JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III CONCRETE TECHNOLOGY Previous Question Paper (January/February - 2023 - R18)

The primary products of the hydration of Portland cement are Calcium Silicate Hydrate (C-S-H) gel, which provides the main strength to the hardened paste, and Calcium Hydroxide (Ca(OH)₂), which is a crystalline byproduct. Additionally, hydration results in the formation of calcium sulfoaluminate hydrates, such as ettringite and monosulfate, depending on the availability of gypsum and the stage of the reaction.

Natural pozzolanas are siliceous or siliceous and aluminous materials which, though not cementitious in themselves, possess the property of reacting with calcium hydroxide at ordinary temperatures in the presence of moisture to form compounds possessing cementitious properties. They are primarily of volcanic origin or derived from sedimentary deposits. The main types include:

• Volcanic Tuffs and Ashes: These include materials like Pozzolana (from Pozzuoli, Italy), Santorini Earth, and Trass, which are formed from the consolidation of volcanic ash and dust.
• Diatomaceous Earth: A sedimentary rock composed of the siliceous skeletons of microscopic aquatic plants called diatoms.
• Rice Husk Ash: While often considered an agricultural byproduct, it is a natural organic pozzolana containing high levels of amorphous silica when burnt under controlled conditions.
• Surkhi: Produced by grinding burnt clay bricks or tiles, which acts as a reactive pozzolanic material.