being maintained by pore water, which acts as electrolyte. At the anode, steel releases electron and takes - 2+ the ionic form, Fe → 2e + Fe At the cathode, water in presence of oxygen and the released electron forms - hydroxyl ions, (OH) - - 2O + H O + 2e → 2(OH) 2 2 - - 2H O+O 4e =4 (OH ) 2 2 ++ - Fe + 2(OH) → Fe (OH) → 2 Iron Hydroxide (Rust) 28